A Modified Weibull Stress Approach to Determine the Reference Temperature in a Pressure Vessel Steel

Abstract

Abstract This work describes a micromechanics methodology based upon a local failure criterion incorporating the effects of plastic strain on cleavage fracture coupled with the statistics of microcracks to correct effects of constraint loss on fracture toughness and to determine the reference temperature, T0, based on the master curve procedure. The methodology approaches the modeling of cleavage fracture from the point of view of a coupling between the local plastic strain and the number of eligible Griffith-like microcracks nucleated from brittle particles dispersed into the ferrite matrix. A modified Weibull stress, ˜σw, incorporating the effects of plastic strain on cleavage fracture emerges as a probabilistic fracture parameter to define conditions leading to (local) material failure. Fracture toughness testing conducted on an A515 Grade 65 pressure vessel steel provides the cleavage fracture resistance data in terms of Jc—values needed to estimate T0. Very detailed non-linear finite-element analyses for 3D models of the fracture specimens provide the relationship between ˜σw and J from which the variation of fracture toughness across different crack configurations is predicted. For the tested material, the modified Weibull stress methodology yields estimates for the reference temperature, T0, from small fracture specimens, which are in very good agreement with the corresponding estimates derived from testing of much larger crack configurations.