The Effect of Metal on Composites Fatigue Damage in Mixed Structure

This paper investigated the fatigue damage coupling of composite laminate and metallic plate in multi-bolt joint. A progressive fatigue damage model for composite laminates and a modified Lemaitre damage model for metal material were developed. A phenomenological elastoplastic constitutive model was used to describe the in-plane shear nonlinearity of composite lamina. A formula for calculating the energy release rate of the low cycle fatigue was derived based on spherical tensor and shear tensor decomposition of the stress. The developed models were validated by the experimental results of a double-lap single-bolt metal-composite joint and were employed to simulate the fatigue damage of a double-lap, multi-bolt metal-composite joint. The result indicates that fatigue damage will harden the materials nearby the bolt region of the metallic plate for a multi-bolt joint structure when suffering to cyclic loads. This hardening behavior results to a transfer of bolt loads towards the harden region, which intensifies bearing damage and reduces tensile stress in the composite laminate, and improves the fatigue life of composite laminates fail in tensile mode.