Discrete element numerical study on fracture mechanism of heterogeneous material under stress wave effects during high-speed cutting process

In high-speed to ultra-high-speed cutting, the dynamic mechanical response of the workpiece material is significantly enhanced. The heterogeneous material at the mesoscopic scale (cutting thickness) makes this response more complex, which in turn alters the fracture mechanism of the material and affects the chip formation process. In this study, a multilayer spring coupling-type discrete element method was used to model a heterogeneous material, to study the effect of different phases and orientations of grains on the stress propagation process and material force state after the tool impacts the workpiece at high speed, to further analyze the crack initiation and expansion mechanism under different cutting speeds, and to reveal the reasons for the change in chip size with cutting speed. The results show that when cutting cast iron at a high speed, the material stress state is in a continuous fluctuation state owing to the continuous reflection and superposition of stress waves at the tissue interface. With the increase in cutting speed, the type II fracture of the material decreases, while the type I fracture increases, which tends to be a more brittle fracture. The initial crack expanded bi-directionally into a single main crack when the cutting speed was lower, whereas the initial crack expanded unidirectional through the formation of multiple main cracks at higher cutting speeds, ultimately forming a crushed chip.