Dynamic Response and Dynamic Fracture of Through-Thickness Reinforced Laminates

A through-thickness reinforcement, in the form of stitching, short fibrous or metallic rods (z-pins), or woven or braided tows, offers a cost-effective approach to control and even suppress delamination fracture in composite laminates subject to static loading [1-9]. Recent experimental tests have demonstrated the effectiveness of a through-thickness reinforcement in improving the performance of laminates and layered systems against dynamic loading, low-velocity impact, ballistic impact and blast loading [10-16]. This paper deals with a theoretical investigation of the response of through-thickness reinforced structures subject to dynamic loading. The preliminary results of two studies aimed at investigating the effectiveness of a through-thickness reinforcement in reducing the delamination-induced degradation of the dynamic properties of composite structures and in improving the response of delaminated beams against dynamic fracture will be presented [17,18]. For the first problem, it will be shown that a through-thickness reinforcement can actually restore the dynamic properties, natural frequencies of vibration and modal shapes, of the intact beam. For the second problem it will be shown that for low to moderate crack velocities a through-thickness reinforcement can substantially improve the response of the structure against dynamic fracture.