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D-A131 696b REVIEW OF AIRCRRFT CRASH STRUCTURAL RESPONSE RESEARCH i/2(U) MASSACHUSETTS INST OF TECH CAMBRIDGE AEROELASTIC
AND STRUCTUR. E A WITMER ET AL. AUG 82 ASRL-TR-198-1
UNCLASSIFIED DOT/FRA/CT-82-i52 F33615 77-C 5155 F/G 11/4 N
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MICROCOPY RESOLUTION TEST CHAR'NA'toNA. l .k
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DOT/FAA/CT82/152 Review of Aircraft CrashStructural Response Research
Emmett A. WitmerDavid J. Steigmann
August 1982
DTIO100This document is available to the U.S. public AUG 2 21903-through the National Technical InformationService, Springfield, Virginia 22161.
0-
U S Department of TransportationFederal Aviftion Administration
Technical CenterAtlantic City Airport, N.J. '05
Technical keport Documentation Page1. Report No. 2. Gorernmenw Accession No. 3 Recp'@nt's Catalog No.
DOT-FAA-CT-82-1 52
4. Title and Subt.tle S. Report Oa e
Review of Aircraft Crash Structural Response Research August 19826. Performing Organi sation Code
Author,~ )8. Performing Orgenisaton Report No.
Emmett A. Witmer and David J. Steignann ASRL TR 198-19. Peforming Organ.zotion Name and Address j10 Work UnIt No (TRAIS)
Aeroelastic and Structures Research LaboratorvDepartment of Aeronautics and Astronaut 1(:s I. Contract o, Grant No.
Massachusetts Institute of Technology F33615-77-C-5155, Task P00010Cambridge, Massachusetts 02139 13. Type of Report and Period Covered
12. Sponsoring Agercy Name end Address FinalU.S. Department of Iransportation August 1981-August 1982Federal Aviation AdministrationTechnical Center 14. Sponsoring Agency Code
Atlantic City, New Jersey 08405
15. Supplementary Notes
16. AbstractA review of aircraft crash structural response research has been carried out by
studying the literature, discussions with researchers working in that area, and visits
to facilities/personnel involved in conducting and/or monitoring aircraft crashstructural response investigations. Aircraft structures consisting of conventionalbuilt-up metallic construction and those consisting of advanced composite materialswere of interest. The latter type of materials and construction is of particularinterest since their use is expanding rapidly, and crashworthiness of such struc-tures is of increasing importance.
Some recent theoretical and experimental studies of the behavior of composite-material structures subjected to severe static, dynamic, and/or impact conditions arenoted. Such topics as crashworthiness testing ot composite fuselage structures, theimpact resistance of graphite and hybrid configurations, and the effects of elasto-meric additives on the mechanical properties of epoxy resin and composite systems are
reviewed.The principal theoretical methods for predicting the nonlinear transient struc-
tural responses of severely loaded structures are reviewed. Available lumped-massand finite-element computer programs tailored to aircraft crash response analysis arenoted.
A review is made of some current and planned research to investigate experimen-tally the mechanical failure, postfailure, and energy-absorbing 'behavior of a sequence
of composite-material structural elements and structural assemblages subjected to
static lads or to simulated crash-impact loads.
17. Key Words 18. Distribution StetementCrash [Impact Fiber-Rein forced Plast ics(Crashworthiness Exer imentLs I)ocument is available to the U.S. publicAircraft Simulation Models through the National Technical Information
Structural Dyvnamics Service, Springfield, Va. 22161.
Composites
19. Security Clessf. (of thins re ot) 20. Security Closef. (of this page) -1. No. of Pages 22. Price
Unclassified Lnclassified 133
Form DOT F 1700.7 (8-72) Reproduction of completed page outhorived
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FOREI-.'ORD
This research was carried out by the Aeroelastic and Structures ResearchLaboratory, Department of Aeronautics and Astronautics, MassachusettsInstitute of Technology, Cambridge, Mass. 02139 under Supplement No. P00010of AFWAL Contract F33615-77-C-5i55. The technical monitors were David
Nesterok and R. Garcia of the FAA Technical Center, Atlantic City Airport, INew Jersey. The advice, guidance, and cooperation of these individuals are
acknowledged most gratefully.
For helpful advice and information, the authors are indebted to M. Card,
H. Carden, R. Hayduk, J. Housner, H. McComb, J.u. Starnes, and R. Thomson ofthe Structures Division, NASA-Langley; to B. Dexter and G. Farley working
at the Process/Applications Branch, Materials Division of NASA-Langley; toR. Burrows, G.T. Galow, and T. Mazza of AVRADCOM, Ft. Eustis, Va.; and to
J.D. Cronkhite of Bell Helicopter Textron. All of these individuals werehelpful in providing information on past, current, and planned research onaircraft structural response under static and/or crash conditions, simulatedor actual.
The authors much appreciate the permission granted to reproduce in fullherein four well-written and informative summary papers on past, current, and/orfuture crash-response research. Reproduced in Subsection 2.1 is the paper
"Investigation of Crash Impact Characteristics of Composite Airframe Structures"[20] by J.D. Cronkhite et al by permission of the American Helicopter Society.The papers by Thomson and Goetz [11] and Thomson and Caiafa [2] are reproducedin Subsections 2.2 and 2.3, respectively, by permission of the authors. Alsoreproduced in Subsection 2.3 is the paper by Wittlin [21] by permission of the
author and the Lockheed-California Company.
NTIS GBM&IDTIC TOunjiLouneed
RE: Classified References, Distribution
Unlimited A. sV4h tv -*.V s
No change per Mrs. Margaret Swannp FAA/ r r:.'.
Library "
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CONTENTS
Section Puge
I INTRODUCTION 1
1.1 Study Objectives 1
1.2 Overall Research Approach 2
1.2.1 Literature Search 2
1.2.2 Facility Visits 3
1.3 Structural Crash Response Overview 4
1.4 Report Organization 6
2 STATUS OF AIRCRAFT CRASH RESPONSE RESEARCH 7
2.1 Helicopters 9
2.2 General Aviation Aircraft 25
2.3 Transport Aircraft 33
3 RECENT STUDIES OF THE BEHAVIOR OF COMPOSITE MATERIALS AND
STRUCTURES UNDER STATIC AND/OR CRASH-IMPACT CONDITIONS 53
3.1 A Crashworthiness Test for Composite Fuselage
Structure 54
3.2 Impact Resistance of Graphite and Hybrid Config-
urations 64
3.3 Effects of Elastomeric Additives on the MechanicalProperties of Epoxy Resin and Composite Systems 70
3.4 Unsymmetrical Buckling of Laterally-Loaded, Thin,Initially-Imperfect, Orthotropic Plates 71
3.5 Finite Element Analysis of Instability-RelatedDelamination Growth 74
3.6 Elastic-Plastic Flexural Analysis of Laminated
Composite Plates by the Finite Element Method 76
3.7 Behavior and Analysis of Bolted Joints in Com-
posite Laminates 77
3.8 Vibration, Buckling, and Postbuckling Studies of
Composite Plates 78
Uiii |
CONTENTS -- CONCLUDED
tection Page
4 REVIEW OF TRANSIENT STRUCTURAL RESPONSE ANALYSIS
METHODS 79
4.1 Introduction 79
4.2 CLP/Hybrid Approximate Methods 81
4.3 More Detailed kiethods 92
5 CRASH RESPONSE RESEARCH NEEDED 96
5.1 Comments on Procedures of Past and Planned Research 96
5.2 Needed Crash Response Research 97
5.2.1 General Goals 97
5.2.2 Crashworthy Airframe Structure 98
5.2.3 Related Areas 99
5.2.4 Laboratory Tests 100
5.2.5 Full-Scale Tests 101
5.2.6 Comments on the Roles of Element, Subscale,and Full-Scale Structural Tests 101
5.3 Current Basic and Helicopter-Related Research 102
5.4 Transport Crash Research 104
5.5 Proposed Research 108
5.5.1 Experimental Structural Studies 109
5.5.2 Prediction Method Developments 110
6 SUMMARY AND CONCLUSIONS 113
6.1 Summary 113
6.2 Conclusions 113
REFERENCES 119
iv
5
LIST OF ILLUSTRATIONS
Figure Page
3.1 Test Specimen Concepts 55
3.2 Some Stiffener-Joint Concepts 56
3.3 Internally-Stiffened Specimens 56
3.4 Externally-Stiffened Specimens 56
3.5 Typical Load-Deflection Curve 58
3.6 Internally-Stiffened Specimens after Failure 59
3.7 Inside View of Internally-Stiffened Specimens after Failure 60
3.8 Load-Deflection Curves for Internally-Stiffened Specimens 60
3.9 Load-Deflection Curves for Externally-Stiffened Specimens 61
3.10 Externally Stiffened Specimens after Failure 61
3.11 Load-Deflection Curves for Honeycomb Sandwich Specimens 62
3.12 Honeycomb Sandwich Specimens after Failure 62
3.13 Comparison of Energy Absorption Capacity of all Specimens 64
3.14 Baseline Monolithic Panel Surface Impact Data 67
3.15 Baseline Sandwich Panel Surface Impact Data 67
3.16 Photomicrographs of Impact Areas of 8-Ply Panels 68
3.17 Effect of Concepts which Add One S-Glass Ply to MonolithicPanels 69
3.18 Effect of Concepts which Add One Ply of Kevlar or Ballistic
Nylon to 16-Ply Monolithic Panels 70
4.1 Structural Behavior Typical of Built-Up Beams 82
4.2 Segment of a Shell Beam under Pure Bending 83
4.3a Basic Postfailure Structural Behavior of Built-up Beams 84
4.3b Additional Postfailure Loading Path Possible for Built-UpBeams 84
v
Figure Page
4.4 Dimensions of Four-Spar Beam 85
4.5 Bending Moment versus Postfailure Rotation for a Three-Spar
Beam 86
4.6 Bending Moment versus Postfailure Rotation for Four-Spar Beam 87
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SU 'ARY
A review of aircraft crash structural response research has been carried
out by studying the literature, discussions with researchers working in thatarea, and visits to facilities/personnel involved in conducting and/or monitoring
aircraft crash structural response investigations. Aircraft structuresconsisting of conventional built-up metallic construction and those consistingof advanced composite materials were of interest. The latter type of materialsand construction is of particular interest since their use is expandingrapidly, and crashworthiness of such structures is of increasing importance.
Some recent theoretical and experimental studies of the behavior ofcomposite-material structures subjected to severe static, dynamic, and/orimpact conditions are noted. Such topics as crashworthiness testing ofcomposite fuselage structures, the impact resistance of graphite and hybridconfigurations, and the effects of elastomeric additives on the mechanicalproperties of epoxy resin and composite systems are reviewed.
The principal theoretical methods for predicting the nonlinear transientstructural responses of severely loaded structures are reviewed. Availablelumped-mass and finite-element computer programs tailored to aircraft crashresponse analysis are noted.
A review is made of some current and planned research to investigateexperimentally the mechanical failure, postfailure, and energy-absorbingbehavior of a sequence of composite-material structural elements and structuralassemblages subjected to static loads or to simulated crash-impact loads. Thesestructures consist of beams, frames, fuselage keelson, tubes, etc. with eitherdiscrete stiffening or sandwich stiffening, utilizing graphite-epoxy, Kevlar-epoxy, and/or other fibrous composite combinations. Plans for drop-impacttests of full-scale composite-material fuselage sections with skin, frame,subfloor, seat and seat-restraint systems are noted. An associated programof structural response predictions and comparisons with measurements isexpected to validate and upgrade those prediction capabilities. These researchefforts are intended to expand the data base for improving the crashworthydesign of composite-material aircraft structures and to improve dynamic
structural response predictions and analytical/design tools.
Some recommendations for further work are offered.
Vii
SECTION I
INTRODUCTION
1.1 Study Objectives
Innovative design and the use of a variety of structural and supplementarymaterials have been undergoing continuous development for decades in order toenhance the survivability of occupants of various types of civilian andmilitary vehicles when subjected to severe loads encountered in crash, impact,blast, and other dangerous conditions. Many governmental agencies andindustrial organizations have sponsored and/or conducted studies designedto improve the state of knowledge concerning the transient response and damagesuffered by both the vehicle structure and the occupants under these severeloading conditions. This, in turn, has led to the development and use ofcrashworthy design procedures and/or requirements for certain classes ofvehicles: aircraft, automotive, rail, etc. Some of the material utilizationand design concepts developed are applicable to a variety of vehicles, butmany others are tailored to the specific type of vehicle involved. Thebasic physics of crash and impact phenomena in the (low) impact velocityregime of interest in these situations are common to all of these variousvehicles.
With the accelerating use of advanced composite materials in military,commercial, and general aviation aircraft as well as in the automotiveindustry, there is an increasing need to develop a better understanding of
the behavior of composite-material structures under crash and impactconditions which are representative of aircraft (and automotive) crashsituations.
While much work has been done both experimentally and theoreticallyon the severe transient structural responses of conventional built-upmetallic aircraft structures (which absorb a considerable amount of energyas they deform and fold), much less information and experience have accruedon the behavior of advanced composite aircraft structures under thesepostulated severe environmental conditions. Hence, it is timely to reviewand assess this overall problem to summarize the state of knowledge (boththeoretical and experimental) for these two generic types of aircraftstructures, with the principal objective being to identify the key un-resolved problems which must be addressed to improve our understanding ofthe crash dynamics of aircraft structures which utilize a significant amountof composite material in structural regions which can undergo severestructural responses.
Recently the Federal Aviation Administration Technical Center prepareda comprehensive report and plan of research on aircraft crashworthinessapplicable to both built-up metallic and composite-material aircraft [11*.Included in that research plan were essent iallv four categories of crash-
* Numbers in square brackets [] denot t retCrences given in the reference listat the end of the text of this report.
worthiness problems:
a. Air framesb. Cabin Safety: Seat/Restraint Systems and Interior Furnishingsc. Fuel System Protect ion
d. Emergency Ev.itcuoation Svstems
The study carried out and documented in the present report does not addressitems c and d at all; it pertains principally to item a with some discussionof item b.
T n 1981, Thomson and Caiafa (21 wrote an excellent , marv of past,present and planned research on aircraft crashworthiness -,.e reader is
urged to consult Ref. 2 for a clear, concise and comprel ive discussionof the highlights of aircraft crashworthiness work.
In 1979, Cronkhite, Haas, Berry, and Winter of Bel: 'copter Textron
under sponsorship by the U.S. Army Research and TechnolL. boratories(AVRADCOM) reported a study [31 of the crash-impact chariLeristics of
advanced airframe structures. Reviewed in that r-eport are many detailson both experiments and prediction methods for investigating the behaviorof basic structural components and/or structural assemblages under severe
deformation conditions (static and/or dynamic). That study included both
built-up metallic and advanced-composite-material structures. The crash-worthiness state of the art reported then largely prevails today, but withsome updates which have occurred in the intervening period. Also, the
research recommendations set forth in Ref. 3 remain pertinent at this time.
The present report seeks to summarize the crashworthiness state of the
art today but in a more specialized and less comprehensive fashion thangiven in Refs. 1, 2, and 3.
1.2 Overall Research Approach
The present state-of-the-art review of crashworthiness was carried out
by conducting a literature search and study, and by visiting (because oftime and fund constraints) only a few of the many organizations experienced
in relevant work. These steps are described briefly in the following twosubsections.
1.2.1 Literature Search
Since MIT Aeroelastic and Structures Research Laboratory personnel havebeen involved actively for more than 25 years, in both experimental work and
analvsis method developments for various types of simple and complexstructures undergoing severe nonlinear transient response behavior, theMIT-ASRL library and files contain many relevant reports and papers -- bothinternallv and externally generated. These were reviewed. In addition,
the MIT libraries contain many pertinent books, i ornals, proceeding, etc.-- covering many years and including the most recent editions; a catalog
search was made and documents were obtained for study.
In the early stages of this study, FAA Technicall Center personnel gaveand/or loaned pertinent reports t l the MIT-ASRI. personnel. Also, the U.S.
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Army Research and Technology Laboratories sent us 111me d' Lmnt I rom t hei rextensive past work on aircraft crashworthiness.
At MIT we conducted a NASIC librarv search for dOcum'nt. on crash researchand crashworthiness for aircraft and automobi I.s, crash simulation, crashmodels, and composite materia ls. Abstracts oi sonie 710 publications wereprinted out and checked to identify useful documents. Among those documentsconsidered to be pertinent and useful in the present review, about one-halfhad already been seen and studied. We sought to obtain the remainder forstudy.
In studying the various documents retrieved, additional interestingreferences were noted. As many of these as feasible were sought and/orobtained for study.
In addition, telephone discussions were held with various individualsworking on crashworhiness (NASA-Langley, AVRADCOM, Bell Helicopter Textron,...).
1.2.2 Facility Visits
Advice, guidance, and crashworthiness information from FAA TechnicalCenter personnel were sought and obtained during two visits to the FAATechnical Center -- on Sept. 4, 1981 and again on April 16, 1982. Discussionswere held principally with R. Garcia, D. Nesterok, aind C. Nuckolls.
On Jan. 27, 1982 we visited the Structural Mechanics Branch of the NASALangley Research Center to become more familiar with Lhe very extensivecrashworthiness work already conduct-d so ably at that facility and of plannedfuture crashworthiness related work. Various structures and impacttest facilities at NASA-Langley were visited. NASA-Langley personnelgave us a stack of pertinent documents for study, and generously shared
their experience and views on crash response matters pertaining to bothbuilt-up metallic aircraft structures and composite-material structures.Effective design concepts for cabin floors/substructure as well as seats/restraints were discussed and illustrated with example hardware. The paucityof crash response experimental data for many structural components and/orassemblies composed of composite material was noted. Many unanswered
questions remain. NASA-Langley personnel involved in parts of thesediscussions included:
M. Card R. Hayduk H. McComb R. ThomsonH. Carden J. Housner J.H. Starnes
During these discussions, it was noted that various design features foundto be effective in enhancing crash survivability have been identified in theNASA-Langley studies, and certain aircraft operators or manufacturers haveadapted these features to improve crash survivability of specific generalaviation aircraft which employ "conventional construction."
On Jan. 28, 1982, we met with R. Burrows, C .T. (;alow, and T. Mazza atthe U.S. Army Research and Technology Laboratories (AVRAI)CtM) , Ft. Eust is,Virginia. The extensive work already carried out bv AVRADCOM and its principalcontractors was reviewed. Crew or occupant survivabil it v in hi 1 it pt ,rcrashes has been a primary concern. Crash allevi;ition featurts in( ludcd inthe landing gear system, the fuselage subfloor, and stroking sat t
3
enhanced crash survivabilitv. The upcoming construction and impact testingof full-scale composite-material fuselages are expected to provide betterinsight into the crash responses Of these advanced types of structures. ['heAdvanced Composite Aircraft Program of AVRAI)COM is expected to include'crash response assessments as an important aspect. Experience to dateindicates that fiberglass composite "covers" offer better abrasionresistance than do Kevlar or / "covers." The use of Kevlar in sandwichtype construction is effective where crash survivability and alleviationare desired. AVRAI)COM personnel provided a number of reports on their andsponsored crash response work for subsequent study.
On March 23, 1982, a visit was made to the Air Force MaterialsLaboratorv and to the Aeronautical Systems Division, Wright-Patterson AFP,Ohio. Discussions were held with Ir. S.W. Tsai and Dr. R.Y. Lim (of theUniversity of Dayton Research Institute) at the AFML, and with .J. Lincolnand W. Dunn at the ASI).
Drs. Tsai and Lim discussed experimental studies (,f failure mechanismsfor various types of laminated composites and exhibited manv specimen. whichillustrated these failure modes. Fatigue and creel) studies for simple1composite structures were reviewed, some ongoing expt, rilents were dermust-irted,
and related papers and reports were provided.
Mr. Lincoln and Mr. Dunn outlined the current Air Force crash loadsrequirements and described recent studies of survivable accidents. AirForce emphasis is on flight safety practices, minimization of landing/takeoffcrash effects by terrain smoothing adjacent to runways, wing root integrity,and the use of self-sealing fuel tanks, foams, and fire extinguishers.
1.3 Structurol Crash Response Overview
Interest in understanding and alleviating the effects on vehicleoccupants of crashes has been active for many years. The work of DeHavenreported in 1944 [41 was pioneering, identified key items that contributedto injuries in aircraft crashes, and offered guidelines for improving thecrashworthiness of light aircraft. Subsequently, these guidelines wereapp] ied in the design of specialized light aircraft. Since then, manyorganizations (NACA, U.S. Army, FAA, NASA,...) have conducted and/orsponsored a succession of studies to develop the state of knowledgeconcerning vehicle crash response for a wide variety of civilian and militaryaircraft, and such work is being pursued vigorously at the present time.
Similarly, the automotive industry and cognizant federal agenciessuch as the National Hlighway Traffic Safety Administration have beencarrying out detailed studies of crash response for a variety of vehiclesand components since about the mid 1960's.
Common to both aircraft and automotive vehicle crash response havebeen considerations of survivable environmental conditions, human toleranceaccelerat ion-time-direct ion levels, load-limiting concepts, intrusionlimitations, structural component crashworthy design and integration, andfire prevention measuc es, including fuel containment. In the folowing,however, discussion will be I imited to structural respoMse behavior --
4
under "survivable" conditions -- the other cited topics are bevond thescope of the present study.
To assist in identifying the principal structural response and failurebehavior under crash conditions, full-scale crash tests [5,61 were conducted
bv the FAA on a DC-7 and a Lockheed L-1649 aircraft in 1964 at the FlightSafety Foundation facility in Phoenix, Arizona. Later in the 1972-1980time period, various types of full-scale light aircraft, a CH-47 helicopter,and aircraft fuselage sections were crash tested at the Impact DynamicsResearch Facility of the NASA Langley Research Center [7,8,9,10]. Accelera-
tion, strain, and photographic instrumentation (interior and exterior) aswell as post-morten studies provided transient response, failure, and post-failure data; data from instrumented dummies provided "transmittedacceleration-time" information. In some cases the vehicles were caused to
impact upon concrete surfaces at appropriate combinations of impact incidenceangle and impact velocity. In other cases, impact against a packed dirtsurface to simulate conditions in a plowed field was employed. These testspermitted observing,under many realistic but controlled conditions,representative types of transient and failure response, but various secondaryeffects such as aircraft overturning, cartwheeling, or tree and obstacle
impact were not covered in these studies [11].
Since the late 1950's [3], the U.S. Army has been carrying out aneffective and comprehensive study of crash behavior of Army aircraft,accident data, and concepts to improve crashworthiness. Highly important
crashworthiness developments were made, and this work resulted in the Crash
Survival Design Guide [12] which subsequently has been revised and updated[13-171. Those guidelines are used by aircraft designers to meet criteriaspelled out in MIL-STD-1290(AV) for I.ight Fixed-and-Rotary-Wing AircraftCrashworthiness [181. This has resulted in a very substantial improvementin aircraft crashworthiness performance and occupant survival in the field.This development program included an extensive Army Flight Safety and Heli-copter Crash Testing Program [19] and a program of laboratory tests.
Similarly, under the auspices of the National Highway Traffic SafetyAdministration various organizations have conducted a wide variety ofcrash tests on many different types of vehicles and structures. Extensivephotographic and other instrumentation provided data to identify theprincipal types and sequences of structural failure and crush-up presentin each of many vehicle/structural systems. This led to innovative designsfor load-limiting and appropriate energy management histories to enhanceoccupant survival. All of this work has been supplemented by laboratorytests of structural components and assemblages under static and (sometimes)dynamic conditions. Many of the automotive manufacturers have conductedsimilar very extensive research the results of which are reported in partin the open literature.
The aircraft and automotive crash/impact experiments have involvedstructures which can be characterized conveniently in two categories:(1) built-up metallic structures (assemblages) and (2) composite-material
(non-metallic) structural components and/or assemblages; of course,combinations of these two types of structures are common in many of todav'svehicles. Built-up metallic structures "fail" tvpically in some mode ofbuckling and then can undergo a cons iderabl c amount Of deformation and strain
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(and energy absorption) before local structural rupture ,ccurs. oin theother hand composite-material structures may "fail" initially in manydifferent possible modes, but typicallv undergo i rel ativul'V small amount ofstraining before structural rupture occurs. Thus, composite-materialstructures often behavtc in a "relative lv brittle" fashion and soak upenergy rather poorly; however, innovative structural concepts and materialcombinations can be effective [2,31 in absorbing C<rash/impact energy andalleviating the attendant transient rcspons. etffects.
1.4 Report Organization
Section 2 is devoted to a concise description of the status of aircraftcrash research in three categories: (a) helicopters, (b) general aviationaircraft, and (r) transport aircraft. Work in category "a" has beencarried out largely by USAVRADCOM and its contractors while the FAA andNASA have conducted studies in categories "b" and "c" together with theircontractors.
Recent studies on the behavior of composite materials and structuresunder static and impact conditions are reviewed in Section 3.
In addition to extensive experimental static and dynamic nonlinearstructural impact-crash response studies, both in the laboratory and in thefield, a considerable effort has been made to develop theoretical methodsfor predicting nonlinear crash-impact structural responses of both conventionalmetallic and composite-material structures. These prediction methodsoften are designed to focus on certain subsystems of the overall system.In some cases a part of the overall system is modeled crudely while theparticular (connected) subsystem of particular interest is modeled with arelatively high degree of fidelity. Since vehicles of interest consistof many different structural arrangements and configurations each of whichrequires specific and appropriate modeling, it is feasible here to reviewonly the two basic types of modeling and analysis employed: (a) simplifiedlumped-parameter and hybrid modeling and (b) more refined finite-elementand hybrid modeling. These matters are discussed in Section 4 for bothcomplex built-up metallic structures and for composite-material structures.
Crash-response research which is needed, as perceived by variousorganizations and individuals in both governmental agencies and industry,is discussed in Section 5. Noted are the general goals of crash responseresearch as well as several current and planned crash response researchinvestigations pertinent to helicopters, general aviation aircraft, andtransports as well as to basic airframe structures. Some suggestions foradditional research are offered.
Finally, a summary of the present review study and some resultingconclusions concerning the current and planned programs of crash responseresearch are given in Section 6.
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SECTION 2
STATUS OF AIRCRAFT CRASH RESPONSE RESEARCH
Authoritative and comprehensive but concise reports on the status ofaircraft crash and crash-response research have appeared in the past fewyears. This work pertains to helicopters, general aviation aircraft, andtransport aircraft. The earlier phases of those studies dealt with vehiclesof conventional built-up metallic construction, but in the past decadeemphasis has focused upon aircraft structures and structural conceptsemploying advanced composite materials which promise greater structuralefficiency and durability with lower costs. Also sought for composite-material aircraft is "a degree of crashworthiness at least equal to itsreplaced built-up metal counterpart".
Crash-response characteristics of airframe structures of both metallicand advanced composite construction with emphasis on helicopter applicationshave been described in an excellent comprehensive paper by Cronkhite, Haas,Winter, Cairo, and Singley [20]; this was followed by a more detailed reportby Cronkhite, Haas, Berry, and Winter [3]. Extensive laboratory and fieldexperiments, analysis method developments, and design concept studies are
reported; this pioneering work was supported by the U.S. Army Research andTechnology Laboratories (and its predecessors).
Studies by NASA and the FAA on the crash response behavior of generalaviation aircraft have been summarized in a clear comprehensive fashion byThomson and Goetz [111 and by Thomson and Caiafa [2]. Laboratory tests,full-scale crash tests, and analysis method developments are reviewed.
Thomson and Caiafa [21 also discuss past and current studies of transportaircraft crash behavior as well as planned future research in this area,including transport aircraft structures composed of advanced composite material.Many aspects of transport aircraft crash response and crash effects arereviewed. Here also laboratory tests of structural elements and assemblages,under both static and crash-impact dynamic conditions as well as a full-scale field crash test of a fully-instrumented B-720 transport aircraft, arebeing employed to develop a fuller understanding of aircraft crash responseand to lead to improved aircraft crashworthiness and occupant survival.
Wittlin [21] has summarized an extensive series of past crash-responsestudies and transient response analysis developments pertaining to helicoptersand light fixed-wing aircraft. He also has summarized current studies beingconducted for the FAA and NASA on transport crash response problems byLockheed, Boeing, and Douglas; this comprises an earl-y phase of a comprehensivetransport crash response research effort planned by the FAA and NASA. Thesestudies strive to identify categories of potentiallv-survivable crashconditions and the principal structural and systems aspects which influenceoccupant response and survival. Cittlin demonstrates the role and effectiveness
of a lumped-parameter simulation model for analyzing the crash responses ofhelicopters, light aircraft, and transport aircraft.
Since the state of knowledge on aircratt crash response as describedin Refs. 2, 3, 11, 20, and 21 is essentiallv as it exists todav, and those
7 7
descriptions are all written in a concise and lucid but comprehensivefashion, the present authors believe that a redescription and paraphrasingof the contents of those papers would not be nearly as useful. to the readeras these complete papers themselves. Also, it is felt that a "redescriptionand translation" of those papers would result in the omission of key insights,crash response experience, and other useful background data which enrichesone's appreciation of aircraft crashworthiness problems. Therefore,permission has been requested to reproduce those papers in full in thisreport for the reader's convenience.
Accordingly, the paper by Cronkhite et.al. [20] with emphasis onhelicopters is reproduced in Subsection 2.1; that by Thomson and Goetz[111 on general aviation aircraft is reproduced in Subsection 2.2; andthose by Thomson and Caiafa [2] and Wittlin [21] which include discussions
of current and planned transport crash response research are reproducedin Subsection 2.3.
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2.1 Helicopters
The kind permission of the American Helicopter Societv for the repro-duction of the following paper presented originally at the 34th Annual NationalForum of the American Helicopter Society, Washington, D.C. in 1978 and
subsequently in the October 1981 issue of the ,Journal of the American Heli-copter Society is acknowledged most gratefully.
Investigation of the Crash Impact Characteristicsof Composite Airframe Structires
J. D. Cronkhite, . 7. Haas
Bell Helicopter Textron
R. Winter, R. R. CairoGruman Aerospace Corporation
G. T. Single-, III, USAAVRADCOM
PRESENTED AT THE 34th ANNUAL NATIONAL FORUMOF THE
AMERICAN HELICOPTER SOCIETY
WASHINGTON, D.C.MAY 1978
ALL PUBLISHING RIGHTS RESERVED BY THEAMERICAN HELICOPTER SOCIETY
1325 18th STREET. NWWASHINGTON. DC 20036
PREPRINT NO 78-51
9
Investigation of the Crash Impact Characteristicsof Composite Airframe Structures
J. D. Cronkhite, T. 3. HaasBell Helicopter Textron
R. Winter, R. R. CairoGrumman Aerospace Corporation
G. T. Singley, IIIUSAAVRADCOM
Abstract Two fundamental guidelines to considerwhen designing the airframe structure for
The results of a joint Bell/Grumman crash impact are first, that a protectivecontracted effort with the Army are dis- shell be maintained around the occupiedcussed. The effort was directed toward the area and second, that the structure beinvestigation of the crash impact charac- crushable and absorb energy, thus reducingteristics of advanced troop transport heli- deceleration forces on the occupants andcopter airframe structures constructed of large masses. These and other crashworthycomposite materials. Currently available design considerations are summarized ininformation was surveyed on the crash impact Figure 1. When considering the applicationbehavior of composite materials, analytical of composites to a crashworthy airframetools for design of crashworthy airframe structure, it is known that these materialsstructures and airframe structure crash- generally exhibit a low strain-to-fa:.lreworthiness design criteria. Information on characteristic behavior compared to metals.the crash impact behavior of composite Ductile metals such as 2024 aluminum canmaterials was found to be limited. An tolerate rather large strains, deformautomotive study showed that by innovative plastically, and absorb considerable energydesign, composite materials could function without fracture or separation. Because ofefficiently as energy absorbers to reduce this characteristic of composites, energycrash impact loads. Other pertinent absorption will probably not come throughstudies were found that are currently in an inherent stress-strain behavior as itprogress at Bell Helicopter Textron, the can with metals, but rather through innc%.a-NASA Langley Research Center and the U. S. tive design configurations. These config-Army's Research and Technology Laboratories urations will provide for energy absorptionand are summarized. Finally, effects of and force attenuation by other means; forcomposite materials on the compliance of example, the protective structural shellairframe structures with current Army can be surrounded by a crushable materialcrashworthiness requirements are discussed, such as foam, honeycomb or a crushable
composite concept.Introduction
Extensive crashworthiness studies forIn recent years, composite materials metal aircraft structures have been con-
such as graphite, fiberglass, boron and ducted in the past. For example, early inKevlar have been used more extensively in 1960 the U. S. Army Transportation Commandthe design of aircraft components, both (now USAAVRADCOM) initiated a long-rangestructural and nonstructural. It is reason- program to study aspects of crashworthinessable to assume that the helicopter industry which culminated in the issuance of a crashwill have large numbers of production air- survival design guide and the associatedcraft with major structural components, military standard (References I and 2).such as the fuselage, wings, empennage, Research into the crashworthiness and energyblades or landing gear, constructed of absorption aspects of aircraft structurescomposite materials in the near future. was initiated in the mid 1960's with studiesEntire composite airframes have already conducted at General Dynamics-Convair andbeen produced for general aviation type Dynamic Science making prime contributionsaircraft. It will therefore benefit the to the understanding and analysis of theindustry to have an understanding of the energy absorption characteristics of air-behavior of composite materials in a crash frame structures (References 3, 4 and 5).environment before large numbers of pro-duction aircraft are in the field. In order to place this investigation
in the proper time perspective, it shouldbe noted that the lag between the initia-
Presented at the 34th Annual National Forum tion of research into airframe impactof the American Helicopter Society, May energy absorption and its incorporation1978.
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Behavior of Composite Materials
Literature Surve.
The first ste in this part of the
TTI 'N h T ! investigation was to survey existingLkXNI ,C E A...I literature on the behavior of composite
14 .materials in a crosh% environment. Trnedata bases used ir the survey were:
I. The National Technical Infor.atc:Service (NTIS)
-" 2. The Defense DocimentatIon Cente:~ -~ (DDC:
U *1 3. The Engineering Index (Compendex,
'4 / 4. "ORBIT (SDC)
5. *DIALOG" (Lockheed)
IA flow diagra' of the literature- :V.NCE OF A PROTECTIVE SELL search methodology used to retrieve infor-
ARO)UN THE OCCUPIED AREA mation from data bases and other sources-ENERGY ASSORBINC STRUCTURi TC is shown in Figure 2. To access a data/REDL: C RAS i LCADS CN XCr; NT blS ;E base, NTIS for example, blocks of keywordsare formed and input to the system so
-CONTROL OF FAILURE MODES SO AS NOT that all information pertinent to theTC CAUSE FUSELAGE pLOWING OR OCCL- particular topic in question can bePAR. STRIXE HAZARDS retrieved. Keyword blocks are then com-
bined to further focus the search on thesub)ect being surveyed. The number of
Figure 1. Helicopter fuselage crash- references found under keyword blocks andworthiness design considera- various combinations of keywords is pre-tions. sented in Figure 3. Combinations of
keywords and a summary of the literatureinto a design, such as the UTTAS, has been found under each combination are discussedor. the order of F - 10 years. Therefore, in the followira paragraphs.tt, s -nvesticator. represents the initialeffort toward designing a crashworthycomposite airframe structure in the mid196- 'S.
Tne ooectives of this investigationare the following: LPTT:% 1 CO" PM1 SC A Of -VI Of PERE:'-.
DAT A URPORH. j0VC'A.. PA.S"
I. Survey the literature and deter- icmine the existing data base on NS KO FS: A.'
the crash impact behavior ofcomposite materials.
2. Review current analytical methods . M-,-S
usad for the design of crashworthy JD E OC '%::airframe structures and assesstheir suitability for analysis of r.composite structures. tRI-Air ,1 Doc? rS
3. Review current crashworthinessdesign criteria for military andcommercial utility helicopter '",m"'N REVIEWS
airframe structures to determine [ $ vSuATI0gits application to a compositeairframe structure.
Figure 2. Literature survey methodology.
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I
KEYWRZS COMBINAT:Ors There are tw, reports atozt autcnsot;iesthat we:e fabricated in whoje or oart Ls n:COM IES focrglass c nstructior. and test& -, a
crash environment (References 8 and 9 .SCOMPOS:TE 25246) The automooile tested by the bujd Ccn.a.)
CO.POSITES I was a 1974 Pinto two-door sedan wh-c:, wasFIBERGLASS rod:fied by replacinc the fror: fenders andGRAPHITE lower longitudinal frames w;.tn f .Der'ass/
polyurethane foam sandwich panels a-.Z *-tes.BORONHWO (121- 5 The panels and tubes were intended tcCAHWORTHIN 155 CRASHWORTh:Ns attenuate the crash forces wnc .rduring a front-end collison (F.Cre 4-I COMPOSI TES
CRASH series of static and dynaric tes - -ereCRASHES conducted on the tubju. r and n,:. Ce -
- CRASHWORTH:NSS mens prior to retr.-ftting ehc
,32, automobile to val.-ate the c:.c .MENFB$OP'.O~h E.ERGARY ABSORPTIo. the automobile was tested bx a
ENERGY ABSORPTION 1l6 j barrier at 50 mph, the tubes and panels-° ENERG ABSORBER - COMPOSITES 1 attenuated the crash forces unt.. a prerna-- ENtRGY ABSORBERure failure occurred in a tube __ t
A- ENERGY TTENUATION off-axis loading. This il'ustrates the- ENERGY ATTENUATOR (732potential problem with directional eerc-
IMPACT absorbers that off-axis loads nr- res , m.P- Z COMPOSITEfailure of the device and a,.e ine.fec-
I tiveco.P rssICN BC ,
-" COM-SST E COMPOS-|
* NUMBERS IN ?ARENTNESES INDcZCATE NC. OFAVAILAITE REFERtNCES
Figure 3. Literature survey results from c tl L ,::' cwe- .-. rcom~binations of keywords.
Crashwor thines s/Conoo sz te MaterialsTwelve documents were located unoer the corn-'-bination of the two keyword subjects "crash- .-s.k¢ . * ~..worthiness" and "composite materials". A - __
visual examination of the 12 documents did -. ,."- not disclose any published reports apeci-
fically on the application of composite -9t materials to an airframe structure for a : -
crash environment.!
Two of the documents reported on , "'molded chopped fiberglass components thatk.were fabricated and tested for use as ahighway median barrier and as an instru-ment panel glare shield (References 6 and7). The tests of the highway barrier con- z z,cluded that it would prevent vehicles from "% - ,penetrating or crossing the median while ______________________also minimizing their rebound and lowering -their deceleration rates below 6g. The c.>- A sr -, . ',;*tests of the glare shield showed it reduceddecelerations from 300g to 60gm however,its failure produced sharp edges which Figure 4. Crash test of corrpcs:te frontcould cause a head injury. end automobile.
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The conclusion of the Budd Company The results of some tests con.ductedwas that the fiberglass reinforced plastic by General Dynar-:cs-Convair to measure :nesandwich structure was superior to the load deflection characteristics of varic.,solid laminate structures tested by others aluminum plate-stringer panel zonfiqjratic7Sfor energy absorption. The' also concluded are shown in Figure 5. Note that tne loadthat a compos:te structure could be fermu- deflection behavior of the integrall:.lated which would be satisfactory in a stiffened panel :s poor in corpar:son tccrash environment if designed properly. the rolled stringer secticns because the
failure mode was an explosive fracture.Several general aviation type aircraft Also note that the load at initial failure
have used composite construction, but refer- was higher; this translates to hlcnerenceable documents on the accident and inertia forces transmitted to the oczar.-tscrash experience with these aircraft could and to the large mass items dc::n a crasrnot be found in the literature or throuq. impact.the FAA.
At least two helicopter composite 1.
fuselage design studies have been con- -ducted in which crashworthiness wasaddressed. These were the preliminarydesign studies of medium utility trans-port (MUT) helicopters conducted for theArmy by Boeing-Vertol and Sikorsky *. : :c' -.
(References 10 and 11). Although crash- vL :: ::worthiness was addressed, the primaryemphasis was placed on optimizing basicdesign concepts, cost, weight and produci-bility. 2--
Energy Absorption/Composite MaterialsWith the exception of the a- mobile tests,the use of composite materials as energy I if U.absorbers or attenuators has been limitedto low velocity impact applications suchas bumpers (References 12, 13 and 14).There has been work on improving the energy RZ:u .absorption characteristics of compositematerials at the micro or local structural 0 C.;level, but no ccrrelaticn has been drawn ....
between this research and its appl:cationin a crash environment. 5n
Impact/Corposite Materials There hasbeen a great deal of research in the area T TT 3:of impact strength of composite materialsbut this research has been mainly directed - 0toward local impacts produced by tool drops, E :K: znL sPTu=Eforeign oblects, missiles and particles. FS 0 ; CAlthough damage due to a local impact can M::c. E;rt::.. :!compromise the compressive failure mode ofa structure, the techniques used in deter- 'Cr " C5IT. CR2Omining this damage are not applicable to Figure 5. Load-deflection curves fora crash impact involving gross structural various aluminum sheet/deformations, stringer panels.
Compression Failure Mode/Composite In contrast to the work done onMaterials During a crash, the compression metallic structures, the research on thefailure modes of the structure influence the compression failure modes of compositeenergy absorption and crash impact behav ior materials has been concerned with pre-of the design. The work that has been done dicting the static allowable load of aon metal structures has sought to predict structural element. Some test results ofand improve the post-buckling characteris- typical research on compression failuretics of the airfrare structure, thereby modes are shown in Figure 6. The research-
increasing the energy absorbel during a ers were primarily interested in the Post-crash (Reference l5). buckling characteristics of these specimens
and increasing the static allowable loadand not the total load-deflection or energyabsorbing characteristics of the structures.
78-51-4
__ture such as man-facturinc defects, c.re5, _ 'cycle variaton, lamina stac,.n_ sequen.,
- * L--- L E and part geometry. Fracture and a
lAl . IgA. .:.I , .. predictior. techniques need to be revisezrOE! E S :" to correlate with observed failure modes.
' The supportive data necessary f-r.vehicle design development shoulc incude
/ - topics such as the crash impact response2'of structural configurations and materials,
/ -0 the survey of crashed advanced compos:tefield components and the assessment of the
low' crash impact response compared to currentmetal helicopter structures. The cras7.
-s,:: A ' "Impact response of the candidate strur:.;ra
.C. :.o- . . ,. components has to be obtained throucn tes:
D]SPALAET (1h.) or analysis before their effect on the over-
Figure 6. Load-deflection curve for all vehicle response can be assessed.
graphite/epoxy plate Particular emphasis should be placed on tne(Reference 40) crashing behavior of the structural el¢-
ments and the fracture and fragmentatior.behavior which is peculiar to composites.
Topics for Further InvestigationThis investigation was concernez w..
Static and fatigue behavior, analytical the structural aspects of crashworthiness,techniques, environmental effects, manu- but the sub3ect of flammability and thefacturing, processing, and nondestructive hazards associated with the thermal decc--evaluation techniques have rece:ved suffi- position of polymeric composites d ur~n=cient attention to support the application post-crash fire should receive furtherof composites in helicopter advanced struc- attention. in particular, what is neeaedtures. However, the survey revealed several is a study of the noxious gas and smoKetopics which will require considerable evolution during the polymer thermal decc-attention before reliable, lightweicht, position. Emphasis should be placed on thecrashworthy, advanced compos:te hel:copter variables which affect decompos:tion and thestructures can be designed. For purposes determination of the human tolerance leve-s
of this discussion, these topics can be to the by-products.summarized under two major categories:support.je data necessary for analytical Another side issue whrch may affect thecrash p:ediction and supportive data for response of a composite material struc..rethe ven-.le design. in a crash environment is that of ser:','ce
life degradation. Since the static proper-The data necessary to support analyti- ties of composite structures can be affected
cal crash prediction should include topics by factors such as low energy impacts
such as structural evaluation, material (e.g., dropped tools, landing site stores)characterization, and failure analysis. and moisture absorption or desorpticn, it
The crash environment also needs to be is logical to expect the crash lnpactbetter defined in terms of tructural properties may also be simularl" affected.attitude, expected strain :Les, and thetime sequence of events. This will helpestablish the criteria for the analytical Review of Analytical Methodssimulation and specific material charac-terization. To fill the gaps in the The recent interest in vehicle crash-current data base, characterization of worthiness has motivated the developmentthe materials should be performed at the of a number of mathematical crash s~mulaticnexpected strain rates for crash impact computer programs. These simulations ca.
and should be in terns of the energy provide a means of evaluatinc the effert."e-
absorption capabilities of laminates and ness of vehicle structures in satisfy-..ccores. This characterization should also a set of crashworthiness criteria, such as
include the post-buckling behavior of the the Army's MIL-STD-1290 (Reference 2). A:
laminated corijisite structures. The area their best, such computer progras can be
of failure analysis needs additional used as a tool in the design process in
attention because of the complex failure which crashworthiness is a new structural
modes of laminated structures for crash requirement in addition to those which a!-
impact loading. Tnis complexity results ready exist for static strength, fat;gue
not only because of the heterogeneous, resistance, dynamic response, and (battle
anisotropic nature of these materials, but damage tolerance.also because of complications which alsoaffect the static performance of the struc-
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As part of this study, an investiga- The main characteristics used fortion was made to determine the usefulness evaluatinc the functionality of the mathe-of currently available plastic, large matical crash s:mulations were:deformation structural crash simulations;especially those which can be applied to - Capazlity Levelairframe structures of composite materials.This investigation was aided substantially - Structural Modelby previous surveys of the crash simulationliterature, particularly those done by - Mathematical TypeSaczalski (Reference 16), Mclvor, et al(Reference 17) and Kamat (Reference 18). - Convenience Features
Use can be made of a mathematical Other features which were of secondarycrash simulation during the design process importance in this investigation were:as shown in Figure 7. The key elements in the mass model, the terrain and barrierthis process are a set of design criteria model, the external loads, and the numer -and a valid crash simulation method. In- cal solution procedure.puts of structural behavior, which take theform of stress-strain curves or component For this study three broad categor.escrush test data, are used to predict the of capability level were established, alonestructure's dynamic response. The crash- with potential uses during design. Theyworthiness of the design can then be evalu- are as.follows:ated against the criteria to determine ifit is satisfactory or if a redeisgn is Simn1e Ca ability These simulationsnecessary. During this process, some simu- can be use to eva uate gross responses andlations require the assumption of internal design trends. They feature:crush modes while others are used to pre-dict them. It should be noted that experi- 1. Large structural assembliesmental crash simulations can also be used, modeled as single crush elementsbut because of cost factors, are probablybest used for validating the final design 2. Up to 10 masses, 50 degrees-cf-as determined by the analytical methods, freedom (unknowns in motion
equations)
3. One or two dimensional geometry
and motions
(nt rN Intermediate Cajability These simula-
cmts~~c:;~tions can be usec ror studies of structura.design parameters and energy dissipaton
I in subassemblies. They feature:
S s~l~'X~tt ,ES 1. Structural subassemblies modeled
separately, no sheet/skin panelmodel
LC A tSG 2. Up to 100 masses, 500 degrees ofo : Jfreedom
C-LOADS, l D FAO
cDMai4ED LOADS 3. Two or three dimensional geometr-stMS;. M?5 'and motions
P Detailed Capability These simulationsLOAC O - can be used opreding failure or
< ACr( UTAAsE_ r collapse modes, and redesigning individ.alR,:st cp:TnE:L components. They feature:
1. Individual structural componentsmodeled separately, includingsheet/skin panels
2. More than 100 masses, 500 degreesas5 of freedom
3. Three dimensional geometry andmotions
Figure 7. Computer crash simulation invehicle design process.
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masses connected by norlnear a>, a_ annrotary scrin s rn a predetermned arranre-
ment. Bctr. of these s5-__a-_cns are :wodimensional.
grams, the most advanced, and Der-.azs the
most widely used, hybrid simulation 's
"KRASH" by W-ttlin and Gamon of Lockheed- California Co. (References 25 and 26.
S-M ir M "KRASH" utilizes a three-dimensional"C P O$, iAt- E AD s arbitrary framework of point masses connec-
r., ted by beams to simulate the fuselacestructure. The remaining intereoa-e
..- capability programs use finite ele-en: cor-." puter codes and include: Shieh's wor, at
..../. > Calspan Corporation (Reference 27,, "CJh" by Young at Philco-Ford (References 2E an
29) and "UMVCS" by McIvor, et a!, at tne2. / . -University of Michigan (Reference C,..
-- V Shiih idealizes the structure as a two-dimensional array of bears with yieldnc:confined to the plastic hinges at theirends, while "CRASH" and "UMVCS" use three
dimensional models of a framework of rods *F- and beams. "UMVCS" could also be consid-
ered a hybrid because it requires testKdata input to define the moment rotatncn
INTE ME,:ATE M3:rL curves for the plastic hinges at the bear*55A55
a-L he e o fn ends.
The detailed crash simulations are
all three-dimensional finite element codeswith the capability of modeling stringers,beams, and structural surfaces such asskins and bulkhead panels. The four codescurrently available are: "WHA.M" by
Belytschko of Northwestern University(Reference 31), "WRECKER" by Welch, et al,tf :llincs Institute of Technology
.:erence 32), "ACTION" by Melosh, et al,c/ Virginia Polytechnic Institute of Tec-
noiogy and State University (Reference 331,and "DYCAST" by Pifko, et al, of Grumznan
DETA:MLD MOrEL Aerospace Corporation (References 34 and[WREC"KLP - WELC B UCE 35). "WHAM" currently can be used to
idealize a structure which contains onl'
Figure 8. Examples of mathematical isotropic material. It uses partly inter-
simulation capability levels, active yielding, i.e., neglects the effectof shear stresses on plasticity. "WRECKEP"contai.-s the same formulations as WH.:' but
Figure 8 shows specific examples of the also has the added convenience features of
capability levels of three mathematical graphics and restart. "ACTION" also has
crash simulations as applied to automobiles partly interactive yielding, and it can be
and rotary-wing aircraft, used only with a structure constructedwith isotropic materials. Adiltional.v,
Numerous simple capability hybrid "ACTION" also contains an internally
simulations are available (References 19 varied time step with numerical error
through 24, for example). Of these, the controls. "DYCAST" can idealize a struc-
two most notable programs are those ture constructed of orthotropic material.
authored by Herridge and Mitchell of Its features include: fully interactive
Battelle Columbus Labs and by Gatlin, et al, yielding internally varied time steps
of Dynamic Sciences, Inc. The work done with error control, restart, and graphicby Herridge and Mitchell was directed output.
toward automobile crash impacts, whilethat done by Gatlin, et al, examined the A surmary of the assessment of these
vertical impact of a helicopter fuselage, specific crash simulations is given in
This latter program (informally called Table 1. Note that the hybrid codes do not
"CRASH") simulates the fuselage as rigid account for collapse or failure under ccn-
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16
:_________________________ _ Researcn in Procress
- -- '. During the survey of the current cata- : ,A A base of information on the crash. impact
behavior of composite structures, somes,:* . AROZ,[ .- pertinent research in-progress was fc,;ni
that has not vet been doumented or . . a;
aviSa~ -o thopuli. h threE areascf researc.
, in-progress that wil be dis-
*r~ZRZS-S~r:. :rc~~.cussed ares
.rn:;. S.. ," The NASA .anoe; s-d,, of a~rfra-eST.!, sT! s:rrFE.,:1Z "F -s:pp crashwcrth' desiar. cor.cepts f_:
KE":D,. aeneral avat-:ln airzraf:.
_ _-2. The Bell Helicopter testing of
Table I. Computer Crash Simulations energy absorbing cylinders.
Assessment. 3. The Army testing of stiffened
cylinders and helicopter fuselagebined loads, because the crash data inputs structure sections.are derived from tests with a sinale load.All of the finite element codes, with the Airframe Crashworthy Design Conceptsexception of Shieh's, can account formultiple load components. The crush test A joint FAA and NASA research procrarcan furnish the hybrid computer codes witn is in progress at Langley Research Centerdata to analyze orthotropic laminates and to develop valid, practical structuralcore-sandwich panels, while only "DYCAST", design criteria and improve crashwcrtninessof the finite element codes, can analyze design technology. The total progra7 isan orthotroptc material, and none of the shown in Figure 9. NASA, under the direc-evaluated finite element codes can tion of R. Thomson, Crash Safety Procrarcurrently analyze a core sandwich. Group Leader, is conducting full-scale"WRECKER" is the only one of these codes crash tests of light fixed wing aircraft,which will account for strain rate effects developing analytical techniques and eval-in a logical way by determining the local uating crashworthy design concepts fcrstrain rate and ad3usting the stiffnesses. seats and airframe structures.All the hybrids can account for jcint fail-ure and crippling, because these effectsare part of the crush test data.
The major conclusions of this investi-gation on computer crash simulations foradvanced material applications are:
I. That there is not a singleexisting code that is satisfactory
2. That hybrid codes are theoreti- ,cally incomplete. I' .00 i TA-r0, p., [-fl°':
3. That finite element codes currently ,ACIc,. .S. -,
lack sufficient advanced material DATA '
capability. (VA UAIL , I ___
The recommendation for current crash simula- I. Si 5"
A%: ,A.I A1tions on advanced materials is to use A C %":C-'- . %., SA.',A.*"KRASH" with applicable crush test data for ,J[s 1 7 .the preliminary parametric studies and gross A ", A---____
evaluations. For a detail design, "DYCAST" 1 N:FP'Scan be used for analyzing designoDCS .c1w,-i0 I.A.(A ] AA .A
laminates. However, this code is stillunder development and has not yet been.experimentally verified. It is not cur-rently possible to perform an extensivedetailed design evaluation of a structurewith sandwich core construction. Thistype of construction seems to hold promisefor increased energy dissipation with Figure 9. Joint FAA/NASA aviation crash-advanced composites. worthiness program.
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H H:GH ST;Er.' TH F'S H Z ';
BEFORE c j x___ ___ __
IMPACT 01i..11.0._.,___,,
AFTER - _
FORMABLE CORRUGATED HONEYCOMB CORRUGATED LOtGI TUZI ALKEEL WEB KEEL WEB OR FOAM SUBFLOOR + FOAM TUBES + FCA!
Figure 10. Energy abscrbing materials in
lower fuselage.
Bell Helicopter is currently under - HONEYCOMB OR FOAM WITHcontract with NASA to develop crashworthy KEVLAR BELLY SKINdesign concepts for the fuselage structureof light aircraft. The primary emphasis ison concepts applied to future airframesconstructed of metal, but consideration is - ENERGY ABSORBING COMPOSITEalso being given to concepts applicable tc CRUSHABLE TUBEScomposite structures.
Energy absorbing concepts that can beapplied to the lower fuselage structure are - FOAM AS"; COMPOSITE LONGI-currently being designed and will be tested TUDINAL TUBESlater. Crushable material in the lowerfuselage is being designed to attenuatecrash forces, absorb energy and distributeloads to the primary structural shell.Typical examples are shown in Figure 10. - KEVLAR/SEMI-RIGID FOAM/Concepts applicable to composite structures FIBERGLASS BELLY PANare shown in Figure 11. Figure 11. Energy absorbing concepts
for composite fuselaqestructures.
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L
t 6 0C r E : G F C H A . F E F
LGRAPh:" TE
C.
20CC
I. .. . C' - . .-
450 300 15 c F 7T
G R A P H I T E / . . . . . .. . . . . .
6000 ANVIL
coA:;
1(EVLA_ ,ooo -.
6000I. 30400°. . .. . ./ . ....
o *
- 2000 FIBERGLASS 30"
--~- - -- z. 5
45 30- 1s5 FLAT )
FIBERGLASS 0 1 2 3
DEFLECTION (IN)
Figure 12. Static crush tests of Figure 13. Load-deflection curves forcomposite tubes for various energy absorbing compositeanvil angles, tubes.
Composite Tube Enerov Absorbtrs lent static strengths and filament woundat 45* angles from three materials:
When discussing composite fuselage graphite/epoxy, Kevlar/epoxy, and fiber-structures, it generally is assumed that glass/epoxy. These tubes are shown in Fig-some other material is needed for energy ure 12 sfter being crushed on coned anvils.absorption, but there does not appear to beany specific information available to sup- The specimens were statically andport this assumption. Bell therefore con- dynamically tested and exhibited goodducted a study to investigate the energy energy absorption characteristics withabsorption characteristics of some simple progressive failure and a flat, rectang-larcomposite material deformation concepts. shaped load-deflection curve as shown ir.Compcsite tubes were desicned w:ith ea.iva- Figure 13.
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The highest specific energy absorptionfor the tubes shown in Figure 12 was ob- --
tained with the graphite/epoxy tubes cr-shedon a flat (0o) surface and was above 15000(ft-lb/lb). It is felt that since thesewere only preliminary tests this value canbe significantly improved by optimizing Zparameters such as fiber orientation. 0
Specific energy absorption values of 40COO(ft-lb/lb) have already been obtained with .improved fiber orientation using graph.ite, Z
epoxy tubes.
Tests of Composite Structure Sections >.
The Research and Technology Labora- - . -
tories (RTL) of the U. S. Army Aviation 0.Research and Development Command 0
(USAAVRADCOM) have been working on two , -
test programs related to the crash impact .2behavior of composite structures. Thefirst program is to develop standard testingmethods for comparison of the response ofdifferent materials to crash type loadingand the second program is to conduct static Figure 14. Specific energy absorptionand dynamic compression testing of scale comparisons of compositehelicopter fuselage type sections. stiffened cylinders to metal.
R. L. Foye of the Advanced Systems During the progra. sponsored by theResearch Office of RTL, Ames Research Applied Technology Laboratory :ATL, ofCenter has conducted compression tests of RTL and documented in Reference 15,stiffened cylinders in an attempt to develop Lockheed analyzed and tested (static andan economical method of testing materials impact) several aluminum structuralassembled in a manner representative of an specimens representative of typical heli-aircraft structure (Reference 36). The copter lower fuselage structure. Thesestiffened cylinders were approximately 9 specimens were approximately 1/2 the sizeinches in diameter by 18 incnes in length of the UN-lIk lower fuselage bulkhead andand had four equally spaced longerons. stiffener arrangement beneath the trans-Specimens of aluminum, fiberglass, Kevlar mission pylon support, except that theand graphite have been tested, skin, web and angle stiffeners were full
scale. The failure modeE and -ost-failureFor the aluminum specimen, Foye noted behavior of this structure are of interest
that the compression failure modes typical since vertical crash loads are transmittedof aircraft structures were in evidence: through it to the transmission pylon struc-local skin buckling, progressive skin ture. The current ATL test program is tobuckling over the entire surface, local investigate the behavior of similar com-crippling of each stiffener, bending of the posite structures subjected to the sameskin and stringer, complex creasing and static and impact conditions. Becausefolding, fastener tearout, skin puncture specimens of the size tested by Lockheedand skin tearing. This indicates the merit could not be accommodated by the existincin the test method since it exercises the ATL drop tower, a dimensional analysiscompression failure modes known to occur was performed, and the validity of cc-in metal. The results of tests to date ducting the tests using specimens 1 2 theindicate composites configured similar to scale of the Lockheed specimens was veri-metal specimens have lower energy absorp- fied by one static and two drop tests.tion than metal and produce splintering The aluminum honeycomb concept of Ficare 15and more separation of the stringers from has also been static and impact testedthe skin. Figure 14 shows that the energy (14 ft/sec impact velocity). This conceptabsorption for composite specimens was weighs 8.6% less and has a Specific Energyabout 1/5 to 1/6 that of aluminum. Foye's sorption,Ener Absorbedgoal is to develop a standard test method AI Structural Weightythat can be achieved for about one thousand 1.82 times that of the baseline aluninu-dollars per test sepcimen. More tests are specimen. Future testing is planned withplanned with different types of loading specimens constructed of composite materi-in the future. als, e.g., graphite/epoxy and fiberglass.
78-51-Il
5 2 ()
1 /2 SCALE kLUNAUN
co'. E , .. ".1 : .: .. .
t'oAFigure .16. Airframe structure crasftwzr-
thiness criteria and currentdesign criteria.
0 0.5 1.0 I 5 2 a These design considerations have b-ee.
a ddressed in civt lian and military recu;:a-DEFLECTION (IN) t.ons, standards and specification wnereir
they have been formulated into criteria.-cA sumary of available criteria and the
Figure 15. Load-elcin urs.o crashworthy design considerations addressedhalf-scale structure sections. by each is presented in Figure 16.
Crashworthiness Design Criteria By far the most comprehensive crash-worthiness requi;rements document is MK:-
There are many considerations in the STD-1290 (Reference 2i. MIL-STD-129Cdesign of a crashworthy airframe structure. establishes minimum crashworth .ness desionFor this investigation, only those that criteria which, when implemented in therelate to the crash impact characteristics initial stages of aircraft systems design,of airframe structures constructed of will provide aircraft possessing improvedcomposite materials will be discussed. crash safety characteristics. This star-These crashworthy design considerations dard was based on the design guidelines ofare as follows: the Crash Survival Desig Guide. Because
these criteria represena needed capability,1. Maintaining an airfrage protective crash impact survivability, modification of
shell for occupant protection this criteria in any manner that would re-duce the level of crash protection to be
2. Providing tiedown strength to provided was not considered. Althoughreact the applied inertia forces some of the material properties of co-rlto large mass items posites run counter to the material proper-
ties preferred for crashworthy structures3. Designing for breakaway airframe (e.g., low ductility, fracture, and
structure to reduce the total mass splintering), nothing learned in thisinvestigation indicates that the crash-
e4. Reducing occupant strike hazards worthiness of M IL-STD-1290 cannotbemetwithin the caoin area with structures constructed fror omposite
materials. On the contrary, the afore-5. Absorbing energy by fuselage mentioned Budd Co. automotive effort with
crushing fiberglass/polyurethane foam sandwich6 panels and tubes indicates that crash-
6. Reducing post-crash hazards worthy composite structures are possiblethrough innovative design. Certainly
7. Designing for failure modes satisfying the crashworthiness guidelinesshown in Figure I with composite struc-
Discussions of crashworthy design considera- tures is challenging; however, availabletions can be found in the Army's Crash RoD results indicate that the challengeSurvival Desin Gede (Reference 1T'ed is not so much one of simply meeting themany other so urcs, for example, References criteria, rather it is how to do sco15, 37, 38, and 39. without significantly compromising the
78-51-12
.u21
substant&~ate t:~ ... .te a. Len a~ cc ;te S aWhereas sLubsta. a a.cf .~..., ca st::_-tur- elee. tve, ar.worthiness is ZiaseZ or s5cr-' a; arenr.-nc: vr:etcrash tests , n;7erc _5 ::ic-. t,'~ w3 rrt.r.e ss ne re i s ev c-e
ir'.eSt.a.2._ -. -t...F~ s2t2 fror cc-. sanai't;ca. C c: ~ ,:.. . .- ~e azt r. tnr...;r irnno.a*.performed on tne crasnwc :tnr.ess co-- des.c*2.posite airframes.
Ccnclusrc:-. tcan zc-this investic2- -c- c! tne z.behav. or of cC7r ; -e rca- ' a,- as Peferees 1fol lows:I
1. Very l~ttle -r. C c*C §Vl6.tek
COrnps ite s. Tnc .--
raion that was :as,;z!=ari:ec as f .- . r ad ti-:
-The autmotiv'e wor.. do-. tne 3a- ;a- ' 4.Budd Con:z:..~~ie CstrurtIr'~s ZIL or:Es'. . :o: e ~ c:if proper r2 SiC __L nwcrtn; :ecrashwortn: r25s estr : , -tn 0._. es," General~-~--design prccess: alsc, f a onvar k Technicoal es andwic- ccnszr,.ctio;: .- rc.e A: -24, Septem-ber 19(4the enerz;; a:_sC:Lt:Cn:to solid larcinac e conr. ,t.t - 4. Reed, Avrv, 2'. P., :nie
fCor """'n Strzc:.: -n- Prelimrinary tes-s t% ti-c A-, woties fcr- ETC-. an-
indicate that when ocrpc !e Aicraft," Aviation Saftstructures are coflstructec inEncineerina and Resear-!-a manner sir-ilar to metals, they t~,:,STecrnica Re;:r-, 6E-19,exhtt lowc: enerz,' a-5:r--- rc. n,more fractures, pee!.rr; ar.7splinterinc than- metals. 5. Greer, 0. L.,held, T. L. , Wener,
j. D.,"Des,cr. Stud. and 1-ode-- The Bell and aitorcc:ve studies Str~ct-,res Test Proarar tc
indicate that compcsites pro- nmprove Luselace Crashwcrtn_-gressively crushed exn:;t cood ness,' General D\'rari.cs, Ccnva:renergy absorption charac:te~i- FA Technic a! Report DS-E7-20,t Ics. October 1907.
2. There is considerable dat;, c.- 6. Riddel.l, R. M'. Molded Fiberglassbasic strength, pro~ect;lciL act Narrow Median Barrier," Rockwelland foreign onject darae (FOD) International, Ashtabula, Ohio,
4of composite materials, o-,t this rederal Hichwav Adrn inistra-iondata does not pertain tc cran Report RD-75-25, Decer-ber 1974.impact.
7. Lancston,' E. D. , Swearincen,3. Conrpiter analysis metnod!s art- 'Ea-aino ~brla lr
still being verified fcr mnetal Shield for Protection Againststructures, while composites will Head :n~ury," Civil Aeronedicalneed special treatment because Institute, Oklahoma Citv, okla-of their brittle failure charac- hors, FM_ Technical Report
4teristics. FAA-AYM-72-7, Februarv 197:..
4. There is some research in-progress S. Jahnle, H. A., "Feasib;lit. Stud. ofby the Army, NASA, and Bell direc- Plastic Automotive Structure,ted towards inves::natior. cf the Budd Cora7:, Fort Was _-tn,crashworthiness of composite air- Penns'~v'an~a, Department cfcraft type structures. Transportation Report NC.
_zPR-3.P3-Tr, AuzuSt 197'.
22
9. Raschbichler, H. G., "Technical and 17. Mclvor, I. K., Wineman,,A.5.,Economic Aspects Concerning the yanc, W. H., Bowman, B.,Application of the Self-Su F - "modelling, Simulation, andporting Plastic Sa; dwich Con- verification of Impact Dynarmics,
struction to Electric Transpcrt Vol. 2, Stdte of Art, ComputerVehicles," Messerschmitt-Boelkcw- Simuations of Vehicle Impact,"
Blohm, International Vehicle S.- DOT Report HS-800-997, Februaryposiur and Exposition, February 1974.1974.
18. Kamat, 11. P., "Survey of Computer
IC. Hcffstadt, -. J., Swatton, S., Procrams for Prediztion of Crash"Advanced Helicopter Structural Response and Its ExperimentalDesign Investigation," Boeing- Validation," Measuremen: and
Vertol Company, Pniladelph~a, Pred:ction of Structura. a7z
Pennsylvania, USAAMRDL TR 75-56, Biodynamic Crash Impact Res--'se,
March 1976. ASKE, New York, 1976, pp. .3-48.
11. Rach, J. 3., "Investigation of Ad- 19. Emori, R. I., "Analytical Approach tovanced Helicopter Structural Automobile Collision," SAE paper
Designs," Sikorsky Aircraft 680016, January 1968.Division, Stratford, Connecti-cut, USA nRZL TR 75-59, May 1976. 20. Miura, N., and Kawamura, K., "Analysls
of Deformation Mechonisns in
12. Jones, B. H., "Design and Productio Head-On Collisions," SAZ paper
of Economical FRP Energy Ab- 680484, May 1968.sorbing Ssytems for Transporta-tion Applications," Goldsworthy 21. Tani, M., Emori, R. I., "A Study on
Engineering, Inc., Torrance, Automobile Crashworthiness."California, SPE National Techni- SAE paper 700175, January 1970.cal Conference: Plastic inSurface Transportation Proc., 22. Kamal, M. M., "Analysis and SimulationNovember 1974. of Vehicle-to-Barrier Impact,"
SAL paper 700414, May 1970.
13. Newton, D. A., "Dunlop Composite
Energy Absorbing Bumper Systems," 23. Herridge, J. T., Mitchell, "Develop-Dunlop Ltd., Leicester, England ment of a Computer Sim-ulaticnSAE Meeting, February 1975. Prograr for Collinear Car'Car
and Car/Barrier Collisions,'
14. Eshelman, R. H., "Future Bumper Battelle Columbus LaboratoryMaterial up for Grabs," Auto- for Dept. of Transportation,motive Industry, 147, December 1, Report DOT-HS-800-645, January1972. 1975.
15. Wittlin, G., Park, K. C., "Development 24. Gatlin, C. I., Goebel, D. E., Larsen,and Experimental Verification of S. E., "Analysis of HelicopterProcedures to Determine Nonlinear Structure Crashworthiness,"Load-Deflection Characteristics USAAVLABS Technical Reportof Helicopter Substructures 70-71A and B, U. S. Arm,' AirSubjected to Crash Forces," Mobility R&D Lab, Ft. Eustis,Lockheed-California Company, VA, January 1971.Burbank, California, USAAMRDL-TR74-12A, May 1974. 25. Gamon, M. A., Wittlin, G., "Analytical
Techniques for Predicting Ve i-le
16. Saczalski, X. J., "Modelling and Crash Reponse," in AircraftAnalysis Techniques for Pre- Crashwcrthiness, Universit. Pressdiction of Structural and Bio- of Virginia, Charlottesvii~e,dynamic Crash Impact Response, 1975, pp 605-622.
Finite Element Analysis ofTransient Nonlinear Structurai 2E. Wittlin, G., Gamon, M. A., "A Method
Behavior, ASME, New York, of Analysis for General AviationPublication AMD Vol. 14, 1975, Structure Crashworthiness,"
pp. 99-117. Meas.rement and Prediction ofStructural and Biodynam-c Crash
Iat Response, ASME, New York,
7_-51-14
S2
Shieh, P. C., "Bas-: Resear:ch 2n 3'. Carrcll, J., Knowles, W., " -- 5Crashworthiness II - Larqe S. Army 'Chinook' Mo:Yu;Devlection Dynam.ic Anals s of Evaluation," Report of CrasnPlane Elasto-Plastic Franc Injury Evaluation Flic t SafetStructures," Calspan Corp, Foundation, Inc., Phoenix,Repcrt YE-2987-v-', Aucust 1972. Arizona, TREC Tecnnica: Rezort
TR 60-54, September 191 .28. Young, J. W., "CRASs: A Computel
Simulator of Nonlinear Transient 38. Wttlirn, G., Gazmon, .. A., "rxperi-Response of Structures,' U. S. mental Program for the Develop-Dept. of Transportation, Report ment of Improved Helic:terDOT-HS-091-1-125B, 19%I. Structural Crashworthine.sE
Analytical and Design Tec-29. Melosh, F. J., "Car-Barrier :mact niques," Lockheed-Califr._a
Response of Conmuter-S;nulated Company, Burbank, Califcr.:a,Mustang," U. S. Dept. c: USAAMRDL Technical Recc:t 7Z--:,Transportation Report DOT-HS- May 1973.091-125A, 1972.
39. Saczalski, K. et al, Aircraft Crasr-3C. McIvor, 1. K., Wineran, A. S., worthiness, Universit,: Press cf
Anderson, W. J., Wang, H. C., Virginia, Charlottesv'ile,"Modelling, Simulation and Verifi- Virginia, October 1975.cation of Impact Dynamics - Vol.Vol. 4, Three Dimensional Plastic 40. Spier, E., Kjouman, F., "PCs-Hinge Frame Simulation Module," BucLling Behavior of Graphite'U. S. Dept. of Transportation Epoxy Plates and Channels,"Report DOT-HS-S00-999, February presented at Army Symposzur on1974. Solid Mechanics, Cape
Mass., Septemiber 197E.31. Belytschkc, T. B., "WHA.M User's
Manual," University of lllinois,Report 74-B2, 1974.
32. Welch, R. E., Bruce, R. W., Belytschko,T. B., "Dynamic Response of Auto-motive Sheet Metal Under CrashLoadings," AIAA paper 75-791,May 1975.
33. Melosh, R. j., Kamat, .. P., "ComputerSimulation of a Light AircraftCrash," Journal of Aircraft,Vol. 14, No. 10, October 1977,pp. 1009-1014. 3
34. Armen, H., Pifko, A., Levine, H.,"Nonlinear Finite Element Tech-niques for Aircraft CrashAnalysis," Aircraft Crashworthi-ness, University Press of--7
inia, Charlottesville, 1975,pp. 517-548
35. Winter, R., Pifko, A. B., Armen, H., P"Crash S~mulation of Skin-FrameStructure Using a FiniteElement Code," SAE paper 770484,April 1977.
36. Foye, R. L., "The Energy AbsorptionP Capacity of Stiffened Composite
Cylinders in Axial Compression,"presented at AIAA/ASME 19th .Structures, Structural Dynamicsand Materials Conference,Betnesda, Maryland, Apr:i 1978.
78-51-15
I
2.2 tener;l Aviation Ai r, rtf t
To rris, r on f t ,uthors for tuo reprodnto't ion tI 1 ol oWin11paper bv '1'ikrrioru a d ;t.t ," 1-,in Lld 1 V L ' d .1t ,'t' AIAA/ASMIt. !ASCtK/AIIS20th Struitnt r.i , S t rict irl )vnrics, nnd M at tori .'l ,; (Ioit,.rtonc . Apri I"-6,1 979 and s oh stqr tuitu t I v in t h, A\u n t 1980 3 t I ss f of t , ,ht imr i I i t A i r 'r,i I ti o know I d d ir to f ii I I
A AIAA 79-0780RNASA/FAA General Aviation Crash DynamicsProgram-A Status ReportR.G. Thomson and R.C. Goetz
Reprinted from
Volume 17. Number 8 August 1980 Page 584This paper is declared a work of the U S Government and therefore is r thse
JOUP11 O A11PIRPublic domain
AMERICAN INSTITUTE OF AERONAUTICS AND ASTRONAUTICS e 1290 AVENUE OF THE AMERICAS * NEW YORK, NEW YORK, N Y 10104
_6
584 AIRCRAfI \()l I- N()
AR 11 1 1f No '9 O'8OR
NASA/FAA General Aviation Crash Dynamics Program-A Status Report
Robert G. Thomson* and Robert C. Goetz t
NASA Langley Research Center, Hampton, Va.
The objective of the Langle) Research Center general aviation crash dynamics program is to developtechnolog. for improved crash safety and occupant survi*ability in general aviation aircraft. The program in-volhes three basic areas of research: controlled full-scale crash testing, nonlinear structural analyses to predictlarge deflection elasto-plastic response, and load attenuating concepts for use in improved seat and subfloorstructure. Both analytical and experimental methods are used to develop exoerflse in these areas. Analyses in-clude simplified procedures for estimating energy disspating capabilities and complex computerized proceduresfor predicting airframe response. These analyses are being developed to provide designers with methods forpredicting accelerations, loads, and displacements of collapsing structure. Tests on typical full-scale aircraft andon full- and subscale structural components are being performed to verify the analyses and to demonstrate loadattenuating concepts.
Introduction Langley's principal research areas in the joint FAA;NASAN 1972, NASA embarked on a cooperative effort with crash dynamics program are depicted in Fig. 2. These areasFAA and industry to develop technology for improsed include full-scale crash testing; nonlinear finite element
crashworthiness and occupant survivability in general analysis; seat, occupant, and restraint simulation; and energsaviation aircraft. The effort includes analytical and ex- absorbing seat and structural design concepts. Subsequentperimental work and structural concept development. The sections deal with these L'pics.methods and concepts developed in this ongoing effort areexpected to make possible future general aviation aircraft Full-Scale Crash Testingdesigns having enhanced survivability under specified crash Full-scale crash testing is performed at the Langley Impactconditions with little or no increase in weight and acceptable Dynamics Research Facility' shown in Fig. 3. This facilit. iscost. The overall program is diagramed in Fig. 1. NASA's the former Lunar Landing Research Facility modified forresponsibility in this joint program is shown by shaded boxes, free-flight crash testing of full-scale aircraft structures andthe FAA's role by unshaded boxes, and joint efforts by cross- structural components under controlled test conditions. Thehatched boxes. basic gantry structure is 73 m (240 ft) high and 122 m (400 ftl
Crashworthiness design technology is divided into three long supported by three sets of inclined legs spread 81 m (26'areas: environmental, airframe design, and component ft) apart at the ground and 20 m (67 ft) apart at the 66 m (218design. The environmental technology consist of acquiring ft) level. A movable bridge with a pullback winch for raisingand evaluating field crash data to support and validate the test specimen spans the top and transverses the length ofparametric studies being conducted under controlled full-scale the gantry.crash testing, the goal being to define a crash envelope within
which the impact parameters allow human tolerable ac- Test Methodceleration levels. The aircraft is suspended from the top of the gantry by two
Airframe design has a twofold objective: to assess and swing cables and is drawn back above the impact surface by aapply current, on-the-shelf, analytical methods to predict pullback cable. An umbilical cable used for data acquisition isstructural collapse; and to develop and validate new and also suspended from the top of the gantry and connects to theadvanced analytical techniques. Full-scale tests are also used top of the aircraft. The test sequence is initiated when theto verify analytical predictions, as well as to demonstrate aircraft is released from the pullback cable, permitting theimproved load attenuating design concepts. Airframe design aircraft to swing pendulum style into the impact surface. Thealso includes the validation of novel load limiting concepts for swing cables are separated from the aircraft by pyrotechnicsuse in aircraft subfloor designs. just prior to impact, freeing the aircraft from restraint. The
Component design technology consists of exploring new umbilical cable remains attached to the aircraft for dataand innovative load limiting concepts to improve the per- acquisition, but it also separates by pyrotechnics before itformance of the seat and occupant restraint systems by becomes taut during skid-out. The separation point is heldproviding for controlled seat collapse while maintaining relatively fixed near the impact surface, and the flight pathseat/occupant integrity. Component design also considers the angle is adjusted from 0 to 60 deg by changing the length ofdesign of nonlethal cabin interiors, the swing cable. The height of the aircraft above the impact
surface at release determines the impact velocity which can bevaried 0 to 26.8 m/s (60 mph). The movable bridge allows the
Presented as Paper 79-0780 at the AIAA/ASME/ASCE/AHS 20th pullback point to be positioned along the gantry to insure thatSructures, Structural Dynamics & Materials Conference, St. Louis, the pullback cables pass through the center of gravity and actMo., April 4-6, 1979; submitted May 7, 1979; revision received Nov.26, 1979. This paper is declared a work of the U.S. Government and at 90 deg to the swing cables.therefore is in the public domain. To obtain flight path velocities in excess of 26.8 m/s (60
Index categories: General Aviation; Structural Design; Structural mph) a velocity augmentation method has been devised whichDynamics. uses wing-mounted rockets to accelerate the test specimen on
*Aero-Space Technologist. its downward swing. Two Falcon rockets are mounted at each+Head, Dynamics Load Branch. Member AIAA. engine nacelle location and provide a total thrust of 77,850 N.
26
AUGUST 1980 CRASIH M) \-\\IS N 1't ,Kt.\\0
___e__ tc 1 o:gFaphi. ,oscragc- hottt inlterior andi~vI~e~MAA RAI 10.* I71:c:.ff t j -ti . aii.r hivh spet-j
A,_______ ,It, ',, 1 ,1
1\t. .al .ti, . din fI a rLKMCn . ir
DA'A . '~ * F .1 .TI ;I.ti~c :t -cc UsCF.gc to ica.'d'c Jice rali."ns both IIIF LAJthe A!.'~ ,,l Fc'iz dtnal direcitoritts t, the aircraft asi.'
____________ . lt,.Aiat:t%.itopi dIttutoc.' oJ n Higrisas
V'i,111AL, I.- ca at C 'du:cdI latilcs I fiL loc:ationVEI 4 d~o i i r dii : ate o IIh Fir naer as atre d iscussed i n Kcet The
CNCFI A%, restratint si trm arrangernew and tyvpe of' restraint used %ar\1 L l 'A 11 a" s ~ trccri test to !s
I esi. ConductedFig. I Agency responsibiities in joini FAA/%ASA general aviation A chronological summary of the full-scale crash tests,crashworthiness program, conducted at the Impact Dynamics Research Facility i,
represented in Fig. 4. The shaded symbols are crash tests thathaye been conducted, the open symbols are planned crashI V. 5,.1 AAS Ittests. Dftfrent symrbolIs represent different types of airvaftuttdcr etiflereti impact conditions; for example, o represei,,sa %4 in-engine specimen impacting at 26.8 in's (60 mph) while
1*1a represents the same twin-engine specimen, using thei~iaN' M~it /*elocty augmentation method, impacting at 40.2 m 's (90
~ -~ mph). Various types of aircraft have been successfully crash-' ~-14tested at I.attgicv from 1974 through 1978 including CH-4'
. *~,. helicopters, high and lovv wing single-engine aircraft, andaircraft faoelage eltions Data from these test) are presented
- '~~' in Rets. 2-(, The aircraft fuselage section tests ate sria~ ~ 'a drop- tests condicced to simulate full-scale aircraft cabin sink
SIAT CCOWrates experienced by twkin-engine aircraft tested earlier. TheY responrse if the aircraft section, two passenger seats, and two
dummies ate being simulated analytically (see section onNonlinear Analysis). Some single-engine crash tests wereconducted using a dirt impact surface but most were con-
Fig.2 Rseach rea InLanleygenralavitio crsh ynaics ducted on a concrete surface. The dirt embankment wa's 12.2Fig.2 Rseach rea in angey eneal viaton ras d~ami~ i (40 fi) wide, 24.4 mn 180 ft) long, and 1.2 m (4 ft) in depth.
program. IT he dirt was packed to the consistency of a ploughed fieldwith a CBR of approximatels 4. The variation of full-scale
The aircraft is released after rocket ignition, and the rock ets crstetpamesisntopleaddesotosdrcontinue to burn during most of the downward accelerati on such effects as aircraft oserturning, and cartwheehtng. fire, ortrajectory but are dormant at impact. The %elocit< tree and obstacle impact.augmentation method provides flight path velocities of 2f 8- Controlled Crash lest and Las Vsegas Accident44.7 in/s (60-100 mph) depending upon the number and burn On Aug. 30, 1978. a twin-engine Navajo Chieftain,time of the rockets used. karrying a pilot and nine passengers crash landed iii the deseri
fil
* Fig. 3 Langley Impact Dynamics Research Facility.
Ail
(6 I If It iNlN ANl D k o&- I/ J AIRCRAI 1
)9.74 A>C. -
60: MPH ;" ,[ Nf CONTROL LED TES'
LA,, NAAACEN
,"AN. PASEN 4
EAT ?' 'KG PASSENGERSEAT 74bKG
tig. 4 (,rnerui 8iatiin rursh Iesf %( hedat. PASSENGER DUMMY
11IlkLAS VEGAS A-CIDE NT CABIN FLOOR CONTROLLED TESI CABIN FLOOP
Fig 6 Damage comparison between controlled test and Las %egasacc¢ident.
P IL •I O0RMA L
Fig. 5a Controlled crash.
A ,A " F; ,N PELt IS LONGITUDINAL
C NI' 15
PELVIS TRASVERS(
fle - L 0 04 06 .08 .10 .12 .14 It 18 .22 2 4
FLORA ORMtAL (NEAR RIGHT FRCT LEG OFrETFig. 7 Acceleration time historie from flt passenger and floor ofcontrolled crash test ( - 12deg pitch. 41.4 m/s flight path velocity with5 deg left roll. I deg yaw).
differ in roll attitude at impact but are comparable. Thestructural damage to the cabin of the Chieftain was much
fig 5b Las ela, iaccident, greater than that exhibited by the NASA controlled crash testunder correspondingly similar impact attitudes. The damagepattern to the standard passenger and crew seats of the
shortly after taking off from the North Las Vegas Airport. Chieftain was similar to that in the NASA tests, but generallyAll 10 persons on board were killed, A comparative study of exhibited more severe distortion. The damage patterns suggestthis Navajo Chieftain crash and a similar NASA controlled similar basic failure modes and, in the case of the seatcrash test was made. The controlled crash test chosen em- distortion, a flight path impact velocity in excess of 41.4 mlsplowed the velocity augmentation method wherein the aircraft (92.5 mph) for the Chieftain. Acceleration time histories fromreachs a flight path ,elociy of 41 4 m -5(92.5 mph) at impact. the first passenger seat and floor of the controlled NASAThe pitch angle was 12 deg, with a 5 deg left roll and I deg crash test are shown in Fig. 7 where the first passengeryaw. Figure 5 shows photographs of the two aircraft. The corresponds to the damaged seat shown in Fig. 6.NASA specimen is a twin engine pressuried Naa)o. which Because of the similarity in the damage patterns exhibitedcarries six to eight pasenger, and although the cabin is by seats 6 and 8 of the Chieftain and the first passenger seat ofshorter in length it is similar in structural configuration to the the NASA controlled test, generalized conclusions can beChieftain drawn relative to certain seat accelerations experienced b.
Structural damage to the scais and cabin of the Navajo those passengers in the Chieftain. The peak pelvic ac-Chieftain and to the seats and cabin of the NASA test celerations of passengers 6 and 8 in the Chieftain accidentspecimen are shown for illustratise puiposes itt Fig 6. Much were probabl% in excess of 60 g normal (to aircraft axis), 40 gmore corroborating structural damage i, ontained in Ref 7. longitudinal, and 10 g transverseIt is conjectured that the Chieftain contacted thc rneiar leseldesert terrain at a I,ation along the Iovset tuseige on the Nonlinear Crash Impacl Analysisright side opposite the tcar dor An intan later, the rcv: of The objective of the analytical efforts in the crash dynamicsthe fuselage and the leel right wing topacted The Chicf- program is to develop the capability of predicting nonlineartain's attitude guf prior to iMpiti is assumed, therelioe. to geometric and material behavior of sheet-stringer aircrafthave the following inmpat attitude pitched up ,lightl,. tolled structures subjected to large deformations and to demonstrateslightly to the righ:, and sawed t,, thi Ic: |he .,th aircraft this capahiit, h,% determining the plastic buckling and
ALGUST 1980 (RASH l)\ NAMI(,S PRORAM
co°llapse response 0f such struct ures untie irny~u' c l~aWngs~tl
I0o specific computer progais are being dcseloped, onet h l pe h r ers a tts e o ' u s a t r u : e o c u n dp r o g a m1 J ! U 1 n o s t r n lFfocused on modeling concepts applicable t, large plastideformations of realistic aircraft structural component,, and~~~~the other a %.ersatile scat occ upanit program to "imula't. e
occupant response. lhce to prostm, ate d ,,,i'icd in the - -"tollo, ing sections.
Plastic and Large Defileclion natisis of%onlinear Structures I PL..4's-I 's'st'rnpr#
For seseral years Langley has been des eloping asophisticated structural analysis computer program whichincludes geometric and material nonlhnearities. ' PLANS isa -
finite element program for the static and dynamic nonlinear [ , ' Lu'analysis of aircraft structures. Ihe PLANS computerprogram is capable of treating problems s, hich containbending and membrane stresses, thick and thin axtsymmetrrbodies, and general three-dimensional bodies. PLANS, rather . .
than being a single comprehensise computer program,represents a collection of special-purpose computer program,, S ,:, zii. RAi Li.
or modules, each associated Aith a distinct physical problem.Using this concept, each module is an independent finite Fig. 8 Computer deformation patterns of an aircraft section im-element computer program with its associated element pacting rigid surface with erlical selocit, of 9.1 m,st30ft 'si.
library. All the programs in PLANS employ the "initialstrain" concept within an incremental procedure to accountfor the effect of plasticity and include the capability for cyclicplastic analysis. The solution procedure for treating material ._
nonlinearities (plasticity) alone reduces the nonlinear material t,-OP,
analysis to the incremental analysis of an elastic body ofidentical shape and boundary conditions, but with an ad-ditional set of applied "pseudo loads." The advantage of thissolution technique is that it does not require modification of. * f , .the element stiffness matrix at each incremental load step. A ,,-, R ' 'l/O 3 ..( ombined material and geometric nonlinearities are included 6 _..s_ _ _
in several of the modules and are treated by using the "up- .. ..
dated" or convected coordinate approach. The convected K -i__coordinate approach, however, requires the reformation of , ---the stiffness matrix during the incremental solution process. 3c,"' " I
After an increment of load has been applied, increments otdisplacement are calculated and the geometry is updated. In ,, ------ -- ,-- ---.-
addition to calculating the element stresses, strains, etc., the C . .1 ' .:t
element stiffness matrices and mechanical load vector are isli. 1
updated because of the geometry changes and the presence of Fig. 9 Experimental and computer dummy aecelerations for the -30initial stresses. A further essential ingredient of PLANS is the deg, 27 m/s full-scale crash test.treatment of dynamic nonlinear behavior using the DYCASTmodule. DYCAST incorporates various time integrationprocedures, both explicit and implicit, as well as the inertia Modified Seat Occupant Model for Light Aircraft (MSOMI.Aleffects of the structure. Description
Considerable effort is being expended in developing a good(A'omparison with Experiment mathematical simulation of occupant, seat, and restraint
PLANS is currentls being evaluated by comparison with system behavior in a crash situation. MSOMLA wasexperimental results on simplified structures. In the order of developed from a computer program SOMLA funded by theincreasing complexity these structure% are: an axial com- FAA as a tool for use in scat design." SOMLA is a three-
pression of a circular cylinder; a tubular structure composed dimensional seat, occupant, and restraint program with aof 12 elements with symmetric cross sections joined at finite element seat and an occupant modeled with 12 rigidcommon rigid joints; an angular frame composed of asym- segments joined together by rotational springs and dampers atmetric angles and bulkheads with nodal eccentricities at the the joints. The response of the occupant is described bsrigid joints; and the same angular frame cosered with sheet Lagrange's equations of motion with 29 independentmaterial. Static and dynamic analyses of these structures generalized coordinates. The seat model consists of beam andloaded into the large deflection plastic collapse regime hase membrane finite elements.been conducted with PLANS and compared with ex- SOMLA was used previously to model a standard seat andperimental data in Ref. 10 and reported on in Ref. I11 dummy occupant in a NASA light aircraft section serticalPresently an analytical simulation of a ,ertical drop test of an drop test. During this simulation, problems were experiencedaircraft section is being compared %kith experimental full-scale with the seat model ,heneser the yield stress of an elementcrash data. Preliminary computer deformation patterns are was exceeded. Several attempts to correlate various finiteshown in Fig. 8 using an implicit Newmark-Beta integration element solutions of the standard seat with OPLANE-Mi,algorithm. The use of implicit time integration methods, for DYCAST, and SOMLA. using only beam and membranethis particular nonlinear problem, resulted in more practical elements, to experimental data from static sertical seattime steps than was previously obtained using an explicit loading tests wcre only panially successful. Consequently, toAdams Predictor-Corrector algorithm. The results of this expedite the analysis of the scat occupant, the finite elementstudy are reported in Ref. 12 seat in SOMI A was remosed and replaced with a spring-
><l '
R.G TH\1SON AN!) R.( GOE-T/ J IR( RAF
damper system. Addirrona! modrficatron, ro SOMLA added the seat back and are atta,:hed to the cabin ceilng to hin bothnonrigid occupant coniact surfaces (nonlinear springs) and sertical and forward loads. Two additional load limiters arcincorporated a threc-dimenmonal computer graphics displa. attached dragorrails between the seatpan at the front and theThis modified SONI1 A , ,alled \ISOlI -. .A more complete tor at the rear to limir forward load, onl. The seatpan indiscussion of I.IS()MI A it; cor'puter input reouirenents. the desigrn reriain parallel to the fl,4 while stroking Theand additional experimental analytical comparisons can be length ot the stroke is approxinatetl 30 cm (12 in. in thefound in Ref 14 set tical d~rection arid Ifs cm I- m ) i the torw ard The w&ire
bending Odad limiter is ,impl, a s% ire element, mounted to pas,Comparison w it Experirnen" oser a three-wheeed trolles.% housed in a tubular casing. in
A comparison of full scale crash rest data from the - 30 operation, the w&ire bending troile., Ahich is attached to thedeg, 26.8 m s (6W mph) crash test and occupant simulation top, housing sleese, translates a wire loop along the axis of theusing MSOMI.A i, presented in Fig. 9. The comparison, wire during seat stroking ar a constant force. This type of loadbetween measured and computed acceleration pulses are limiter provides a near constant force during stroking, thu,excellent considering the seat and occupant were subjected to making it possible to absorb maximum loads at humanforward, normal, and rotational acclerations. This corn- tolerance lesels oser a gisen stroking distance.parison, using full-scale crash data, demonstrates the ser. The floor-mounted load limiting seat weighs 10 kg 123 lbmlsatilit. of the program's simulation capabiltts and emplo:s two \wire bending load limiters which are at-
tached diagonally between the seatpan at the top of the rearCrashworthy Seat and Subfloor Structure Concepts strut and the bottom of the front legs. While stroking, the rearThe development of structural concepts to limit the load struts pivot on the floor thus forcing the load limiter housing
transmitted to the occupant is another research area in to slide up inside the seatback (Fig. I Ib). The third loadLangley's crashworthiness program. The objective of this limiting concept tested uses a rocker swing stroke to changeresearch is to attenuate the load transmitted by a structure the attitude of the occupant from an upright seated position toeither by modifying its structural assembly, changing the a semi-supine position.geometry of its elements. or adding specific load limiting In dynamic tests conducted at CAMI (FAA Cisildevices to help dissipate the kinetic energy. Recent efforts in AeroMedical Institute). the sled or carriage is linearly ac-this area at Langley have concentrated on the deelopment of celerated along rails to the required velocity and brought tocrashworthy aircraft seat and subfloor systems, rest by wires stretched across the track in a sequence designed
The concepts of available stroke are paramount in deter- to provide the desired impact loading to the sled. A hybrid 11.mining the load attenuating capabilities of different designconcepts. Shown in Fig. 10 are the three load-attenuatingareas which exist between an occupant and the impact surfaceduring sertical descent: the landing gear, the cabin subfloor, Cli.K A ,.and the aircraft seat. Attenuation provided by the landinggear will not be included in this discussion since it is moreapplicable to helicopter crash attenuators. Using the upward is , ci
human acceleration tolerance of 25 g as established in Ref. 15,a relationship between stroke and vertical descent velocit) canbe established for a constant stroking device which fullystrok :n less than the maximum time allowable (0.10 s) for /hurnj olerance. This relationshop is illustrated in Fig. 10. /Under the condition of a constant 25 g deceleration stroke the /maximum velocity decrease for the stroking available is 12.2 V R r0'
m s k40 ft s) for the seats and 8.2 m/s (27 ft. s) for the sub-floor assuming 30 and 15 cm [12 and 6 in.I in general for atwin-engine light aircraft). For a combination of stroking seatand stroking subfloor. the maximum selocit> decrease WIER sRI,-becomes 15.2 m s (50 ft %l. These vertical sink rates are -comparable to the Arms Design Guide recommendations!' .--for crashw'orth> seat design.
-"at ,-A ceiling-mounted load limiting seat, showIn in Fig. I la. is -SEAT BACK TUBES
similar in design to a troop seat designed for Arms - BA Ehelicopters '
" and weighs 9 kg (20 Ibm). This seat is equipped /twith two %ire bending load limiters which are located inside
l. Y , -- LOAD LIMITER PATH INTO SEAT BACK" -A- 2, ', OCCUPANT CG
* A' o- -... VERIICAL STROKE2 .1 "-*. 30 cm 12 in,
- " ' .F . 2 -" F? . 1 LINK , LINK'C ACCE.CRA
A,2* Qt. hN 4. ,, . .. .. . -,t ,- °( - LOAD LIMITER
tig. I0l Aallable %Iroke for energi dissipation in tpical twin engine lig I I Pownger sealt with wire bending load liniers. ai ( tiling-general asiation aircraft. supported passenger wat: hi tllor-suppurted pasenger seat
AUGLST 1980 CRAsH D)YNAMI(s PRO(R,\\ l89
IV
k- - - -- -.- . ,.rN
Fig. 14 load limiting subfloor concepts.
- -.-- ' ,.. Fig. 15 Load deflection curves for load limiting subfloor concepts.
pulse (Fig. 12b) the seats were yawed 30 deg to the direction ofsled travel. The sled pulses are also included in the figure andrepresent the axial impulse imparted to the inclined dummies.The x- and z-axis of the dummy are local axes perpendicular
Fig. 12 Pelvis accelerations for dummy in standard and ceiling- and parallel to its spine, respectively. The figure shows thatmounted (load limiting) sea subjected to "vetlcal" and for both impact conditions the load limiting seat in general"longltudlnal" sled pulses. provided a sizable reduction in pelvis acceleration over those
recorded during similar impacts using the standard seat.The impact condition associated with a dummy passenger
"'. . in one of the full-scale NtSA crash tests were quite similar to- .. ... ... those defined by the sled est of Fig. 12a, particularl in terms
21f s.. - " "\ oof velocity change, thereby permitting a gross comparison of.their relative accelerations. Figure 13 shows that comparison
Although the dummy acceleration traced from the two tet,-. - , are similar in both magnitude and shape. some pha.e shii i,
AUSiRAt0[ 2A- evident. This agreement suggests that sled e,, ig ptro ide, a
good approximation of durum sea' ,p.,, * .. 'i
aircraft crashes
4- iS _ 'r Subfloor Structure
The subfloor structure o! ,, " . ,. -.aviation aircraft offers about !1 21'
- t. ' stroking distance. which suggesi , : .:
velocity change o1 approsina.r.s10). Aside from that nee,,ai ', A
Fig. 13 Dummy accelerations from sled test and from a full-scale electrical conducts some o.i , . . .crash test underslmllarimpact conditions. subfloor for cnctg. dissipaiion thr,' "u' ' . ,, '
number of energ, absorbing suwfl. . ', - '-vadvanced and Fig 14 ptesen:, Nketn.h'. L
50th percentile dummy instrumented with accelerometers candidates The first three concepts, m, . "loaded the seats and restraint system on impact. The restraint right, would replace existing subfloor sirJu,,,.J all"s.system for these seats consisted of continuous, one-piece, lap I) the metal working of floor beam web, ti lc :7h ene,,belt and double shoulder harness arrangement. dissipating foam. 21) the collapsing ot 'trr Ugaied t-'.
Time histories of dummy pelts accelerations recorded beam webs filled with foam: or 1) the .ollapstig otduring two different impact loadings are presented in Fig. 12 precorrugate, foam filled webs interla,:ced %4ih a noi,:hcdwith the dummy installed in a standard seat and in a ceiling lateral oulkhead The remaining t'o concept, eliminate tncmounted, load limiting seat. The sertica! impulse of Fig. 12a floor beam entirely and replace it %kith a precorrugated canoepositioned the seats (and dumm, to impact at a pitch angle (the corrugations running circumferenttall% around the cro,s(angle between dummy spine and direction of sled trasel) of section) with energ, dissipating foam exterior to the canoe,- 30 deg and a roll angle of 10 deg. In the "longitudinal" and foam-filled Kelar cslinder, supporting the floor loads
590 R.G. THOMSON AND R (J* / I Xlk( RAI I
These five promising concepts are being tested both statically deceleration levels and for reahsti crash data on sutand dynamically to determine their load deflection charac- isability. The anal',tical predictic methods dc'seloped herein
teristics. Some examples of the static load deflection behavior for crash analyses are to be documented and released throughobtained from fourofthe fiseconcepts areshoAn in Fig I5 COSMIC
After repeated testing and sizing (geometric optimiztng) o.these load limiting devices, the three most promising will bechosen for integration into complete subfloor units to be used Referencesas the subfloors in aircraft sections. Drop tests of these air- N aughan, V L and Alfaro-Bou. E , "Impact Dsnami., Research
craft sections will then be conducted at velocities up to 15.2 tacihtN for t-uil-,,alc Aircrati (rash Testing," NASA T' D). "9m's (50 ft/s) to evaluate their performance as compared to April 1976
unmodified subfloor structure. A static crush test will also be :Castle, C B., "Full-Scale C rah Test of a CH -- Helicopter.'
performed on one of each of the subfloor units NASA TM X-3412, Dec 19'6'Alfaro-Bou. E and Vaughan, V L ."Light Airplane ( rash Test.
Conclusion at Impact Velocities of 13 and 2' m sec." NASA TP l(W2, No% 19"4Castle, C B. and Alfaro-Bou. E., "Light Airplane (rash Tests at
Langley Research Center has initiated a crash safety Three Flight-Path Angles, NASA TP 1210. June 191hprogram that will lead ,o the development of technology to 'Castle, and Alfaro-Bou, E , "Light Airplane Crash Tests ar Three
define and demonstrate new, structural concepts for improved Roll Angles," NASA TP 1477, OcI, 1979
crash safety and occupant survivability in general aviation 'Vaughan, V.L. and Allaro-Bou, E ."Light Airplane (rash Test,aircraft. This technology will make possible the integration of at Three Pitch Angles," NASA TP 1481, Nos. 1979crashworthy structural design concepts into general aviation 'Hayduk, RJ., "Comparative Anaiysis of PA-31-350 Chieftain
design methods and will include airframe, seat, and restraint (N44LV) Accident and NASA CRASH Test Data,' NASA TM X-
system concepts that will dissipate energy and properly 80102, 1979.restrain the occupants w~ithin the cabin interior. Curren't gPfko, A., Levine, H.S., and Armen, H. Jr.. "PLANS- A Finite
t Element Program for Nonlinear Analysts of Structures-Vol I-
efforts are focused on deseloping load limiting aircraft Theoretical Manual," NASA CR-2568, No% 1975components needed for crash load attenuation, in addition to 9 Pifko, A., Armen, H. Jr., Levy, A., and Leome, H._
* considerations of modified seat and restraint systems as well "PLANS-A Finite Element Program for Nonlinear Analysis ofas structural airframe reconfigurations. The dynamic Structures-Vol. Il-User's Manual," NASA CR-145244, Ma, 19"
'7
nonlinear behavior of these components is being analytically i°Alfaro-Bou, E., Hasduk, R.J , Thomson, R.G .and Vaughan,evaluated to determine their dynamic response and to verify V.L., Jr., "Simulation of Aircraft Crash and Its Validation.'' Air
design modifications and structural crushing efficiency. Seats cra/t Crashworihmes.N, Saczalski, Kenneth, Single%, 11. George T
and restraint systems with incorporated deceleration devices Plkey, Walter D., and Huston. Ronald L., eds., Uniersti. Press of
are being studied that wili limit the load transmitted to the Virginia, Charlottess ile, Va., 1975, pp. 485-49.W Winter, R., Pifko, A.B., and Armen, H. Jr., "Crash Simulation
occupant, remain firmly attached to the cabin floor, and of Skin-Frame Structures Using a Finite Element Code," SAF Paper
adequately restrain the occupant from impact with the cabin 77-i484 presented at SAE Business Aircraft Meeting. Wichita, Kan.,interior. Full-scale mockups of structural components in- March 29-April I, 197".corporating load limiting devices are being used to evaluate ' .Hayduk, R.J., Thomson, R.G., W ttlin, G., and Kamat, M.P
their performance and provide corroboration to the analytical "Nonlinear Structural Crash Dynamics Analyses," SAE Paper 79-predictive techniques. 0588 SAE Business Aircraft Meeting, Wichita, Kan , April 3-6, 1979
In the development of aircraft crash scenarios, a set of tLaananen. D H., "Development of a Scientific Basis for
crash test parameters are to be determined from both FAA Analysis of Aircraft Seating Systems" FAA-RD-74-130, Jan. 1975
field data and Langley controiled crash test data. The con- Fasanella, EL ,"NASA General Aviation Crashorthiness SearDe\.elopment,- SAE Business Aircraft Meeting. Whichita, Kan.
trolled crash test data will included crashes at velocities 1979
comparable with the stall velocity of most general aviation '5 "D.'namic Science Report: Crash Survival Design Guide."aircraft. Close cooperation with other governmental agencies USAAMRDL TR-71-22, Fort Eustis, Va., 1971.is being maintained to provide inputs for human tolerance '
6Reill., M.J., "Crash~orths Troop Seat Inestigation,''
crteria concerning the magnitude and duration of USAAMRDL TR-74-93, Fort Eustis, \a., 1974
'SJ
S.
2.13 Transport Aircraft
In addition to some disc'ussi on f .l c,,ptt, r inld j Ljfli I Vi;at ion
aircraft , the following two papers ck ,liu ,X,, ,nt ).v ',i ,I t ron. ,rtLcrash response research. Thosc two i1pLr e , rt rv iln I i 1 in t hfollowing by the kind permission o! the authors.
AIAA-81-0803Designing for AircraftStructural CrashworthinessR. G. Thompson, NASALangley Research Center,Hampton, VA; and C. Caiafa,Federal Aviation Administration,Atlantic City, NJ
AIAA/SAE/ASCE/ATRIF/TRB1981 International
Air Transportation Conference50*A.,,,,,n May 26-28, 1981 /Atlantic City, New Jersey
For to.f4o to a" W""Ofth. "a A laU IngtgRgi o AguMina nd .a AsIrfiIcs 120 Avlnuo o INo Am.c&s W YI.. wY 104
33
•, .' ' be,
On 'e,1, A a A 'A, nd tr o"
ana t , eal c o re s A tri* -rg " "++'f ' ....
ant sPat Qfiora.'ns tested dona' aue't'cA' Oro[, tests ant in a hcZorint! le :eera-c, ,'c1 lit. o'tuter prediction Ir" i Ad d ''t"''5in'te-element rn-"' ea' computer 'I ra" c. . t. a'm; ,
a' the acceleratier time-histories of these'n - - A 'Aft e ' .vat Ie seat and S.b'loor Structure are Drese-Prr e .Proios'o d;i, catIin of these computer tech' 'e f 'rxs' 'ro n. per" ,'' ,and the nonlinear lumoped mass compter orer i- ove'd I, h I I.thiness .t ' . .KAASn, to transport aircraft crash d.namics s ha teer .tat td 1 1 O l'' in . ; ..discsoed. A proposed FAA fulI-scale rras' testI Safet, art 1'rP, 1 ODr na. "t'n r"!ra'of a folly instrimented radio contralled transport (Fig I .al'dated seiectel crasnwrtI. pe..airplane Is also described. conceit 'rie Arj s interet ' a.',--
continues tc this day 'he -y5'isr 1.1',
recent.,odatnd on the basis c t"e 't'Introduction research resilts, a cnashwOrth, .t' 't, ne '
(Blackha.n; h been out into "rduc a
Aviation crash dynamics research has a production ' a crashwnrtn attack ne'',history (fig l> datin back to the pioneering mmine r"work of Hugh DeHaven in the 1940's. Havingsurvived a midair collision and the ensuinn crash Adva'ced materials and in Aart c'that took three lives. Defaven initiated research qranhite-epoxo coyosites, are betno Corii'erel tinto crashworthiness wherein ie did onsight inves- the A'my for future helicopter weiqht-sa
tinations of aircraft accidents to identify com- designs. The Army has embarked on a Proqra .ponents and/or subsystems contributing to injuries build an all composite airframe he! copter, t,#and/or fatalities. Results from this research still reduirinq that the crashworthiness reProduced deslqn guidelines that are still Pertinent mentS. ac;:, Icable to metal aircrat, be ad- 'even today.: in the design stage :
The A-I croodusting aircraft, built by Fred In lm'?, NASA embarked on a cooperatlve elf-rWeick at Texas A & M College, incorporated a with FAA and industry to develop techInolog c'-number of origiial crashworthiness features based improved crashworthiness in general aviationuaon the principles espoused by DeHaven.
;' These aircraft The effort included analytical and
features are still found in today's production experimental structural concept development and in-agricultural airplanes. vnlved full-scale crash testin.1
- Prior to 19',.
little full-scale crash testing o0 general aviatior
Another milestone in the progress of im- airplanes had been done except for some high wino.proved structural crashworthiness of aircraft is single entire tests preformed by NASA in 19%.the first series of airplane crash/fire tests and a crash test prooram involving two TC-46Jconducted by the National Advisory Conmnittee for twin-engine airplanes performed by Aviation SafetyAeronautics (NACA) Lewis Research Center in 1952. Engineering and Research (AVSEP) in 1964-65 fo"These tests demonstrated some mechanisms which the U S A rmy ' ." The NASA Langley full-scaleinitiate Post-crash aircraft fires.' In 1964, three-dimensional crash simulations are examininthe Federal Aviation Administration (FAA) conducted the response of the st~ucture, seats, and ant
h "-
4 two full-scale crash tests of transport airplanes pmorphic durnies to realistic crash dereleratoir
at the Flight Safety Foundation facility, Phoenix, pulses Definitive data such as the i%,actArizona. One of these tests was using a Jouqlas attitode and velocity, crash forces, and dunr,OC-7 and the other was usino a Lockheed L-164g accelerations are beino obtained in these (,as'These tests were performed -'ith these ob'e t' tests that cannot be obtained by irvestqatlQnoin mind: (1) to obtain crash environmental date. field accidents(21 to study fie? containment, and (M: to rollectdata on the behavior of various components and The general aviatior crash dynamics programequipment aboard the airplane.
, After nearly is currently being expanded to include comercal
a twenty-year hiatus, the FVAA is proposing another transport aircraft It IS recognized that therefoil-scale transport crash test to be condicted 'n are sinicantly fewer transport accidents thancooperation with the National Aeronautics an, either pneral aviation airplanes or militar,Space Administratlion (NASA) This proposa' helicopters Hoever, in a smnle transportinvolves crashino a remotely piloted Beiiin 8-'L: acciderL, thv lives 'if several hundred passengers
TI..ule I la*cl a elThll to i 5
II
ant At.e, art ieicpar.'drd v~si)st cases, abIve ,uman toleranc. lrv ,th, -,n the livable ,)I"m and 1 r - ' 1 "
'he two pr'md'v fa-ts cat,lr area had ten mainteinld Tn- 'i ,
fataI'ties ' transprrt aic ' I l ar I aJw rer n firir d , ntroled r ' - ,
reS.'th fro impact fnrce: a' fi , e tudl Su LIOO and .ertlcai strikin0 j.5 ,
fnarn al toss for corner.-al ets etee' lbs merhan'srs f(- seats he~ame alianr"
*i' •
and '" lie to accident,. 1 es *'atvt at A ' j c rj e 1, sra mh s Im'la tIOn,
b I I These estImates '"JAe -S e KS',
at t million. hj daI o r d/ -, 11280C 'at' lit, cases (fatals omi' at (52 '"1 'c Orfeaso 't ."'A r l.i.l
nhe initial effort aI t"' c'> .0 is''es,
on a oe''n:'on o~~~,If a mearii' ret aar"oa ~ ~ r t jjr' a tw jere , ''
based 1n Dart on a care1Q ,u of
11 ta'd I I Tno'ved ir . fdtd dJ lnt s Sh'i' Ir
accidnt data fro 955-15 'hem lAdt fiqare 'o,, flSour undulatiors ., tNl
revea!et That aorreximatel, v. nPrCe' 'I: fat1" Cr, Q ,! cv,?rturninq moelnts eret
Coiirec1ral trarsport accident CCc,',i' t-a'- the seated o(,iparts as the rant le , "$
atrOicrts ,r-nj either atproach. aa' ' - seat, at's e t P,-Csixf loads to tn 'Io.r w,
of' ooeratnns 'he aircraft -rin' rese-<ira- A the sane t''e. the rear legs experenet 1ns 0 s tvca'l. be)ow noral Cruise sOeNt and tnsii cud'n; the intersectiors o' thr
It wix docear trat potentivi fir srv,'aci ty tidInnl beams and the lateral bulkhads' In I'-
du e enhancedi t h rovr acol el crasurnns ''oar :rcvided said points" or columts why
techno cC, n the desiur nl t ar'a are ver, effIiPnt load paths fror the u,,r r.of the a;rolaie t(. the seat rails
Genedl 'viaton -as- ljnar'cs Projram 'he airframe structural design philos I.... . .. .developed under the general aviation progra"i
.n 1972, the CAP. S, an int_ sr. embarked illustrated in figure 4 The concept is SI":*,
on a cooperative effort t- de elor lecnholc v for to provide an integral stiff upper floor (a:;- r
improved crashworthiness and OcLpant survi.ability mately 5 cm (2 in.)) to maintain structural
in general aviation aircraft. nhe efort Included integrity between the floor and seat and I'
analvtical and experimental verification of prevent seat rotation (either transverse o"
structiral airframe and seat configiration riodifi- tudinai) but not allow the floor panels and
cations to limit the loads transm'tted through floor beams to separate. The lower suifloOr 's
the a'" frame and seat subs/stem to th, oc cpant. designed to provide a uniforn crush zone and
The methods and concepts developed in the general various structural subfloor concepts have beer
aviatior crash dynamics prosrar will be examined developed in which the floor beams and latera
and e a!uated to determine their apoiicabilite _i bulkheads were modified.:' One such concept xhr
the transport crash dynamics program The cirrent features corrugated floor beams with notche!
research efforts in the general aviation program corners at the intersections of the beams w.ta
are expected to make possible future aircraft the lateral bulkheads, is Shown in figure ,, adesign concepts having enhanced survivabilit with an unmodified airplane section. These
under specified crash conditions ith littf "r airplane sections are approximately 120 ci' ''
no increase in eiqht de acLectace crst. ; lon y 107 cm (4? in.) in width and repreve,'
research r-aram intended tc accomeliSe this the first passenger row location behind the cL tt
oblective is defined by five tenrlca' areas and the 0opilot
indicated I, figure 2. A summar, o' the pertinert
technical accomplisnments performed in four of StatiC crush test results are Shown In
these technical areas - il '-scale crash simula- figure 5 for the two subfloor sections. Thetion. a" rframe 5tructura! Conce ts, dyramir ainmcdified subfloor section exhibits much higheraaivs s methods, and seat'restaint amic (15 kip) crush loads than the modified subfloor
anlsi ehos adsatetritsysten Con- ilO kip; and experienced loss of structuralcepts - are discussed in the Oollowxn sections
(under general aviation crasn dyram 5). The five integrity between the floor panels and floo-
technical areas indicated in ilre 1 are aisc beams by buckling of the floor beams (sudden
applicable to transport crash d "a-irs includinq decrease in load) and tearing of the floor panels.
the data base technical area under the transoort nhe same amount of work (area under the load
crash dynamics program acrcdert data De tinent tn deflection curve) is involved in the two static
crash dynamics are heinq eamiinv a' a data base crushes but the work is much better controlled In
t, ;' iPent'y r,ii l area: #4
',asiw ',nss the modified section. Dynamic tests were also
resear, r and to ae'ine transir'- cra' s; rn'cS. condicted on the modified and unmodified sections
and a dynamic analysis was performed for com[,arisun
fll-Sale ~'rash '.inulatini w' tthe experimental data. The static crust dataof the corrugated beam with notched corners was
l-scale ree-lht cras' t.'s -e,- ised as input to the analytical model in the forn
cohdo('ed tr the lmta't Dvra-,cs esea' r iaci' ' f nonlinear sorinq elements representing the
Landlev hesearcn renter ir .rc, e rp ' l
cortugated beams. The dynamic test was a vertical
histOr's an: strtural def-a-''' m, I were dirq test ont, a concerte surface with an impact
eas-el ir tweni r - .- 1 --" a-' ., 'elcite ,' 7 3 s/s (24 fps) The results are
he ' '"i ter erase 'ps , ,'" .,''i-n .as ;resent.1 in fiqure 6 and show the lower flocr
a:sr mal btweer acr-der'* 'r l , a t." accele'atin' provided by the modified subflocrs
enine aroanp and !i~r * '' 'l . 'he agreement between theory and experimenta
enqine 5'r'are 'a'tt Ai
(, 't data pP' 's mass acceleration) for the modoilfr
mnd' 'red that i -c impa, 'a', . " -crriati'l beam sibfloor is excellent
measlre ! i the 'atir area '' ii . " trw
sea ts an ir the i' n'
- - ~f , t e-----
test o a full atrcraft setton, s'.-" ir Seat- a ncpe .-'t.a,- s-Ar t .
fiourt 7, was usel as a venv. 'A is er .1ri5 toe asse'rert of toe . *' -sp a e anonlinear comP r rter roa; f0 - Cr . (,aotes' l (IS . t.P ,-enj'f -The aircraft section, the first 0 asselP n 11P r', t lees ar( -at attx§"',' Oiv'
pos~tion behind toe p'lot and 5!2 ' is suDortec. xeie dl J 1, .Su'r e-approx'matev '27 ..r (4 ' ir er:' an of r- c -rot-t.e seats worn rt tec a " .(47 in.) in ildt". 'ni specimen s nomrl.t, Aeo Me ca
7 n 50 te'-. " _ ".
cabn section in contras't to the s tOr IA',: slec is linear .c rate
Sections discusses in tn :irev is. snition 1' thye reqii ei venc~c', ar 'ry1
t A ,t.j r
this paper. The aircraft re ion was rope stretched acros- tn ' ' r "
vertically lane Culled by guide post, t, t ti c trc iti tie lvsir, 'ie 50 ad.symretrically at 8.5 n/s (28 fps> "Is sleC: A ,r r. rcent'Ir .rw -. IvertIcal impact velocity represents tne ve t ial mented t, acceleroie'rs Icadec toe v 'sink speed measured in a -15 c)itct P ' an le restraint svst-' as de v'uration of tneof attac) full-scale crash test at . m's h<' occurs. 'irn , .e podSti,mohl 0 comoa;ison o
t fuselae fIrr )itbpoar' Ou'rv art ,eat af'v r a sled decei '! -'
vertical accelerations are qive in idiqure , witr toe ste' se vo' n a Olduv 11Cir n
for three nonlinear struCtural adarvis COmPiter t , ,d arI a 'hdra''-'c S 'Ay
Proorams. Two of these programs. AC-TiN anr is tilte 35 fror- ,e verca! and is aet '
DYCAST are finite element representations ant The charo- ' i' '5 r 's t
the program KR44 i s a lumped-mass representation tc rest Note n 'C eas- in accelerat'of the structure. Details of these computer toe 34 " s'e ' " S1t: " d oel'i afcevrs.programs, their capabilities, and developmental Floor mounted ical-hil ,,tI seat desgOtS naveassumptions can be found in references 26-29. provided i to " a. atlon,-eductinsThe results of this comparison indicates a good similar sled tests " onocified lncrstr'0.-analytical representation of the first major seat) conf iralirn no.e.er, exni~tt dcla'splastic Puckling load by all three programs, amolificat r 'act rs i rqn as Ic # si-1however, the DYCAST computer pronran is sees riniditv an the rt-i te Occupant relato follow more closely the second and third peaks to the seat '
both in magnitude and duration. The KRASH com- 'ranstort cras0
"rarics Prsraputer program, however, is more economical to ........... _... . .
execute. ' For these reasons, both OYCAST and In 1979, the 1A. 'UP, and industo, -tv."KRASH will be further developed and evaluated or a coopertive effort t- cevelop technr.c Icc,for use in transport crash dynamics modt ing. improved crasnqth'ness and occupart sur.'.a .ACTVON will be used as a smaller scale test bed in transport a'-cra'f 'me effort incudesfor evaluatino new analytical techniques. analyt'cal iodellnc ant eDerienta comp r ..r
and full-scale testrn tc corroborate struct.rai onsiderable effort has also beer expended concept development and to characterize adasce
in developino a good mathematical simulation material cTswOrtniness Ohe technology deelc,:of occupant, seat, and restraint system behavior ,ner the -enea'.a.iatio- crasr dynaricc,'durino a crash The FAA-funded comoter Drogram disrssec o3
1'r ir this paper may pro.'de aSOMLA is a three dimensional seat, OcLuoant, and fo toavnce toe crash da cthreet'o I% adac tecas c ics tecr
, '
restraint system program with a fin'te element o transtort d'rcra't, recocoing toat tr's:-'
seat and an occupart modeled with I rigid airplanes 1ve 'Ifeert ar unI ue strucctura'segments joined together by rotational springs features oese Strvcturat 'eat res in ',e
and dampers at the ioints ) The fimite element containme nt ,it,occcart seat arc floor e'a-seat model consists of beam and membrane finite response aol malt -occucar, eelementst capable oefose anddin rigi-dcuan e , 'eelements capable of modeling rigid tid behavior. The trarspo, t :rash dyna-mcs technoloy 's e vcto:SOMLA was used previously to nodel d standardseat and dummy occupant in a NASA liaht aircraft to make poss ble future transport aircraft desi,1issection vertical drop test During this ha,,inq enhanced survivatilit, under seci'ic _ltsimulation, the seat model was replaced witn a scenarios wtn 'ittle cr no increase in weirtnonlinear spring damper system. A d'scusson of and acceotatle ' ost.SOMLA, its computer input requirements, andadditional experimental/analytical comparisons Acc-ident_ ata Base
can be found in reference 31 TO explore the
possibility of incorporating e dynam'c finite In tne first poase of the transport prcca .element seat model in SCIMLA, the cei:ing supported it was essential that industr/ and governoert
1oad-limiting seat and occupant was modeled examine colle:tively the accident data base orusino YCAST as shown in figure 9. The occupant transport ai'craft to ident'y and define fr,'t+'
model was restricted to two body masses with areas of craShworthiness research (Cia. 2, Dataa C location in the pelvic region. The seat Base). Many crashworthiness design features ,a .
was modelled usinn beams, axial rods and non- as thei- 'oundation an accident data base idert - --
linear Springs (renresentino the wire bending inq the specif'c aircraft structure and sus)'stes
energy absorbers (l'A's)) The comparison with which contribute to inijries and fatalities tothe test data in Table I and figure 9 shows many years, emphasms in accident insestidatiorexcellent agreement. Consequently, tne occupant/ was placei on letermininq the cause o
f the ascrcent
restraint system model of SOMLA is being with little or no consideratios being giver tsintegrated with the dynamic finite element DYCA
1T crashworthiness as relates tc inuries and:,
program for increased versatility, fatalities. -titnn the past f'fteer years, to_lifesavin] and inlurv-"ini-Zing bene,ts t f
36
crasnwQth vdesin were realizei witohnthe l6' kn tl and t: I 's, respe(ti.*,, na v Iat i cr co-]quj , and.),, oar-, ic 13, t t , . , d I c) I a t t t Je I sMrnet !r !Ca w t .
evolied based cr accident data, wherb, safety .afeatures un i woild reduce inuri c talltiesin a crash were incorporated early i- the A0d s with an otstacle nr th,aircraft design stages. .avinc a sirla- otier- ground ditch. lino ples, veil les. etc wlr
'
tive, three identical transport acc t io d, gear down, level airolane attite, anl swerecontracts were awarded to Boeing Cornra' ne ranges o forwar speed and .!o, speed u'
Aircraft Company, Lockneed-Clifon'a omoar, in 's V m's (63 tO 10, knots) a-. . , % ,. .Doualas Aircra't Company, (LOrn Beach . The rnLpe.tively. The ,rclane ;s ir d synmetriL r,specific tasks In tnese three co.t,a ts J-( level, ittitu-At or tr runway or wittin CDI"summarized as follows t.4 the runway.
(al 7c reu'ew and evaluate tra,'.o2 (!I!. A seere impact on runway withaircaft accident data. define a ranoe of dear down, nigh arole of attack and ranoes ofsurvivable crash conditions or crash scenario% forward speed and Sink speed of 7 to 103 .that may for- a basis for develop!i ipr ,,e (13, to 203 knott, and I 3 to 10 , reSpe tlyel,.crashworthress design technology. irpiane attitude, :;t.n 0 -5 , roil 5 -
yaw 0 -10', on runway.(bi 1c 'dentify structural features and
subsystems that nluence ,ntjres',ta!ities (IV) A sesere ground/water Impact Of'
in tne crash scenarios definet in 'a. runway with gear up or down, hign anole ofattack Coll 'sion. and ranges of forward see:
(C ,ef;ne areas yf researr and aooroaches and sink speed of 1l ao 103 m/s (100 to 200 knotSfor improving transport crashwothiness. and 1.5 to 10 m/s, respectively. Airplane
attitude; pitch 0 -45 , roll *5 - +45 , yaw(d, :denti~f test techniques, aral'fiscal 0 -10 , off runway
methods, etc. needed to assess ari evaluate thecrash response of transport aircraft The range of impact conditions for these
scenarios are tentative and are only given asThe data base for this study began wtth a an illustrative example in this paper. Until
review of the 993 transport accidents which had such time that all data are finalized, theseoccurred between the years 1958-1979 and the scenarios and parameter ranges are subject toestablishment of a selection process. First channe.disregarded were those accidents in which thestructural airframe played no significant role, Fuel Containmentsuch as in fli'ht turbulence accidents ormaintenance personnel accidents on the around. One of the identifiable structural featuresNext to be disregarded were the more severe, and subsystems that influence injuries/fatalitiesnonsurvivable midair collision accidents, from the in transport accidents is the wing structureaccident data base. In an objective, but somewhat fuel tank system. Fuel spillage from a damaqedunavoidably subjective manner, a combined total wing structure is one of the primary causes ofof 241 "survivable' accidents remained to form the catastrophic fires and passenger fatalities.data base. The criteria that was generally The accident studies, previously addressed,applied in the selection process included the clearly identify mechanisms in which wingfollowing conditions: (1) at least I1- of the structure damage Could result in fuel spillage;cabin volume was maintained, (2) the trauma namely, for example, main gear penetration intoforces were estimated to be within human tolerance the fuel tank area, wing-mounted engine pylonlevels, and (3) at least one survivor was failure, or simply failure of the wing structureidentified. In a few isolated cases the one itself.survivor condition was waivered when it was feltthat trauma forces were within human tolerance Fuel containment is also a research arealevels but a fire hazard existed. The distribu- in which advanced analytical techniques willtion of accident data is illustrated in figure 10. play a role in analyzing the response of the wingThe three transport manufacturers generally tank to localize crash loadings and studying theexamined different accidents, but some accidents main gear and engine pylon failure mechanisms.were examined by all three manufacturers as The nonlinear analytical techniques developedindicated in the figure by the cross-hatched area, under the general aviation crash dynamics programsome by two of the three as indicated by the will be applied to these unique nonlinear trans-hatched areas, and other accidents solely by port failure mechanisms. Consideration ofone manufacturer (primarily the accidents advanced composite structural materials and theirinvolving his aircraft), effect on structural behavior and failure
mechanisms must be included in future transportSome preliminary survivable accident airplane design The necessary modeling cap
scenarios are evolving from the studies and are ability for nonlinear dynamic composite struc-being used in definins classes of accidents. tural analysis needs to be developed and verified,The scenarios consist of four different accident first on an element level, and then on moreconditions representative aircraft structural component level
Full-scale dynamic testing of instrumented in-(1) A hard landing involving high sink board wing tank and fuselage sections sublected
speed with gear collapse, wheels-up airplane to impact (with obstacles) under controlledattitude, and some swerve. The ranges of forward deceleration and attitude conditions are alsospeed and sink speed are 65 to 82 m/s (126 to anticipated thesr full-scale dynamic tests May
4
3 7
be conducted at th- A Technical Cent'n In I can. in',! 1 nStrurerted andnewly proposed 68,U 00 1 50,0O0 1 c. , 7i t.) s certa.n , cnas 'tn se a dea L(150 knots), catapult fa ty, I'' -,1 , ,%st "' e ed anthrcp Con'nic lII 'rIC
CnaswvL - s tr.'' a fIooe 'net,'. j - teAdvance. Analt'cai Techniues fr, 'ansort asSessecdn fn tnt mni tore' eras' sequen tnAircraft adc lI n, t yroteznri egress de.icn cofcepts w-
be edalvated and e,acuotIor slide tech'Airframe and Subsystemn. The Iie-tive of verifie, c hp S-7, -3 sn test prodran tie
the analy-tical efforts in crash dvnr( S is is gvn in nicr fern in fis~re 11 :ne 11-to develop the capabillty of predictln: eon- represent -aC- onloilng actisitles that are alinear geometric and materiul bfehvir o sneet part of tn prn.aidtieii arid assessmenit evernse,Stringer aircraft structures sub;ected to are associated 'itn th, full-scale crash test. sc'e
-
deformations and to demonstrate this caoat'l':; uled tentatue', f'r the sunmer of 1984by determinino the plastic buchlino an. col apseresponse of sJL" structures under ir[,Isive A tel c 3eitectives associated &th tn,loadinqs. Two specific computer proqrams nave different cras.:.rth, researcn areas save teebeen developed under the general aviatir c-ash identified in t'e proposed B-720 full-scale ras
dynamics program and have been discussct test cla, These tnee crasnworthv reseachpreviously in this paper. One called, Dice>, areas are structira airframe and seat reson-e,is a finite element program which focuses on anti-mistio kerosene performance cnaracteriatis.modelling concepts applicable to large dyna-ic and cabin fire safety materials testins. 'hey
deformations of realistic aircraft structures; are discussed riefl in the following sect'-sand the other called KRASH, is a versatilelumped-mass computer program which models the Structural Anframe and Seat Test 'megross behavior of the total aircraft structure. objectI-is-of' e the structu--ur-'ar?'raTe-arid seatBoth of these programs have specific strengths tests are as foliws (ia to define dina-ic sea'and weaknesses depending on the particular pulse data in the for- cf acceleration timenonlinear problem that is being addressed. Both histories at the seat''loor interface, fb) tohave been evaluated in the general aviation crash measure acceleration time-history data tnroug .,dynamics program, and will be used to mode the cabin interior for comparison with nnlinea,transport aircraft structure.-' analytical predictions of structural behaviur ari
to determine the level of injury by acceleraticrOccupant!Seat!estraint System. As mentioned indices, (c) to determine accuracy of current
previously, the occupant/restraint system model flight recorder data, (d) to assess current andof SOMLA is being integrated with the dynamic improved seat/-estraint system/floor behavior,finite element DYCAST program for increased and, (el to determine structural deformations an'versatility. The new pronram., called DYSOM, will failure modes.be used to predict the structural response andoccupant behavior of fully or partially loaded Anti-Misting Kerosene. The FAA and NASAmulti-occupant transport seats under specific are heaviTy committed to the research apdcrash loadings. development of an anti-misting fuel additive, which
has the potential for precluding the developmentBoth the structural and the occupant-seat of the fine mist and associated fireball resulting
programs will be updated to include advanced from fuel spillage. In addition, this additivematerial modeling to accommodate the newer should exhibit the potential for allowing estera-composite materials anisotropic properties in tion of the filtration and atomizing characteris-a macroscopic sense. However, much research tics of the fuel, a mator requirement for aircraftwork needs to be conducted on sost-bucklin engine and fuel systems operations.composite behavior characteristics before anadequate representation of composite failure The proposed 5-720 full-scale test utilizingmechanisms can be predicted. the anti-misting additive will afford the
participants an opportunity to: (a) evaluateAll of these structural predictive methods the performance of the additive's in-flight engine
will be compared with full-scale and component burning characteristics, (b) determine thetesting of representative transport structure, additive's compatibility with aircraft engines; and,
(c) determine 'lammability and pluming charac-P osed Full Scale B-720 Transport Crash Test teristics in a post crash environment.
In order to corroborate analytical pred'c- Cabin Fire Safety. The cabin fire safet,tive methods, test crashworthy structural design area has as its overall objective characterizationconcepts, and verify the performance of anti- of aircraft cabin hazards created by externalmisting kerosene additives, the FAA will conduct fuel fire especially the contribution of interiora full-scale transport crash test in 1984. The materials, and to increase the survivability andprOpOsed test specimen, an FAA B-720 four engine safety of occupants in the event of a cabin fire.jet transport with a 160,000 kg (350,000 Ibs) The proposed 8-720 crash test could provide a testtakeoff weight will be crash-tested, by remote bed to evaluate the effectiveness of interiorcontrol into a designated impact site. The materials as fire retardants when exposed to acrash scenario will be one selected from the fire in a second phase fire test with the airplaneaccident data studies. Provisions will be made at rest.for the structural failure of the inboard fueltanks, to take place at maximum approach crashspeed, to provide an adequate time period forthe testing of the anti-mistino kerosene. 'he
S
o(phI 19 2 Renart S ' u'r ii'' Ca
The FAA, NASA, and industry na.'e iPtatel Ad hnpor' in'a transport crash dynamics Oroqra- to levelo3
tu n, "o. .',
technolooy to define and demonstrate ne, . an, , ,
rash .1a 'structural concepts that will enhance oassenser Ai ''de 'e, ec aporand crew Survivability by imnimzing crash force Relse, 'so' -trauma and the potential fire hazard caused t; 7,r, & _ra7hnt'recfuel spillage. This technology will facilitate na
1 heo'rt. 'ontract No 'C-624, Fl"t
the intearation of crashworthy structural Oesl' -a '', Fourarlor. :;ece-ter 19E0. 'R-- 'egconcepts into transport design methols and w',! crt E--, 7 -- _I7 - ,Consider airframe, seat, floor, fuel tanks ar, covd i. 's",landinq gear behavior. In addition, tme potential Sinors8, '-r', , d-Aof anti-mistina kerosene additives to redce the 32nd -- rrn wee,:., may 197f, re,fire hazard are to be determined as cell as the o arn'l, B'ar ,,. Crashwcri resadditives compatibility with airo-a': engines. Des1, *eatures f-r A(voceo N'i t
Air-raft -rasnworth'nes- Editors. k. Saza'The dynamic nonlinear behavior of struct.ral I I . Pilnev, ard P. .st
components wilt be determined analytically and Press o -, Cnar ttesuille, ' 7 ,verified by full-scale and scaled dyna-ic tests. .!Aoance" 'omposite AirplaneThe nonlinear analytical techniques deceloped Preliminary Des'gn Phase. 36th Ail
0rt -ee-
under the general aviation crash dynarics crosram May 1980 prepr n 0-4-Awill provide a foundation for application to -mson, A. 5, and uoetz, Pmetal transport structure. Consideration ,f General n-iatloo Crash "inamics PRorF'aadvanced composite structural materia's and their Status Report, journa
1 of Aircraft, , e
affect on structural behavior and failure Number E, Auoust 19., pp. 584-S9
mechanisms will be studied and design tools ' Eibarnd, Martir A., Simpkinsct,developed to aid in future transport airplane and Black, 5.,;ald ,.. Acceleratic"; rodesidn. Passenger Harness Loads Measured n i
Light-Airoiane Crashes,' NACA T 299.In the development of transport crash 1953.
scenarios, a thorouqh evaluation of accident data -.Reed, W. H. an? Avery. A., lr'nc ,Ieswill be made to provide a fundamental under- for Improving Structiral Crashwortn,nes frstanding of occupant injury mechanisms and and CTOL Aircraft." 'SAA,LAS 'ecn. Aet1 _aircraft structural response. The e''ort will Army Aviation Materials .< ., Es s,,sbe a continuino one, with both industry and June 1966.government participation and should provide a
t Enders, .. n, Overview or Ca'e-' he.
data base from which design philosohy can search, NS P-., PT, or 197R.
evolve. Close cooperation with other governmental search, NASA -203 , P7. a r- 1971.
agencies is being maintained to provide data on 'Impact Dynamics Research Facility for- -
human tolerance limits concerning the magnitude Aircraft Crass Testing; NASA TN f-rT,! 1'9
and duration of deceleration levels, toxicity al CasB C.snd A T .
levels, and heat exposure. "Alfaro-Bou, E. and Vaughan, V. L . '- I
"Liqht Airplane Crash Tests at Impact .e'ic--To date, the L. S. Army experiences indicate of 13 and 27 m/sec." NASA TP-1042. 19'
that crashworthy design technology has been a ' Castle, B. and Alfaro-Bou, E..
most Productive art not only in reducing Aircraft Crash Tests at Three Pimm-Pa
injuries/fatalities but in achieving these bene- NASA TP-120, 1978.
fits economically. Through continue research : Castle, C. B. and Alfaro-Bou, E L' -
and development efforts of gcvernmert and industry Airplane CraSs Tests at Three AI) Ar e
significant gains can be achieved in reducing NASA TP-1476, 1979.
transport crash hazards by crashwcrtny design ' -Vaughan, V. L., Jr. and Alfaro-Btechnology. Light Airplane Crash ests at Three P0''-
Angles." NASA TP-14B1. 1979.'Vaughan, V. L., Jr. and 'oivduk, P.
References Crash Tests For Identical Higr-W'nQ ''''Engine Airplanes.' NASA TP-1899, 19K2
'eHaven, v.nn. "Causes c' Inluries n Light -. Castle, C. 9.. 'Full-Scale Crash est '0lane Accidents , Sepo Digest Aviaton enhihe- a C'-47 Helicopter,' NASA TMX-3412, De 197t,erinq, March 1, 1944. - nayduk, R. 2., Comparative Ana'ys' 'A
'Hasbro,,k. Howard, "What a Spray Plane PA-31-350 Chieftain (NaOLVl Accident and N-ZShould Have, Aviation Wee. February 13, 1990. CRASH test Data," NASA TMX-BO02, 1979
'Hoekstra, H C. and iuan, S. C., "aety 'Alfaro-Bou, Emilio, Fasanella, ,in General Aviation," Fliqnt Safety -oundatlon, and Wiliiams, 4, Susan, 'ecern'natior
Inc.. d-linohon. WA, December 1971. -est Pilses an? "hei, Application to '-c'o'
nkre, . . Preston, G, ., and besman, Seat Adalosvs. Paper 81061T ISAE Buslie,
0 J . Mecharis of ',tart and Cevelopnient Hf Aircraft Meetinq, W1c lta. K, April - . -
Aircraft Crash Fires. MACA Research Memorandum ''Larder, n 3. and Haydun, Pt5rFrft, August 19?. Aircraft Sub'loor 'esponse to lrash oadln,-.
' eed, W. H. Robertson, s. H , Wei'berg, Paper P!31,14, SAE B.siness Aircraft Menti.c.A. '; and Tyndall , c , Cash Tests of a Wichita, K. 41'
iuq'as I9C-', FAA Report A-h-37, Aoi'il 196$. ' ' d. ,, 2 ., Thomson., ' G , W
'Blgham. James P., Bingham, Wl 'an o, and era't, v Nonlinear ltruct.,a 'ry,"
Dynamics Analyses, SAE Peper 79-05B, SAE .,
Business Aircract Meeting, Wichita, k5, mApril 3-6, 1979.
'Pirko. A. Levine, H. S.; and Armen, -,, . - - . ,N '.
Jr., "PLANS - A Fin te Element Proram for ' .. ,,, ... .Nonlinear Analysis of Structures - *ol - A,'"
Theoretical Manual ," NASA CP 258, veter - , ,, . - , .1975. -. .. • r . : - .
.Pifko. A.; Armen, H., Jr., Levy, ̂ .. and
Levine, H., "PLANS - A Finite Element Vroqram [ .-for Nonlinear Analysis of Structures - Vol. Ii -User's Manual,' NASA CR-145244, May l
797
'"Aittlin. G. 'Development, ExperimentalVerification and Application of Program K9iPA ,for General Aviation Airplane Structural CrashDynamics" FAA - RD - 78- 19, December 1978. ' ' ,'_.,r ,'t .ra'," ,ye i - . ,, ,
'-Laananen, 0. H., 'Development of j Scien-tific Basis for Analysis of Aircraft SeatinqSystems' FAA-RD-74-130, Jan. 1975.
i:Fasanella, E. L. and Alfaro-Bo, E., 'NAS............ . , .'General Aviation Crashworthiness Sea, Develop- , .,,.;;-,-. ,
ment." Paper 790591, SAE Business AircraftMeeting, Wichita, KS, 1979. ". '' I ,,
31Reilly, M. J., "Crashworthy Troop Seat '"''1 -. 'il. ,-
Investigation,' USAAMRDL TP-74-93, Fort Eustis,VA, 1974.
Table 1. Ceiling Suspended Seat Commarison L '''; -
Impact Parameters L_ ""' , ' .Vertical, 12.8 m/s
G = 34, T = .066s Fiq. 2 Aircraft -rash ,vnamics Te hnical Proirarman 30' Pitch
Sled Test DYCAS, Model
Upper E/AStroke 22.2 cm (B.75 in) 22.9 cm (9.0 in)
Lowe, EAStroke 0.0 0.0
ShoulderHarness(Total) 3251 N (73 lb) 3398 N (764 lb)
Lao Belt -- 5026 N (1130 lb)
Accelerations, Body Axes (G) .
For-ward
Pelvis 16.0 G 22.0 G
Vertical Fig. 3 Cabir floor of crashed airplane.Pelvis 25.1 G 26.0 r
- A'
" -SuctjRAl FLiuP
.i.-N3 fl 11L. OAC I
Fiq 4 Lower f,selaq. devige philosophy.
All I7
A R ,AM .
4.
ITS
vet-tcal dICeeatio',
F* rq. 9 Analytical exietelt Pelv C
Fig 6 DV,4,Tlc tests anj 3" 1sis 0f ioad-CC''t'fl tior inC load-limitCCC sea,-
5~bf0drstr~tjCeS.993 ACC IDENTS
1958 - 1979
BOEING
1153 TOTAL'I
100 TTAL 182
31
COMBINED TOTAL
3? 3 , 8 OF SEECTID
SUORV IVABL4 51 ACCIDENTS
'96 TOTAL
Fig. 7 Fuselage section drop -test soeireri. Fi,1 ~ ,sr, c~e!
.-
C
I'x
7.
*ey
I
I
'I
C
9
C
I
/ -)
F '', . . . . . "" -. . . . - - --. - - "" . .-- - -.' - - . . .
The permission of tile author Vi] 'dir: I in :,nd the Jrchhc-.d-& iIornia (Xro panvfor the reproduction of A1AA Paper S2-()94 present c d at thi,,l A / A, S/S LAiS2 3rd Structures, Strtt ral l)vcntj.trics , nd I-ttc r i .l (Is G I!crcnLII is ,-knowIedgt!di'rateful ly.
82-0694 ANALtSIS OF AIRCR.F-T Ds %AMI(' BEHA-I.,IOR IN tR ASH I NVIRONMENFT
(;it %!hn
L ikheed-kahlirma ( npaii
Abstract'i A !i fra mtfl uitlOfnpta,.rat Tnt percentagt ot uccup,abln space !n lu'rg tranpor . .t.
Ddlren.e ir the cra "'J. no- n 20 design at "IA- a',> tilt'.a' o! sni-lit rh0! l t trllh1 ir i..h-va' , -: 4inttfru e ocupant surxi'lih!n in mLiar' and nrmrr.:a ait: a ~rr itt low disc' Ito the aitrime terra., miat poi n t .,ra't are di,,ussed Aaijahle ainNli- nujo l't astt55:n I t .J i raite .. tnstroctlnn ditrene 1It ra'n r- u:structural hehasior danng a crast. ate descnfiec The a : e..,r v e,'ien.ed h% Itar-%rspi ivcvpats n art l'ant uit lerl.of a ibnd reltque in assessing .crut: stru.jral hc t I'rd t sa e mirso tran do the pulse tor the smailIer airra!trend l- crash enironments is pits ded Rerrtttntat tnrtt-
I tima. sinulation' t, aircraft rasl- tests and corteat ITn w;!!' 'I I tat 'J or mernt lot tmtlar' hel 'tltr i Jet-. 4 J .tight fivnd-ing aid rolat-itng aural? test ist, ate srin Q: e . ,,Lnable Tash puses in dleirti,-
aThe results or a recent F.AA xASA sponsortd reseatt
program va, estat'l s'ied for 1 S Ar% he' .cpoe" on t "ai 'insolving the resiei of transport accidents from I d 4- ' und t e accidenl ta otarred between thn time pnod J,. Iformulation of potential cras ienanos ttibe.unsidted vih, Junt !t
,61 h1 a recent update of the S Anmi ra -
future analysis and rest .t-ni'cation are presented Current and Vito gn Guide' 2 tie retommended design entrtnien' a,future anal.tical model studies o asertar the crasl di namics of sented as tile design pulse Although the . raist en'ireni',',large transports are also discussed identiLal ro the risronsal
9th persentile Stiiuae Ia ,"
the I S Arm' recognizes that improved jahworlhrtsl - rt.."INTRODUCTION fite iient C o the sunsiable crash. lheret'rod.cia-rg '
ending increase in the letel of cras-wortniness at Tne stper".-'In the 1955-1O5 era. a popular approach to a determination urraft pe iformance The U S Arm: definei, s,-tl e-
of aircraft structural crash design capabihtr was to perform full- lope; :i as 'the range of impact conditons tclcd,-g ma , :.,d,scale crash tests Tests of this nature are exrrenels expensite and diretion of pulses and the duratisn tr totes i c t -,,particularIN as the test article increases in sie, such as current aircraft acident - wherein the occupiable area i' tn ,wide-bodv lets hase In addition to cost. the test condition, are remains suhstantialln intact. both durg -,! lot a in tn ii pnot repetitive. the rilts are high dependent on the impact and the tortces iransmiled to the oiupant do t rtn.nt' '!c
conditions. and alpu;4ot configuration a% well as measurertent limits of human tolerance when curent state, .rtnat r-i r-l4 :selection. Lonsequentl' . essential onl one lest parameter data stsrems are used The LI S Arm Jesgn tus are at,:'l t ,set pet test is available L nfortunateln darng this tine penod all atcrtt in a given catejor regardless o' "tet ' 2 d ! e, atoinathere ias limited correlation with anaks:s and ext rapod ton f req-,temenis Figure ; - I shout a r eren d:irie nu to: ,;the test data Howeser the 19?Zs ,tlnessed sigriariant adance, cornnitted tonprudinal. lateral and 1ertica. Y e, -ir >t . tin,-rgo-
in computer modeling of nonbneat crash dnam. behator both for heticoptersat the substructure and airtlrame level In pariculat n, ibnd cor-btning analytical and empmcail data i and finite element tehnques
have had the opporturt to be correlated with test data generatedfor the purpose of venfying and improsing the analv tical methodsThis paper describes differences in the crust: environment asioc-ated wirh vanous categores of aircralt. discusses experimental
senficalion of hybnd analysis with light flxed-ving and rotar• y 30
wing aircratt. and descnbes efforts to deselop analytical lechniques
lot transport aircraft 2
Crash Environment
The definition of the crash environment is essential before ansaircraft crash dynamics capabilit, can be determined lnlortu - /natel, no single crash environment is applicable to all aircraft ,' /
Size. speed. configuration. and operational aspects associated with 4aircraft influence the crash environment No universal definition 4 -'
of a crash environment is therefore possihit Descriptions of a sot. . ."vitable crash can include velocrtt1 enselopes. crash pulses crash
load factors, and crash scenanos Companson of the surviablecrash ensironment and responses of the stiructues indicates significant differences between small and large aircraft The surivabielarge transport accident usuallh ovcurs around airports at flight Fig I Three-dimensonal displan of desigr ielocI.path velocities below 150 knots and vertical descent rates at less change enselope for hetiiopethan 20 ft sec These conditions are normal' associated with laght fl-ied- wng general aviation i ait,raft weigitrng . t isuch landing and take-off operations as landing short overruns trainds operate at speeds up to 280 knots a ans I toi '
and skidding off the runwa Smaller airralr such as heliiplent have one or twio enles and hat a low- or i;q . -gand general asiation airplanes hae lower ingitudinai velo,ht:es lin &.,rtar of its s pt can be ich!ed ir jal. , -lbut higher sertcal rates of descent, daring a ,rash csndttion. the, s,,nos and cillhti 't osith ,l. Its A, denti tat' o,. on'.I
or' err that ate flat i 4(-, rolling i "2 I tanu'*Senior Research Specialist t t , niw ii - t dense wit tieri ,w tat aI a r I.
Rti..*g,, AA Io pubids an ,i toe.,,31
316
4
-r' -1 -O )', ato.3us 'I0-,c %
CATEGORY I CRUISE sCATEGORY ICAT EGORY 2 SPEED *CATEGOR Y 2 STALL SPEED .~,
.CATG -y 3 *5 CATEGORY] 3 FLAPS DOWN)IA:CATEGORY 4 POWER CATEGOR AT 4 r-~rNOTE SEE REFERENCE 3 FOR CATEGORY DEFINITION
CA ItGOA, I2/ CATEGOPO, 2
I' CATEGOROY 4 RANGE cc CO.I0.'Ro -.-. c
I 2150 L RANGE -
VELOCITY Aa I" ~"KNOT S A:TIGORY 3 Lrfa- , ' ,Rust APEil D-' ' '.. 010 . .
2000 4 60
D~tA
are ~ ~ ~ ~ ~ ~ ~ ~ ~ Aopal 7 ejF AItcII'V;' JI ~ ~ t oI 0j h,
56 31 1~ Cre,~ toI\ A, :,.1 '>o, ! I ga -'' I'' -t o u' o. are nooo 0 TAble oe A000 frg :.0 -tare. orpOtOr,tl~ Olloas
1e ..erogned to goe ea,,.o )o-pj~l,, Oor'C' 001-~ sCrosTc-f'Eegu 41p-'o ''eoo'
11"J"'r I :esaptog Injoor o- AMiorl .1000 landing ReocIn dpthSl , ! c "Fe r~roos -'oof-, .oi t'encs the trend u .- lo arpoor !f t '-* V '
most re~et X0 ,c-r penod roocaird that Wllioe nO acoole-is.a'' 040,2 dc01450, 00n0 ofalte350s. a50 tano 12.rTabo 3' rdtJ
alike in Coors respect. there are b'road o;molanloos for gYOo."'S - F to CI Ho.eoco imis ia 12(0)0 genera: olaoror :,,~ 'ac dent' These smoatesallow for A rat-oa) arage' top,-ose .ar be Os 70 cld I, oa, along the long)7 of 0000 I :e.ag:hund reds or acc do rts onto a tow (4nddte tocrash Sicona'o ,. IIfl ,ilutae -,, ,-sla h ,dopicted on 'Table I Accidenots that1 arc irotoated when .e ePn Magniootrae I, pl angl ucll stho' ef for. 0:is on the Fround And whore no unprodictable hazards are iro. 40 op~s rpotd i rpc ~l notroeofrtaooare rarolo fatas ( oritoersol whor impact occuor at high speed and airplanes crash test data are limited The Iargo'st airplae crash
with a large impact angle. as jocodents 3aa roo)m airpoorts often , slt~ed weighedI 1Q0000 poonrds who>' os cisubaint.ll, bner tI.4'
the accident has a hogh protoabit, ott fatlifty In bet-err file 0M2r0 courrent Otjnsoort 4Jrplaoe partocuiaatl 0)0 ude-tbodood oei
it00000005 thle oalcomo'. on terms of o,iopamt sutrsisabolt -"lokel oh marlagtar rf i!b t c, rsdo~' tosted or the near tootore ( oirsoquorl, It IS Iro~p0 t I'0U~, athte sarrouodoing hazards Figure 3" shos the doistnrttc' c)
the srv001, of accident versus a,.ident 00 pe T'horo arc distor_,' il ,a ef d r aleatril\ .dt ,er,
0000110s It an40O or dunn g a transport aiorplanoe a. ctdero F, doJ n a' I) cs c h ArT3akeno I bo ft IO r lan spocrtI aot'rpIarii r
KR ASH Espelnmeotal VenI'icatioT-ble I IdenittficatIon of candidate coash seenios
______-Thte cr450- arai of l ight fosed-Aingl I I'and rotary wing_______________________ & aral using rog' an- lR ASH1 a to '.oo01 dog;i, conrip.ier roc~ n o s n f toz -, -0 , *h * r , h s , 1 es F o c r r A o , ot mf in -o o n t r c on n ec e-
....... . . ...~'~tfl~ .... . . "assec ot ao~ fssoeneo0 odi.Tep-eT-haMC If ge-e'ao dc eptan i gereralv-:-
'I" ~ ~ ~~~r-,l r..o.-r "r o;po,0nla.oo40 arteotod lit hn, tre .rronO butt>numhr ot KRASH-D ascn Fogoro I shoo toe, post .roPa,:
4444 4I1~4A, .'hrodl model afoonO. t~o user ho' llesobbhi to ulotie aoajlIah
0 ~- - oroictore reprose'; tat n
6 317
L
SA
5>I> a
L 1-1 1S. cr
fFs age atr '11 L ais 0r alCr,seren , Trama
-a,,.. a- Fmeass ru!- se run
Peeff*t r,10- all aa. ~ec:aro os-, at 1,-oI, sear ---- raw, Oq bo . ned'
Wogs or
I kse age ruor -4 Futeage :beau set aratnl NMa's 'et' sea-& Trana-P l~oa ds00m
IF, c, z & a r E Faccaotrl
Srtone dlr~t --- Fuselage -Prad - Fuselage bred. -031'a Loss of serel c' F a
sqears toriasrsea I orericad fuse age -n asnrt.
I ~~~ ~ ~l or ;erMss lerr sear & Trauta
"'1 an- rIPerload FePlanhrluoture Fr
Fuel ,e ruoture
IFeu lnk Lncture .jIFure lre rupture
Fig -2 Fbi diagranm iandidlate crash scenaric
configrainjt or O a cornted sertical 1: 3 It se, allt liters. tn ft In both fish tess programs high-speed fin.,. a-vldtronretc
I lS 5 It ,-, l ull scale crasr test rf a ulbi I 1 r0
o hlhlrniet Fig. resorded dalz anid deflection measurerments %ete used to' .. rrtr i
sirer iIC -'slims sthe post irepact conftigu ration lot foo llst al tnI ~ i est and anain so, results Thre iest condirions for the
crash lest, oi a single-erginse high-I.ng general as sal on air -rft acraft are pints I~d Pn Table 4 The aircraf5 ttfgra,,, Figurer ' and 'a ettc used t, )sif icr, rotIj! k R ASrH
0Table Seammars of transpnrl airplane ixed-ing analc tIca; tossI tiot rashi d- am"ncrash first conditirrns
ATaal £ local R. .. r,.. Table 31 Comparison of peak deceleratrons and uao%
LODESTAR 17n9 12 O! 3 1791 nl
0 cad rer2n &00 00 taot, to [" FIGHTER FM l 4o CA3 5 't42* r
0611 72n2t 161000 on 2 .a rr72a n PACP5ET-YPf CARGO C-82 is 02335s Otleo 00
oc 1 accan2 no- ' 12200- 1 o5 1 UNPRESSURrZEO TRANSPORT. 16 oR 00
.1 3 14t 1, an LODESTARPRESSUiRIZED TRANSPORT 9 200
M03 SOF~I *ErGcrS Its' lnrrt NO' S-ArcC C-S
31,
Co
.APnSAl. D1
L.ONGITUDINAL. 301 Nl2~
ACCELERATION9
20 7cI
.10 PV 200 c0 2M
DISTANCE FROM .MPACTCPOINT ON AIRIPLANE 'N%
10 20 3L, 0I' ' 1 .'.,V .1 .1
ANGL E Ol~ IMPACT DEC,
T h, .....C: tA P a , r ',M c nT)I
P l. j< t.IIr~, r~n aI ~vn1
'IX>' 0-j1. 1 I :7Cj.j . ~ .
-t j T * *' - ,41* 11 I .
.1~~~i 4.4 'll A::
F.~til 41.4' j1I1. A V
J*II1 4' ' 1-01 .- 111 : !'I ;Vj Tl4 $ .A 1 A >
ll ~1 'VIA I .'V l r t- 'I 'w0 .
77 -2
b- I
* -~-J-
r" I 1t~, ,lo th r~ i ' *- ~ 1,!, used~'' ottiedi. thcie d im, 000.-
hellal Ori isin no:'.1 .0
Au..ll~ilri .- enil az-ri'","> *di >2> . ,>o adfIo~
I~~'r ableo 4. airpfunet (io ingle tilene
hig''.n ai;.
p' I a'" ale Is, II the11 rai l~ ' 'rat.. tIE lur
('I i ttl0lli.llfl!0l2'0' erer h ip!hd .e
till lI i 1A LIm C
''A.
M A IMUM fLSEL AGE '5OEFEC T ION A.4 NA,
PERMANENT F USE LACE
2E1) RMAT ON t.
ACC L AlTm t MAX COS TMYI C AF T I; M AT
ENGINE VE R11CAL 24 li2 6 129
ENGINE LATE RAL II__________)__________
I TRANSMISSION 2T 110I VERTICAL 3D 117
I TRANSMIS.SIONO 9 1U LATERAL 123PILOT SEAT PAN 200VERTICAL 204
FWO FLOOR 26 0VERTICAL 2 M2AFT FLOOR 40~loo-VERTICAL 2? 114
*PEAK TRANSIENT RESPONSE OP eRC'i @ 94 MSEC
'. p :I tl' ciLa
nc -
0-1 El S-[ L1
* ~... Age ,I
< '~c
* ceal .... ;l321
1£C-
ANA, V SIS
3. 80 ~PER-ENTAGE 100~ ~.i QsotoD AsF AG F. ~, C Ots E ~ s
21 2
40 13 30 4.4
19 t33 123 2?4 39 21
120t
53
40) 141
00
N- 13 S:gtergN W N - nl j-, 1, - , tN
th !".-! 1 jrJ ... 1h. - /147- - a
pulse , a lpll dl " n104'I~ .. "atnflJ 0 lguf t . SI- L111
En rp n of12 the fuea ri''~r tnittpak'Y l-rc'
diftrsmn! s Cth ml rI i .rprasnine iluali tri) o! v,
cradspr s str..Inar - ould he. ~rr 4 .!I' 41 ' t ", 10 '" *thttU OS
desre Afro M ie Moadel U.'sdito obin figr e re,; r0i e I' 11,5 in '001 -'0TU S
aure a'an iut i into ocsupa' model it)n blira~. pul' A . . . . . .. U.. . .
.,.UTStM -t 2.S 1111CI
Iea rfrm mode is FnCoo anfs~~ e'''s t- So oSMON
11 ,
TZST A VIS! 3
a2 1: I- d'q F
Aai 5 ppieI, b'. I"af helC h 1''.. J.. j,",e
APPIICASLE 11ihi ANALYSIS PROGRAM PROCEDUCRE PURPOSE ADATGOISADVANAGEC
L AS C-O'AE
::::~ z:: A~'U 00 ~l.. SWOL ~i ~oWO:OTTL :O 7U, 0,LAIDT soMVSLUM *OSOro .o0. .'CLU .*LO. .O. '.U.0' .
So,0*'O oOL1
O 0K SLI OOT 0UT5* UP0 r N.TO Do ",U' O.... -tw~osTo'Uooco ioO* UoS..OT
5OL* SnT SOSOUUTOSOiSO .. ,~o 50.0 0 Oa' S~wT OUTO'0.
* OOOUOLS PSOTUATLOU O~oL~i TOWSU'LC~w 0,*OLS'To.., t SwwI 00otCoo' 5* 00
fUSS ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ c1. WU oqSSOSOTI000UUTLOTOUT SUS:U0ULCwoICS'T0C NiS .I1US0 .... 0 1 SOO.
* LAO'OOGUS OOSR07'O SO C0-AIt
ISDS onm SOS I~ ItOSO.T.OUS1
4t r o, "r ld.0 t -n l, 0* 0*0l,5 SewctIo ni F re i, ,dWO O LS'0 T UwSM' SSSOOUS , OU SOTOW'O n, -UId
*p cj SOIOSOL Owteo.S *055 550550 U, e It0: *-r r.55* do'oo 0. ' [, OSOUT tUS
Il e1740* 550'"i- LOI 'I, ITU~S 05 US 1711OA T!,TOU.O 5 Tt
OeIr~,- fOOUA ic' O7057ii f,05L eLLOT ! 0nn e j~. UVI UI nA 5r TSOIS.I.,
AnU i o n h SOILijt T!O 0071 SLLUSSnf 1OLTCt:U UTO ITOU ~ U'Sln l~i
nd~ ~~ OUUSOOOSULO ,!t 11OU SO I
prt~~~i0,5T0.. Tp, ~ 7,0U rOULL01050
500 05 oos to 500007 I OOT * A:. 0 '510*500 50 Uoo'SS C,0rT
meOT A, Soopr MUOU ,i OSThI ISTIL :,' Kk iI.,:, :rs. SU T
Un 11,05 hUUO , UOULO U,- TSTUlSUU WUOMUT
hOOLUS U57500STL 5 UtU UL7STmow! d\TSW naL, PROS It@OS7O 00 0" USLO OSnLL IOO SIT OT hl tOUS0'
O~, S 1itS hLU wOiO *050 I070 SiLL -n eToo *0ATOSOTT 50.0
m-, __ _ _ __ _ _ In _____ ____ _____ ____
~CT'af'C I VJC~C TpTtd .C C.~a TLCTC r~s' -'. n A! C i.''C C'L
(CTa o:,TC s I.r''~o7 CCCALoAIL~i CC 3 I''TCCCT 14C IC'CC.! . 4. Ci.7
TYuTCOTSh~s:T ~ .. Ld23 iITTA:~ i:'n .. % a! C:l-cAIL 7C n ''It'' Id
apcjV..:TSSTCC LIT Ic 31T. 4L~LC C 'tacdc 0 dC 1M C Vp'C L.CCCaCCh'' C;JCTL.cCCd;T'C~T T icC4; .: 'C ITi "'0.1' P '
CLCCCrTCC~g:CJ" C'CTCTCC' ASC.CL 4:C s",c 'C'.. ''A '6 2i -k~ 627 ;.e ' l .
and0 4i 4Cn T3ATI'IT;C1 60iC:CTCcC C0 . . ' 2:( -: CC37', S'
d...CTcTC~ AJIT:? .TeTSL.LTL C~ .~rC IsC - - ' 2' C:.. C .:C 'C." .. ,
mNCC Ofc'DRAWd 177l~'aCLLUCC TL:'.0C, C;g.o .'..<'A:L.CU.L''CTJTVIC~ a~ah .11 T2LCCTL"L .LJaI~i..C LI CIIJ ,4
I NO Of. SEAM -:' 34.,M< .'Jl/Fgr'IN 3- LJUIAC W4.IITIe 1'.pTaT'g MC T C: .'CCa~CCLC' ai C.
n~~C A C I a' ~ 1T C ':.C ':. C .; -N0. .TCC :'C': LC ICC2I ',. R51'I aC 4~cCCL~lCV p~I' iCT~c a'c 'CI' .:''.': ''v~ C. ' ': J'CLIIC" :':': I'C'.r'SCC'I'.'.1
FLIGHT R AFT-
STAT ION BODYDOWN DATA NORMALIZED ANALYSIS
TO MAXIMUM 0 FUSELAGE RESPONSE
.5 RESPONSE LEVEL FLOOR RESPONSEGROUND FLEXIBILITY GROUND COEFFICIENT
VERTICAL
.5' ANALYSIS=5_
FLOOR TEST DATA 0 FUSELAGE RESPONSEUP 0 '20 HZ FILTER [ FLOOR RESPONSE
I \ *50 HZ FILTER GROUND FLEXIBILITY= I X 1 IN/LB
20 40 60 80PERCENT FUSELAGE LENGTH
f ig l' \erlwal a..elcI flens tPiae ]alon slOp Impact
nIr3 g: hIa' t Illrv.aI , IIC, 5fnItatCd Inc 1ot tr rfode. Q u It sutjc i tW is the ultimate goal I the design lot
r- ir trll ' l, rasI onsiderjtons The transport aircraft seating onftig raitol
V al I,,n ,~.~n. "I IsR .\iIIlI te Ia."' an.t id ttiC 3' wI parrs ~~size and *ciptt var nlfsca ttcri
...... Itlld'. .jg ..... 1- e,11 Cer 1,- fo1 esam pte Voe art t~ c and three neat ofi gralcr it'f.l c~lil,: LI c, .t,;j, .1)[1.,! re.. 1 .0 11tIl~lfHlqi ish be 14 n It he Ijll' occupied F\er i ocupied the tetg i,
al~j Ja a tI'11¢I l/l' l atI~lll .t'r5.II li It i I t floor and ... 1 1i1 lh J-cJi l 111c11d carl !rorr. VI l"t',renIlC females to "t'.
II.. 'all 1111 l tli',l ltCl I Ilt III tlIII lldLl arprl'a,1
'1I letcelfile males TIe respOlse and loadtng ofleac, accupanI scat
h .1~ ahltC . ast,
IJ~l +l in.Jl ln. ilra'I rcncd b=Ie . : glC -lnTqralltt" ould %ar\ tol the same floor pulse esxctait-
1.
FWD STATION BODY~ANALYSIS.0 FUSELAGE RESPONSE
X FLOOR RESPONSE GROUND
GROU NDIJLEXIBILIT"y COEFFICIENT.
4 X 10'IN/LB 1 0
" " " ......... .0.. ................ O....0........,(
LONGITUDINAL 1
DATA NORMALIZED FLOOR TEST DATA
TO MAXIMUM ,0o20 NZ, FILTER
RESPONSE LEVEL # 60 HZ. FILTER
.5AFT
20 40 60 so
PERCENT FUSELAGE LENGTH
324
4aq ~ j ,i ..fl d 1
L ,
[alien~~~~~~~ RJt Nii k_,cclcccc c;'cc0. I ta A. C : Il. V A
c.1 "' Alct:rl
jei satIlbet l acv Z.O iratci% D-c ,ccne,, 'o covia .c. i Colr~ NASirtaItp a' 1 c c. Icctrtt- Cmlod.1il mic SiZ~ccctO ojte~a' c i i cePaotcr'~fc rirj A" ctc
r~ ti ut, c n die o t e rcchctntcall 1'r rj, I aI Cotlmart C ' ncsac %IAScckrclco of :, ,tc panic rcctcd .irc d r, 'IcA circ ceaci'- rode
or al l et "Icc cchccl nca need ap toprite I. 'c o cijmn or , -,Ith rra'i~l,-,na io h o i rcnt fe d toesmet ohe lar e T apopri Fra d ral I. pra m ci AS lie (,cdCic-h lag NASH a f : th s rc re aeing vcncd thicie r rrcb . and c II;; or T!rrcprAcc
idcit ha'ditona crefo eeto c i th rocor lfi,i rl lirh r lngac:. i1) Anl C.l ifianielmn a ,rti e Fo ir el .ecpi e iacccr ah , ta R aca rc
n I t ASi & ti ite cirv coed to el ir r ipr o cdeii hds 'Tr,-,m C i cc i,capproatedocrin mth di ass ssi reit cflrglie d r nor pr t d ir i F \Aige Fc wRASI \A' aIc-.
ThrS pigl' c ic p A lice str cealn ir t teofj"' n 1i. an rcc ce~ o~o'- A.ricriocdspantspincoiced andltheliseplaned otentia 1 cah sea. Rep H F AA*R[ T&. mr P r A1 aIi- 'c
bdicae diinatl preeem ti, mthopdsto c nh~ C krr'r~r U D~r
fite lement teschniq c e eotnaor e ip~tio oth KRl LA ) ltSich B, 1and ~ ~ ~ ~ ~ ~ Ai DoC ASP, toi th faru: trnpr cese eniome viac ho A Ar'; ri vtra -ra cci
in itc nd methdl end r~ isztoI he p rl sirder gciiron FA kNA', FeeaWNS spoctrors A c al c r an Oof aiLOWr \1 Ai Gar. (o~fnil c D" JiitciNAS
inesute ir r ip n t5 e air, a it ish plan wi n np ill! ho icc N Has d (. olR orn A cp - (5 co ' -0 I A
cotolrccea re ctn al> tea pi tedirtiejl meth o hi 'NicA lci coa StIia I ra' b. ai
method tend3 preesne heroint ne pro fcico iccic. ti hir6 c A al' ijc or- Air ratt S a ic S lc-c . A Al , h
tothi cniin icasetcci c te eccopmertofprngarnIc ASi. iir ( an asinii 1)(<'2 I'I
to Cterditi US ired 1 Uas t S ror ti o hlt L ~ i Sokie AttnliiolM de (
4 o~rpert ir l iting the o is Ftd'Lcsns 4crgraft Ora i: ~ en )7 R~ieo ci F AA le andc arl R c i FA .53 -
Resar~ Lhorto' F Lati Aigica.(Cr~tr 'TIADS-35 Federal AccaioccArinrron Aao'
*irilCrarh Enicconment and Human Iccierance ii 11 (Icticher t1icf
.4c, Cla': Ccaacc S aci cia!Fliigr (sc , Swtnci ic USARISTR-" '2H Januars 1980 1 Q Aloer L %k ci al Acelewricin I icherVr
( rarcen \A( A RA5',1 I; p e r or3 Wittl~n C and Camon. MI A A Method 01 Acralc or
General Avcation Airplane Strucural ('tarlcuortricnsc Th comcc Rc Hic AS A. (a ai I A Ac ,iFAA-RD-c2. > Iockheed-kalonc Concpaen FANA Aircraii Sirccui''a ( .,c ., -tI: -\I Al , A , Al A1 ATechical1 Report Federal Accaion Adiinccirair S Al A"S I A l T Ph' -c l' " 1 1 c At.
.6 ~ ~ ~ ashic gton Dt Septempetr IQ- t-1 t no M--c t.> c At.c
325j
52
RECENT STUDI ES OF THE BiiAVIOR OK (N'P MliI .TE MATERIAI,AND STRUCTURES UNDER STATIC ANWD/)R CRA !!-I ,fPACT C)NDI)TTONs
The literature on composit, materiala and t ru tures has undergone anexplosive growth especially in the past 10 years of the past two decades.
Very extensive studies on the mechanical, failure, and poe.tfailure behaviorof many types of materials, layups, and structural arrangements have been
investigated and reported for many types of static, dynamic, impact, and
loading situations. Very significant advantages and improvements have
been demonstrated by the use of composite materials and structural concepts
to replace former all-metallic construction in both secondary and primary
structures.
Because of the vastness of the composite materials/structures literature,
it is feasible in this review to call attention to only a few of the more recentdevelopments reported in the literature. In particular, attention is called tothe following three volumes of recent technical papers [22, 23, and 24,respectivelyl:
1. Lenoe, E.M., Oplinger, D.W., and Burke, J.J. (Editors), Fibrous
Composites in Structural Design, Plenum Press, New York and London,
1980.
2. J.R. Vinson (Editor), Emerging Technologies in Aerospace Structures,
ASME, New York 1980.
3. 1.1. Marshall (Editor), Composite Structures, Applied Science Pub-lishers, Ltd, Essex, England, and Applied Science Publishers, Inc.,
Englewood, New Jersey 1981.
In addition,the Journal of Composite Materials has reported many valuable
developments in the past 15 years.
In the following subsections,brief reviews of selected papers from thesesources are given. These topics include: (a) crashworthiness tests of com-
posite fuselage structure, (b) impact resistance of graphite and hybrid con-figurations, (c) the effects of elastomeric additives on the mechanical pro-perties of epoxy resin and composite systems, (d) unsymmetrical buckling of
thin initially-imperfect orthotropic plates, (e) finite element analysis of
instability-related delamination growth, (f) elastic-plastic flexural analysisof laminated composite plates, and (g) behavior and analysis of bolted joints
in composite structures. There are, of course, in the literature many papers
on each of these topics. Those chosen for this review are considered to be
reasonably typical of the current state of the art. Also, the topics selected
represent only a small portion of those pertinent to the mechanical behavior
and analysis of composite-material tructures under loading conditions simulating
crash-response cond it ions.p
3.1 A Crashworthiness Test for lhii2 it__'l l-t, ,tructure
Fove, Swindlehurst, and liodues 12 K1 rp,rt , results of an experimentalinvestigation of various structurtal and m:l , c onept., seeking, to obtain
improved crashworthincss for Compos ito fusl I t ge trlcturL.;. Sta: iV failure
and postfailure tests were conducted as a for future dvnamic crash-impact tests to be conducted on prom is in.; a Lpts. Highilights and excerptsof that paper are summarized in th, fol]owing; all figures and tables are
taken directly from Ref. 25.
Composite materials arc being considered for application to primary
fuselage structure. It is essential that the energy absorption capacity of
the composite be as good as that of metallic construction. The complex response
of composite structures in the crash environment is difficult to determine
analytically and expensive to determine experimentallv. In [25! an inexpensivetest method is proposed for the quantitative evaluation of different material/structural configurations with regard to their energy absorption capacity.
The test specimens are cylindrical shells 9 inches in diameter and 18
inches long. Some specimens are hat stiffened while others are of honeycombsandwich construction. The materials used are aluminum, graphite, fiberglass,
and Kevlar 49. The cylinders are axially compressed and their load/deflection
curves determined. The areas under the curves are the energies dissipated or
absorbed during crushing.
The stiffened composite specimens absorbed less energy than the aluminum
specimens. Stiffened and sandwich aluminum designs performed comparably. The
sandwich composite specimens performed considerably better than the stiffened
ones but failed to match the performance of aluminum. It seems that additional
energy absorption must be incorporated into the design of composite fuselages
to match the performance of comparable aluminum fuselages.
Crashworthiness design has many facets. Among these are fuel containment,
seat design, landing gear design, body restraints, flammability, smoke toxicity,
flotation equipment, peak deceleration, preservation of occupant space, design
criteria, soil scooping, crew escape svstems, etc. Present attention is directed
only to the capacity of the fuselage structure to crush near the point of impact,
thereby dissipating the kinetic energy of the vehicle.
There have been numerous investigations of the various aspects of the energy
absorption problem within the scope of structural dynamics, static analysis,structural testing, materials engineering, etc. Each of these investigations
is inevitably deficient in some respect. For example, material data alone do
not reflect the strengths or shortcomings of the design concept. Analysismethods are of questionable reliability for this class of problem, and full
scale testing is very expensive. In [25 1, however, the authors propose a
standard test specimen and large deformation compress.uon test procedure whichis simple, economical, and sensitive to materials selection and design concept.
It permits the quantitative evaluation of several important material/designconfigurations of pract ical importanc c in fuse] age configurations with regard
to their ability to absorb or dissipate enorgy.
The most popular choice of test ,;pecl,,en to simulate the response of heli-
copter or fixed wing fuselage structo res is a circular cvi inder or truncated
cone. Bothi are rem inicent of for i, , . Li ,rt, ' Lt iili
test art icles. Prvsentlv th, c vli i.r!n r < q,: o ) ",: for testin g.
'Tie cviindricaL :pecimon, i', te. I i i , d ', inches
in diameter. The former dimension ,:,io t', t hi j! .tii, .ht-w n
frames in a cargo hel icopter usw!re . P , i r- lIicP4, i. imatelv
four times the typical strin'er s;" in . Kr-, ,!. ,, .pt-, ,. rc t,-tt-d:internally hot stiffen ed with . , , iv, . > !. . .: M iin -:0, P>-ntd concept,
and an unstiffcned honevcoi' pid...: W icn.
Internally Kx; ernZ y H~ con s
Stiffened 5tlffen-' Sandwic
Figure 3.1. Test ,ptv i7'on ( n, .pt> f O f. . 2,)
All of the specimens were required to have An ilt ir<at c ompresioi
strength of at least 20,000 lbs. and an iniit ial t r: ,nal st i ff On: of atleast 100,000 lbs. per inch of circumference. The cx:-taernal stringer concept
is not practical in fuselage but it does f;r il itate the ,oervat ion o:
stringer behavior.
The longitudinallv st iffened cyl inders had K iir ,t 0 tif I ucr qpa ed
equally (900 Intervals) around the c ircumfuve c wi hile th ,t ,;andwi( specimens
all used .25 inch thick aluminum honecomb core o 1 r.,,i, i tV Ioomrg -
tudinal joints in the aluminum ipecimens ',,ere al I I -J '11)'' apart ,rod werelocated at the stiffeners so that svmmet rv w;s tm inn K . hOU test spe CiMliTnn
was potted at each end in an epox. tompolind o prytit . ,ii itt ini; nid
delamination (Fig. 1.2).
At least four different material cOmbiAit iOn, %-e I-'. with LIc'b Of the
three design concepts, For each, A metal ha.- i ink, -:,et i,.i. ,:a,; co structed
from 2024-T3 aluminum. The skin thi-knc ,i. c.2N Anol .)012" for the stiffenedand sandwich specimens rcspect ie i , ilp the ii moi m ot i ff n.r thickn ss was
* n p ". 'The st iffened aluminum pc ci -n.-r, ri tcd t" , ther with prot rudin,-hea aluminum rivetts.
*V
Internal 1 tte rr. N, Hon~eycombStiffened St2Anec ac'.c
Figure 3.2. Some Stiftenur-.Joinit Concepts (Ref . 25)
The composite specimens of each design confiirat ion used three Com-Ibinat ions of materials: all fiberglass/epoxv, all graphite/epoxy, and] Keviar49 combined with graphite/epoxy. The fiberglass spvC(imens were constructedof Narmco 5208/E7781 woven prepreg with (145') skins and (0/90) stiffeners.The graphite specimens used Rigidite 5208/T300 tape. The skins and stringerswere (±+45) and (0) respectively with Harmco 5208/Keviar 49 fabric added tothe stiffeners to prevent splitting. The graphite/iKeviar 49 specimens used
* Narmco 5208/Keviar 49 ( 45) for the skin panels and Rigidite 5208/T300 tape(0) for the stiffeners. The hybrid sandwich cyl inder, the same above ment ionedgraphite and Kevlar 49 materials were plied together at (0) and (45) respec-tively. All composite specimens were cocured.
A' urninuflCnpst
Figure 3.3. Internally Stiffened Specimens (Ref. 25)
A 1 Lim i-oi ue
Fhigure 3.-4. Fx t r na lx I ti ith Sp,, i7--i)
Two addit ional test qpecimen-; .,rr im i w (, ' ..,i: inteut IL l l,
d if fered from the specif iat ion: 4i'Vn aoVe. uc .- i a Fvlr -kin/pr:phiteexternal stiffener design while Ac , tr .:1 a tN-, VII K lo inu.- externalstringer design. The tolloin.. )l. :tli:-, or: " , tit y t,,ril/dtvsig,.
combinat ions of- each t e t S pt.c n-i
T E S T L TC 7 7 7 7 L I S T
SPEC. SKIN SKIN TTFT ST FN ER COR 01 NT IBROEN.NO. IEATL. THICK. (IN)l NAt.. T-SITF. (IN) M.. CONEST
IA IS AL 0.025 AL C.'32IB IS FA 0.050 FG 6.) B 5 0/90
IC IS FG 0.050 FG 7. (,0 B 5 0/90ID IS GR 0.032 GR/K, P '.070 h -45 0/:45
IF IS CR 0.032 GR/KA9 0.C70 -. 5 0/:45IF IS K49 0.050 GR/K49 0. "7 i '45 0/:45
IG is K49 0.050 GR/K49 0.70 B _45 0/:45
IIA ES AL 0.025 AL C.732 RIIB ES FG 0.050 FG 0.060 B 45 0/90
IIC ES GR 0.032 GR/K49 0.0/0 B :45 0/±45
lID ES K49 0.050 GR/K49 0.070 B i45 0/:45lIE ES K49 0.050 GR/K49 0.070 B&R -45 0/-t45
IIF ES K49 0.050 AL 0.032 B&R t45
IIIA HS AL 0.012 AL P,IIIB HS FG 0.060 AL B 0/90IiiC HS GR 0.048 AL B 0/t45IIID HS K49&GR 0.060 AL B 0/-45IS - Internal Stringer B - Bonded FG - Fiberglass/Epoxy
ES - External Stringer R - Riveted GR - Graphite/EpoxyHS - Honeycomb Sandwich AL - Aluminum 2024-13 i:49 - Kevlar 49/Epoxy
The test procedure involved placing one of the cIindrical spec imens betweenthe heads of a hydraulic testing machine and slowly compressing it axially untilit was approximately one-half its original length. An initial 100(0 lb. loadwas applied to securely seat the specimen to the heads. The total axial loadwas measured with a load cell and the output continually plotted against headmotion on an X-Y recorder.
Typical specimens were loaded to ultimate strength at roughly 0.04 inches/
minute of head motion, and at 1 inch/min. beyond ultimate load. Within thisrange of testing rates the residual load carrying capacities of the specimenswere insensitive to changes in rate. These rates are several orders of magnitude
slower than those experienced in crashes, however.
A typical plot of compression load vs. rel at ive head not ion is given inFig. 3.5. Buckling of the skin was always evident prior to the attainment of
peak load for the stiffened vlinders but not for the sandwich cviinders.When ultimate load was reached, there was a sharp and pronounced decrease inthe load level. The failed cylinders invariably continued to support load in
a spurious manner as fractures progressed. Despite the load irreg,,larit iesin this region, an average post-n Itimate load carrvin g-c capahi Ii tv could eas iIyhe discerned. This load level began to increase onl' when One or more of thebroken stiffeners made contact with thet. end epox: ptt ill' c mrtiotilld alld !Orallt.) ! pp) io t load again.
With the observation that a local i ed volnime ot material undergoes tiltprimary fracture and defonnat ion it m-Ac: be -urm i ed that t bt emergy lhbsorp[ ion
L
Load
Def ect ion
Figure 3.5. Typical Load-Deflection Curve (Ref. 25)
rate is independent of specimen length but is approximately proportional tothe circumferential distance around the specimen. This measure of performancecannot be separated from cylinder design details, however. Thus, the energyabsorption rate is not a pure property of the material/design configurationalone.
4
Results for Stiffened (Wlinders
Each of the four basic material configurations (aluminum, fiberglass,graphite, and Kevlar/graphite) behaved similarly up to their ultimate strengthlevels. At approximately one-half ultimate strength, each cylinder began toshow evidence of skin buckling near the epoxy ends and between the stringers.This initial pattern developed into a diamond pattern between the stiffenersas the load increased. The slope of the load/deflection curve decreased withincreased buckling. In several tests, an audible noise and altered externalappearance indicated that one of the stringers had buckled or failed or de-laminated from the skin. This was immediately followed by the remainingstringers failing in rapid succession and the load reduced to a fraction ofits peak value. Increasing the average compression strain beyond this pointhad different effects on different materials. The aluminum cylinder creasedat the flexure lines of the buckling pattern. The bent stiffeners ripped theskin and the skin tore itself at the crease intersections (Figs. 3.6, 3.7).Progressive local crippling of the stringers and rolling of portions of thehot sections are apparent. The peak load level of the aluminum specimen was27,750 lbs. (Fig. 3.9).
The fiberglass cylinder reached a peak load of 36,850 lbs. befoce theskin fractured around the circumference in a jagged pattern. Interferencebetween the stringers and skin caused a cutting action at various points andresulted in large pieces of the skin pctalling and breaking off (Fig. 3.8).Compared to the aluminum cMinder, the post-ultimat , load capacity was muchlower. Parts of the stiffenoers remained intaLt with some completely detachedfrom the skin.
The ultimate load for the ;c,,,hite ;j cimen was 24, 3-lU lbs. The salientpost-ultimate feature or this test was local circuft-rential cracking of theskin. There was extensive separat ion of the nt iffcners from the skin accompaniedby longitudinal stiffener splittiin,. Thu ,ruph itt <".indor; had the lowestpost-ultimate load cap:acit-; of A i th, ; pAUio *<t,.
i p.
0
r* *
N
0
CD
* 'vi 1 -
1 ii 1
*
I I' *'
Ii
~lt I r*''*'*~
0Ii
S
~~41-
7F Keva
I
b . " ' , " oC - - I 1
En
A7 u:-.4ite .evlF 49/l r
Grapphte
Load!A
/~ IC
6 tr ~r
.... In) '1 .-
I
AIL -Iinulr Fibe r P.ass
Load
U~~ I FI
Deflection (In)
Figure 3.9. Load/Deflection Curves for Externally Stiffened Specimens (Ref. 25)
IIA (Aluminum) 1I F'e cjas0 (F h rg a s IlI11 (Graphite)
IID (FCcvl rII(ear 49/ h (Keviar 49/ Almn)Grpie Graiphite)Alinu)
eta
A-A
Aluminum Fiberglass Graphite Yevlar .91
LaO ad
(Kips)
II~IA -l uic 11
0 5 "
Deflecton ('n)
Figure 3.11. Load/1)eflection Curves for Honeycomb Sandwich Specimens (Ref. 25)
I
IIID IIIA IIIB IIIC
(Keviar 49/ (Aluminum) (Fiberglass) (Graphite)
Gra pite)I
4r' " ij
Figure 3.12. Honeycomb Sandwich Specimens After Failure (Ref. 25)
02
7
0
The graphite sandwich specimen failed at i9,5 !i,. a- a result of
circumferential skin cracking or buckling. The post-uIt imate behavior was
characterized by cusping of the skin at the pointA; of fracture and progressive
delamination of the skin from the core. Vnergy aihsorpt ion was much higher
than that of the stiffened cvlinders.
Similar response was observed for hvbrid Kevlar/graphite sandwich design
(Fig. 3.12). However, unlike the corresponding stiffened cvl inders, considerable
tearing of the Kevlar was observed.
The ultimate and aver:age post-ultimate load capacities of all specimensare summarized below.
Test Specimen Load Carrying Ca acities
Material/ 1 Ultimate Avg Post-
Specimen Concept Load (lbs) Ult. Load (lbs)
IA AL/IS 27,750 9,000
IB FG/IS 36,850 4,000
IC FC/IS 41,900 2,300
ID GR/IS --
IE GS/IS 24,350 850
IF K49/GR/IS 26,700 850
IG K49/GR/IS 23,400 900
IIA AL/ES 29,000 5,000
IIB FG/ES 22,500 1,200
TIC GR/ES 26,700 1,000
IID K49/GR/ES 22,950 1,600IIE K49/GR/ES* 22,550 1,850
IIF K49/AL/ES* 21,450 4,500
IIIA AL/HS 59,950 9,400
IIIE FG/HS 112,500 8,200IIIC GR/HS 39,500 5,600IIID K49/GR/HS 33,600 6,400
*Bonded and Riveted
IS - Internal Stringer FG - Fiberglass Epoxy
ES - External Stringer GR - Graphite/EpoxyHS - Honeycomb Sandwich K49 - Kevlar 49/Epoxy
AL - Aluminum
The skin/stiffener tests show conclusively that unless energy absorption
requirements are a design consideration, conventional sheet/stringer aluminum
construction is superior to composite sheet/stringer construction regarding
compressive energy absorpt !on characterist ics.
However, honeycomb sandwich composite skins fared much better in com-
parisons against aluminum. Thus,it may be possible to match aluminum crash
energy absorption without serious weight penaltv. These conclusions are
P summarized in Fig. 3.13.
C, >
-. -- S
< >-7E
Internaliy Externaliy HoneycombSt i ffened Stiffened Sandwich
Figure 3.13. Comparison of Energy Absorption Capacity ofAll Specimens (Ref. 25)
3.2 Impact Resistance of Graphite and Hybrid Configurations
Labor and Bhatia [261 report the results of impact studies on variousthin and thick laminates of graphite/epoxy and hybrid configurations. High-lights and excerpts from that paper follow.
The effects of configuration variations on the impact resistance ofgraphite/epoxy laminates is discussed in [261. These effects were evaluatedby conducting tests on monolithic panels of .04" to .18" thickness and sandwichpanels with face sheets of thickness .02" to .5". Additional tests were alsoconducted on .5" thick monolithic panels typical of aircraft wing structures.
Several materials were investigated to determine their effect on theenhancement of impact resistance of baseline panels. Plies of ductilematerials were added to the base graphite/epoxy panel and, in some cases,parts of graphite/epoxy plies were replaced by woven graphite/epoxy.
Impact tests were conducted using a falling weight with sharp and bluntimpactors, strain-gauged to give force-time histories during the impactsequence. From these histories, the absorbed energy histories were calculated.Acoustic scans and photomicrographs of cross sections were made to determinethe extent of internal damage as well as to identify failure modes.
Internal damage occurred for impacts causing little or no visibleexterior damage. Thin laminates had more back surface damage while thicklaminates had more front surface damage for damage near the visible threshold.
Impact damage has been shown to cause significant strength losses forcomposite specimens. However, the strains to failure for impacted specimensare usually above permissible levels currently adopted for design, which arelimited by effects of fastener holes rid moisturre and temperature on matrixpropert tes.
46
4
Low velocity impact studies were conducted using instrumented impactorsto obtain force and energy values during impact. Several geometric config-uration variables have been investigated including panel size, i:mipact location,impactor size and shape, panel thickness, type of edge support, and variationsin mass and velocity of the impactor.
Laboratory procedures for simulating impact damage employed three separateimpacting systems. A conventional drop tower was used for low speed impactsup to approximately 5 feet per sec. on laminates of thickness '0.25 in. For.5" thick laminates, a falling mass in a guide tube was used at velocitiesup to 20 ft. per sec. Both the drop tower and guide tube assemblies usedinstrumented impactors. A gas gun was used to fire various projectiles tosimulate foreign object impact at velocities up to several hundred feet persecond.
The drop tower was a DYNATUP Model 8000A. It is a gravity driven devicewith remote controls for release of the hammer and impactor.
Interchangeable impactors were mounted on the hammer. Semi-conductorstrain gauges attached to the neck of the impactor gave a continuous measure-ment of the contact force between the specimen and the impactor over a periodof milliseconds. Integration of the output gives the energy absorbed by thespecimen at any instant during the impact.
Most panels were impacted at the center of the five-inch square unsupportedarea and were impacted four times, once in each bay of the support fixture,with the depth of penetration varied from through-penetration to that causingslightly more than incipient damage.
Foreign object damage studies were conducted with a 1.18 in. diameter gasgun, consisting of a launcher system capable of sabot launching projectilesat velocities from under 100 ft/sec. up to several thousand ft/sec. The gunemploys rapid expansion of a highly compressed gas to accelerate the sabotout of the launch tube.
Projectile impact velocity was measured by two laser beams placed alongthe trajectory at a predetermined distance. A high speed camera was used todetermine projectile impact and rebound velocity and to record projectile-panel interaction.
Both impact velocity and angle of incidence were varied and severaltypes of projectiles were used including glass and steel spheres and agranite projectile machined to be cylindrical with conical ends.
Three types of specimens were fabricated and impacted. These are(a) "thin laminates" up to 32 plies (0.176") thi k,(b) "thick laminates"
(0.5" thick),and (c) "improved concept" laminates in wlhich mat erial or con-figuration was changed to increase impact resistance.
Table 1. Concepts for Improved impact Resistance
ADD: S-Glass cloth (surface and interleaved)
Kevlar cl -h
Nylon cloth
Kevlar phenolic (precured)
REPLACE ALL PLIES WITH:
Woven Cr/Ep (HMF-133/3501-6)
Woven 109 S-Glass hybrid
Woven Gr/Ep (H.F-134/3501-6)
REPLACE TO SURFACE PLIES WITH:
Woven Cr/Ep (HMF-133/3501-6)
Woven 10% S-Glass hybrid
MISCELLANEOUS CONCEPTS
Foam adhesive at core
Increased core density
Stiffeners: Foam fill/stapled
EXPERIMENTAL RESULTS
Thin Laminates
The larger panels, or ones with more flexible edge supports, tended toexhibit more flexual deflection during the impact, and as a result, more energy
was absorbed prior to the initiation of damage.
Limited tests were made on a few boron/epoxy panels. Comparable impacts
against boron and graphite panels indicate that the boron panels absorb lessenergy to cause incipient damage, evidently the result of stiffer filaments
which allow less flexual energy dissipation. Damage typically consists of
matrix cracking with no fiber breakage. The damage in the boron panels tends
to be more localized with less delamination or splintering away from the point
of impact.
Stiffened panels were impacted over the stiffener attachment on the side
of the panel opposite the stiffener. The stiffener debonded slightly at in-cipient damage, and at more severe loading debonded over an extended length.
Incipient damage for the riveted stiffener consisted of minor matrix crackingin the stiffener at the rivets adjacent to the impact. The riveted stiffener
absorbed 43 per cent more energy at incipient damage and also showed a less
critical type of damage, and is therefore considered superior for impact
resistance. The effect of the rivet holes on the panel strength may affect
the choice of stiffener attachment for a specific application.
All sandwich panels had a core thickness of 0.5 inches. Incipient damagefor these occurs at very low energy levels. Local crushing of the core occursfirst but face sheet cracking and delamination also occur at low energy levels.
66 (
A comparison of an eight p l sand iIich panel hav;)(,I. -f -orti wiLian eight ply monolithic (non-sandwich) panel indicat e- tliat t, '& ,oiolithic
panel absorbed nearly five times as much ener ;: t, in it iatt dalmA';. In
the monolithic panel, the initial dama,,c ,' 'ur. b% ;littii, the back face
between the fibers, thus requirin no'-o entrr: t han to L-rll tl' ,ne .'omh
in the sandwich panel.
BLUNt (5/& INCH DIA.) :MFACERGRAPHITE/EPOXY PANELS
CENTER
C LA... E
AT AT (2. )mEDGE EDGE AT
BONDED FAST'NR CENTER
CLAMPEDTHROUGH AT AT
PENETRATION CENTER CENTER
40 l CLAMPED FAST'NR
z 10- ATCENTERWITH I
AT FAST'NR l0 EDGE
WITH
5- FAST*NR IIINCIPIENTDA.MAGE
y
8-PLY 16-PLY 32-PLY
Figure 3.14. Baseline Monolithic Panel Surface Impact Data (Ref. 26)
IMPACTS AT CENTER OF PANELGRAPHITE EPOXY FACES
BLUNT BLUNT
CLAMPED Q/R FAST'NR
15THROUGH
F_ PENETRATION
BLUNT0 CLAMPED
SHARP SHARPCLAMPED CLAMPED
BLUNTBUNS CLAMPED r] CLAMPED
5-lN lENT .20.
DAMAGE .20.
READ RIGHT .15SCALE - .10(-
___.0
-I C -w 6.1 pcf 5.5 pcf 6.1 pcf
3.1 pcf A. Core 5.5 pcf F/C Core A! Core F/G Core Al Core
Y _" Y-
4 -PLY FACE SHEET 8-PLY FACE SHEET
Figure i.1 tl ine 'iandwiclh Pane.l Surf c Impact Data (Ref. 6)
r
4
Foreign object damage testing was conducted to deturmine whether highvelocity impact would significantly affect panel impact damage. All FODspecimens were six inches square and were clamped in a fixture which lefta five inch square unsupported area. Impacts were conducted on eight-plyand 16-ply monolithic panels and on aluminum honeycomb sandwich panels withfour-ply and eight-ply face sheets. (;lass and steel spherical projectileswere used as well as cylinders of glass or granite with cone-shaped ends.Projectiles were 3/8 inch and 5/8 inch in diameter. Both 90 and 450 impactangles were used with velocities ranging from 52 ft/sec to 480 ft/sec.
Photomicrographs of cross sections through the impact areas were madefor several specimens to observe failure modes (Fig. 3.16).
-.-PALI
. . .. .... .- - --*, .2 .- -.-1
6 PL ItS GR EP - 45 0 W,! 8 PLIESGCR EP, 45 0 'q
H1 N', T kPAC T(JR A T CEN T ER O.F ', INCH SO-UARE ARE A S AHP IMPAr_' 'R rT Lf N71 R ) b I-%Ci SOUARE ARFAT,14 ABSORUED[NERGY 1;'4FI LEI~a BO~ I, h 04-fT LB
ItLN' f DAMAGE INDIC(ATE 0AT 082 FT LBE11tHN A Ao %JL;[[ T 0FTL
!,ITMATRix CRACK ON" 8AC- F A0i l ,, T NIATR C.A ;I C)',
BALI FACE
Figure 3.16. Photomicrographs of Impact Areas of 8-Ply Panels (Ref. 26)
Although delamination is probably the dominant failure, considerable matrixcracking is also evident, and broken fibers can be seen in internal plieseven though fibers are not broken in the surface plies. Th1inner panels showmore delamination, probably because they flex locally under the impact, thusdeveloping high interlaminar shear stresses which cause delamination.
T4 ~ Thik Laminates
Because of their greater thickness, considerably higher energy levels-were required to cause damage in the l/2-inch thick laminatce . The majordifference In COMparisonIs With thin laminates was tht, variation in the amountof damage on th~e front and back f-ac(e.,; and internallv-.
4For impact energy less than 30 ft-lbs, the low velocttv impact.- causesmaller damage sizes for center impacts, which is prob.ahly, a res,|ult of mort.energy being used for flexual deflection at the, 1,ow(r .',!lo'ities . ThL' datal
6. St-''--
0
k10d1nonst rat c cdi [ (1 1) , L itV 0f tht ifpiD.,t phel A i ,,w n cmnd ; t t !at lana ;c size is
affected by a number of parameters, including impact locat ion, panel thickness,impactor shape and size, flexual deflection and viot itv Of impa,.t.
Improved Impact Resistance Laminates
The effects of concepts which add one ply of ;-v:las. to monolithic
panels are shown in Fig. 3.17.
- 0'.' - -
--' I I'"- .
U I I
o I
t I
SI AI I
F-1--T --1
-P P I F- - I , I
6I P Tnickto Mo n l I
Th enrge reuie cmltpetaioanicien daag ar shwn
I I I I I
I I I , 1
I M ' I , o*1 I I I --. I
-P it,-P, -P1 Fri tah, t:o t a Front Back- '- -J. - -Fl it-PN Trick 32-Nvy
Figu re 3.17. Effect of Concepts Uhich Add One -ly ass Ply
Sbto MonoI lithic Panels (Ref. 26)
The ene resin r ,quired fr complete peet ration and inc ipient damage are shon.Data for haseline panel are shown for 8-, 16-, and 3 2 -ply panels made ofAVg/ 5(I-5 t ape mat ,r ja 1. The. results of tests on improved concept panels are
compartid with iith ha sel in dl la;.
Data arc shown in i 1 . 3. 18 for th~e addit ion of one ply of e itlher Kevlaror hall jst I- ,Nvlon. The Key 1ar b 1irec 't onal woven cloth was prepregged with3501-6 res in and la id ,:p and (Tired with the basic ,graphito/epoxy tape. The
12-ounce per sqq. yd. tiilli-A i,. '; onl was not prcpregeld, hut was laid d irectly
on the graphite / epo,x t.ipk
When on the ha, k sura-,, tht Kvlar ply is effective in limiting thedimage to a localizd ire;i. li :,1m ,, t hhack -urfa(e deliinated overa larger arta thlin tl r, ,rrt;,d V, lar pIv. nd ht '! , ,1, I' of t he
t)(!
4 "
• F
I L
7
- ., II E- ' I I
:1 ,t o
I I I
I I Sd'.
1 'F K-
Figure 3.18. Effect of Concepts Which Add On e Ph'I of Keviar orBallistic NyLon to 16 Ply Monolithic Panels, (Ref. 26)
extra energy absorbed by the ballistic Nylon panel was us,:ed in causing thisincreased delamination which is not advantageous sinice it tends to increasethe size of the damaged zone. Neither Keviar nor ballistic Nylon was effectivein conceal 1mg damage when used on the front surface.
1 11
Adding surface plies of a ductile material such as glass or Keviar in-creases the energy required to cause incipient damage by about the same amount
ci:
a;adding a comparable thickness of the basic material. The duct ile materials,11017vcr, can hel p to contain damage. Development of more ductile resin systemsor techn iques to increase the interlininar and intralaminar shear and tensile
-4 s-trengths of the matrix seem to offer promise of sign if icantly'. increasedincipient damage energy level.
3. 3 Effects of Elastomeric Additives on the Mechanical Properties of EpoxyResin- and Composite Systems
Moul ton and Ting [2 7] report studies expl1or ing th ii clic of elast Om r 1i caddtivs t iproe te tugness of epoxy, resin andl composite systems. A
conc ise summary of that paper fol lows.
Thermosett ing res ins sucha epox.' and polyiid are, widelyv used a-;
mat rix materials in orgaic cmoie. These polvmers, are hr itt le materialswith low resistance to flaw growth an ack propcigat ion. A remedy is theaddition Of elastoMer ic -irtfcIes to -britt -matr toL improve resi 11
7,-
toughness. The mechanisms for this enliancement invove tr iaxIal ii latat ion ofrubber particles at crack tips, particle shearing, and matrix plasticity.In [271 , tie Iracture behavior and mechanical prope t is of such enhancedcomposites have been investigated c:xe rimentall'.
A series of acrvlonitrile-butadiene modified epux' polymers were inves-tigated. Resin fracture en-"gies were determined by testing stardard compacttension specimens and Nod impact specimen,;. The e astomeric additivesgreatly increased the fracture energies of the base upo':. .aminates con-sisting of 7781 glass and T300/3K graphite erce used. Enhanced toughness isobserved to correlate with decreaed stre:gth and modulus. Elastomericadditives were found to improve laminate fatigue life by a factor of ten.Thus the modified composites have a a L cidtrarl improved fatigue design limit,with a trade-off in sLren,
Increased toughness doe- not ' ,' without some sacrifice of initial
matrix-control led met ,h1an .cl prIpt .. Interlaminar strength (short beamshear test), high te.mperat re :trcn, rt tention, and wet strength retentionarm examples of matrix-wontroll,.d pi ' crti i;. Ultimate compression andflexural strentth are also h,'v iinfluenced by matrix properties. Generallythe modulus of tic resin is lonrd in proportion to tile volume content of thesecond phase. 'he secand pi a>c cvidrotL1 rduccs the nitial load bearingsurface area.
Lower in the modllus oan actual1" increase some fiber-controlled initialproperties such as t ens ile strength, and improve matrix-controlled propertieswhere the strain-to-failure is critical (e.g. off-axis tensile, transversetensile, and fle'xural fatigue propert ies).
An added benefit of composite toughening is improved laminate process-ability, particularly in applications involving complex curvatures andvarying thicknesses.
All elastomer epoxy compositions showed a decrease in fracture energy(energy required to initiate dynamic fracture propagation) with increasingstrain rate. It seems that the second phase has a time dependent capabilityto distribute, stress and toughen.
The toughness of the resin should be at least I ki/m' so that, when acomposite with woven fiber is made, the lav lip geomet and fiber volumefraction will not affect flow sensitivit'. Approximatelv 9- matrix strainwill be required to prevent premature interfaLV failure due to uneven stressconcentration between fibers under transverse stress 'onditions. The secondphase appears to dominate critical fracture energ,-., but onlv moderatelyaffects high rate stresses such as impact. This is becll>c the second phaserequires time for its various deformat ion mechan isms t o ,'t(tom' tptrat Wrefor energy dissipation.
3.4 'nQsvmmettrical Bunkling of iturallv-loaded, 'hinIn itialI!v-mrperfect,OrthotropicPl ates-_~J _P -~j ____
In Ref. 28, Marshall present; a ta'orcicat a al ,s, i, ur msytmrc eicalbifurcat ion buckliny of thin initial Iv-imperfect ortlut ropic plate; lo/adedliturallv on the convex face. !bsomvl''-t ri.l h::'kok! n i -, ShA, to be A f'inCt ion
of the plate 's initial geom trv ani! I'' I-t''!ll't ' r at 1: I it ti' ffective loil-bear i rig a;Ipac itV.
U!
Til I:' t. 1, ' ' ~ i t I- I c 'on ie rai 1 1IttLl t i )II H 1" - r r n rc 1F r I,. k;vI': i ~ 1 01. 1711e C ' ith
I i L t I u ~It t -n t i on
The, VOl Kif r~nlaltli I tll I- f' t )1 r ic CIo fall ortliot reop 10 c 1
p a t- ' itl I it ii ttt
r : 2 w 2Y , 3)Zw
Ev axy 4- dxd? dxy
2 2
whclo F is tile Air%- st-r(--s !uinctiton, I i t w i s t /I I i tl
1)latL e dlejfILettt i ofn, wO i t IeI ot ti It .ct ion , f." 11 I re Ilas tic modulIi* K s te shtirmoduus,~ isol;,t. riL io t rzm:ltF'or~o tk tihe direct ion o
re nfo r comoniit The total peoict 1,it ~ t !5 Ot. L" rofMidplaiest retch tng 1'.. , endlni; ce ri' 1,, ini tA IL),( !nd p tcolt ii]l , V I't + I' I'whe roe i
/ :) 2 d2 d FU5 IT J ~~2 -- y dx y
jA x
(ii~~ ~ +'1-, c 2
Ub J} 4. Dxdy (4)
A
whore 'I, is trainsverse odloo u t lni:,P lt flexutral rigid it': inx-d irec t io(n (similnriv for Kif- v-.dirctionl) .1Id D"=pIl A wsttn ,dtih p lute tlii ckiwsS I t i ; I 't t tlit tilL dol- i ot ;im!c Jre- 1filtt t i'l can
Pt: expanded in (illhbl sek'r i "
,'0V0v
w ~ ~ = Y)\A-II z' -K y
It is a ssumed that the platc i i p I , ri d
z C) 4 ,7) ,y -0 -0 (7)
,)2 , ' 2JF
x=: " , w = o - --- - (8)2 X x ., Z x = Z,One may choose
w (x y> = 2 f [ 0 - (9)
w (x y) z iTrx vrryY)- 7 - "/ sl^ Z! Sim,
Since these truncated series cannot satisfy the coundarv conditions, asolution is souht using the alurkin meth;od:
I Y4 2
- IJ ,: 4 FX - z ")7c4- f " -- ) P x ) y t (y) dx dy,
wy x )y . jX(12)
A 2 1W ,_. w 2W g,, (y) d dy
where'(x), t(y) are weighting functions. Substitutiny, (9), (10), (11)into (2), (3), (4) and noting (12), the total potential of the loaded plate.an be written in terms of do! .Act iii fuction cocfVicients only. For
un iform preiurc load ing, ont obta ins
= _ v,, - w w -2 . w v '.
4 Z 3 2 Z--L- w -4kA VV t VV
vv- -2-v vt C4 v 2 ,
3
A :,
S h __ 2 j~ cz-4
1Z 7)
par e Ii mo a I i-., ) ili . l -!, !a X
t t i, I t r 1 it I r I:
r i F iit CI t I)- t
t xl t I iIr . r Lc i itci Ir.- Ii'i -v: t uIc t t f r ur i-
da i:: in l . dy ;a, ill i tit c , it till~ il-~', cjitr(.- tictat
di I nI rf t 11 1 ! I 1 l stFk 1 i -r
ts Li. lwin .:il () , mU dr C La I- I t i ;''I n IT .nt-( i l Wi ifil 0i f~s.'v t ivi Ot Idi-,
t .I 1 ,- ' ! ; * 1 I1 1 1,II a ji ' I.i2,' l tw - T( 1 i l i
in.ti I nt Ii : I v 1)L. )Ll J I- ,*iIdv t1 t- p )t
t, - -1~ It. Id t ) t - JIn'Cla t I ,lfl ) l I .
.'t1 ,11 1' 11 o t 11 1i
oI I
Tl~~~~~ ~ ~ ~ ~ ,"-, (t 1 1 val~ p " t ,t i
Gr- CSA
who re.
an (I
11 e experiment al specimen used to ver I t-w luompitai on-; (-ons, ist td )t f our-
ply% unid irectional 14raph itec/epoxy bonded to 20?4-1]3 AI,.-iith EA9 2-4 adhesive.Trhe adhesive was; cured at room t emperactire.. To s imul Iate a do laminat ion,teflon t ape was used to pre-vent bon d inm giI the rooet ral part of the0 spec imen.
Some of the spec imens were loaded s tat ica-llIv so( that lateral deflect ionsI ~coulId be measured with1 a micromete~r. T.e fa-gesecie wr tested under
constant-amplitude, load controlledl in~~i dlj-pi :Ine loadinmg.
T'he present numerical anal v- is wasyer if ted Is; ama I vain4 g wo problIemsfor which exact sol ut ions are ava ilable . Al so, compijarison of measured andpred icoted lateral doeflIect ions of pos-t -hocki (d through-width tielaminatiomscorroborated the numerical predict ions. A small nIUMber of speciMems werewc re fat iguec tested to obta in do lamilotion g rowth data. (:aIctulated strain-energy release rates w-ere quial itati1volyv correLaited with thie observed growthrates to determine the relat ivo impo rtanct- of Mode I (opeuliimg) and Mode 11(sliding) component s of st ra in-energy rol ease rattes.
flLoad transfer near the delaminat ion wavs very comlplex. Interlamimarstresses wore not a simple funct ion of' applited I oatl or lateral deflect ion.Very steep graditents in the cal cUILated str ;sIt- the dola1minat ion frontsuggested the presence of a stress singular it v. Hence the peak values ofinterlamimar st resses have little meaning, since the.' depend on mesh refine-moint . However, ;t ra in-unergv release rates arec much less sons it ivo to meshrefinement than cal culated stresses.
Calculated at ra in-energy release. rates for Mode I and Mode IT crackext ens ion were wi.ry sensit iwo to (101amimat ion length, do lamination depth,and ( 1( lad IIe ve I ~ Mod Ie I S t r a I. n oe r- gv r e I ease rat to , inc reasod with
inc r ea s in g l oad ( and ( I atoL era] d efl ec t i onI in rit t:ial lIv hu It thIien d ec re a se d, wh IilIe0the Mode TI rate (G T) inc reased ionet on i callv with I nc reasinmg load. If
theo st ructurc had responded I iuiarlv (; wold ha1 l~v nra monoton ical lvw it ht the squlare of the load, and thle raitio C I/(;, wooul have remained fixed.Fer a given lateral ilefltoct ion, (; was greiitcr ticorre And deeperdelam111 ilat LOnS . or fifxed remote clIoad inug ( was ilut nectssar ilI greateUr orsa 1il 1 o r for t lie alho t or aind doe per 'ILI lAM ioa ions.;
u) Ia I i t a t i vt o ) or-rel a t on 11 1t (, i Ii :I ,t ed '11d (IIVaI Io wi t I obse,' Cr vedde L m I;IMaItJt io g0 11 ,I,)W t I Ii rates 4' liowc I l a at Id anI; i Ioa It i n gr 1' W 1: i do maII 1,1t Ld hs ~Teven1 t Iotg 01 nIi vmie r i c a I Iv G may li ii I I i or. Ct.i C1 i- not a .i impl ef[M)st ion Of Ik'];l Io I, it ' 1, klgt I, fc11rIi'. Ot ii1 delpth, ap1y] i od 1 ii. or Iitera'
deleclot ion, predict ingt, gr1h 1-071 tri I Kitted1 d1t11in lotL iOnI growth; daita 1 ,ts-peo tel to lie di t It'i t alud si it to jo i t r i" Ya o
*7C
3.1 El1Lst it 1 1st i I cl II,i Ali 1;1ti
thic Iled b-(r Cl I i :II i - I it it
mnd ins' M1) !I1 ~t i0 \I Al IaL tI i t I tt
I orrnuila t-cl bv t'(i mb I t 1! ilLo r v f j at U i t r wiI 1Lw i t I cIa s [c ; I IamIfnatrcd pl t 1 Lw F- in, r- 1- ti * IM' (I fi I
The Iliminat , i r7cC' '111 Ct I r 1) !,it L i TiUL t, C) 1il, SI it 1)
bonded tospether sO t) L lt L ii. i I it ;I 1I1( K 7 fln'71t 4 1 i riS in i( 1 1W aMid i .-; l 111iwi1, 'ds I 1 0 i ir()j'i' rt i 1) r" 7- t t t lic
a-I.Stiiti-pt io o I 1 ovtru lr i ttO i t- i i Si cc 1w I I' I" tt r(
'I'ic st;rain itlret'i nt L a ;rt (V illlo~ itO iil1i i sc I- at :c a Ir t -
II h c r i 1 )t L ii ide-nt i *, i t t - :-At tI I:v
liInrttn; I i j tit Iik re Iat io s! Ii p
I' j (2)
LT -- -r C 3 ~()
whuru I i L L~ 11 c- o pk~ u ; ey viil eunt oL ii t r s-it va li t h) 1 i p i tir a t r ve
e- t 3i I4yI
1K, ini t. 1iume' i t interpol ations ,i,,o
4A = Ad (9)
r, i .r t i cmree t,il general ized U-greAa. : , rcl d . ,n the el men t
An, L r app! ir.t ir -if e l i load in('rtiu,.nt , c th laver is checked in order tontp,,it t , ,con t itut ive matrix and tli st i fNess matrix. The solution methodout Iined hvr, in th, i1near inc romental mtod.
The model pru untod here has dciionstrated very goo'd agreement in Lom-
pari sons with experimental data obtained for atumnnum-alumnn oxidei.Mdwi 'h Copor it ,Lw.
1.7 Behavior and Analvsis of Bolted Joints in Composite Laminates
The joining of and load transfer between composite material structural
components have been studied extensive' botl experimentally and analytically
to develop effective joining procedures and to obtain an understanding ofthe physical behavior of the structure throughout the joint reg'on. For
example, Oplinger [31] has reported extensive experimental and theoretical
studies of the behavior of various types of fastener arrangements. Wong
and Matthews [32] and Soni [331 report examples of finite-element analyses
for the stresses and strains in the vicinitt of holtud joints.
Oplinger [31] reports the application of both finit(-elemen!t methodsand complex-variable/boundary-callocation methods to analyze the two-
dimensional stresses in orthotropic plates with fasteners. Stress concentration
factors in the plate adjacent to the fasLener were evaluated and the effects
of variations of plate orthotropic properties were demonstrated. Both glass/'
epoxy and graphite/epoxy plates were included. Extensive experimental studiesof joint strength for single-fastener lugs are reported for both glass/epoxy
and qraphite/l'eoxy to assess the effe:t: s of the ralio of fastener diameter Dto panel width W for various values of fastener-center to plate-edge distance
e, for e/W " 1. When one evaluates jo int design for an array of parallel
fasteners based upon results for a single-pin fastener, al lowauce must lemade for the fact that fasteners in paral1el may give highier net tension
strength and lower hearing strength than single-fastciner lugs [31].
Also reported in Ref. 11 are experimental studics of the strength of
series (rather than parallel) type fasteners. These fasteners experience
a significant variation of load from fastener to fastener. lence it is
shown that the use of elongated holen alleviates tIe ,trt.ss concentrations
and improves the strength of the overall joint.
Single-fasten>r studies of laminates such as 0, '45' where the principal
Yong's modulus along the 0" fiber is very different I orn that along the
fiber in the 15" pl iVen can reduce the net-sect ion st rc:;s concent rat ion factor
significantly. Ilus, the use of various diff-rent composite plies (i.e.,
hybrid material layups) can he vr efoLt ivt- in improving tens ion strength.However, this can lead to invrasr- in te sUPhear st r.; con-cout rat ion factor
77
[3 11 Reference 31 also presents ai s . t ot01 fliurt ee fc1or i)0itudt joints,and derior trates that the NU 1s1-Xt C"ne' mU isL i<r.d toare ew ith ex pe rimen talI reslts.3 Fina V 1 ift 1 noteL d tha1-1t 7) 11 d;5)
Lam inat cs wi chI exh ib1i t dulc t ; bil it': t, t cn;i,)1 .; 11 'eilr , r(' spe I vt1:show signi Fi cant reluc t ion - li st (e' orl(ent, rat ion)[., lacatnse of hIiduct [l it%--; the '45' 1,1M illilte sO.Xh il)t 1aoo1 i!Wi iuo ~t o tM in t A-- netsect !on wh Lch1 resembles thait in 11t:, ro -tu ll b/bc Ina it
e- Xh ib1 it pig f ormat i on in front of I eor
3 .8 Vib rat ion , Buckl ing ,_and. Plo-tb1uc i, 1 Stud ies- 'C omposi. e Plates
Tlhere are numerou s papers on th [a ' ]riit i on and Luck 1 ing behaivior ofcomposite pl 1at es. AlSO in rcoent Yea , i coriside rubl 1 e : rit L-of e xp1eur -mental and theo ret ic al work has been done on the post h~uekI ing behavior ofcomposite plate,,;; this tyvpe of beha io r is- expected to be observed f recjuentl1'.
I in the crash rpoesOf co-mposite ;t ructiirus. Two representat ive recentpapers on these topics are- those of I~ sa[34] and 'Starnes , Kn ighlt, and
Rause [ 351 The essence at thosec papers is captured i-n the. followingabstracts from thlese twopars
Abstract trom Ref. 34
Advances- inl th1)e understand ing of v ibrat ion and buck] ing behlavior of Dlaminated plates made of- f iiamentar,. compos ite material are . mmar ized in4th is survey paper . l(epend inc., un the number of 1:iam me alld thei rOrient atioll, vi bratitoll and hicki inc, analvses, of composite plates mav betreaited with: (1) orthotropic tijeor': , (2) anisotropic theory, or (3) moreCOrupl1icated , genieral theicr': Invo lv ing coupl ing between bend ing and stretchingof thle plate. The emphasis of thle present overview is upon the last.Spuc jul cons i1derittion is, given to thle complicating effects of: inpiane7in it i il stress-es, large ampl itude (lion 1 incur) Lransverse displacements,shear deformjt ion, rotior., i nert ia, ef feet s of surround ing media, inpianenonhomogene~t it'id1( var i able thickness;. Nonclass,ical buckling cons iderat ionsstir h as in it ial imperfect ions, are inTchiuded , as well as posthUckl ing behavior.
Abs trtict from Ref. 15
Resul ts of ;il C xperi mental] study. of thle postlhc ki inlg behauvior ofso ec t-ed flIat s;t I f filed gra phit e-epox w; panelIs I oadt,(1 in compre ss ion are
K present ed . The poa;thuck in,1,h re.sponlse and 1'illure chalracterist ics of
unpange is10, a~nd pa;ne s daia'dI,-lwspeed impact are described.I%;el panI11)ii el ha i d I-ouiir e (I i 1 1 ; 1 I I-s I)L.p d -if 01 1 nd 1(6- or 24-p 1(p1ils i- isot'rop ic skins . PanelIs withi thIree d iftferent -;t if tokner spac ings weretested. S0111 unldamaged Spcimlsupportet i:a; muc'; i.s three t imes theirillit ial hiicki load01 before lail 1115. !Vi I i i re ()o iIf .11 inlls fiit iated in
aj skill-fit If ftol' iltorl*taco reg ion. An1,1'.t i cal Ive obt a mod from a1101illell r g0110r.ii f;hl I t illi t- o 01 L-ll t .10 XSI c1 OfllIt Orl' ode cor relate
wellI with t'.'picail pos)t htckl iug tes;t 11cm 1) u to toi lure PIt anlaI'.t i ca ImodelIing1 ' dt i I 11ect': ; i tr. t o pre~di c t :i r, li te t .' , t Iit (i50tl to a panel is
dlest' r [ bed,.T ls t rt-11 I tO !;~~ t hoit I n-sped inmpaot iiaeOin reduc e thepost hut' k I i ug ; t ron g ri h(ICt a t i t te:' l ni~ in t 1 I ii1li t Ititt ht', Jilh-s-t i f f elerSnte r fatfe reg ion lis More on t''eto i1'11100 t dl1laie thoul t he s;kin m idwa'
bet ween s;t i en
78 p
,I - - ' ; U
REVIEW OF TRANSIENT STR'("'TIRAI RESPIUSt A AIKSIS METHODS
4.1 Introduction
Methods for the theoretical prediction of noniinuar transient structuralresponses of the type and extent produed b, severe impact, blast, or otherloads are needed for many uses. Such methods can he used for parametricand/or preliminary design studies or to aid in the design of transient struc-tural response experiments and in estimating the response levels which instru-mentation is intended to record. However, there are many structures ofinterest whose complexity is such that mathematical model ng to provide finedetails of transient response would he either prohibitively expensive and/orimpractical because of the lack of adequate knowledge to permit proper modeling.Thus, theoretical analysis must be applied appropriately and with discretion.The use of such methods can help limit the scope of mechanical experimentation,but the use of well-designed and carefully-conducted experiments will alwaysbe necessary to determine and/or verify many important details of the nonlineartransient structural responses of either complex built-up metallic or ofcomposite-material structures of the type found in aircraft and automotiveapplications. Well-designed and conducted experiments are essential forvalidating the final design in this type of nonlinear structural responseproblem.
In the following, attention is confined to discussing transient structuralresponse prediction methods. It is convenient to discuss these methods in tworegimes: (a) linear and (b) nonlinear. Historically, the simpler linearresponse methods were explored and developed first; then the methods were ex-tended and modified to accommodate nonlinear geometric and/or material behavior.
Linear transient structural response prediction methods consist of three*types:
1. Conventional Lumped Parameter (CLIP) wherein the structure is modeledby an appropriate col lection of general ized masses connected by linearstiffness elements (beams, springs, etc.).
2. Finite Difference (PD) method wherein the governing differentialequation of equilibrium of each structural region is approximatedby spatial finite difference expressions in term of displacementdata at the grid station , with appropr iate compat ibil ity enforced.
3. Finite Element (FE) method wherein the variiut rcc;ions of the structureare modeled spatially bv appropriate finite .1tints with appropriatecompatibility enforced.
*All three of these app aes nay be applied to citr A very simple or a
very complex a;t ructurt.
7,
11, easli cjase, one ohta ins a lifA on] tid ! t al. (ii ! 'ee L ia equaL ions-of motion which subsequently can he so ved h7 , ,in i.n al r oplat( wimew i.uCfin ite-di fference or t imewise fn it, t-,l twun L .o ulit io-n pr,ndure. Of nilrseif one wishes to do so, these qen ai i ,h, con 5t rtc :t int,, nrm.al-n'C t f r'
and solved timewise anaklvti , la ' lv', - ain r t rn.s tlnL reLop.n i i!,volved.
For the I Wear transient rtsn,' . ft i c, t he CI. arid the T'd) methods areembod ied in dozens of computer pro4r:! v. have n appl ied extensivelv.Hundreds of compuLer program; bad upn t'- . ,,t t. Al method exist andare used most commonly today beca: e ,, ava i la1W 1 n::put in facil it ie. andbecause of the fact that the FEK mathnod per"ils - tho nnala','st to approximateand represent his ,tricturt reavii 1,' vron t rival N.
Turning next to the nonl inear tran inient respn.-m regime, the FD and theFE method have been applied successfu! v in a direct and straightforwardfashion to relatively simple structures such as beam-,, plates, cylindricalshells, curved shells, and s ,eal of revolut ion; nonlinear material behavior,large deflections, bucklin,g fail ure, and postbuckling behavior have beenaccommodated and represented property. H{owevrl for complex built-up struc-tures, practical feasibility dictates that one emplov a modification of thebasic CLP, F), or FE methods to reresent and ap rox imrate in a practical way
* the overall postfailure, unloading , reversed loading, reloading, ... load
deflection behavior of cer Lain ant,,ma ticall ,-selected0 regions of the structure.This type of approximat ion -,atuire is currentIv termeud the hybrid approach.This hybrid approach inl most commoni" emplovd in c'onjucnction with eitherthe M1.Y< or the FE method. A,'o dinn]v, the cq;:ential features of these twoschemes (CLP/Hybrid and FI/Hivbrid) for predicting tiu nonlinear transient
structural responses for in mpJa x Iorunt-iires; will e a.; oribed in Subhsections
4.2 and 4.3, respect ivelv. >,
Finally, the folloving tabulation depicts the di scussed probliem-and-method categories:
Type of- mtructure
Re, imc -Mth.od. S imp I :ompl, x -
CIP X X
Linear IMP -. X
0 - ,- -. ------------ - -- -
Nonlinea FhI) X
( (;ortiet r in ti.: A' x
and/or v
Ker/ialH Or i d
X: I Idel v n1: k-d
x: c f ' an i Lr a 1 1 I
* In Sect ion 4, only rv r ,jt t i , , 'i. ,A. , i it tI l 011 A h 17ai t. inI i s ( I Is ,d ; il I lI'," i r k r - l4 t,,tv K u-t il- ti t t I ' I ,1 ' ':': i t , xiP nt ,attempt in a O re t o 1- i I iI rll i '\'1 L I I .1 ' .
0
4.2 CLP/Hybrid Appoxir tv Methods
The method now ki- n as the convt tional Iumpcd-paramet Lr/h'br methodfor predicting the n( linear transjIent rfponses f complex built-up structures
originated in the 1c O's in connect ion with ltld is; tO predict the severefailure and post failure responses ol 1 if t in g-.surface st ractures subjected toblast loading [36-41. It was real ized that suW ic i ent Iv severe blast loadingof typical comp] ex built-up lift iig surface st ru t urcs could cause the structureto buckle at onte or more spanwise stations durin, tliu trans ient response.
After buckle initiation, the structure tends to "fold" about that buckledstation which remains at a fixed spanwise location. Also, after buckle initi-
ation, the moment-carrying ability of the structure at that "buckled station"decreases as the postfailure deflection angle (see Figs. 4.1 and 4.2) increases,
as one expects theoretically and confirms experimentally [36-47] from testingvarious simple as well as model and full-scale complex built-up structures.
Unloading occurs along a "pseudo-elastic" straight line whose slope depends
upon the maximum 0 angle from which unloading occurs. This unloading slope
decreases as 0 increases.max
Figure 4.11 is a schematic illustrating typical moment versus angularrotation behavior at a buckled station of a built-up beam structure, including
unloading and reloading. If unloading is followed by reversed loading
sufficient to produce buckling in that direction followed by continued reversed
loading, unloading, and reloading, thLe associated typical moment vs. behavior
is as depicted in Fig. 4. 3b. Hence, if the structure is subjected to transient
loads such that these types of behavior can arise, one must accommodate this
type of behavior in a simulation model intended to predict this type of nonlinear
response.
Figure 4.4 [45] depicts a cross-section of a 4 -spar wing (beam). The
static postfailure bending moment versus postfailure rotation angle -, behavior
of a similar 3-spar wing is given in Fig. 4.5, together with predicted behavior
from a simple conceptual model. The load-deflection characteristics of this
4-spar structure in the postfailure range with unloading, reversed loading,
reversed failure, etc. are shown in Fig. 4.6 together with predicted behavior
for this static-test example.
Similar experiments and analysis have been conducted on helicopter and/orgeneral aviation aircraft structures and substructures [48-59] to evaluate
the failure modes, failure loads, and postfailure load-deflection behaviorof various components and structural assemblies of typictal helicopters.Fuselage frames, larding gear structure, stroking seats, etc. have been studied
both experimentally and analvticallv.
Similarly, typical automobile frames, body structure, and stiffeningstructure exhibit buckl ing and subsequent foldin, and crush-up behavior both
in static-load ing tests and in crash-impact tests [58-77]. Each of the manypossible modes of initial "failure" and subsequent load-deformation behavior
must be ident if ied and accommodated properiv in a pred ict ion model in orderto obtain realistic predict ions o1 the, noulinear t r-s ent structural responses.
In the C1P/11ybrid method of ainal':sis, the structure is represented bv anassemblage of generalized masses c noected by st iffntess clements (extensionaland/or bending) !such a; planar or 1-d beam [8, far example . Tvp i call v the
0
equations of mot ia: :,c ,: i:. *.: :,dcl , r, "]. o a ::. r n r. 1.r I Iv,while accounting for the appl i d 1,ladin , ' i ,: r,: i i I!, i:- , t , . ,etc. At t h1 l i :t i n 1 L0 , t hu tr - : .
1 ., 1s t: r,, ;,, t 1nt - 1, cv. 1 t I te d
at many 1 ocat ions al ong tie ,tr ni r, W c ,:r, d 'it. t ! , T-t i: va ic
at that station (for incipie:7t h ck' ' , 1 r I t:. '.' tt - t valleexceeds the critiLcal value At tint uit , i 'w, tuLe itlr rti; initructed
to account thereafter for tUP prta , t"f i i:, ir Yt'LrL'et i" -pring at thatstat ion; appropriate onl itlnesr 1oNO-d Vfl i Ion ci :, , t-ri.t i,: arc ;is igned tothat nonlinear spring. The ti:,ewie u, ,n ' r,.dur, 'nt Li t inc, withadditional nonlinear spr in s int rodu cd AL ,t nler 1-( lit as til
response and attendant crituria dimatt. i a '1 ii I 011tio ,. until
structural rupture occurs at some stat ion ,i thl, ann.,'t dtv ides to :aitthe calculat ion for some other re ;n.
The CIP/Hlvhrid method reported in Ref . 41 in an i ssnrcd-modc methodwhiih utii izes the natural-mode normal--,idWe elpiht ionls )f not in heforebuckliog failure. 'Ihs,,rcnltr', these samet ni ti-m I lmi1 5 are aole,? togetherwith a hinge 11ode jotrodutced at thi a, -ihir .t at [[ a; iiencv , thne method becomesan /assumed-mode method. This is a speciail W:ed l1,i1vsi s 4 1] wh ich for theappl ical le s;truiture Wi much more eIf icent compit at in al P: than the eneralizd-
coordinate ClP/liibrid analyses [381,.
BUCKLING
MFAIL A A B
z ALU NM2 M0
7- LENGTH CHARACTERISTIC0 OF BUCKLED ZONE
zOCUS OF POST FAILURE
ELASTIC RENGTH"' C D
=; //.BINDING OF< /-' BUCKLED
SI 'ELASTICM C ELEMENTS1 B C
9 FAIL
ANGULAR DEFLECTION, &
t r I t I I I I ~ ~ ,i 1 1i tL IIlt'
Upper Surface
Lower Surface
AM (a) Before Failure
* r Upper Surface
-Lower Surface
(b) After Failure of Upper Surface
*A-A A-A
(c) Typical Cross Sections of Shell Beam
*Fig. 4.2. segment of shl[ Rin I'nd or Pur(e I/nd ing (Ref. 45)
U8
KMmCO -----
b i
c d
0 C"e
Pig. 4~.3a. B a ic 1'os t Ii I Iire St ruc L ur I Be a io r cf Bui It -Up Be am s (Ref . 45)
M
/
c
MM 0b
Fig. 4.31). AddiL iorial Post 1-ii lurc 1,i:~iinu Piitlie, 1Pnu,,slile for Built-IUpBas (Ref. '5)
c0
030
CC
100
C\J -IO 0I
0
00
E o
o- C 4C\j 0l
CCl)
0 0
0P
00
Waa)
00
PO re) re -. r
I< I;- -Q- 7I 7O 7
0 0 0 0~ 0
0 CC IIZ I C
Isq Cl Ja o up a
0~x
4Ou4)
C)0
-4-1
*- e _m n~i
a a'Ou c(ted
AD-R131 696 REVIEW~ OF AIRCRAFT CRASH STRUCTURAL RESPONSE RESEARCH 2/ 2. '(U) MASSACHUSETTS INST OF TECH CAMBRIDGE AEROELASTICA ND STRUCTUR. E A WITMER ET AL. AUG 82 ASRL-TR-198-ir UNCLASSIFIED DOT/FRA/CT-82-t52 F33615-77-C-5t55 F/G 11/4 NLE|h|hhhEEEiEI
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MICROCOPY RESOLUTION TEST CHART
NATIONAl fIRAlAU 0f AMNIAND S 14' A
P-
The load-deflection behavior of the generic nonlinear hysteretic springmay depend upon the current value of a measure of the deflection--such as,for example, the angle 0 shown in Fig. 4.2 to represent the static momentversus angular rotation behavior at the "buckled station" of this examplemulti-spar wing structure [45]. The internal moment which can be carriedthere depends not only upon 0' but also upon how that value of 0 was reached;that is, whether that 0 angle was reached by a monotonically-increasingpath or by pseudo-elastic unloading from an earlier maximum value of I", etc.(Figs. 4.5 and 4.6 depict schematicalLy the types of hysteretic behaviorthat such models must be able to represent.)
In transient response problems, however, one must account for dynamicrather than just static conditions. In the present failure-postfailure con-text, dynamic effects may manifest themselves primarily in two ways. First,the incipient-buckling stress or incipient-buckling moment or buckling mode
itself under dynamic conditions may differ from that observed under staticconditions; this matter has been studied by various researchers for varioustypes of simple and of complex built-up structures [78-83]. Second, thestructural material comprising the "buckled zone" of the structure may becomposed of material whose yield strength depends significantly upon thelocal strain rate; hence, the load-carrying ability at that structuralstation may depend upon both the deflection and the deflection rate (orstrain rate).
Note that the internal structural generalized force of interest may be
a moment and the associated measure of overall deflection may be an angularrotation 6 of that buckled region. On the other hand, the "axial forceresultant" F (rather than the moment) may be of interest and the associated
measure of overall deflection of that buckled-folded region may be an axialdisplacement A. Thus, one may characterize these force dependencies bywriting
M = M(0, Opath, 6)F = F(A, A path, A)
where (*) means the strain rate d( )/dt, where t denotes time.
While in principle one could carry out very detailed modeling of thestructure in the "failure region" and could include a strain and strain-ratedependent description for the material throughout that region, practicalityand expedience lead normally instead to the use of empirical test resultsto modify the static failure criteria and postfailure load-deflection behaviorto account approximately for strain rate effects [77]. Some analysts neglectstrain rate effects entirely because they believe that the practical fidelityof modeling employed is insufficient to warrant attempting to include strain-
rate effects or because the strain-rate dependence of the material beingemployed is either unknown or believed to be small [39, 49].
For various types of ductile-metal built-up complex structures (multispar-skin, discretely-stiffened skin, honeycomb-stiffened skin, skin-stringer-frame, etc.) extensive static and/or dynamic tests have been conducted tomeasure their incipient-failure and postfailure load-deflection behavior[42-59, 75]. Simplified energy-based prediction methods have been developedand display generally very good agreement between predicted and measured staticpostfailure load-deflection behavior for essentially all configurations studied
88
[42-59, 75]. Thus, a considerable body of information has been ;enerated toguide the analyst (who is seeking to analyze a built-up ductile-metal struc-ture) in devising realistic and reliable approximations of the postfailurebehavior at possible stations of interest of his structure; however, corres-ponding data for composite-material structures are relatively sparse.Carrying out a CLP/Hybrid analysis successfully requires the analyst toexercise skilled judgment and to call upon a significant background of ex-perience on failure and postfailure behavior of complex built-up structures.In this problem area, the inexperienced analyst will encounter a considerableamount of difficulty and frustration.
It should be noted that the CLP/Hybrid approach can be applied to ductile-metal complex built-up structures or to composite-material structures. For
each type of structure, one must provide for accommodating (a) the propermodes of incipient failure that can occur (and the associated incipient-failure criteria) and (b) appropriate descriptions of the postfailure load/deflection and/or load/deflection/deflection-rate behavior.
Also, the "hybrid" feature which represents the nonlinear hystereticload/deflection/deflection-rate behavior of an automatically-selected "failedstructural region" can be employed with equal facility with either:
(1) The Conventional Lumped Parameter Method
or(2) The Finite-Element Modeling Method
Accordingly, in Subsection 4.3 where the more detailed methods (FE and theFE/Hybrid methods) are discussed, a description of this Hybrid Feature isnot repeated.
Numerous specialized limited-capability computer programs of the CLP/Hybrid type exist [48, 49, 68, 72, 74, 76, 82, 84-86]. For example,Catlin et al [48, 49] simulate the vertical impact of a helicopter fuselageby representing the structure by lumped masses connected by a preselected2-d aurangement of nonlinear axial and rotational springs. The other citedprograms pertain to portions of automobile structure simulating a crashsituation; Kamal et al [74, 76, 771 developed the FEBIS program to simulate
vehicle-to-barrier head-on impact wherein the vehicle is modeled by lumpedmasses interconnected by various nonlinear springs to represent the internalforces associated with the torque box, front frame and bumper system, drive-train, sheetmetal, firewall, radiator, engine mounts, and transmission mounts.Laboratory crush tests of these various components provide the nonlinear
hysteretic spring data. The SCORES program by Fitzpatrick (861 is concernedwith a 2-d model of an occupant which collides with the steering wheel,steering column, and knee-restraint system of an automobile in a head-oncrash; here again the system is modeled by lumped masses with nonlinear
hysteretic springs representing the load-deformation characteristics of thedeformable steucture. Prescribed are the crash input g-loads g(t) to thefront of the occupant compartment; primary interest centers upon predictingthe g-loads experienced at several locations on the occupant model.
Computer programs representative of the hybrid type but with a moreextensive capability are those of Wittlin et al 152-57], Mclvor et al [87],
89
Shieh [881, and Young [89]. The KRASH program [52-57] is a lumpod-parameter/
hybrid simulation, while those of Refs. 87, 88, and 89 are of tht finite-
element/hybrid type. The UMVCS program [87] and the CRASH program [891 repre-sent the structure by a 3-d array of rods and beams, with yielding and plastic-hinge behavior accommodated at the ends of these elements; test data are usedto define the moment-rotation behavior at those hinges. Shieh's program [88]is similar but represents the structure by a 2-d array of beams, with plastichinges permitted only at the ends.
Program KRASH [50-57] has undergone the most extensive development and- application of any of these hybrid codes, and is generally considered to be
the most convenient, useful, and comprehensive for use in preliminary andparametric design studies. In this program the structure is represented by
* point masses each with 6 degrees of freedom connected by an arbitrary 3-darray of beams. The effects of plastic behavior are taken into account
through the use of nonlinear loading, unloading, reloading stiffness properties;
those prescribed nonlinear spring properties are provided from crush testsand/or from supplementary analysis [50-573. The KRASH program has been applied
to the crash response analysis of helicopters [3, 90], general aviation air-
craft [91], and locomotives [92], for example.
As summarized in Ref. 3 (pp 89-90), the capabilities available in KRASH
are:
Primarv Features
- Lumped mass representation.
- Nonlinear external spring and internal beam structural elements: the
external springs represent nonlinear crushable structure, landing gear,soil, friction, and plowing reactions, while the internal beams representairframe structure nonlinearities via stiffness reduction factors (KR),
and, also, structure failure (rupture force or deflection) and damping.
- Large structure displacements and rotations.
- Three-dimensional impact simulations, model symmetry, sloped surface
impact.
- Rigid elements via massless nodes.
- Automated occupant survival indicators: livable volume change, volume
penetration by hazardous masses, Dynamic Response Index (DRI).
- Miscellaneous features, such as aerodynamic lift, angular moments asmass points, cross products of inertia, prescribed acceleration pulses
at mass points.
- Restart.
Output Information
- Mass point response time histories (displacement, velocity, acceleration).
- Energy distribution:Mass - kinetic, potential
Beam - strain, damping
Spring - crushing, friction
90
- Beam element strain and damping forces, stresses, relative displacements,rupture summaries.
- Spring element loads and deflections.
- DRI response, cg velocity, volune change/penetration.
- Print and plot of responses, elerent data.
-Energy summaries.
These KRASH capabilities are summarized in slightly different terms on pp 1-2
of Ref. 57 as follows:
• Define the response of six degrees of freedom (DOF) at each representativelocation, including three translations and three rotations.
Determine mass accelerations, velocities, and displacements and internal
member loads and deformations at each time interval.
* Provide for general nonlinear stiffness properties in the plastic regime,including different types of load-limiting devices, and determine theamount of permanent deformation.
* Define how and when rupture of an element takes place and redistribute theloading over the structural elements involved.
o Define mass penetration into an occupiable volume.
. Define the volume change due to structural deformations of an occupiablevolume.
o Provide for ground contact by external structure including sliding frictionand a nonrigid ground surface.
* Include internal structural damping.
* Include a measure of injury potential to the occupants; for instance, theprobability of spinal injury indicated by the Dynamic Response Index (DRI).
* Determine the distribution of kinetic and potential energy by mass item,the distribution of strain and damping energy by beam element, and thecrushing and sliding friction energy associated with each external spring.
Determine the vehicle response to an initial condition that includes linear
and angular velocity about three axes and any arbitrary vehicle attitudeand position.
Provide a measure of the airplane cg velocity by means of translational
momentum relationships.
• Analyze an impact into a horizontal ground and/or an inclined slope.
. Provide a measure of the internal stress state of internal beam elements.
. Analyze a mathematical model containing up to 80 masses and 150 internal
beam elements.
- Treat up to 180 nonlinear element degrees-of-freedom.
The structural modeling provided by KRASH is quite realistic for aircraftframes and trusses but modeling of skin panels, sandwich panels, or composite-
material panels can be done only roughly and requires the exercise of considerable
91
engineering judgment and experience. The nonlinear internal or externalsprings which represent the failure and postfailure behavior of built-upmetallic or composite-material beams under 1-d (not combined) lurilings requireseither pertinent experimental data or independent model estimate; of these pro-perties such as found in Refs. 48 or 3, for example. Thus KRASH! can representmany of the main features present in the crash responses of vehicles of conven-tional and of composite-material construction. Because of the limited fidelity
of structural and material modeling available, KRASH can be expected to provideuseful overall crash response data, but fine-detail transient response data ofhith accuracy is beyond the capability of program KRASH. Hence, KRASH isversatile and highly useful, but must be applied for appropriate purposes andexpectations. To be productive in meaningful engineering design and screeningstudies, KRASH must be applied by an analyst who has the experience and judgmentto construct a structural/material model which contains the principal featuresof importance in crash-impact situations. The likely modes or patterns of in-cipient failure and associated failure criteria as well as the patterns of sub-sequent progressive failure and the associated load-carrying ability must beanticipated realistically; the simulation model then must be constructed soas to accommodate and represent this behavior. In this regard, the analystis advised to become thoroughly familiar with the wealth of information andexperience contained in Refs. 3, 48-58, and 90-92.
4.3 More Detailed Methods
Many analyses and computer codes have been developed (and much additionalwork is in progress) to represent simple and complex structures by a much moredetailed model so that the many types of transient structural response, failure,and postfailure behavior present in a given structure can be accommodatedfaithfully and automatically--rather than crudely and by built-in rough pre-selected limited failure-postfailure models. Some progress has been madetoward this goal; detailed modeling of limited categories of structures canbe accomplished, but there are many types of modern composite built-upstructures for which detailed rational models to represent nonlinear transientresponse behavior are not yet available.
From time to time surveys and compilations of structural analyses andcomputer code capabilities have been made; for example, Pilkey et al [93],Kamat [94], Belytschko [951, Chang and Padovan [96], Armen and Pifko [97],and Noor [98]. Both spatial finite-element and spatial finite-differencecomputer codes of widely-varying capabilities are available. Of particularinterest here are those which accommodate geometrically- and materially-nonlinear transient structural response behavior; Ref. 98 cites 20 suchcomputer programs;
ADINA DANUTA HONDO-II NEPSAP STAGSC-lANSR-I DIAL LARSTRAN-80 SAMCEF STRAWANSR-II DRAIN-2D MARC SAMSON WECANANSYS DYCAST MSC/NASTRkN SESAM-69 WHAMS
--- and there are many more. Recently Fong [99] reported an evaluation of 8general-purpose finite-element computer programs:
ABAQUS COSMIC/NASTRAN MSC/NASTRANADINA EASE2 STARD)YNEANSYS MARC
92
--- only 4 of which (ANSYS, ABAQUS, ADINA, and MARC) have operational nonlineargeometric-material transient response prediction capabilities, including re-stricted classes of impact problems. See Refs. 98 and/or 99 (and/or also Refs.51 and 93-97) for a tabulation of the various features and capabilities ofthese computer programs.
Certain of these computer codes have been written to analyze impact-crashresponses of certain categories of structures. The most comprehensive andversatile of these programs is the finite-element program DYCAST [101-104]developed by the Grumman Aerospace Corporation under Grumman, NASA, and FAAsponsorship. Another similar computer program with more limited capabilityis ACTION [105, 106], which is also a finite-element program. For the cate-gories of structures which each of these codes can model, the transient responseincluding incipient-buckling, yielding, plastic behavior, etc. is accounted forautomatically; no prescribed internal failure initiation and no prescribedinternal postfailure hybrid-type load-deflection behavior is injected. Anexample of the application of DYCAST and ACTION (and of KRASH) to the analysisof and comparison with experimental data for a fuselage section impacted ina drop test is given in Ref. 91. Demonstrated is good overall transient responseagreement between experiment and the predictions of KRASH, ACTION, and DYCAST
but the superior modeling fidelity of the DYCAST code produced distinctlybetter detailed predictions and comparisons with experiment, as expected.
DYCAST has also been applied by Carden and Hayduk [107] to the analysisof the drop-test impact responses of various aircraft fuselage load-limitingsubfloor structural concepts. A representative fuselage floor and subfloorsections with simulated attached "seats and passengers" was drop tested foreach of several concepts. Accelerometers provided acceleration time historiesat various locations on the specimen. High speed photographic measurementsprovided deflection data. Static load-deflection tests on each subfloor con-figuration provided data which were used in DYCAST to represent this subfloorbehavior by nonlinear springs. Generally good experimental-theoretical agree-ment was found. However, in some instances the static failure patternsdiffered somewhat from those observed in the dynamic tests. This is suspectedto be one of the principal reasons for the theoretical-experimental discrepanciesnoted. Also, no strain-rate dependent material effects were included in theanalysis. The experiments conducted demonstrated the effectiveness of severalvery attractive load-limiting concepts for fuselage subfloor structure.
For detailed crash response analysis and design, it appears that theDYCAST program provides an excellent extensive baseline modular capabilityto which future needed features could be added effectively. This might in-clude, for example, elements to represent various structural elements andcomposite-material layups, as well as appropriate descriptions for failurecriteria and postfailure behavior of these items.
For convenient reference, the major features of DYCAST are quotedverbatim from pages 105-107 of Ref. 3, as follows:
- Nonlinear spring, stringer, beam, and orthotropic thin sheet elements.- Plasticity.
- Very large deformations.
93
.. 74
- Variable problem size.
- Restart (stop, review, and continue).
- Deletion of failed members.
- Four different numerical solution methods, three with internally variedtime steps.
- Modular formulation.
The basic element library of stringers (axial stiffness only), beams (axial,two shears, torsion, and two bending stiffnesses), and orthotropic membraneskin triangles (in-plane normal and shear stiffnesses) allows the convenientmodeling of aircraft-type structures built up from such components. The non-linear spring element is a general-purpose axial stiffness unit with a user-specified force-displacement curve.
The changing stiffnesses in the structure are accounted for by plasticity(material nonlinearity) and very large deflections (geometric nonlinearities).The plasticity enters the model through the nonlinear stress-strain curve foreach element. The geometric nonlinearities are modeled by reforming thestructure into its new shape after small time increments, while accumulatingdeformations, strains, stresses, and forces. In this way, the progressivecrushing and folding of structural elements can be followed. The nonlinearitiesdue to combined loadings (such as beam-column effects) are maintained, and thestiffness of the elements can vary depending on the combination of loadsimposed on them.
The restart feature allows for a large problem, or one of long event duration,to be run in small time sequences. This minimizes the tie-up of computerfacilities, allows the user to examine the response as it progresses, permitsthe ending of a simulation if a critical damage occurs, or permits the dele-tion of elements that appear to have failed as indicated by the stress andstrain output.
The numerical time-integrators available are fixed-step central difference,modified Adams, Newmark Beta, and Wilson Theta. The last three have variabletime steps, controlled internally by a solution convergence error measurement.Thus, the time steps increase and decrease as required during the simulation.
The modular formulation allows for easier addition of new elements, materialtypes, time-integrations, etc. by structuring the program in well-definedmodules with a minimum of interfaces with other modules.
The overall accuracy and computational cost of the simulation will depend onthe quantity of elements used (fineness of the geometric model). The finerthe model, the greater the accuracy and cost.
A user-oriented input/output format is utilized. The primary input datagroups are:
- Numerical controls and options.
- Geometry (nodes and elements).
- Motion constraints (and impact surface).
94
- Initial conditions.
- Rigid masses.
Material properties.
- Element cross-ssection geometries.
- Applitd dynamic loads (if any).
The output data are in the form of
Printed displacement, velocities, accelerations, strains, stresses,and forces.
Plotted histories of displacement, velocity, and acceleration at chosennodes.
T'imne- vqucnctd drawings of deforming structure or portions from anyviewing angle.
This ends tlLe verbatim quotation from pages 105-107 of Ref. 3.
It shouild he noted that although DYCAST models the (interior) structure
in detail with finite elements which accommodate nonlinear geometric and
material behavior, it also provides for accounting for nonlinear support or
attachment structure by the use of nonlinear hysteretic springs whosemechanical properties must be prescribed by the user (from supplementary
tests and/or analyses). In this sense, DYCAST also contains a hybrid
capability.
To date the documentation found in the open literature for DYCAST israther sparse [3, 103, 104]. Perhaps this is because DYCAST is regarded as
a modular addition to PLANS (for static loading) which is documented in
Refs. 101 and 102. However, it is hoped that similar comprehensive docu-mentation for the nonlinear transient response program DYCAST will be pro-
vided soon to enable other researchers to use DYCAST, to appreciate fullyits current capabilities, and to add further modules to extend its capabilitiesin useful directions. For example, although DYCAST has orthotropic plateelements including the Mises-Hill yield criterion, the Drucker flow rule,
and Prager-Ziegler kinematic hardening [100], it may be useful to consider
adding the present (or a modification of the) orthotropic elastic-plasticpanel elements of the BR-lFC code of Ref. 108 which has been appliedsuccessfully to the blast response analysis of composite panel structures[109]. Also, it may be effective to consider the use of Quasi-Newtoniteration methods for the implicit-time-operator solution of the nonlinear
equations of motion in DYCAST, as discussed, for example, in Ref. 110. In
this regard Bathe and Cimento [111] have shown by application of the ADINAcode that the Broyden-Fletcher-Goldfarb-Shanno (BFGS) scheme (one of the
Quasi-Newton methods) is particularly effective for the nonlinear transient
response solution of the equations of motion by using implicit timewise
finite difference operators.
r
95
- " [ "- 1 -I.. .0"
. . . . -
SECTION 5
CRASH RESPONSE RESEARCH NEEDED
General comments on crash response research conducted during the past twodecades are given in Subsection 5.1. Needed crash response research isdiscussed in Subsection 5.2, noting the general goals, the need for crash-worthy airframe structures, and related crash response work -- much asdescribed by Cronkhite et al [3] in USARTL-TR-79-11; the roles of laboratorytest and full-scale tests are also noted. Ongoing and planned crash-responseresearch of both general and helicopter related applicability is outlinedsuccintly in Subsection 5.3. Crash-response research focussed on transportaircraft is indicated in Subsection 5.4 together with comments on a plannedfull-scale crash test. Finally, some comments on the roles of specimen level,subscale, and full-scale structural tests are offered in Subsection 5.5.
5.1 Comments on Procedures of Past and Planned Research
As pointed out by Thomson and Caiafa [2], very significant progress hasbeen made in the past two decades in improving the state of knowledge ofcrash response and factors affecting the crashworthiness of aircraft and
helicopters (as well as automobiles).
This progress has been achieved through the efforts of the U.S. Army,FAA, NASA, DOT, their numerous contractors. Static testing, impact testing,and crash testing of a succession of structural components, substructures,and structural assemblies has led to an understanding of the modes of failureand of the postfailure structural behavior (load-deflection, energy absorption,etc.) of various types of built-up metallic structures. Effective combina-tions and arrangements of structural materials and components were identified.Concurrent and subsequent full-scale crash testing of helicopters and air-craft served to provide confirming failure mode and detailed postfailuretransient response data which could serve as "proof data" against whichtheoretical transient response prediction methods could be checked, andsubsequently revised to remedy noted deficiencies.
Going hand-in-hand with this experimental work were efforts to developreliable methods for predicting the failure modes and loads of each of theprincipal types of structural components involved, as well as their post-failure load-deflection and energy-absorbing behavior. The experimentalobservations were extremely important in guiding and channeling this theoreticaleffort along productive lines. Experimental failure and postfailure structuraldata enabled the analysts to devise effective and appropriate theoreticalmodels of the structure to minimize the computational effort while accountingfor the salient behavioral features of the structure. Consequently,theoretical methods have been developed for predicting successfully the non-linear transient responses of severely loaded structures for crashworthinessresponse purposes.
This type of integrated t heo ret i cal-experimental procedure has beenfollowed by the U.S. Army, FAA, NASA, D0'1, and associated investigators in
96
the case of built-up metallic structures and in the more recent work onstructures composed of composite materials [2,3,11]. In this newercategory of structural materials and construction, the diversity of struc-tural materials, arrangements, attachments, etc. is much more extensivethan in the past. Hence, considerable effort will be required to identifythe most effective and practical coimbinations of materialb, layups, andstructural concepts to achieve acceptable crashworthy design; progress inthis direction has been made as reported by Cronkhite et al [31, Thomsonand Goetz [11], Thomson and Caiafa [2], Carden and Hayduk [1071, and inthe studies leading to the U.S. Army Crash Survival Design Guide [13-17].Much more work along these lines will be needed to assess the comparativeeffectiveness and practicality of the numerous candidate materials andstructural concepts [112,113]; this will be an evolutionary process.
The overall structural crashworthiness research plan outlined inRefs. 1, 2, 113, and 114 appears to represent a logical and orderlysuccession of investigations judiciously combining experiment and analysis.Recommended are static and impact tests on a succession of laminates,structural elements (beams, frames, etc.), and substructure configurationssuch as fuselage floors, fuselage shell with floor, wing box structure, etc.
Skins of graphite/epoxy, glass/epoxy, Kevlar/epoxy or hybrid combinations ofthese materials in cloth (or unidirectional ply form) are to be studiedtogether with these materials used as facings on various types of honey-comb sandwich beams and frames. Also, concepts utilizing discrete long-itudinal and/or circumferential stiffeners of composite material are to bestudied. Various joint concepts need to be assessed in this crash responsecontext. These tests are intended to assess the energy absorption, failure,and postfailure behavior of these various configurations and materials, underboth static and crash loading conditions. Laboratory scale models andtests (static and dynamic) are to be followed by subsequent tests on large-scale components which simulate closely real-scale fabrication; these maybe regarded as proof-of-concept or final-validation tests.
5.2 Needed Crash Response Research
The crash response research which is needed to develop better crash-worthy designs for aircraft has been described clearly and concisely byCronkhite et al [3], Thomson and Goetz [11], and Thomson and Caiafa [2];those observations still apply and are largely paraphrased in Subsections5.2.1, 5.2.2 and 5.2.3. The roles of element and subscale laboratoryexperiments and tests of full-scale structures are noted in Subsections5.2.4 and 5.2.5, respectively.
5.2.1 General Goals
As described in Ref. 2, the general goals of (a) crash response researchand (b) the use of advanced composite materials to achieve crashworthinessperformance equal to or better than achieved with conventional built-upmetallic configurations are as follows:
0 Crash response performance of aircraft (a) of conventional metalconstruction and (b) of composite-material construction both designedto the same basic requirements need to be measured and assessed in
97
order to draw upon the extensive accumulated experience on crash
performance of metallic structures. Such comparisons are neededto permit assessing how well composite structures fare in meetingcrash requirements which have been developed and based onexperience with metallic structures.
O Seek improved crashworthy design concepts which serve as part of theprimary load-carrying structure under normal conditions and absorbenergy effectively in a crash. Effective performance with a minimumweight penalty is desired.
O A program of study which provides a systematic and growing body ofknowledge and experience on aircraft crash response is needed. Thisresearch should build from the material-coupon level to the structuralelement level, to small structure assemblages with i its and cutouts,to structural assemblages with skins, frames, stiff, rs, and attach-ments, and to "complete" airframes. An integrated I *ram of tests,analyses, and design studies should be carried out a Dach stage.
O Design information on the characteristics of candid; mposite
materials and of structural elements composed of con ations ofcomposite and/or honeycomb materials need to be developed further.Failure loads, failure modes and mechanisms, and energy-absorptioncharacteristics of these items need to be determined by systematictesting and analysis to assess their behavior in a crash environment.Crash environmental conditions pertinent to transport, general
aviation aircraft, and helicopters must be included.
O Analysis and design tools in the form of computer programs forseveral levels of detail and for various portions of the system
are needed.
O Accumulated crash response experience may lead in turn to revisedcrashworthiness requirements.
5.2.2 Crashworthy Airframe Structures
To develop crashworthy composite-material airframe structures, informationneeds to be developed further in the following areas [3,1141:
O Composite-material behavior under static and crash conditions (couponlevel and structural element level)
* + Failure modes and mechanisms
+ Structural integrity after incipient failure
+ Postfailure load-deflection and energy-absorption behavior
+ Abrasion and tearing behavior of skins
+ Crushing behavior of cores and honeycomb sandwich concepts
r
0 98
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+ Strain rate and temperature ef f ects on fil urc modes and post fil ure
behav i or
Testing and eva Iuation of Int s, hardpo int., and cutout s to det erminetheir strengths and tailure Iies, inc'1ud inu their 1"huLvior underdvnamic crash tend it ioiis.
0 Deve lop analysis tools on several levels for composite-material structures.
+ Analysis of structural elements (will require and be guidcd byobservations and measurements in each of various categories ofelement-level experimtfents).
+ Analvsis of aircraft-type structural assemblies (portions of theentire aircraft) -- experimental static and dynamic data are neededto guide the development of necessary analysis modules which couldbe added to the appropriate computer code 1)YCAST and to validateDYCAST prediction capabilities.
+ Gross analy.is of the overall aircraft system, including the landinggear, fuselage-wing airframe, and seat/restraint system (KRASH, DYCAST,and/or DYSOM could be applied but each requires further validation)
o Investigate crashworthy concepts for possible integration into futuredesigns
+ Sandwich stiffeners with honeycomb cone with Kevlar or hybridfacings
+ Graphite-epoxy and hybrid frames
+ Energy absorbing load-limiting subfloors (Carden and Hayduk [1071)
+ Crack stopping arrangements and attachments of structural elements
5.2.3 Related Areas
Some additional problem areas needing study in the crashworthinesscontext for general aviation and transport aircraft are [3,11,114]:
O interaction of the landing gear and Loads with the composite airframestructure. Load transfers, failure mechanisms, and failure sequenceneeds to be investigated for typical crash scenarios. Appropriateattachment and load-transfer structural concepts should be analyzedand evaluated by impact and typical crash test conditions.
Energy absorbing seat/restraint concepts should he evaluated inconjunction with composite-material structures to which these areattached at various representat ire locations along the fuselage.Impact tests tinder tvpical cras-h conditions should be conducted toassess the overall effectiveness of the seat/ airframe-structure
comb imla t i on.
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The cited laboratorv-scale (subscale) static and dynamic experimentson the various composite-material and structural concepts will be vl uablefor identifying the principal modes of failure under crash conditions, andwill be use ful for "suggesting" effectiv' modeling; simp lifcations. Thts,simplified models are exp ,cted to focus on and emphasize the principal types
of behavior involved withou including burdensome unnecessary detail. Suchmodels will accommodate the Fertinent incipient-failure criteria such asbuckling, delamination, debonding, tear, etc. Appropriate materialcharacterization information (stiffness, strength, inelastic behavior,...)will need to be supplied for each particular material/layup system.
5.2.5 Full-Scale Tests
Full-scale static and crash-response tests play an essential role inconfirming the validity of the design of the aircraft and perhaps inuncovering certain full-scale structural behavior that earlier subscalestructural tests had not revealed. Data from such tests provide additional
information to validate and upgrade analysis/design procedures and computercodes. However, a full-scale crash response test is very expensive and
permits one to study the response of the system to only one condition of the
many crash conditions of practical interest.
In contrast with crash tests of full-scale general aviation aircraft
where a limited number of seats and occupants is involved, crash response
testing of transport aircraft provides the opportunity to investigate and
compare the performance of a variety of seat and restraint systems at
various stations along the fuselage, thereby, including a range of impact
conditions. Many photographic, strain, displacement, acceleration, and load
measurements are needed to extract maximum benefit from such an opportunity.
This will require careful design, planning, and instrumentation -- as is
currently being done by FAA/NASA, for example, in preparing for a full-scale
crash test of a B-720 aircraft [2].
5.2.6 Comments on the Roles of Element, Subscale, and Full-Scale
Crash-Impact Tests
The extreme expense involved in carrying out a full-scale crash test,
and the fact that only one impact condition of one of many important crash
scenarios possible can be explored in a single test, requires the investigator
to carry out nearly all of the experimental basic data and assessment work
on laboratory type subscale structural models for both static and dynamic
purposes. In this cntext, one can develop a high degree of understandingof nonlinear crash response behavior and can develop and validate boththeoretical transient response prediction methods and crashworthy materials/structures concepts. Still needed, however, are a small number of full-scale tests to provide data to validate these transient response methods indetail for full-scale conditions to give one a clear level of confidence inthe reliability/adequacy of such prediction methods for design use. Theseprediction methods (like KRANSH and IDYCAS'I, for example), in turn, can he usedfor preliminary design studies encompassing a reasonabiv wide range ofcMditions. I)rawing upon SUch cal culiations, li boraitorv tests, backgroundinformation from the Crash Survival I)es ign (;uide, etc., the designer should
lo1
be able to develop a design which meets reasonable crashworthiness standards,but this is an area in which a succession of developments and improvementscan be expected, given the appropriate level of government and industrysupport and cooperation.
5.3 Current Basic and Helicopter-Related Research
The report USARTI.-TR-79-11 by Cronkhite et al (3] has documented the
state of designs, experiments, and :pxalvsis methods for dealing with thecrash-impact characteristics of advanced airframe structures, includingan extensive period of pioneering work by the U.S. Army Research andTechnology Laboratories (AVRADCOM) and its contractors.
Subsequent to (or in parallel with) the Ref. 3 report, there have beenat least four research efforts designed to extend the information base on
crash response of advanced-composite structures. These four programs aresketched in key-word outline form in the following under the headings [113,114,115]:
A. Extension of Work Reported in USARTL-TR-79-11 by Bell HelicopterTextron under AVRADCOM.
B. Development of Data Base on Composite Materials/Structures withEmphasis on Helicopter Applications (AVRADCOM at NASA-LangleyProcess/Application Branch, Materials Division)
C. Extension of Data Base Studies (AVRADCOM/NASA/Bell)
D. Advanced Composite Airframe Program (Bell Helicopter Textron and
Sikorsky Aircraft under AVRADCOM)
A. Extension of Work Reported in USARTL-TR-79-11 by Bell Helicopter Textronunder AVRAJ)COM
0 Failure and Postfailure Behavior of Helicopter Fuselage Components
0 Subfloor Concepts: Various Sandwich-Composites
0 Graphite-Epoxy Sandwich
0 Kevlar-Epoxy Sandwich
0 Small Structural Components
+ Static Tests, Impact-Drop Tests
+ Impact Response
o Graphite-Epoxy Readily Loses Structural Integrity
0 Kevlar-Epoxy: Superior Retention of Structural Integrity
0 Full-Scale Fuselage Sections: Frame, Skin, Subfloor
+ Drop-Impact Tests of Two Specimens
102
+ Transient Response Data Obtained, Analyzed, and Correlated with
Predictions
0 Report Release is Imminent (by Bell Helicopter Textron and AVRADCOM)
B. Development of Data Base on Composite Materials/Structures with Emphasison Helicopter Applications
(AVRADCOM at NASA-Langley Process/Applications Branch of the MaterialsDivision)
0 Tube and Beam Configurations
+ Failure Modes and Postfailure Behavior
+ Energy Absorption Characteristics
+ Crush Characteristics
+ Assess Structural Integrity from Incipient Failure to Loss of
Load-Carrying Ability
0 Composite Subfloor Concepts
+ Design to Same Specifications as Metallic Designs Tested by Carden
and Hayduk of NASA-Langley
+ Static Tests for Failure Modes and Load-Deflection Behavior
+ Impact Tests for Failure Modes and Transient Crush Behavior
+ Compare Composites Designs with Behavior of Previous NASA-LangleyMetallic and Composite Designs
0 Helicopters: Steep-Descent Impacts are Dominant
C. Extension of Data Base Studies (AVRADCOM/NASA/Bell)
0 Several-Year Extended Parametric Study Now Starting
0 Failure Mechanisms and Modes
0 Energy Absorption
0 Various Composite Materials
+ Graphite-Epoxy
" Kevlar-Epoxy Fabrics vs. Tapes
+ Glass-Epoxy
+ Hybrids
+ Advanced Graphite Fibers and Toughened Resins
0 Cylindrical Tubes
+ Variation of Layup Sequences and Angles
+ Vary Diameters
+ Various Diameter-to-Thickness Ratios
0 Beam and Sandwich Configurations (Cruciform)
0 Static Tests
0 Impact (Drop) Test - Impact Velocity Variation Effects
103
0 Scaling Effects0 Test Specimens to be Fabricated by Bell Helicopter Textron
,'*- 0 Tests to be Conducted Mainly at NASA-Langley (Static, impact-Drop,and Impact-Tower)
D. Advanced Composite Airframe Program- (Bell Helicopter Textron and Sikorsky Aircraft under AVRADCOM)
0 Development of All-Composite Airframe Structures for Army Applications:Primary and Secondary Structure
0 Crashworthiness is One Requirement (MiL-STD-1290AV)
0 Two Contractors Selected: Bell Helicopter Textron and Sikorsky Aircraft
0 Advanced Composites for Airframe, Landing Gear, Rotor,...
0 Critical Problems: Attachments, Joints, Fittings, Cutouts
0 Design and Tests of Components: Static and Impact-Drop
0 Tower-Drop impact-Crash Test of Full-Scale Configuration
The latter two studies (C and D) are of a longer-range nature. Study D isvery broad, and crash response is only one of many facets of that developmentprogram [113].
-:5.4 Transport Crash Research
For transport aircraft, Thomson and Caiafa [2] and Wittlin [21] report
that NASA and the FAA are sponsoring studies of transport aircraft crashdynamics by Boeing [1161, Douglas (117], and Lockheed (1181. These studies
are expected to identify the prevalent potentially-survivable crash scenarios.For each such scenario, the likely sequence of failures and associatedstructural regions principally involved will be noted. The associatedconsequences such as fuel tank/line rupture, mass item failure, floor/doordeformation, loss of seat integrity, and excessive occupant loads are to beconsidered [21]. These studies should provide guidance for focusingsubsequent crashworthiness development work on those structural and systemsregions which most seriously affect occupant survival. The region of theaircraft most immediately involved in many crash scenarios, of course, is
the lower crown of the fuselage structure and/or the landing gear and itsattachment structure. Hence, the elastic, failure, and postfailure responses
of shell/frame/keelson structure of metallic and/or composite-materialconstruction must be understood and the consequences to the occupants held
to acceptable limits.
Shown on the next page is a NASA/FAA flow chart depicting a logicalsequence of studies on the behavior of composite-material structures
subjected to crasi load g conditions. These studies commence at the laminatelevel, procced to the clement level, ind go on to tle s;ubstructure level. Ina future tim, frame, a full-scale crash test of a composite airplane can beexpected to take place.
104
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In support of the early stages of that outlined NASA/FAA transport
crash response study, at least two research efforts are in progress. Thesestudies are outlined in the following under headings E and F [114,119]:
E. Accident Data Base Studies (by Boeing, Douglas, and Lockheed)
F. Crashworthiness of Composite Fuselage Structural Components(NASA-Langley and Lockheed Aircraft)
NASA/FAA Transport Crash Response Research
E. Accident Data Base Studies (by Boeing, Douglas, and Lockheed)
0 Identify Range of Survivable Crash Conditions
0 Main Structural Features and Subsystems Affecting Injuries
0 Research and Approaches to Improve Transport Crashworthiness
0 Identify Test Techniques, Analytical Methods,... Needed to Assessand Evaluate Transport Crash Response
0 Preliminary Results
+ Four Survivable Accident-Condition Categories
+ Transports: Shallow Descent Impacts are Dominanto Small Vertical Velocity at Impact
o Large Forward Velocity at Impact
+ Structure-Surface Interactions Important for
o Rigid Surfaces: Concrete
o Compliant Surfaces: Packed or Plowed Ground
+ Worst Threat is Fuel Spillage from
o Main Gear Penetration into Fuel Tank Areao Failure of Wing-Mounted Engine Pylons0 Wing Structure Failure
+ Useful Analysis Tools
o Airframe and Subsystems: KRASH for Gross Response andDYCAST for Detailed Response
(Improvements Needed for Composite-Structure Analysis)0 Occupant-Seat-Restraint System: Use of SOMLA and DYCAST
(new code DYSOM)
+ Variety of Typical Lower Fuselage Configurations
+ Need Study to Enhance Crash Response Understanding and Behaviorof Each Type
+ Analysis of Occupant/Seat/Restraint/Floor/Subfloor Responses atVarious Stations Along the Fuselage
F. Crashworthiness of Composite Fuselage Structural Components(NASA-Langley and Lockheed Aire raft)
OBJECTIVES
0 Identify Important Strm'tural Paraimeters, Strtictural ResponseCharacteristics, and Potcntial Fa ilure Modes
i06
0 Define Appropriate Test Methods
0 Compare Damage Sensitiviev of Composites to Conventional AluminumFuselage Structure
0 Investigate Graphite-Epoxy and Hybrid Laminates
0 Focus on Structural Concepts for Lower Crown of Fuselage
STRUCTURAL PARAMETERS
0 Strength, Stiffness, Inelastic Behavior
STRUCTURAL RESPONSE CHARACTERISTICS
0 Crash Environment
*0 Load-Deflection Behavior
0 Energy Absorption
0 Static vs. Dynamic Behavior
POTENTIAL FAILURE MODES
0 Buckling, Delamination, Tearing, Abrasion, Thermal Degradation
COUPON TYPE TESTS
0 Tearing Resistance: Aluminum vs. Composite Laminates Out-of-Plane*and In-Plane Tearing
0 Abrasion Resistance Skin-Stringer and Orthogrid Coupons Against aConcrete Surface
+ Conditions: Velocity 50 to 100 mphPressure 50, 100, 150 psi
+ Aims: Wear Resistance of Laminite SkinsTemperature Effects on Resin
Compare Results with Aluminum Coupons
+ Material: Aluminum, Graphite-Epoxy, and Hybrid Laminates
STRUCTURAL ELEMENT TESTS
0 Elements of Frame and Keelson Structure (Aluminum Beam vs. G/EHoneycomb vs. Kevlar Honeycomb)
0 Failure Mode and Load-Deflection Behavior
+ Through-Depth Compression: Crushing
+ Axial Compression
+ Axial Sheer
0 Static Tests and Impact (Drop) Tests
TESTS OF SUBSCALE A IRIERME (OMPONENTS
0 Fuselage Skin-Frame-Stringer-Keel son Structure
0 Static Tests: Vailure Molt and load-Def Itct ion Behavior
10)7
6
Sl)vnamic Drop-Impact Tests: lFailtre Mod o., LOad-)eflection, andEnergy Absorption Behavior (Measure,: lowid, Strain, Accelerationand Deflection vs. Time)
o Assess Post faiLure Behavior of Grill -ge Structurt.
At a reasonablv early stage in Oiis overall pro;ram (suminmr of 1984),a full-scale B-20 transport crash test is planned. This will permit studiesin three crashworthy research areas 121: structural airframe and seatresponse, anti-mistinf kerosene performance characteristics, and cabinfire safety materials testing. The structural airframe and seat responseobjectives of those studies are 121: "(a) to define dynamic seat pulse data
in the form of acceleration time histories at the seat/floor interface,(b) to measure acceleration time-history data throughout the cabin interiorfor comparison with nonlinear analvtical predictions* of structural behaviorand to determine the level of injury by acceleration indices, (c) to determinethe accuracv of current flight recorder data, (d) to assess current andimproved seat/restraint-system/floor behavior, and (e) to determine structuraldeformations and failure modes." Both current and new seats and restraintsystems could be assessed and compared directly.
In addition to these structural component and structural assemblytests, new seat and restraint systems may be tested and assessed separately orin conjunction with impact tests on proposed composite-structure floor/sUbfloor load-limiting concepts such as explored, for example, by Carden
and Havduk [1071. Transient response, interaction, failure-mode, andpostfailure response data could be obtained to assess the overall conceptsand nonlinear transient response prediction methods.
Another important objective of the B-720 transpo rt crash experiment isto provide more comprehensive crash response data than obtained heretoforefor conventional metal-structure transports. This information can serve asbaseline data against which crash response behavior of future composite-material transports can bt compared in the quest for comparable or better" rashworth [hess.
5.5 Proposed Research
The present review of aircraft crash-response research indicates thatcomposite-material aircraft structures ,re receiving and will receiveincreased emphasis in the future. However, selective subscale and full-scale impact crash-response measurements of c.nvent ional built-up metallicaircraft structures will be made to form a basel ine comparison againstwhich to assess the crashworthy performance of future "replacement vehicles"composed largely of composite materials. This useful role is included in theNASA-FAA research plan [2,11,114,1191.
The overall crash-response research plan indicated in the NASA flow
diagram shown in Subsection 3.4 is schematic btlt cLmpreliensive. Thomson andhis colleagues at NASA-Langley have giien careful thought to the composition,
* Such as provided bv KRASH and/or )Y(CAS'i , t(,r rxinnple v.il idating aidupgrading of these prediction mt,thtuds i: -lso ,i g ll.
i 08
0
succession, and appropriate timing of work to develop comprehensive infor-mation on the crash-response behavior of composito-maLerial structural elementsand structural assemblages. Detailed lans for tht entiro rese'arch programhave not been seen, and the present rcvf ewirs J{1 not prcslume Lo :Idvist, thosevery capable and knowledgeable NASA/ I:,A rese, r, h rs ;,ii planners . Rat herwe wish to cite a few matters that are believ ed to merit studv, althoughthese and other more important items may ,ilreaody b included in the NASA/FA\research plan. Those matters are noted brictfiv in two categories (a) experi-mental structural studies and (b) prudiction methoU duvelopment in Subsections5.5.1 and 5.5.2, respectively.
5.5.1 Experimental Structural StUdies
The assistance and advice of transport and general aviation (GA) airframemanufacturers such as Boeing, Douglas, Lockheed, Lear,. should be sought toidentify the principal structural el emints and conf igurations which theirexperience and design studies show most likely to he employed in futurecomposite-material transport and CA aircraft. This should include representa-tive stations all along the fuselage From the nose to the tail, including thewing box and landing gear support and load transfer structure.
This information could serve to set priorities on and initially emphasizedetailed failure and postfailure studies of the most important structuralelements and subassemblies. Recommended material composition and layupsfor beam, keelson, frame, or other basic elements should be sought sincedesign and feasibility studlies will have led to a narrowing of the multitudeof possibilities offered by composite-material construction. Based upon thisinformation, one could select a small set of high priority configurations forsubsequent construction and testing.
For each configuration selected*, it is proposed that subscale structuralassemblies be constructed and tested first in vertical impact tests todetermine the modes and sequence of impact-induced structural failures.A second set of impact tests should be conducted employing a representativeratio of horizontal-to-vertical impact velocity with impact against a"concrete runway" surface -- again to assess the failure modes and sequencesassociated with these conditions. In all cases detailed observations andtransient response measurements should be made. Based upon these results andobservations, a subsequent set of static tests should be carried out on eitherthe "same" structural assemblage or upon selected portions (if feasible) ofthat assemblage to evaluate and compare these failure modes with thoseobserved in the two dynamic test conditions, and to obtain postfailure load-deflection and other structural-behavior data. These results should indicatethe nature and extent of subsequent static-test studies which may be useful.These impact tests and static tests will provide transient response andmechanical-behavior data of intrinsic value but also information which canguide the analyst in deciding the minimal necessary level of structuralmodeling required to permit realistic predictions Of nonlinear transientstructural response of selected structural regions (,r assemblages. Thenecessity of developing more comprehensive finite elements or the adequacyof employing relatively simple firit e elements in corijuniction with thehybrid procedure (and guidance for so I cting an effect ivi hvbrid procedure)
* -Appropriate account mutst be takun li much pr i ,r , o:. ri in,'e ,v NA,%,, AVRADCOM,Bell, Lockheed ,...to select crasliworil. r.athe.r ti , -roalti t mt(rilals/configurations.
i 09
should become evident from these test re rlit and subsCquent analysiscomparisons (using DYCAST and KR.AS1I, ,or cxamplt,).
It is recommended that studiC. 01 ti,. ty,,v- outlined above be carriedout on each of several "typicail fusl'1tge s.,tion'" conI igurat ions to coverin a subscale laboratory fashion aill of tihe irp, rtant regions of the fuselage,wing-fuselage, etc. which can unde", o impci.an ra sh-induced failure andpost failure responses. In selected insatinces (when timely), seat/occupant/restraints and attachments should hb in(c ,]ad their responses measured.Subsequent analysis should be carried out tO vaIlidate and upgrade transientresponse prediction procedures.
With the proposed sequence of impact and static tests of (a) structuralassemblages and (b) structural elements a lund of failure and post failureinformation will be generated for compos it.-material combinations andConfigurations which are most likely to be employed in future transportand GA aircraft. This data base should be valuable for conducting designstudies to meet specified crashworthiness requirements. Also, thisexperience will lead to additional structural/material concepts for improvedcrashworthiness.
Also, when timely, similar structural-assemblage "sliding-impact" testsagainst packed earth should be conducted to uncover any different modes ofresponse and failure produced in these composite structures by these
impact-interaction conditions.
5.5.2 Prediction Method Developments
Restricting attention to methods for predicting transient nonlinear
structural response of aircraft structures produced by impact or crash loads,it appears reasonable to assume that essentially two types of analyses (orcomputer programs) will serve as the prediction workhorses. The conventional-
lumped-parameter/hybrid method as represented by program KRASH will continueto provide useful overall-response preliminary-design information because ofits comparative economy and simplicity. For detailed transient response
predictions, the finite-element procedure as represented typically by theDYCAST program will likely find much but selective use; because of its higherfidelity modeling capabilities, this program can provide very detailed
transient response information but the computational expense involved tendsto limit its use to certai, selected portions of the entire structure.
In applications to composite airframe structures, KKASH has beendemonstrated to be effective [3,21] but its effectiveness depends heavilyupon the selection of an appropriate lumped-parameter model of the structureinvolved. 'hat selection requires much skill and judgment on the part of
the analyst; this in turn requires first-hand modeling-and-applicationexperience with KRASH and evaluations of predictions versus transientstructural response measurements. It is urged that such studies continueas the NASA/iAA program of impact and crash experiments proceeds. Thatexperience wil I produce improved skill i and guidelines for appropriatestructural modeling and will also suggest (a) where in the structural modelthat the prescribed nonlinear hybrid load-deflection behavior needs to be
provided and (b) the nature and pr yert ies of that ivbrid behavior. V; r ions
i l
types of composite arrangements for rasela;e frame, skiiu-I rame, and keelsonstructure mav require different liv- id propertito. (iarfullv selectedstatic-test experiments to produce fai ire :ind post ailure structuraldeformation patterns closely simulat iul, th ose obse rvd il crash-impact testswill be needed to generate the fund ol hybriu-stat ion :e, lan ica]-behavior
data to represent the mechanical hchnvior o tpical generic compositeconfigurations. As this data base 'rows, tie analyst will be able to useKRASH more effectively for preliminary design stud is.
With respect to the more refined finite clemenL transient nonlinearstructural response prediction methods, it should ho noted that the finite-element structural model results in .i set of ordinary nonlinear differentialequations of motion which can be solved timewise in small increments 't intime by the use of an appropriate finite-difference operator, either explicitor implicit. When the finite-element model consists of a relatively small
* number of degrees of freedom (DOF), it is most efficient to solve thoseequations timewisc by using an expiit operator such as, for example. thetimewise central-difference operator. However, explicit operators whenapplied to either linear or nonlinear systems require that ,At be sufficientlysmall; otherwise, the calculation will blow-up from (unavoidable) errorgrowth. Hence, when the finite element model has a great many DOF, therequired At size is so small that the computational expense involved incarrying out the calculation for the necessary amount of total time becomesprohibitive. In such cases, timewise implicit operators are used since suchoperators permit one to use much larger values of 't without computationalblow-up.
When timewise implicit methods are used to solve nonlinear transient
structural response problems, one of two approaches is used commonly. inone case, the internal nonlinear loads at a given time instant tn are
estimated by extrapolating known internal nonlinear loads at earlier timeinstants tn-l and tn_2; the result is an ajproximat ion of the properequations, and the solution can be carried out in a straightforward noniter-ative fashion [120]. However, tne solution is guaranteed always to beincorrect. But if t is not "too large", the solution accuracy may be
acceptable for engineering purposes. If tne entire solution is repeatedby using a fixed .,t whiich is half as large as the former At, one can concludethat a "converged" solution has been iound if both predictions agree. Ifnot, the process can be repeated until a converged result is obtained. Whileeach of these ci lc, elations is comparit ivelv inexpensive, the overall computa-tional expense can become large if many repeat calculations are needed toreach convergence. This "efficient but uncertain trial-and-error procedure"can be circumvented by solving the correct rather than the approximatenonlinear equations at eacin time instant.
To solve the correct nonlinear equations 3t each time instant withimplicit methods requires thiat iteration he carried out to convergence ateach time instant. Here also if severe noli incaritie.; are present, certainiteration procedures will fail to c)nverge Ior a yivcn 't size. For presentPurposes let it suf ice to note that rerenit .itdi,,s have shown quasi-Newtonmethods to be both effective and effiictnt [110illj; to (late these are themost et fective methods known for solvhin nonli n.ar transient structuralresponse problems. The documLentP aTt 101)e on th, wrkltorse I)YCAST programsuggests thaIt implicit st'lltianis wit: t- i. re , rried out, but the
Iii
p1 O.'edurc17 li~t 1oi I iL llk'fti' kr1 ttr iji tl ovol aIrt. tint' t 1r
I t i s r tc k:'imi it I cl Ait i I t o I o Ial o I'II 'kf [nIIo ft'as it) iI i t , of I- dap t) Ljont lk EFGS vtrsitin iio t ,i IC tjk i:K i -tV t I Ti <t hot' 11 1 1 t o 1) YCA STI as a p it i t,III 11 C. I IntS ino 011 111 4 I , i ts k t I ic j t'' '' , "! !tot' t v 't'io (- t llS i S 1, po,,1 )0WeCr I Li I IVttiil VCr tilt ilnt! I f it' i t,11t lict 1100 0 11iO t0, il 11 ;1 o 0ft tiL' S e IILet lin .s Lilt k
t l IC S to s i1".L t I -ist hn o-mi I ti t '1121 to ( Dv ri i t I oi Iow 1114,,L to rc si)tinlstc
Ii ito()r vlvt ta itIs o f ilt o rost . t 14-t I n Ilt tfes t to tint anazl ''I iYi\ SI III n'i sso t di it te it c'ii) t 'Vot i s t Intr
AlI so, al til~i DYiCASI C 1 1nt , inIs ,,'otr:li it mw i It i t c-d l f feron11oe
tptra tors (some W iti11 f i sod and ot Icr L'I."1'i ti hVlr i A b I(t t: ilkt: step s i ze .t
Which thle analovst niav select for ns, mort r tecLIn1t \,,Ir i abl e t inme -s top1)-S i te p~roc~dure dove I opei by IiH bb it tlPor to ()!' vcr\' at t ract i ve;. IIi b b i tt
It j mIa- proposed a1 schefllO to O'lILit ' t iltc stop'j size' in anoI ttt ll]lI e~C f foo t i V ' mainner aIs til sot -t (cii p ot tds thlit 00 cr411 I :cc iiriov P13 beMi 11 ; itiett wi I IIi 1c] ciLtit i 1n Lin necc.s!-;:i' i I v (an ld Lilntc onoil i ct a iv) smal Lt
stepJs whenever toss ible (i.e. , dir int ~PL' nods of sltmwlv otirving response)His proednre, ni'kos use of a mutt ifi i Nowiark tpitltor doLvised by hither andHIg,-tie s [121 1 Ti 1 tlprOihiI tugethcr xc ith B liGS tt'rat ion hats been demon-strated to be p'01 to e(2F fec-t i VC 1 101. 1it i S S sg g LSt Od that t- e4 p)OSSi )e
'iprtat ion of til' is roC ed U rc to LYCAST In' explIored (it- no t ii ready (tull).
"I NSU ',.\R'i ANXD C,0Xk_.:IXSN
6. 1 Summarv
The present studV was intendvd t ons i st oi a review o f the state o ftie art of aircraIt crashworth1in cs; work bioth xperim.ntal and theoretical,nut restricted to cons iderat ions o I -c vt r- t<ruc tural response aspects.(onsiderations pertaining to fuel ss pt :) rotection (and fires) and toemergencv evacuation systems weru to !) . omi[ted.
Principal attention, therefore, was given to examining the state of
experimental investigations and of theoretical methods for predicting severetransient structural responses of (a) conventional b,,ilt-up metallic aircraftstructures and (b) the newer compon;ite-material structures. This informationwas sought by searchinl the literature, by contacting personnel from involvedgovernmental agencies and the airframe industry, and by visits to the FAATechnical Center, NASA-Langley, AVRADCOM, AFML and ASD, within the contines
o! the available time and effort for this project.
As a result of these contacts and visits, various reports and papers on
past research ot the crash responses of helicopters, general aviation aircraft,and transports were furnished to us for study bv those contacted individuals.
In addition to reports on a succession of specific experimental and theoreticalinvestigations on aircraft crash response, summary state-of-the-art papers or
reports on crashworthiness were provided. Most of this information applies to
aircraft of built-up metallic construction, but two of these summaries includedinformation on both past work and planned work on the crash responses ofcomposite-material aircraft structures. Information in this latter category,
however, appears to be quite limited but is growing.
In personal visits to, telephone discussions with, and/or writteninformation from the FAA Technicail C(nter, NASA-Langley, AV'-DCOM (Ft. Eustisand NASA-Langl v), and Bell tel icopt r Te:trn personnel, some information
was ohta tIud on both -'urr'nt and p 1 anned le , c:1ro on the. crash-impact responses'f advanct,d co,m posf tL 1 rtfra me s t Ltkrt- s .
The results of this information colection-and-study are given in
Sections 2 through 3 of this report.
6.2 Conclus ions
The current state of available aircraft crash response information isdescribed in a very concise but comprehensive manner in the followingcrategor :es bv the indicated d cum.nt,
;enral Aviation Aircratt: Ref. II bv I'homson and (oetzRe . 2 by Thomson and Caiafa
Hel icopters: Ref. 2( (,awdl, r Ref. 3) by Cronkijite et :l21 t)v Wit t I in
I
lransports Ref. 2 by Iliomson and CatafLiRef. 2i by kWittlia
(;eneral Aviation Aircraft
Crash response research for genvrat aviation (GA) aircraft has oeenled and sponsored by the FA% and NASA since the eari-v 1970's. Many full-scale crash experiments have been conducted on GA type aircraft at the NASA-Langley tower impact facility (Impact Dynamics Kesarch Facility). Detailedmeasurements ot strainis, deflections, and accelerations (as well as high-speed photographic observations) were made at man\% locations in each air-craft. in many cases, instrumented dummv occupants also were used. Thishas led to an understanding of the principal modes and patterns of failureand postfailure response foi these types oif metallic and built-up metallicaircraft structures. Subsequent static tests on these principal structuralcomponents has provided failure and postfailure load-deflection data whichhas oeen employed empirically in nonlinear transient response computerprograms to carry out theoretical-experimental correlation studies.
Since these experimental measurements and comparisons with fieldaccident data indicated that the g-forces measured in the cabin area werein most cases well above human tolerance levels even though the livable
volume and structural integrity of the cabin area had been maintained, aneed was seen to develop modified structural concepts to permit moreuniform and controlled crushing of the subfloor and better vertical-seat-stroking load attenuation mechanisms. Subsequently, an extensive seriesof subfloor concepts was designed, built, and tested. Static load-deflectioncrush tests as well as drop-impact tests on full fuselage section, subfloor,seat, and simulated occupant configurations were conducted at NASA-Langleyas reported by Carden and Hayduk (107]. This work has demonstrated theeffectiveness of a variety of subfloor concepts for reducing the g-forcesin the occupant pelvic area. The development and validation of these subfloorconcepts represents a significant improvement in potential crashworthinessof GA aircraft.
Subsequent comparisons between transient response measurements forthese fuselage-subfloor-seat-occupant configurations and predictions from(a) the lumped-mass program KRASH model and (b) the finite-element DYCASTmodel demonstrated reasonably good theoretical-experimental agreement.However, the more refined DYCAST model and calculations provide much moredetailed and realistic transient response histories than does program KRASH.These complementary prediction capabilities, KRASH and DYCASI, have beendeveloped to a very useful stage but further development of each will beneeded to deal with future types of composite-material airframe structures.It should be noted that various of tiese subfloor concepts consist ofcombinations of metal i ic and non-metallic materials in various arrangements;static load-deflection crush tests were carried out both to assess theperformance ot a given concept and to provide failure loads and nonlinearload-defle'ction data needed as input into both the KRAS{ and the I)YCASTprogram. A similar in! ormit ion gtcner;at ion-and-ust, procedure is ant i cipatedwhen future composite-material c()nf iiurat ions are investigated. In thisway an expanding data base wil bi he developed for future crashworth inessdesign and analysis purposes.
4114
Load-limit ing seats antId et -at tar LIen t dVi ',s I ave Been designedbuilt, and tested; the trani;lent r'spin;e resuits mlt1ured in crashdeceleration simulations have Den ,ni:,rcd witli those tor "unmodif ieddesigns" as reported by F'assiiiorl la ind Al ,ro-BL 1 221 . Sii,,ni ficantimprovements have been demonstrated. Also described ii, Rel. 122 is anFA-funded computer program called SOMLX wtich models an aircralt seat,an occupant, and a restraint svstem. This 3-d finite-element seat andlumped-mass/spring/damper occupalt modei Wa.; us'd to predict occupantresponse in a seat-occupant drop test, with excellent experimental-theoretical comparisons. F or a more versatile and comprehensive predictioncapability, SOMI.\ is being combined ',,,ith the finite-element DYCAST program;ali indications are that this Will proyVtIe a very useful and reliable designtool .
Hel icopt ers
The U.S. Army Research and technology Laboratories (AVRAUCOM) and itspredecessor organizations at Ft. Eustis, Va. have been conducting crash-worthiness research since the late 1950's. This work has led to thedevelopment of a set of aircraft crashworthiness requirements [181 and tothe 5-volume Aircraft Crash Survival design Guide [13-17] which is regardedwidely as the bible for the crashworthiness design community. Crashworthinessdesign principles and guidelines spelled out in Refs. 13-17 have been appliedand have increased significantly the crashworthiness and occupant survival ofArmy helicopters and light aircraft.
Also, AVRADCOM was the first organization to investigate at some lengththe use of composite materials in airframe structures and their behavior incrash situations. References 3 and 20 summarize those developments. Variousairframe elements and components consisting of composite materials have under-gone static ;and impact testing to assess their failure, postfailure, andenergy-absorbing behavior.
AVRADCOM is sponsoring a very comprehensive development activity calledthe Advanced Composite Airframe Program [113] in which two airframemanufacturers Bell Helicopter Textron and Sikorsky Aircraft are playingparallel leading roles. in this ACAP activity, aircraft crashworthiness isonly one of many design objectives and requirements in developing all-
composite airframe designs.
A systematic series of studies following the recommendations of Ref. 3to assess parametrically the behavior of various composite-material structuralconcepts for helicopter fuselage structure in both static and impact situations,as noted under item A in Subsection 5.3, has been carried out and will bereported upon shortly. Since the amount of essential experiments and dataavailable to reveal the failure and post failure behavior ot the many composite-material conf igurations and arrangements of practical interest is still very
i.,I ll, an ex'tended program of expe riments, as outlined tinder item B in Sub-st-ction 5. 5, i; currently being tonuducied with emphasis on items with hell-copter app] icaLtIons. A more generail data base extension to take place overthe next few vears is outlined under itent C of Subsection 5.3.
I1I 5
It is apparent that a very good start has been made in obtaining failure,postfailure, and energy absorption data for various structural elementscomposed of composite materials. Mucih remains to be done. As the currentoutlined program proceeds, useful avenues along which to extend theseinvestigations will become evident; the variety and complexity of potentiallyviable materials and configurations to provide enhanced crasnworthiness istoo vast to encourage speculation on useful directions except in very generalterms. Innovative structural concepts which provide load limiting behavior,a large energy-absorbing capacity before collapse, and the use of hybridmaterial layups with enhanced toughness resins are self-evident goals.
Transports
In the mid i960's, the AA conducted full-scale crash tests [21 on twodifferent transport aircraft: (a) to obtain crash environmental data, (b) tostudy fuel containment, and (c) to collect data on the Dehavior of variouscomponents and equipment aboard the airplane.
In 1984 the FAA and NASA are proposing to crash a remotely-pilotedBoeing B-720 into the ground to simulate a survivable crash landing; tneprincipal objectives [2] are to: (1) corroborate analytical predictions,(2) test crashworthy design concepts, and (3) verify the performance ofanti-misting kerosene additives. The cabin interior will be fullyinstrumented [2] and will contain both standard and crashworthy seatdesigns with fully instrumented anthropomorphic dummies. Crashworthystructural floor features will be assessed during the monitored crashsequence. The test objectives focus upon (i) structural airframe and seatbehavior, (ii) the performance of anti-misting kerosene, and (iii) charac-terization of cabin hazards created by external fuel fire; these are elabor-ated upon more tully in Ref. 2. The structural and occupant response data tobe obtained in this test are to serve as baseline crash response informationassociated with a conventional metallic airframe structure -- for comparisonin the future with structural response data from "a composite materials/structures replacement" designed to meet the same basic specifications asthe older design but to exhibit crashworthiness behavior at least the equalof its older counterpart with little or no increase in weight and withacceptable cost.
Thomson and Gaiafa [2] and Wittlin [21] describe the current and plannedprogram of transport crash dynamics research being conducted cooperatively bythe FAA, NASA, and industry to develop technology for improved crashworthinessand occupant survivability in transport aircraft. Aside from the baselinetransport crash response data to be obtained for a conventional (B-720)transport, emphasis is given to investigating the behavior and effectivenessof composite-material transport airframe structures in future designs. Inpursuing this area, the past information and experience developed in thegeneral aviation and helicopter crash dynamics programs are being taken intoaccount. It is noted [21 that transport aircratt have somewhat difterentfat ures from those of GA aircrft and heI icopters with respect to fuelcontainment, multi-occupant seat and floor behavior, composite crash response,
and multi-occupant egress.
116
.I
Under the FAA/NASA transport aircrai t crash ivnimics research program,Boeing, Douglas, and LAO ~dieed- .aliiornii are condtict ;i Ludies of pastaircraft accidents to identify thei principal ctt.gori,'s of potential lvsurvivable crash scenarios and conditions as a tocL.u for subsequent invest-igations [2,21]; four categories and the associated impact conditions havebeen identified. Also, these airframe desi,ners and companies are seekingto identify the various typical structural confi;uratins and arrangementsof composite-material structures likely to i-e emloved at various fuselageand wing stations: the overall objectives and preliminary results obtainedare outlined under item F on page 106. In parallei and in collaborationwith this work, NASA and the FA.A have laid out a composite materials/structures test program to investigate tre response characteristics of a
succession of structural components and assemblages to simulated crashloadings as indicated in the NASA/CAA planning chart shown on page 105.Some of the facets and objectives of this part of the FAA/NASA program areindicated under item F on page- 106-108.
As this FAA/NASA/industry transport crash dvnamic,; research programproceeds, data and experience on the crash responses of structural elements
and assemblages comprised of various different composite materials andcombinations thereof, honeycomb structure, etc. wiil point the way to evermore effective structural concepts and materials for copin,,- with crashconditions efficiently. The basic -P/NASA plan is a very logical andorderly one, and can be expected to produce a valuable fund of structuralbehavior and design information which can be applied to reduce crash hazardsand achieve a high level of crashworthiness in future composite-materialtransport aircraft. A very important ingredient in achieving these goals willbe the close and continuing involvement of and collaboration between theairframe industry and the FAA/NASA team in all aspects ot this research:experimental, analytical, and design. In addition to developing necessarybasic data, this collaboration should lead to an effective focussing ot efforton design and material concepts which will find practical application infuture transport aircraft.
Summary Comments
The available information on current programs ot experiments toinvestigate the failure, postfailure, and energy absorbing behavior ofcomposite-material structural elements and assemblages under both staticand simulated crash conditions has been outlined under items A, B, C, andD in Subsection 5.3 and under items rf and F in Subsection 5.4. Aside fromRefs 2 and 21, no progress or status reports have been received to providean up-to-date assessment of progress and problem, encountered in those studies.The most meaningful and authoritative recommendat ions for subsequent necessarycrash response work will come from the investigators who are activelycarrying out and monitoring those experiments. These include personnel at:
a. Bell Helicopter Textron
b. sikorsky Aircraftc . lockheed Cal I tforn iad. AVRADCOM, Ft. Eustis;e. AVRADC)M at NASA-l-angley
f. NASA-Langley Structures Divisiong. NASA Langley Process/,pp icat ions tranch, Materials Divisionh. F A Technical Center
117
among others. R. Thomson of the NASA-Langley Research Center, C. Caiafaof the FAA Technical Center, and R. Burrows of AVRADCOM, Ft. Eustis, Va.have provided strong leadership in planning and sponsoring crash responseresearch work. Close collaboration and cooperation amongst these individualsand agencies as well as amongst their contractors will be effective in theorderly and rapid development of crashworthy technology for future composite-material aircraft.
1
118
I: I: N IS
1.Ca ja Ia ,C. A . and Nc r i L 1. M . *l_ in ineurjLnj;, I nd Deve Io ment Pro ra in P lanA ircraf t Crashwort Iiiness , 1 edi, ri ! .*\'iit itn Adin ini -st rat ion T'echtn italI Center,FA A-FD-i 3-6, June 1980.
2. Thoms;on, R. G. and Cajia fa, CA. L, Design i ng for Aircraft StructuralCrashwort himess , A IAA/ SAE'/ASC E! ASILI F/'FRl 1981 I nt ernat ionalI AirTransportation Con e rencjl'0 W iv 26-28, 1981, Atlntic (Iitv, N.J. PaperAIAA-81-080 1.
'3. Cronkhite, I1.D. , Haas, T.J ., Be-rry, V. L., and Winter R., tnvesti i onof the Crash-Impact Character ist ics of Advanced Ai rframe Structures.Bell HelIicopter Text ron, USART-'IR-79- 11 . Sept . 1979.
4. IDeHaven, Hugh, CaulSeS Of Injuries in Light P1 ane -Accidents, Aero D~igest,March 1, 1944.
5. Reed, W.H., Robertson, S.H., Weinberg, L.W.T. and TIvnidall, L.H., Full-Scale Dynamic Crash Test of a Dougls D-7 icat lgtSft
* - Foundation, Phoenix, FAA-ADS-37, April 1965.
6. Bigham, T.P. and Binghamn W.W., Theoretical Determination of Crash Loadsfor a Lockheed 1649 Aircraft in a Crash Test P rp-grm, FAA-ADS-iS,July 1964.
7. Vaughn, V.L. and Alfaro-Bou, E. Impact Dynamics ResearchFacility for
Full-Scale Aircraft Crash Test ins, NASA TN D)-8179, April 1976.
8. Castle, C.B., -Full-Scale Crash Test of a CH-47 Helicopt er, NASA TMX-3412, December 1976.
9. Alfaro-Bon, E. and Vaughn, V.L., Liht Aipe Crash Tests at Impact
Velocities of 13 and 27 rn/sec. NASA TP 1042, Nov. 1977.
10. Castle, C.B. and Alfaro-Bou, F., Ligt Airplane Crash Tests at ThreeFlight-Patth Angles, NASA TP 1210, June 1978.
I1. Thomson, R.G. and Goetz, R.C., NASA/FAA General Aviation Crash DynamicsProgram - A Status Report, ATALA, Journal of Aircraft, Vol. 17 No. 8,Aug. 1980, pp. 584-590 (also Paper AIAA 79-0780 AIAA/ASME/ASCE/AHS 20thSSDM Conference St. Louis, Mo. April 4-6, 1979).
12. '1urnbow, J .W. et a] , CahSria Dsi Gn ide, USAV1.ABS-TR-70-22,Revised Aug. 1969 (see al so t'SAAM0RIDi-TR-7 1-22, O't . 1971).
I 1.Desiardins, S.P. , Laanienen, [).Il. , and Singlev, G.T. Ill I, Aircraf -t c Lr as -heSurvival IDesl'n_(;_uide._ _Vol. _1_ _- Design_ Criteuria and ChecklistLs, S imula
Inc. , (SARTL-TR- 79-22A, Dec. 1 980.
14. Laanenen, D. f., Aircra f t cras h Stu, vivaI I)sL( I (uide. Vol. Ii A irc ra f tCrash Environmn, nt and_ Luman o_ ran , S mu a I c . , E.SARI .- TR-79-22B,Jan. 1980.
15. Laanenen, D.H., Singlev .T. Ill, -ar , A.E., and lurnbow, ,i.W.Aircraft Crash Survival Desi gn G ui de. V ol. I Aircraft Str_ucturalCrashworthiness, Simula Incl , U'SARTI.-TR-79-22C, Aug. 1980.
16. Desjardins, S.P. and Laanenen, D. H., Aircraft Crash Survival Design Guide.Vol. IV - Aircraft Seats, Restraints, Litters, and Paddinj , Simula Inc.,USARTL-TR-79-22D, June 1980.
17. Johnson, N.B. and Robertson, S.H., Aircraft Crash Survival Design Guide.Vol. V - Aircraft Postcrash Survival, Simula Inc., USARTL-TR-79-22E,Jan. 1980.
18. Anon. Military Standard: Light Fixed- and Rotary-Wing Aircraft Crashworthiness,Dept. of Defense, MIL-STD-1290(AV), 25 Jan. 1974 (updated 21 July 1977).
19. Anon. Crash Injury and Crashworthiness, Flight Safety Foundation, TREC-TR-60-77, Dec. 1960 (AvCir 70-0-128).
20. Cronkhite, J.D., Haas, T.J., Winter R., Cairo, R.R. and Singley, G.T.III,
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26
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