Interlaminar shear behaviour and meso damage suppression mechanism of stitched composite under short beam shear using X-ray CT

The stitching pattern and space play important roles in the mechanical behaviour of stitched composites, while their effects on interlaminar shear behaviour and corresponding damage suppression mechanism have not been studied. Here, the short beam shear (SBS) test and X-ray computed tomography (XCT) were systematically performed to explore the influences of different stitching patterns and spaces on the interlaminar shear behaviour and damage suppression mechanism of stitched composites. The SBS test results reveal that a reduction in the stitching space improves the interlaminar shear performance. Especially, when the stitching patterns enable the stitch thread to bind the load-bearing yarns, the final SBS load is increased after reaching the elastic limit. Furthermore, the XCT results identify the suppression mechanism. That is, the enclosed loops formed by the stitch thread separate the fabrics into several cells. Damage propagation is interrupted within the cells in the cross-sections containing the stitch thread. Damage propagation is also suppressed in the cross-sections parallel or perpendicular to the stitch thread. Stitched composites exhibit a lower damage extension and damaged volume than unstitched composites. In particular, when the stitching pattern is perpendicular to the damage propagation direction, the damage extension is significantly reduced and depends on the stitching space. The results obtained in this study can contribute to the mechanical performance design of stitched composites in future engineering applications through purposeful modulation of the stitching pattern and space.