Strategy of plasticity induced crack closure numerical evaluation

Abstract

A propagating fatigue crack may be partly retarded thanks to a phenomenon called fatigue crack closure. The ability to accurately describe this phenomenon is of interest for the scientific and engineering community, because of its significant impact on the fatigue crack propagation rate. A strategy for numerical modelling of the most common closure mechanism – the plasticity induced crack closure – is presented in this paper. It was observed that the generally adopted suggestions for this type of simulations, such as the length of the crack growth or the number of substeps, are not necessarily valid in general, but require to be individually specified for particular conditions. The size of the elements in the vicinity of the crack front is also a widely discussed issue and it is shown here that even without convergence, the element size may be chosen as a fixed parameter leading to very reasonable closure values with low computational costs. A method of closure level determination based on change in specimen stiffness is described here and its performance is compared to the traditional first node displacement method with Load-Debond-Unload (LDU) and Load-Debond-Unload-Load-Unload (LDULU) loading schemes.