Strength prediction of composite π joint under bending load and study of geometric and material variations effects

This article concentrates on the design of composite pi joint, which is an effective connector for integrated composite structures in aerospace structures. A brief review of research on out-of-plane joints is first presented to current practice towards the design of such pi joints. Progressive damage models are established to trace failure analysis from damage onset to ultimate collapse of joints, which highlight the failure mechanism and internal mechanical behaviours. Four kinds of failure criteria are used firstly, and after comparing the numerical prediction results with the experimental results, one failure criterion is chosen for the simulation of this joint. Influences of structural and geometric parameters such as structural configuration, overlaminate material, ply angle, fillet radius and upstanding/horizontal leg length of overlaminate on flexural resistance ability are studied to provide 'optimal' design schemes. Moment-displacement graphs from the mechanical experiments are presented and physical failure phenomena of the joint under bending load are depicted. The good agreement between the predictions and experimental results gives evidence of the efficiency of numerical analysis.