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

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.