benefits of the world-wide failure exercise to the ... · pdf filetier 1 member at ncc ......

© QinetiQ Limited 2015 QinetiQ Proprietary

Dr Sam Kaddour

Senior Engineer/QinetiQ Fellow

Date 16 Sept 2015

Presented at: ‘Future Trends in Certification of Advanced Technology Structures’, Workshop at NCC (Bristol), organised by Royal Aeronautical Society.

Benefits of the World-Wide Failure Exercise to the certification of composites

structures

People Who

Know How

DIIS: QINETIQ/MS/AD/CP1503970


Contents

Brief Introduction to Airworthiness at QinetiQ

Composites at QinetiQ

Challenges in Certification of Composites

The World-Wide Failure Exercises (WWFE)

Vision

WWFE-1, -2 and -3

Impact and achievements

Conclusions


Mission of Air Division: De-risk complex aviation programmes

Advice on structural integrity and safety of military aircrafts.

Not a certification authority.

help in Acceptable Means of Compliance (AMC).

Independent Technical Evaluation (ITE).

Introduction

Independent Release to Service (RTS) safety recommendations. Technical review of verification, qualification and certification (VQ&C)

evidence and programme risk reduction. Certification.

.

,

. .


Tier 1 member at NCC Testing facilities Design and simulation Forensic analysis Airworthiness and Structural Integrity NDE New technologies, e.g.

Shape memory alloy composites Method development Automated 3D NDE

Composites at QinetiQ

A

F

B

D

E C

G

H


5

ACARE (The Advisory Council for Aeronautics Research in Europe): 50% in CO2 emissions by 2020 versus 2000.

Aerospace industry is growing. 27,000 new passenger aircraft by 2030.

– worth potentially up to $3.7 trillion.

Life cycles ( qualification time)

Automated manufacture Production of high volumes

Move toward infusion and RTM, ATL, AFP etc..

Integrating 3D structures into 3D architectures

Cost of continued airworthiness and maintenance

Development of simulation tools/ standards

Challenges facing composites industry


6

Strength/Allowables development

Identifying and understanding failure modes

Loads, extreme critical locations etc..

Damage tolerance

To retain structural integrity (repeated loading effects, damage)

Durability

Environmental requirements/ Accidental hazards

Challenges facing certification of composites

Increased certification by modelling

Subpart C, D and F: Structure(Strength Requirements), Design And Construction, Equipment

Main standards

How mature are current predictive tools?


7

There is a lack of faith in the failure criteria currently used at the lamina / laminate/ structure level.

a lack of objective evidence of :-

– accuracy

– bounds of validity (materials, laminate lay-ups, stress ratios).

Micro-cracking catastrophic failure?

Modes of failure?

Vision of the World-Wide Failure Exercises (WWFE)


Vision of the World-Wide Failure Exercises (WWFE)

Organisers: Experienced group

committed to better methods

Aims: Independent

assessment of Composites failure

Participants: Experts, widely

recognised groups

Targets:

Academia, Research centres,

Software houses & Industry

Where are we? What to do next?

International activities involving established experts


9

Objectives

Establish a benchmark

− How accurately can we predict the strength of composites?

Method

Identify originators of leading failure theories

Test the general applicability of the theories across a range of problems

Compare the theories against each other

Compare the theories against experimental evidence

Recommend way forward

Vision of WWFE: Objectives


10

Range of test parameters chosen to exercise the theories fully

Where good experimental data is available for comparison

Identical test problems analysed by all participants

Identical input data

Predictions made by the originators of the theories without their access

to the experimental results

i.e. ‘blind’ predictions

Covers a wide variety of theoretical approaches

Output data and format clearly specified to allow direct comparisons

Two phase strategy (Parts A and B)

Vision of WWFE: Key features


11

Summary of Stages of WWFE

Established groups

Level playing field benchmark

Blind predictions

Improved predictions

maturity of methods


12

QinetiQ Nottingham University Manchester University (UK) Surrey University (UK) Imperial college (UK) Leeds University (UK) Lancaster University (UK) Aberdeen University (UK) National Physical Laboratory (UK) NASA (USA) Northwestern University (USA) Wyoming University (USA) Firehole composites, Wyoming, (USA) Stanford University (USA) Ohio State University (USA) Stuttgart University (Germany) MAN Technologies (Germany) Technion (Israel) ICT, Moscow, (Russia)

Participating institutions in WWFEs

ETZ Zurich (Switzerland) Tongji University (China) Vienna University of Technology (Austria) South Ural State University (Russia) Lulea University of Technology (Sweden) ONERA (France) lmt.ens-cachan (France) Hanyang University (South Korea) Toronto University (Canada) University of British Columbia (Canada) Texas University (USA) Boeing (USA) BAe Systems (UK) Army Research Laboratory (ARL,USA) AEAT (UK) Alfred University (USA) Alphastar Corporation (USA) University of Porto (Portugal) Purdue University (USA) Delft University (Holland)


13

WWFE Achievements

Material models/ theories and WWFE information being used in commercial software packages

www.hypersizer.com www.alphastarcorp.com www.esacomp.com www.ls-dyna.com www.3ds.com www.firehole.com www.autodesk.com www.mscsoftware.com


14

The 1st World Wide Failure Exercise

(WWFE-1)

Benchmarking of traditional biaxial failure criteria for fibre reinforced composites under

in-plane loading


15

The 1st World Wide Failure Exercise (WWFE)

Selection criteria

- Availability of test data.

- Stretch theories to full.

- Practical loading cases.

-illustrate certain peculiarities.

-Sensible number of Cases.


The 1st World-Wide Failure Exercise

19 recognised failure criteria evaluated

Level playing field benchmark

Some of 2D failure criteria were still immature

Gaps identified WWFE2 &3

-1200 -800 -400 0 400 800 1200

-1200

-800

-400

0

400

800

1200

SR=2:1

SR=1:0

y MPa

x M

Pa

SR=1:-1

SR=-

1:-1

SR=1

:1

Tsai Wolfe

Rotem

SR=y/x

All 19 theories 4 top theories


17

The 2nd World Wide Failure Exercise

(WWFE-2)

Benchmarking of triaxial (3D) failure criteria for fibre reinforced composites


18

The 2nd World Wide Failure Exercise (WWFE-2)

Effects of 3D stresses on the strength and deformation of isotropic, unidirectional and multi-directional laminates

Hydrostatic pressure effects

Open/closed strength envelopes

3D elastic constants of multidirectional laminates

Effects of lay-up on through-thickness strength of laminates

Validated constitutive equations for 3D response of composites

Important for thick composites


19

The 2nd World Wide Failure Exercise (WWFE-2)

Competing failure criteria

Nonlinear Maximum Strain

Micro/Mesoscopic approach

Cuntze’s FMC

Multi-continuum mechanics

Micro-mechanics/bridging

Hashin

Puck

Pinho

Rotem

Tsai’s based MMF

Maximum strain energy

Christensen


20

WWFE-2 Test Case 2

7 closed envelopes 5 open envelopes, (Watch for run-out time in codes!!)

Failure under 12 versus 2 (1 =2 = 3 ) stresses

Material: UD carbon/epoxy

Results from WWFE-2


21

The 3rd World Wide Failure Exercise

(WWFE-3)

Benchmarking of cracking and

damage models for fibre

reinforced polymer composites


22

The 3rd World Wide Failure Exercise (WWFE-3)

Damage initiation and evolution

Cracking under thermal loading

Delamination initiation and propagation

Effects of ply stacking sequence

Leakage

Failure at a notch (e.g. open hole)

Tension/ Compression

Size/scaling effects

Ply thickness’ constraints

Statistical nature of failure

Unloading and reloading


Test Case 12 (WWFE-3): Variation of strength of [45°/90°/−45°/0°]s Carbon/epoxy laminate with hole diameter

Keep W/D=5 and L/D=20. Laminate thickness = 4mm

[45°m/90°m/−45°m/0°m]s, m=4 hply=0.125mm


24

Impact and achievements

Resulted in improvements to theories by identifying weaknesses:

50% of theories were modified.

Theories, adopted for 40 years, modified for the first time.

Provided designers with guidelines on accuracy and bounds of applicability for current failure theories.

It sets directions for further improvement in composites failure criteria.


‘Periodic Table’ for failure of composites

Next step: Certification by Simulation

?

Ref: Paris (2015)


26

Overall Closing Remarks

3 WWFEs of composites failure predictions have been conducted:

All major modes of failure of composites identified and analysed.

Boundaries of applicability of models drawn.

Improvement in design methodologies.

Designers are now better equipped with benchmarked tools.

Benchmarked models may be used:

Good for industry/ manufacturing ( steps towards shorter life cycles).

Reducing qualification time of composites.

In-service damage assessment/continued airworthiness.

Greater acceptance of simulation evidence for certification.


27

o The Royal Society for the award of a Royal Society Industry Fellowship, hosted at the University of Surrey.

o All of the participating authors. Due to their generous support, the Exercise has been made possible and a great opportunity created to make significant progress in this difficult area.

o Co-workers Prof Mike Hinton (HVM Catapult), Prof Paul Smith (University of Surrey), Prof Shuguang Li (University of Nottingham)

Acknowledgements


28

Thank you for your attention

Any Questions?

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