Plasticity-induced crack closure in the presence of loading irregularities in short cracks initiated at interior defects

A crack propagation finite-element model of interior defect-initiated short cracks under near-threshold loading conditions is used to investigate the effect of plasticity-induced crack closure in the presence of a single overload and underload. The effect of an overload predicted by the present model is qualitatively very similar to what is commonly reported, but in this case an underload produces a differing result to the literature consensus, yielding a similar but weaker effect as the overload. Extended acceleration of crack propagation due to a single underload might not be attributable to plasticity-induced crack closure under plane strain conditions. A distinct crack profile shape consequent of crack tip blunting is present with both loading irregularities. A new method for examining crack closure for the entire crack surface is presented.