Effects of stitch density and stitch thread thickness on mode II delamination properties of Vectran stitched composites

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 G(IIC) was negligible. Crack bridging by the stitch threads at the crack zone were mostly compensated for the effect of fibre compaction, which reduced the G(IIC) values. Conversely, in densely stitched laminates (high stitch density), G(IIC) 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 G(IIC) values that were 45.7% higher than thinner stitch thread (200 denier).