Experimental Study on Impact Fracture of Side-Wing Offset Crack in Jointed Medium

Abstract

Herein, to explore the interaction between joint and moving cracks under dynamic loads, bonded polymethyl methacrylate (PMMA) was selected to simulate the medium-containing joint. Using digital laser dynamic caustics experiments and the precrack offset distance as a single variable, the interaction mechanism between the moving crack and joint was investigated from the macro and micro perspectives. The failure mode of the specimens displayed significant differences. According to the fracture form when the crack passes the joint, it can be divided into three types: Type 1: the crack propagates directly along the original path when passing through the joint; Type 2: when the crack passes through the joint, it moves a certain distance along the joint and then cracks again to form a crack; Type 3: the crack moves for a certain distance along the joint and then cracks again to form main cracks and several subcracks of different lengths. With an increase in offset distance, the angle between the crack and joint decreases nonlinearly when passing through the joint, and the ability of the crack to propagate through the joint is continuously weakened. The macroscopic manifestation for the phenomenon is that the displacement of the crack along the joint movement gradually rises in steps. The offset distance of the crack along the joint and the number of cracks after passing through the joint were affected by the energy release rate along the joint direction. The microscopic appearance is that when the crack passes the joint, the stagnation time presents a gradually rising trend. The physical quantities such as the stress intensity factor at the initiation of the crack tip, the initial crack initiation time, and the time for the crack to penetrate the specimen all displayed a gradual enhancement with the increase in offset distance.