Use of Instrumented Charpy Test for Determination of Ductile Crack Initiation Toughness

The present paper reports the determination of dynamic crack initiation (Jid) values using the instrumented Charpy test. Under the condition of the impact bending test the critical step for evaluating of Jid is detection of ductile crack initiation point on the impact load displacement curve. In this paper the crack initiation is determined by using emission of acoustic waves (AE). Different kind of AE events can be observed during loading of a precracked and side-grooved Charpy size specimen. It was shown that characteristic AE signals appear in the vicinity of crack initiation for the first time. These results have been verified by the results of COD measurements using the inverted impact pendulum developed and installed by VTT Espoo/Finland (VTT Tester). Additionally "Cleavage R-Curves" (Ju- a), have been evaluated and the physical crack initiation toughness (JidSZW) was deduced by measurement of the stretch zone width (SZW).