Damage in laminated composite plates subjected to low-velocity impact

The aim of the study is to investigate the impact response of laminated composites were constructed from orthotropic layers containing collimated unidirectional fibers or woven fabrics made of glass fabrics and an epoxy matrix. The effects of the following parameters on the impact resistance of composite plates were studied: the angle between adjacent layers, weaving gaps, the curing pressure, the size of weaving cell, the stitching reinforcement through the composite thickness and the weaving angle between fill and warp yarns.An instrumented drop-weight impact testing machine was used in the investigations. Because of the special fiber geometries involved in the study, all woven composites were fabricated manually. Some of the composite prepregs were stitched after stacking together by hand, using a needle. The perforation threshold, peak force and bending stiffnesses were identified to be the primary impact characteristics of the composites.Experimental results reveal that weaving with gap and curing with low pressure increases the perforation threshold. The perforation thresholds increases as the angles between adjacent layer and the weaving angle between fill and warp yarns decrease. Since the fill and warp yarns constrain the damage propagation, the cell size plays an important role in the damage process. Damage size and perforation threshold reduce with stitching.A numerical evaluation was carried out by using a finite element code. The contact force history between impactor and the composite plate consist of unidirectional plies was found for the specimens which occurred no fiber breakage in experiments. The experimental results and numerical results are reasonable.