Ductile-brittle transition characterisation of NESC-I spinning cylinder steel using the small punch test

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 through CEN (2007) and a standardisation proposal. For nuclear applications, the extremely low volumes of material that are required allow specimens to be manufactured from quasi non-destructive scoop samples, surveillance specimens or even previously tested Charpy specimens. The low volume of material also alleviates the health and safety requirements and therefore the cost of testing radioactive 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 the SA 508-3 NESC-I spinning cylinder material to establish ductile-brittle transition data. The extremely well characterised nature of the NESC material provides a good platform for comparisons to 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, together with the application of relatively high strain rates, are described. Post-test fractography illustrates the influence of both stress raising features and strain rate on small punch fracture behaviour, plus any effect on the SP/Charpy correlation 'a' factor. Finally the SP test enables comparisons against previously published NESC fracture data.