PSI - Issue 2_B

Susanne Hörrmann et al. / Procedia Structural Integrity 2 (2016) 158–165 S. Ho¨rrmann et al. / Structural Integrity Procedia 00 (2016) 000–000

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e ff ects is assessed to quantify the introduced stresses by increase of the specimens gauge length, however specimen alignment could not be guaranteed in this configuration. It might be possible to improve the bonding method of the specimens for the stack to get comparable results to determine possible small tab e ff ects. The fracture surfaces are investigated by optical microscopy and it is found that the main failure mode is interlam inar failure due to stitching yarn debonding and matrix fracture. Specimens with introduced folds fail in the same ply interfaces, however they are curved in the defect area, so fracture is not straight through the whole specimen. The use of a di ff erent stitching pattern (e.g. pillar) or a lower concentration of stitches between the plies might improve the through-thickness properties. A reduction of static and fatigue strength of 10 % due to the introduced folds was observed, so the folds are not considered to be very critical. However, in areas with increased occurrence of folds the strength reduction should be considered in the design state. Specimens with introduced waviness defect will be investigated in future work as well as the influence of tension-compression fatigue loading.

Acknowledgements

The financial support by the Austrian Federal Ministry of Economy, Family and Youth and the National Foundation for Research, Technology and Development is gratefully acknowledged. The authors are grateful to Mr. Erich Humer for his technical support during the experiments.

References

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