Effects of Weave Styles and Crimp Gradients in Woven Kevlar/Epoxy Composites

This research investigates the effects of weave styles and crimp gradients (CGs) on the damage tolerance levels and energy absorption capacities of woven fabric reinforced polymer (WFRP) composites. A comparative study was conducted to determine the specific failure mechanisms including fiber/matrix cohesive failures, matrix cracking, fiber breakage and fiber buckling resulting from static and dynamic loading events. The tests included flexure, short beam shear, drop impact, flexure-after-impact, ballistic impact, and split Hopkinson compression bar (SHCB) and were performed on 20-ply Kevlar/epoxy WFRP laminates. Laminates of three different Kevlar fabric weave styles were fabricated using plain, 2 × 2 twill and 4H satin weaves. A fourth laminate was constructed having a mixture of weave styles forming a hybrid crimp gradient construction. The experimental results demonstrated (1) that weave style selections and CGs can positively influence the spatial and temporal distributions of stress resulting from severe loading events and (2) that the fiber/matrix cohesive zone stresses that often lead to delaminations can be reduced. Accordingly, the dependence of mechanical performance on weave styles, crimp contents, and CGs can be exploited to increase the damage tolerance levels and energy absorption capacities in WFRP composites.