Fracture toughness evaluation of fusion reactor structural steels at low temperatures by small punch tests

Abstract

A small punch (SP) test using miniaturized specimens has been performed for cryogenic austenitic steels at 4.2, 77 and 293 K to evaluate fracture toughness in a fusion material program. An SP testing cryostat for load versus deflection curve measurements has been successfully constructed. A universal relationship between valid fracture toughness, J IC , and equivalent fracture strain, \\ ̄ ge qf , for austenitic steels at different test temperatures has been confirmed and empirical parameters for that relation have been determined using a linear regression model. A linear correlation between valid J IC and \\ ̄ ge qf has been clarified for austenitic steels at low temperatures, where the regression coefficient is found to be 845 kJ/m 2. Using the results of the SP test above room temperature, a new attempt at statistical analysis has been proposed to estimate the relative change in fracture toughness due to neutron irradiation.