Evaluation of fracture toughness by small-punch testing techniques using sharp notched specimens

Abstract

The small punch (SP) testing method has been used to assess the reliability of industrial facilities such as fusion reactor structures and power-generation systems. Conventional SP tests have evaluated flow properties, transition temperature, fracture strain, and other mechanical properties by analyzing load-deflection curves. However, previous research has not used a fracture-mechanics approach that considers flaws, stress analysis and fracture toughness. In this study, in order to obtain the fracture toughness based on fracture mechanics by SP tests, a sharp notch was machined into the central part of the SP specimens. A stress-intensity factor for sharp-notched SP specimens is proposed from analysis of stress fields near the crack tip. The crack initiation point was determined by analysis of the load-deflection curves combined with acoustic emission signals. The fracture toughness of SA 508 Class 3 steel was successfully evaluated by using the load at the crack initiation point.