Abstract

The Heavy Section Steel Technology Programme (HSST) is investigating the influence of flaw depth on the fracture toughness of reactor pressure vessel (RPV) steel. To complete this investigation, techniques were developed to determine the fracture toughness from shallow-crack specimens. A total of 38 deep and shallow-crack tests have been performed on beam specimens about 100 mm deep loaded in 3-point bending. Two crack depths (a ≈ 50 and 9 mm) and three beam thicknesses (B ≈ 50, 100, and 150 mm) have been considered. Techniques were developed to estimate the toughness in terms of both the J-integral and crack-tip-opening displacement (CTOD). Analytical J-integral results were consistent with experimental J-integral results, confirming the validity of the J-estimation schemes used and the effect of flaw depth on fracture toughness. Test results indicate a significant increase in the fracture toughness associated with the shallow-flaw specimens in the lower transition region compared to the deep-crack fracture toughness. The increase in shallow-flaw toughness compared with deep-flaw results appears to be well characterised by a temperature shift of 35°C. There is, however, little or no difference in toughness on the lower shelf, where linear-elastic conditions exist for specimens with either deep or shallow flaws.

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