Evaluation of dynamic fracture toughness J_Id using instrumented charpy impact test

This paper presents two methods of calculation of dynamic fracture toughness J_jd for 40 HMNA steel. In this study, it is attempted to detect the crack initiation moment by calculating the compliance changing rate from a load-deflection curve obtained in the instrumented Charpy impact test. Next, a (J-Delta a) curve is estimated by using the stop block test which is a multiple specimen technique. The above results are compared to those obtained with the aid of technique based on the F_max concept.