Out-of-plane biaxial loading effects on shallow-flaw fracture toughness of reactor pressure vessels (RPV) steels

A testing program is being conducted to determine the effects of tensile out-of-plane biaxial loading on the fracture toughness of shallow flaws in reactor pressure vessel (RPV) shells. A cruciform bend-type test specimen was developed to generate shallow-flaw toughness data under uniaxial and biaxial loading conditions. Limited data obtained to date indicate that biaxial loading can produce a significant reduction in shallow-flaw fracture toughness in the transition temperature region of A533 B steel. These data are being used to evaluate both stress-based and strain-based fracture correlation methodologies. Fracture methodologies based on the in-plane stress fields could not predict the reduction in fracture toughness observed in the biaxial tests. An alternative toughness correlation based on the width of the plastic zone in the plane of the crack propagation was shown to perform acceptably. (author). 14 refs., 6 figs