SIMULATIONS OF FATIGUE CRACK GROWTH BY BLUNTING-RESHARPENING: CONTRIBUTION TO THE ISSUE OF PLASTICITY INDUCED CRACK CLOSURE

摘要

Despite plasticity induced crack closure (PICC) has long been focused as an important factor of fatigue crack growth (FCG), it lacks of straightforward evidence when the plane-strain near-tip constraint is approached, so that its significance in FCG, and even the very existence, remain debatable. To add insight into this matter, large-deformation elastoplastic simulations of plane-strain crack under constant amplitude cyclic loadings at different load ranges and ratios, as well as with an overload, have been performed. Modelling visualises the Laird-Smith conceptual mechanism of FCG by plastic blunting and resharpening. Simulations reproduce experimental trends of FCG concerning the roles of AK and overload, but PICC has never been detected. Near-tip deformation patterns discard the filling-in the crack with material stretched out of the crack plane in the wake behind the tip as supposed PICC origin. Despite the absence of closure, load-deformation curves appear bent, which raises doubts about the trustworthiness of closure assessment from the compliance variation. These ambiguities of PICC as a supposedly intrinsic factor of FCG, by implication, favour the stresses and strains in front of the crack tip as the genuine fatigue drivers.