Effects of steady ductile crack growth on cleavage fracture from three-dimensional, small-scale yielding simulations

Highly refined simulations of steady, ductile crack growth in a three-dimensional small-scale yielding (SSY) framework provide detailed crack-front fields for computation of Weibull stress values in plane-sided and side-grooved configurations. The scalar Weibull stress values define a probabilistic measure for cleavage fracture with strong sensitivity to the volume of highly-stressed material – ductile crack extension subjects increasingly larger volumes of material to high stresses. The model treats all crack growth as steady-state with total Weibull stress values approximated by the value at the onset of tearing and increases caused by each increment of crack advance. The computations indicate that (1) Weibull stress values increase rapidly with steady ductile tearing, (2) side grooves slightly lower the rate of increase of Weibull stress values with crack advance – higher stresses at the root of the side-groove cannot compensate for the decreased thickness (volume loss) on the crack plane, and (3) plane-strain models remain realistic only at small load levels. Comparisons with prior analytical and experimental work indicate the model captures the increasing probability of cleavage fracture with continued crack advance. Within the restrictions of SSY, the model has particular application, for example, to low-upper shelf steels embrittled in nuclear reactor pressure vessels – materials with low-to-moderate initiation toughness, and lower resistance to ductile tearing.