Miniature Compact Tension Specimens for Upper Shelf Fracture Toughness Measurements on RPV Steels

Abstract

Miniature compact tension, MC(T), specimens (thickness B = 4.15 mm) have been recently investigated at SCK∙CEN for measuring the fracture toughness of steels under fully ductile conditions (upper shelf regime). The first results of this assessment, made by comparison with results obtained from 1TC(T) samples of various RPV steels with quite different toughness properties, have been described in a previous paper by the same authors. It was observed that, although a systematic and significant underestimation of both critical toughness values and crack propagation resistance was observed for the MC(T) samples with respect to the bigger specimens, it is possible to establish an empirical correlation between the two geometries which allows deriving acceptable estimates of the material's critical toughness. In this work, further investigations are presented, related to: (1) the behavior of MC(T) and 1TC(T) specimens in the crack tip blunting phase; (2) the role of work hardening in decreasing the tearing resistance of MC(T) specimens; and (3) the use of alternative parameters (crack-tip opening displacement, crack-tip opening angle, Ernst's modified J-integral JM). Evidence is also presented which could justify a revision of the specimen measuring capacity (Jmax) in the current ASTM Standard E1820-05, which appears too severe and could be relaxed. Further work will include validating on irradiated materials the empirical correlations established between 1TC(T) and MC(T) test results.