Study of crack extension and branching behavior of layered materials under impact loading

This study utilized a digital laser dynamic caustics experimental system to conduct three-point bending impact experiments on layered epoxy specimens with different values of angle alpha between the bedding and the prefabricated crack, as well as the epoxy specimen without bedding. A high speed camera was employed to record the dynamic caustic spot at the crack tip during specimen extension and branching, analyze the dynamic stress intensity factor for crack tip for Mode I and II, crack extension speed, and exploration of the influence of angle alpha on crack extension and branching behavior. Numerical simulations were performed using the cohesive element method. The findings indicate an increase in crack initiation toughness as the angle alpha increases. After the initiation of the main crack, the failure mode was Mode I-dominated damage. When it extended near the bedding, the failure mode of the main crack changed to Mode II-dominated damage due to the influence of the bedding, resulting in the formation of branching cracks and microcracks. The main crack again exhibited Mode I dominated damage after branching. Notably, the branching cracks primarily exhibited Mode II-dominated damage. The occurrence of branching cracks and microcracks intensifies with higher alpha. The variation of alpha significantly influences the speed of crack extension.