Fatigue life and backface strain predictions in adhesively bonded joints

Fatigue is a very important factor in any adhesively bonded structure subject to service loads. Prediction of fatigue life using finite element analysis (FEA) techniques is very complicated due to the complex nature of fatigue damage. This paper presents experimental data obtained by testing single lap joints (SLJs) in constant amplitude fatigue at a range of load levels and associated fatigue damage modelling. Six strain gauges (SGs) placed along the overlap were used to monitor fatigue initiation and propagation within the adhesive layer. An elasto-plastic damage model was developed that was capable of predicting the experimentally observed backface strain patterns and fatigue life at different fatigue loads. It was implemented in the finite element code ABAQUS and used a user defined subroutine to calculate the damage, and the resultant degradation in adhesive Young's modulus and yield stress.