Fatigue life prediction of adhesively bonded assemblies under mixed-mode loading based on an energy criterion

This study deals with the development of a predictive tool to estimate the fatigue life of adhesively bonded assemblies submitted to mixed-mode loading. This numerical approach is based on an energy-based criterion. The use of this fatigue criterion requires the adhesive behaviour model to calculate the dissipated energy per cycle. An epoxy-based adhesive was investigated using modified Scarf specimens, under mixed-mode loading, and a generalised viscoelastic Maxwell-type model was first identified by performing multi-level creep tests. In addition, a finite element model of Scarf specimens was developed to identify the parameters of the behaviour law and of the energy-based criterion. Then, finite element calculations were post-processed to produce S-N curves under mixed-load loading. Parallelly, fatigue tests were performed for three load ratios (−1, −0.2 and 0.2) and three loading frequencies (1, 5 and 10 Hz) to build a strong database. It was found that the fatigue lifetime was especially influenced by the load ratio R, but no significant frequency effect was observed within the studied range, excepted for R = 0.2. The fatigue criterion accurately reproduces the effects observed experimentally and the numerical fatigue lifetimes, given by the model, were in good agreement with the experimental results.