On the accuracy of measurement of dynamic elastic-plastic fracture toughness parameters by the instrumented charpy test

Abstract

It had been developed in a previous study [ Engng Fracture Mech. 24, 773–782 (1986)] that dynamic elastic-plastic fracture toughness parameters J d and T mat could be evaluated from the instrumented Charpy impact test. However, to popularize this method, strict measuring methods and judging standards on the validity of obtained values must be established. One old and important problem to be clarified is a relationship between an instrumented energy ( E t ) obtained from the area under a load-deflection curve and a dial reading energy ( E r ) calculated from the potential energy of the hammer. The purpose of this study is, therefore, to solve this problem first, and moreover to clarify the dynamic phenomena accompanying the measurement of the load-deflection curve. It is concluded that the energy condition necessary for the test without changing the load-deflection relationship is E 0 (applied energy) ≧ 3 E (total absorbed energy). This is the necessary condition to evaluate meaningful values of J d and the tearing modulus ( T mat ). Moreover, it is shown how the vibrational wave superimposes the load-deflection curve, analyzing the vibrational mode shape of the hammer.