The main purpose of this study was to establish an experimental method determining the dynamic fracture toughness of material at high loading rate. The experimental procedure used was based on the split Hopkinson bar technique that gives a load-displacement curve for each dynamic test. The dynamic stress intensity factor was evaluated from the dynamic strain measured by a small strain gage at the vicinity of the crack. Dynamic and static tests were conducted on 2017-T4 and 7075-T651 Al alloys using specimens of the same shape under loading rates of 1.0×106MPa√m/s and 0.2MPa√m/s, respectively. It was clarified that the fracture toughness of these materials was considerably reduced with increasing loading rate. This result was consistent with the fractographical observation using SEM.
