Numerical simulation of plasticity induced crack closure under overloads and high–low blocks

The present work performs a numerical analysis of the plasticity induced crack closure under variable amplitude loading, namely under single tensile overloads and High–Low block loading sequences. The optimisation of the numerical procedure was previously performed under constant amplitude loading for the same material. The physical model was analysed using MARC, a commercial finite element package. The numerical analysis was performed considering constant ΔK baseline level and stress ratio conditions. The crack opening values were based on the last contact in the first node behind the crack tip. The numerical results are compared with experimental measurements. Crack closure numerical results are consistent with experimental observations under peak overloads and High–Low load blocks, indicating that crack growth retardation under variable amplitude loading sequences is closely linked to the plasticity induced crack closure phenomenon. Moreover, the obtained crack profiles predict the formation of an enlarged hump of residual stretched material ahead of the load variation location. The numerical analysis produced reasonable closure levels when compared to experimental results when the partial closure phenomenon is taken into account in the closure measurements.