Dynamic Tear Test Definition of the Temperature Transition From Linear Elastic to Gross Strain Fracture Conditions

Abstract

Transition temperature concepts for fracture-safe design have been based on the relatively narrow temperature range evidenced by the fracture mode transition from plane strain to plane stress. Fracture mechanics theory has suggested that large increases of section size should provide sufficient mechanical constraint for retention of plane strain conditions through the transition temperature range. Recent investigations, based on Dynamic Tear (DT) tests of thick section reactor grade steels (A-533B), have provided clear evidence that the plane strain to plane stress transition is not eliminated. These findings are of major consequence to concepts of fracture-safe design and show that temperatures significantly above NDT + 100 F can provide a conservative margin of safety, even for the condition of very large flaws and plastic overload. The DT test, as conducted using a small specimen, defines the temperature range of transition from linear elastic to gross strain mechanical conditions of fracture and therefore the required analytical treatment for flaw size-stress calculations. Fracture mechanics concepts are brought into consonance with transition temperature concepts of long standing, and the importance of considering fracture initiation in terms of limiting dynamic fracture toughness values is emphasized.