Simulation of pin-reinforced single-lap composite joints

A simple and efficient computational approach is presented for analyzing the benefits of through-thickness pins for restricting debond failure in joints. Experiments have shown that increases in debond resistance and ultimate strength depend on the material, size, density, location, and angle of deployment of the pins and the mechanisms of pin deformation, which are complex and strongly affected by the mode ratio of the debond crack. Here the mechanics problem is simplified by representing the effects of the pins by tractions acting on the fracture surfaces of the debond crack. The tractions are prescribed as functions of the crack displacement, which are available in simple forms that summarize the complex deformations to a reasonable accuracy. The resulting model can be used to track the evolution of competing failure mechanisms, including tensile or compressive failure of the adherends, joint debonding (creating leak, for example, if the joint is in a pipeline), and ultimate failure associated with pin rupture or pullout. Calculations illustrating complex mode ratio variations are presented for a lap joint specimen comprising curved laminate segments cut from pipes.