Process variables of I-fiber stitching in Mode I failure

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Laminated composites have excellent mechanical properties in the in-plane direction but poor mechanical properties in the thickness direction. To overcome this problem, several z-directional reinforcement methods such as z-pinning, stitching, and tufting for composites have been developed. However, most of these methods require complicated equipment and processes. They also pose limitations on applicable materials depending on the reinforcement process employed. The I-fiber stitching method is applicable to both prepreg and dry preforms. In addition, because this method involves a process of inserting discontinuous fibers in one direction a high-stiffness fiber such as a carbon fiber can be applied.In this study, to find the optimal process variables of I-fiber stitching in the Mode Ⅰ failure, the failure loads of double cantilever beam (DCB) and in-plane tensile specimens were experimentally investigated based on the stitching pattern, bundle size, and head length of the I-fiber. The Mode I DCB test revealed that the failure loads of DCB specimens with I-fiber heads were greater than those of DCB specimens without I-fiber heads, and the smaller the bundle sizes of the I-fibers, the greater the failure loads of the DCB specimens.