Study of the effect of lengths on the propagation mechanism of interconnected cracks under impact loads

Interconnected cracks are prefabricated on plexiglass plates (polymethyl methacrylate, PMMA) to study the effect of crack length on the initiation and propagation of interconnected cracks under impact loads. A new dynamic caustics test system was constructed to analyze the specimen's initiation process; the fractal method was used to quantify crack propagation; and the numerical simulation was used to monitor the specimen's full-field stress change. The results show that, with the direction of the impact loads as the axis of symmetry, interconnected cracks with different lengths and symmetrical angles, only the longer cracks initiate under the action of impact loads. With the increase in the length of one side of the interconnected crack, the crack initiation time is delayed, the trajectory of crack propagation becomes more irregular, and the peak propagation velocity of the crack increases first and then decreases. After the analysis, it was concluded that there is a certain competitive relationship in the crack tip propagation law between interconnected cracks with different lengths. In the energy storage stage, the tip of the longer crack is more likely to accumulate energy than that of the shorter crack, and it also has a suppressive effect on the energy storage of the latter. In the initiation and propagation stages, the energy at the tip of the uninitiated shorter crack will transfer to the tip of the longer crack, promoting its propagation. The research provides a basis for analyzing the initiation and propagation laws of interconnected cracks in practical engineering applications.