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.
Bernolin et al. (Mon,) studied this question.