Research on the mechanism of rock breaking and the characteristics of rock chips generated by A-shaped PDC cutting teeth

Abstract The mining of coal resources in China has gradually shifted from shallow to deep, which has higher requirements for the efficiency of the drill bit to break the rock. This paper takes the A-shaped PDC (polycrystalline diamond compact) teeth as the research object, and analyses the mechanism of rock breaking and the characteristics of rock chips generated by the A-shaped teeth through the rock-breaking test and ABAQUS numerical simulation for different lithologies. The results of the study show that: As the depth of cut increases, the rock-breaking force increases, when the depth of cut exceeds the value of 1.2 mm, the increase in tangential force is significant, which is essentially induced by a fundamental shift in the rock fragmentation mechanism. As the angle of backward inclination gradually increases. The cutting teeth are gradually deflected towards the interior of the rock by the outward ‘squeezing’ force on the rock. There is a clear correlation between the tangential force and the rock chip generation process. The triangular prismatic ridge structure not only enhances the intrusion ability into the rock, but also promotes the creation and expansion of transverse cracks. The shallower depths of cut lead mainly to surface grinding, which produces fine and uniform rock chips. And the greater depth of cut provides a higher energy input. The rock-breaking performance of different rock types varies due to differences in physical and mechanical properties and microstructure. Numerical simulation analyses yielded that smaller backward inclination tends to cause high local stress concentrations, leading to rapid and localised rock fracture. In contrast, a larger backward angle of inclination is favourable for distributing the stresses uniformly and inducing the cracks inside the rock to expand along the lateral direction. Shallower depths of cut have smaller and more restricted areas of localised stress concentration. Deeper cutting depths, on the other hand, can induce rapid accumulation of internal rock stresses and expansion in multiple directions. It provides technical support for the development of more adaptable and efficient coal mine PDC drill bits to improve mine drilling efficiency and reduce operating costs.