Determination of Dynamic Fracture-Initiation Toughness Using a Novel Impact Bend Test Procedure

Abstract

A novel impact bend test procedure is described/or determining the dynamic fracture-initiation toughness, KId , at a loading rate (stress intensity factor rate), K̇I , of the order of 106 MPam/s. A special arrangement of the split Hopkins on pressure bar is adopted to measure accurately dynamic loads applied to a fatigue-precracked bend specimen. The dynamic stress intensity factor history for the bend specimen is evaluated by means of a dynamic finite element technique. The onset of crack initiation is detected using a strain gage attached on the side of the specimen near a crack tip. The value of KId is determined from the critical dynamic stress intensity factor at crack initiation. A series of dynamic fracture tests is carried out on a 7075-T6 aluminum alloy, a Ti-6246 alloy and an AISI 4340 steel. The KId values obtained for the three structural materials are compared with the corresponding values obtained under quasi-static loading conditions.