Determination of Crack Tip Energy Dissipation and Elastic-Plastic Fracture Toughness Parameter with Ductile Crack Extension

Abstract

Abstract In order to evaluate the elastic-plastic fracture toughness parameter of nuclear pressure vessel steel, SA533B-C1 1 (Unified Numbering System [UNS] K12539), near and beyond general yielding, a newly developed technique for large plastic strain measurement, that is, the recrystallziation-etch technique, was applied to compact tension and three-point bend specimens with a crack length/specimen width of 0.6 that were tested to draw resistance curves for stable crack extension. Based on the results reported previously that the equivalent plastic strain distribution around the blunted crack tip could be measured by means of the recrystallization-etch technique, the plastic energy dissipation or work done within an intense strain region at the crack tip accompanying ductile crack extension was measured experimentally. Furthermore, the size and loading condition effects on this crack tip energy dissipation rate were examined in comparison with other candidate parameters for crack extension criteria in the presence of large scale plasticity. The size of the intense strain region could be regarded as equal to the process zone size where the fracture is taking place. Formation and extension characteristics of this zone were discussed from a view point of elastic-plastic fracture toughness parameters including the relationships with existing fracture toughness parameters such as crack opening displacement and J integral.