Simultaneously measuring initiation toughness of pure mode I and mode II cracks subjected to impact loads

Abstract

In order to simultaneously measure the initiation toughness of pure mode I and mode II cracks in one specimen, a large-size double-cracked concave-convex plate (DCCP) specimen configuration was proposed. Impacting tests were implemented in the drop plate impact device. Strain gauges were employed to measure impact loads and crack initiation time. The corresponding numerical model was established by using the dynamic finite difference program AUTODYN, and the experimental-numerical method and ABAQUS code were utilized to obtain the initial fracture toughness of the crack. Using experiments and numerical research, we concluded that the DCCP specimen is suitable for measuring the initial fracture toughness of pure mode I and mode II cracks at the same time; the dynamic initiation toughness increases with the increase of loading rate and the crack initiation time decreases with increasing loading rate; the initiation toughness of mode II crack is 0.5 times that of mode I crack when subjected to the same loading rate. For the pre-crack in the vicinity of the bottom of a sample, when its length increases from 20 to 100 mm, the dynamic initiation toughness of the pure mode I crack gradually decreases, and the longer the lower crack length is, the easier the crack would initiate, but the dynamic initiation toughness of pure mode II crack varies little.

Keywords

initiation toughness / crack initiation time / mode I crack / mode II crack / impact loads

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