INFLUENCE OF SPECIMEN GEOMETRY AND STRAIN RATE ON DUCTILE-BRITTLE TRANSITION CHARACTERISATION OF REACTOR PRESSURE VESSEL STEELS USING THE SMALL PUNCH TECHNIQUE

摘要

The small punch (SP) tensile test, originally developed for assessing the integrity of nuclear containments, has seen a renaissance in recent years with the introduction of a Code of Practice and a standardisation proposal. For nuclear applications, the extremely low volumes of material that are required allows specimens to be manufactured from quasi-destructive scoop samples, surveillance specimens or even previously tested Charpy specimens. The low volume of material also alleviates the health and safety requirements and the cost associated with testing active materials. By assessing the energy absorbed before fracture, it is possible to build an entire SP ductile-brittle transition curve using less material than is required for a single Charpy test. Small punch testing has been performed on SA 508-3 NESC-1 spinning cylinder material to establish ductile-brittle transition data, for comparison to that obtained by conventional Charpy impact test techniques. Multiple SP ductile-brittle transition curves have been constructed, building upon the framework of the existing Code of Practice. Novel geometries and associated machining techniques employed to incorporate notches into the surface of the SP specimen, and also the application of relatively high strain rates have been investigated. Post-test fractography illustrates the influence of both stress raising features and strain rate on small punch fracture behaviour.