Tensile failure strain mechanism of stitched composites with z‐stitch method: Influence of stitch pattern and density

Abstract The tensile failure mechanism of standard composites has been extensively investigated, but is not clear for stitched composites with z‐stitch method. This work systematically explored the tensile performance of the stitched composites with z‐stitch method under different stitch patterns and densities. The tensile strength and Poisson's ratio of stitched composites are reduced especially under high stitch density and 45° and 90° stitch patterns due to the induced defects and suppression effect on the crimp of load‐bearing yarn. Most importantly, the strain at failure moment is meticulously characterized to elucidate the failure strain mechanism by digital image correlation. For the stitched composite with 0° stitch pattern, obvious strain concentration only occurs in high stitch density specimen. In contrast, the strain concentration occurs in any stitch density for stitched composites with 45° and 90° stitch patterns, and is located around the stitch thread, especially becomes small with the increase of stitch density. Highlights High stitch density, 45° and 90°patterns reduce strength and Poisson's ratio. Strain concentration occurs at failure moment in high stitch density specimen. Strain concentration is located around stitch thread.