In this study, the CAI (Compression after impact) strength of the stitched CFRP laminate was investigated by experimental and numerical method. First, the CAI tests were carried out for various impact energies and stitch densities. Results showed that on the stitched laminate, the delamination area generated by the impact load was slightly smaller than that on the unstitched one. However, the higher stitch density did not always give the smaller delamination area. CAI strength was significantly improved by the stitching, up to about 1.6 times from that of the unstitched specimen. Two-dimensional finite element analysis was carried out in order to investigate the effect of stitching on the local buckling behavior of the laminate containing delamination. In this analysis, stitch thread was modeled by truss elements, and laminate was modeled by solid elements. Truss elements and solid elements were connected by the elements expressing the pullout process between the stitch thread and laminate. The buckling strength was improved up to 1.8 times by stitching. The tendency of the strength improvement by stitching agreed well with experimental results.
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