Experimental Investigation of the Effectiveness of Various Stitching Methods on Arresting Mode-II Interlaminar Damage Propagation in Stitched Resin-Infused Composites

This work is focused on investigating the impact of various out-of-plane stitching methods on enhancing mode-II interlaminar fracture toughness (or energy). Additionally, it aims to characterize local damage progression and crack arrestment in stitched resin-infused composites. For the experimental work, quasi-isotropic end-notched flexure specimens were manufactured using ±45 non-crimp carbon-fiber fabrics through a resin-infusion process. Four specimen sets corresponding to four stitch types (i.e., chain stitching, modified lock stitching, modified chain stitching, and tufting) were designed for comparison. Global analysis based on the load-displacement data provided the fracture energy along with other characteristics of the quasi-isotropic layups. These values were compared between the various stitching cases to assess how each perform in crack arrestment and reinforcement. For local analysis, a digital image correlation system was employed. By analyzing in-plane displacement through the thickness, local separation development during the mode-II interlaminar fracture process was characterized along predicted fracture process zones. Based on this global-local damage analysis, the impact of out-of-plane stitches on separation along fracture process zones was discussed. This work will contribute to determining the effectiveness of four commonly used stitching techniques as out-of-plane reinforcement to enhance mode-II interlaminar damage resistance.