Applicability of ultrasonic technique for evaluation of elastic plastic fracture toughness of high manganese steel at low temperatures

A study on the evaluation of elastic-plastic fracture toughness, J_IC, by ultrasonic technique is described for a newly developed high manganese steel at low temperature. In order to see the applicability of the ultrasonic technique based on pulse echo method at low temperature, special attention was paid to detect change point of ultrasonic echo due to the onset of stable crack growth. The J_IC values are evaluated by the ultrasonic method (which needs single specimen) and by stretched zone method (which needs several specimens) for compact tension (CT) specimens and three-point bend (3PB) specimens. The temperature dependence of these J_IC values of theCT specimens by the ultrasonic method show almost the same values to 3PB specimens over the temperature range tested. The J_IC values of 3PB specimens by the stretched zone method show slightly higher values than those of theCT specimens at low temperature. The J_IC values evaluated by the ultrasonic method give more conservative values than those evaluated by the stretched zone method for bothCT and 3PB specimens.