Experimental behaviour of composite laminates containing a hole

Experiment studies were carried out on the effect of stitching reinforcement for composite laminates containing a circular hole. The effects of stitching parameters, such as stitching needle distance, row spacing, edge distance, single stitching or double stitching, etc., were compared and analysed. The tensile strength and failure strain were measured for composite laminates containing a circular hole. The strain concentration and strain distribution regularity were investigated analytically and experimentally. By studing failure sections, the reinforcing effect and failure mechanisms were analysed and discussed for stitching on the edge of hole. The experimental results showed a distinct efficiency of stitching reinforcement for composite laminates containing a circular hole and gave a design method about stitching on the edge of hole. From the current work, it is concluded that; stiffness and the failure strength of the composite laminates are somewhat increased. Reinforced by stitching, there exists a notch strengthing effect, which implies that the maximum strain at the hole edge becomes higher. Compared the stitching reinforcement with unstitching, the scope of strain decling is roughly the same, but the level of strain declining obviously increase. There exist a transform point for tensile strain to compressing strain between 0° and 90°, that is ε_θ at the transform point. The transform point for single stitching is about θ=56°, and for double stitching is about θ=53°. Synthesizing the data and analysis, the single stitching 1 and the double stitching 1 are the better choices for the composite laminates when reinforced by stitching on the hole.