Determination of crack growth for 6082-T6 aluminium subjected to periodic single and block overloads and underloads using a two dimensional finite element model

•A numerical model has been developed to predict crack opening and closing loads.•Predicted crack growth correlated well for overloads applied at low frequency.•The retardation delay distance matched experimental data.•Multiple load cycles applied at the same nodal point created excessive plasticity.•A mixed kinematic/isotropic hardening rule improved the crack growth prediction. The estimation of crack growth under variable amplitude loading is complex due to interaction effects such as plasticity, crack tip blunting, residual stresses, crack tip closure and crack tip branching. Crack closure has been identified to be one of the main interaction effects. In order to study the effect of crack closure the authors have previously carried out experimental testing to obtain more accurate measurements of crack opening and closure (Aguilar-Espinosa, 2009, Aguilar-Espinosa et al., 2013). They have also developed two dimensional plane stress Finite Element models utilising high mesh density whilst maintaining the ability to measure crack growth over long crack lengths (Aguilar Espinosa et al. 2017). This initial work has been extended in this paper to examine the effects of single and block overloads and random spectrum loading on crack growth. The crack length distance that is affected by overloads and underloads measured experimentally and predicted numerically are shown to be very close when using cyclic hardening material properties and kinematic hardening. In addition the comparison of experimental and numerical crack growth versus crack length graphs shows good correlation of the crack growth acceleration and retardation after the applied overload which has not been seen previously. These comparisons seem to be a very useful tool to validate numerical models.