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The use of 4 mm thickness Mini-C(T) specimens for Master Curve evaluation is drawing attention as a possible alternative / supplemental surveillance test method to current Charpy-based approaches in on-going efforts to update JEAC4201[1]. Obtaining a “valid” To per ASTM E1921 [2] and JEAC4216 [3] is a challenge for the Mini-C(T) because its tests must be performed at a low temperature relative to To to stay below the plasticity limit (KJclimit) of the testing standards while remaining above another limit on minimum test temperature (To – 50 °C) imposed by the testing standards. Minimizing the number of censored data caused by the violation of the KJclimit requirement is important in practical surveillance testing applications, since only a limited number (e.g., 12) of specimens may be available. Therefore, finding the appropriate test temperature within the first few specimens tested is essential. In this paper, the authors develop a KJc test temperature selection algorithm to maximize the chance of obtaining an E1921 and JEAC4216-valid To value with 12 or fewer tests. By the combined consideration of rejecting fewer specimens for being conducted below the low-temperature limit and having fewer specimens censored due to excess plasticity, we assumed that the test temperature of the next specimen in a series could be identified as the intersection of the KJclimit curve and the 98% tolerance bound of the KJc distribution, which is determined from an estimate of To made using already tested specimens. The appropriateness of this assumption is confirmed by a series of Monte-Carlo calculations, which demonstrates that this approach produces a valid To by testing 12 Mini-C(T)s > 98 % of the time. The study validated this testing reliability for a realistic range of yield stress and To values for reactor pressure vessel steels. |
