Specimen Size Limitations in J-R Curve Testing—Standards versus Reality

Abstract

Testing standards contain limitations on allowable J and crack growth, related to specimen size. In the case of unirradiated pressure vessel steel, it is usually possible to extract specimens of sufficient size to allow a standard determination of the J-R curve. However, in the case of irradiated materials, especially irradiated internals, it is normally not possible to use specimens that would provide valid results according to the standard requirement. This raises the question as to the relevance of the standard requirements. The size requirements stem from the dawn of elastic-plastic fracture mechanics. They have remained practically unchanged ever since, even though the understanding of elastic-plastic fracture mechanics and ductile fracture has evolved considerably. In this paper, the state-of-art understanding of the ductile fracture process, and elastic-plastic fracture mechanics is combined with experimental test results to derive new more realistic size requirements for J-R curve testing. It is shown that a considerable relaxation of the standard requirements is possible without affecting the reliability of the test result. This enables an effective and reliable testing of irradiated materials and structures whose dimensions inhibit the extraction of large specimens.