2nd int. conference on buckling and postbuckling behaviour ......buckling and postbuckling behaviour...
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Institut für Faserverbundleichtbau und Adaptronik
Improved Material Exploitation of Composite Airframe Structures by Accurate Simulation of Collapse –
The COCOMAT project
2nd Int. Conference on
Buckling and Postbuckling Behaviour of Composite Laminated Shell Structures
R. Degenhardt, D. Wilckens, K. Rohwer, R. Zimmermann, J. Teßmer3 -5 September 2008, Braunschweig, Germany
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Outline
1. The EC 6th Framework Programme
2. Forerunner projects (interaction, results)
3. Consortium
4. Structures considered, what is collapse
5. Overall objective, kind of degradation, main results
6. Examples of results
7. Summary
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The EC 6th Framework ProgrammeIntegrating and strengthening the European Research Area
Priority 4: Aeronautics and Space
Work Programme:
Area: Strengthening competitiveness
Objective: Reduction of aircraft development and operating costs by 20% and 50% in the short and long term, respectively.
The EC 6th Framework ProgrammeIntegrating and strengthening the European Research Area
COCOMAT contributes to this aim by:
Instrument: Specific Targeted REsearch Project (STREP)
Goal: Reducing structural weight at safe design by exploitation of considerable reserves in primary fibre composite fuselage structures through accurate simulation of collapse
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ImprovedPOstbuckling
SImulation for Design of FibreCOmposite
Stiffened FuselageStructures
Improved MATerial Exploitation at Safe Design of COmposite Airframe Structures
by Accurate Simulation of COllapse
Forerunner projects - Interaction
Year
GARTEUR AG 25
POSICOSS
COCOMAT
2000 2001 2006 200720052002 2003 2004
Group for Aeronautical Research and Technology in EURopeAction Group 25:Postbuckling and Collapse Analysis
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ConsortiumCOCOMAT Consortium
SMEs Research establishments UniversitiesLarge
industries
PL
IL
E
B
AUS
D
I
GR
D
SS IL
CH
I
D
LV
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Next generation –All composite fuselage structure
COCOMAT considers curved CFRP panelswhich are understood as parts of a fuselage section.
Structures considered
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Scale factor: 10
Scale factor: 8
Scale factor: 5
Scale factor: 3
1st global (stringer-based) buckling
1st local buckling
Scale factor: 5
Shortening
Load
Real curve
Collapse load
Simplified curve
What is collapse(Example: Axially compressed curved stiffened CFRP panel)
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degradation (OD)
Current design scenario
Shortening
Not allowed
Safety region
Load
I
II
III
First Buckling Load (1. BL)
Collapse (CL)
Ultimate Load (UL)
Limit Load (LL)
Onset of
Allowed under operating flight conditions
LoadFuture design scenario
1. BL
CL
UL
LL
OD
Shortening
III
I
II
COCOMAT – Main objective (1)
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Fast and accurate simulation of the collapse load of
stringer stiffened CFRP curved panels with taking
degradation and cyclic loading into account, in addition to
geometrical nonlinearity.
cyclic loading = repeated static loading
COCOMAT – Main objective (2)
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Failure propagation will be taken into account
Skin-stringer separation is considered as the most important and dangerous mode and is investigated in any case.
Delamination in the stringer blade was also observed in the POSICOSS project and is considered.
Delamination in the skin is be considered as less important case, however, is also taken into account.
Kind of degradation
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Work plan
WP 1: Benchmarking on collapse analysis of undamaged and damaged structures with existing tools
WP 2: Material characterisation, damage investigationand design of structures for static and cyclic tests
WP 3: Development of improved simulation proceduresfor collapse
WP 4: Manufacture, inspection and testing by static and cyclic loading of undamaged panels from WP2
WP 5: Manufacture, inspection and testing by static and cyclic loading of pre-damaged panels from WP2
WP 6: Design guidelines and industrial validation
WP 7: Management and exploitation
Year 200820072004 2005 2006
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Experimental data base Slow certification tools and fast design tools
Mai
n re
sults
Mai
n ob
ject
ive
C O C O M A T
Design guidelines
Future design scenario
COCOMAT – Main results
Personnel resources: 716 person-monthsTotal costs: 6.7 Mio EurosEC funding: 4.0 Mio Euros
Some details:
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pre-damagedpanelsWP 5
Validation of the improved
tools
undamagedpanels Manufacture,
inspection and testing by static and cyclic loading of
WP 4
Degradation models for
the improvedtools
Investigation of degradation by tests and development of degradation models
WP 2.2
Material properties
Characterisation of material propertiesWP 2.1
ObjectiveKind of structureWorkpakage
Panels
Stiffened strips
SpecimensGFRP layer
Experimental data base
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Analysis
Fast toolsTools with analytical and semi-
analytical approach
For design process For certification
Slow toolsCommercial FE tools (e.g.
SAMCEF, NASTRAN, ABAQUS ,etc.)
Simulation Tools
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Outline
1. The EC 6th Framework Programme
2. Forerunner projects (interaction, results)
3. Consortium
4. Structures considered, what is collapse
5. Overall objective, kind of degradation, main results
6. Examples of results
7. Summary and conclusions
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WP 1 - Benchmarking - Example
0
20
40
60
80
100
120
140
0 0.5 1 1.5 2 2.5 3 3.5 4Shortening [mm]
Load
[kN]
Experiment P12Abaqus, Nominal, No ImperfectionsSOL 106, Compdat, No ImperfectionsSOL 106, Compdat, With ImperfectionsSOL 600, Compdat, No ImperfectionsLS-Dyna, Compdat, No Imperfections
Not correct because 1) Degradation is not considered2) Sensitive for modelling of the lateral boundary conditions
Collapse
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WP 2 - Material properties, degradation models and panel designs
Material properties: - IM7/8552 UD- 985-GT6-135 UD- 950-GF3-5H-1000 carbon fabric
Degradation models (experiments and mechanical models)Designed panels which should be manufactured and tested(85 designed, 6 selected)
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WP 3 - Improved simulation procedures for collapse -Slow certification tools
Commercial software'sIn-house software's
ABAQUS
MARC
NASTRAN
FEAP
SAMCEF
STRIPE
Stress based
Fracture based
Degradation models
Tsai Hill, Maximum stress, Minimum strain, Puck
VCCT energy release rates
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WP 3 - Improved simulation procedures for collapse -Fast design tools
Seconds Minutes Hours Days
Full FEM
Computing Time
Prec
isio
n
DLR
RTUTraining
RWTH
TECHNION
RTUFast tool
SMR UKA
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WP 4 / WP 5 Buckling tests until collapse
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0
20
40
60
80
100
120
0 0,5 1 1,5 2 2,5 3 3,5
Shortening [mm]
Load
[kN
]
Cycle 0001Cycle 0401Cycle 0801Cycle 1201Cycle 1601Cycle 2001Cycle 2401Cycle 2601Cycle 2801Cycle 3001Cycle 3201Cycle 3401Cycle 3601Cycle 3801 Collapse
WP 4 - Test Panel P29 – Load shortening curve with Thermography
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0
20
40
60
80
100
120
0 0,5 1 1,5 2 2,5 3 3,5
Shortening [mm]
Load
[kN
]
1
2
3
4
5
6
WP 4 - Panel P29 – Load shortening curve
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WP 4 – Panel P29 – Measurements after collapse
ARAMIS Ultrasonic inspectionThermography1
1In co-operation with Institut für Kunststoffprüfung und Kunststoffkunde Universität Stuttgart
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WP 5 – Test Results TECHNION
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Comparison Test and Simulation
Selcected highlights
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• A 1D-element with adhesive layer, linear softening model and a mixed mode fracture criterion has been developed
• The approach was validated with simulations of DCB, ENF and MMB tests
Comparison of test results and simulations MMB test
• A 1D-element with adhesive layer, linear softening model and a mixed mode fracture criterion has been developed
• The approach was validated with simulations of DCB, ENF and MMB tests
Comparison of test results and simulations MMB test
Partner: RWTH
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Highlights
Rib-Stiffened DCB Test
Small-Scale PanelsSmall-Scale Panels Large-Scale Panels
Rib-Stiffened 3PB Test
FE tool for composites:• Delamination / skin-stringer separation:
Cohesive interface elements
• Ply failure: Shell elements with Tsai-Wu or Hashin criteria (optional) and ply discountmodel for degradation
• Applicability proven by various simulations
0
10
20
30
40
50
60
70
0 5 10 15 20Crack Opening [mm]
App
lied
Load
[N]
DCB Test
Partner: University of Karlsruhe
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Partner: CRC-ACS
Aernnova panel (D2), comparison with intact panel test1-2
fibre failure
D2 intact panelFE analysisDebond prediction
520
260
1.92 mm axial compression
Experiment Numerical
ExperimentNumerical
Experiment Numerical
0 0.5 1.0 1.5 2.0 2.5 3.0
250
200
150
100
50
0
Load
[kN
]
Displacement [mm]
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5Displacement [mm]
120
100
80
60
40
20
0Lo
ad [k
N]
1) Orifici, A.C. et al., Composites 2007, Porto, Portugal, 12-14 Sep., 2007.2) Orifici, A.C. et al., Composite Structures, 86: 186-193, 2008.
DLR panel (D1), comparison with panel after cyclic loading (producing pre-damage)1
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Partner: SMR
Improved post-buckling analysis of composite with the B2000++ finite element simulation environment
New fast and robust family of shell elements with finite rotation with 5 or 6 degrees of freedom and pre-integration of the material equations, Assumed Natural Strain and Enhanced Assumed Strain to reduce locking.New parallel static and dynamic non-linear FEM solvers.
Dynamic post-bucking analysis of industrial panel
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Partner: RTUDCB test for rib stiffened panel
Ultrasonic inspection of COCOMAT tested panels
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Partner: DLR
0
20
40
60
80
100
120
140
0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0Shortening [mm]
Load
[kN
]
Simulation - No considaration of degradation
Simulation with degradation of the adhesive (Reduction of E to 0.1%)
Test on Design 1
0
20
40
60
80
100
120
0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0
Shortening [mm]
Load
[kN
]
No degradation UMAT implicit standardUMAT implicit advancedFirst von Mises failureFigure 1Figure 2Figure 3Figure 4
Simulation of DLR Design 1 panelReduction of E->0.1%
Max Strength of the adhesive layer 48 MPa
DLR Design 1 panel -USDFLD
DLR Design 1 panel – UMAT implicit
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Simulation of buckling and post buckling with adhesive and ply
degradation.
0
50
100
150
200
250
0 20 40 60 80 100Opening (mm)
Load
(N)
Eperiment 1 Eperiment 2
Eperiment 3 Eperiment 4
Eperiment 5 Eperiment 6
Smax = 3.6 Gc = 0.96 Smax = 3.1 Gc = 1.1
0
20
40
60
80
100
120
0 0.5 1 1.5 2 2.5 3 3.5Shortening [mm]
TEST P29Elastic Ply - Elastic Interface
Elastic Ply - Damage InterfacePly Degradation - Elastic Interface
Ply Degradation - Damage Interface
Simulation of Skin-Stringer separation
Partner: SAMTECH
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0
5
10
15
20
0.00 0.50 1.00 1.50 2.00
Rotation [deg]
Torq
ue [k
Nm]
FE - Damaged box
SN4
100 200 300 400 500 600 700 800
Horizontal axis [mm]
500
600
700
800
900
1000
1100Ve
rtica
l axi
s [m
m]
-10.00-9.00-8.00-7.00-6.00-5.00-4.00-3.00-2.00-1.000.001.002.003.004.005.006.007.008.009.0010.00
Partner: POLIMITests and analyses of pre-damaged panels
Damagedareas
Zone A
Zone B
Zone C
Zone A Zone B Zone C
Tsai-Wu failure
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1st Buckling & Collapse Load vs Damage Length
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 800.00
Characteristic Damage Length [mm]
Nor
mal
ized
Loa
d
collapse: test
collapse: analysis
buckling:test
buckling: analysis
absent stringer
absent stringer
Conventional design is not too sensitive to damage size.
Even with detached or completely absent central stringer, the buckling and collapse loads do not change dramatically.
WP 6 – Design guidelines
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Rib A
Rib B
Different (from COCOMAT) manufacturing process:
cobonded stiffeners instead ofcocured ones.
Different (from COCOMAT) material :
250°F per IAI MS instead ofCOCOMAT 350°F IM7/8552
WP 6 – IAI contribution - structure for industrial validation
Composite Stiffened Panel for A/C Stabilizer.Carbon/Epoxy Stiffened skin structure.Industrial validation, both analytical and experimental, for the section bounded by Ribs A & B. Test specimen has been manufactured by IAI and tested by TECHNION.
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Summary
2004 20082004 2008
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ProgrammTime Time Time
9.00
10.45 8.30 - 10.00 8.30 - 10.00
11.00 - 12.30 10.30 - 12.10 10.30 - 12.10
13.30 - 15.1012.10 - 15.00
13.10 - 14.50
15.40 - 17.40 15.00 - 17.00 15.20 - 17.00
18.00 17.15
18.30-22.30 18.00 - 20.0017.00
20.00
Registration
Transfer University - Dinner
3rd September (Day 1) 4th September (Day 2)
DLR - Technical visiting tour (Finger food available)
2) Dinner speech: Prof. Joachim Block (ROSETTA Lander - a challenging mission to the origins of the solar system)
Conference Dinner (Dornse)
1) Welcome by Mr. Lehmann (Chief city councilor of the City of Braunschweig)
Transfer DLR - Hotels
Semi-analytical concepts
Unstiffened structures II / Analysis and validation II
Analysis and validation I
Unstiffened structures I
End of Conference
Optimisation
Transfer University - DLR
5th September (Day 3)
Keynote lectures
COCOMAT - Workpackage summaries
Degradation I
COCOMAT - Achievements of the PhD students (Fast simulation tools, tests)
Structure tests
Keynote lecturesKeynote lecturesR. Degenhardt Welcome
Degradation II
Keynote lectures: Design handbooks
COCOMAT Workshop
Conference Venue:Technical University of Braunschweig,Pockelsstrasse 4 (Altgebäude), Braunschweig, Germany
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Internet: www.cocomat.de