Unified methodology for the prediction of the fatigue behaviour of adhesively bonded joints

A unified model is proposed to predict the fatigue behaviour of adhesively bonded joints. The model is based on a damage mechanics approach, wherein the evolution of fatigue damage in the adhesive is defined as a power law function of the micro-plastic strain. The model is implemented as an external subroutine for commercial finite element analysis software. Three dimensional damage evolution and crack propagation were simulated using this method and an element deletion technique was employed to represent crack propagation. The model was able to predict the damage evolution, crack initiation and propagation lives, strength and stiffness degradation and the backface strain during fatigue loading. Hence the model is able to unify previous approaches based on total life, strength or stiffness wearout, backface strain monitoring and crack initiation and propagation modelling. A comparison was made with experimental results for an epoxy bonded aluminium single lap joint and a good match was found.