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Abstract
Mode II delamination properties of Vectran stitched composites were investigated, and tabbed end notch flexural specimen testing was used to prevent premature failure. The effects of stitch density and stitch thread thickness were explored, and fibre compaction due to the stitching process was also verified. The results show that, in moderately stitched laminates (low stitch density), the improvement in GIIC was negligible. Crack bridging by the stitch threads at the crack zone were mostly compensated for the effect of fibre compaction, which reduced the GIIC values. Conversely, in densely stitched laminates (high stitch density), GIIC values were improved significantly (2·4 times higher than those of unstitched laminates). The effects of stitch thread thickness appeared to be negligible in moderately stitched laminates. For densely stitched laminates, thicker stitch thread (500 denier) possessed GIIC values that were 45·7% higher than thinner stitch thread (200 denier).
Acknowledgements
The authors gratefully acknowledge Tokyo Metropolitan Government for its financial support from the Asian Human Resources Fund and Asian Network of Major Cities 21 (ANMC-21) Project. Special gratitude is extended to Professor L. A. Carlsson (Florida Atlantic University) for helpful discussion concerning the compliance calibration method, Dr A. Yudhanto (currently at King Abdullah University of Science and Technology) for guidance during our stay at Tokyo Metropolitan University, Dr H. Hoshi (Japan Aerospace Exploration Agency) for valuable input on this work and Mr P. Joshi for correcting the language of this manuscript.