On the determination of dynamic fracture toughness properties by instrumented impact testing

In the engineering practice it is of importance to know the effect of loading rate on the material behaviour, e.g., on the fracture mechanics properties. One of the most widely used testing techniques for determining these properties is the instrumented impact test. Depending on the material behaviour under a given loading condition, different fracture mechanics parameters should be determined. Most of the evaluation procedures of these parameters are still not standardised for higher loading rates. So the aim of the present work was to investigate the applicability of different methods for determining dynamic fracture toughness properties. Instrumented impact experiments combining with magnetic emission measurement have been performed on pre-cracked Charpy-V specimens of E420 C and QStE 690 TM high strength steels. Critical values of stress intensity factor (K-Id, K-Ji) related to the initiation of the fracture at different temperatures have been determined using different methods depending on the type of the fracture.