The application of biaxial cruciform testing to understanding the performance of composite structuresCaroline JonesCompTest 2003January 2003

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Summary

This presentation highlights recent developments in the field of biaxial cruciform testing and discusses how the benefits from these experimental programmes are being used to optimise composite structures and reduce the duration of the certification process.

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Contents

1 Development of the biaxial cruciform test

2 The biaxial test

– Experimental arrangement

3 Using biaxial cruciform test data

– Failure criteria development

– Numerical modelling tools

4 Conclusions

5 Any Questions?

Development of the biaxial cruciform test

Section 1

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Specimen Design

Cruciform specimen designGRP claddingAluminium end tabs

adhesive with low residual stress post-cure

Test area 90mm-120mmHoneycomb, sandwich panels, structures, through thickness reinforcement

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The biaxial test machine

•Four primary actuators

-500kN/1500kN loads

•Two secondary actuators

-bolt hole loading•Grip system•Safety

The biaxial test

Section 2

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Experimental Arrangement

•orientation•loading ratios/testing ratios•calibration•performance envelope•failure strength•use of anti-buckle guide•hot/wet testing

X, 0°

Y, 90°

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Use of the bolt hole loading rig

X, 0°, Fx=+1.0

Y, 90°, Fy=-0.7

N.B. Load on bolt is 12kN

•Open hole•Filled hole•Loaded hole

Using biaxial cruciform data

Section 3

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Uniaxial or biaxial?

•Uniaxial -less expensive per test-high experimental scatter-one result per test-large test programme-time consuming-boundary conditions

unrepresentative

•Biaxial-more expensive per test-minimal experimental

scatter-several results per test-smaller test programme-less time consuming-boundary conditions

representative

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How is the data being used?

Development of failure criteria

Development of structural concepts

More realistic representation of a structure

in service – leading to more efficient designs

Development of novel materials

Development of modelling tools

13Development of performance and failure criteria

Use failure strength to test and develop biaxial failure

criteria

Use performance envelope to confirm predictions

14Development of Numerical Modelling tools

Bolted joint structures

Coupled global-local modeling toolsOpen holes

Loaded fasteners

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Global-local analysis (1)

1. Create global model (ABAQUS)(arbitrary curvature and mesh)2. Run Q_global_bolt to add bolts &foundations

3. Run updated global model (ABAQUS)

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Global-local analysis (2)

4. Use Q_global_local to create local models

5. Run local models

6. Run Q_predict for multi-axial strength prediction with bolt load

ConclusionsSection 4

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Conclusions

• Boundary conditions representative of those found in structures make the data obtained from biaxial cruciform tests extremely valuable.

• Direct benefits being derived from biaxial cruciform test work include the development of performance and failure criteria and numerical modeling tools used to analyse complex composite bolted structures.

• Recent developments made in biaxial cruciform testing represent major steps in understanding materials and their use in structural design

Any Questions?Section 5

Appendix

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Instrumentation

• Shadow moiré

• Photoelasticity

• Thermoelasticity

• NDE (ANDSCAN)

• Video strain mapping

• Combined thermo/photoelasticity

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Sensitivity to delamination growth

Photoelastic coatings are used to obtain both the optical and thermal data

High operational strains require multiple coatings to monitor both global and local delamination fronts

23Thermal monitoring of loading sequence

Deltatherm image (200 f/sec) of specimen surface loaded to

6000-3000