Cracking Behaviors of Rocks Subjected to the Dynamic Percussion of a Single PDC Cutter: A Finite-Discrete Element Study

Percussive drilling is a promising rock-breaking method for developing geological resources in deep-hard formations. The interaction between polycrystalline diamond compact (PDC) cutter and rock, as well as the corresponding cracking behaviors, are the crucial engineering concern for revealing rock-breaking mechanism and optimizing percussive drilling performance. This paper focuses on the rock-cracking characteristics around a PDC cutter subjected to dynamic percussion. The cutter-rock interaction and random cracking behaviors were modeled with a finite-discrete element method (FDEM), and corresponding experiments were performed to validate the FDEM model. The crack fractal dimension, crack area, and the number of failure elements were employed as indicators to investigate the effect of percussion loads, including percussion mode, amplitude, frequency and waveform on rock-cracking behaviors. Unlike static loading (SL) mode, the long-straight shaped and Y-shaped tensile cracks with larger geometry dimensions, play a more dominant role in rock-breaking process of single axial and torsional percussion. In contrast, the axial-torsional coupled percussion loading (A-TCPL) mode improves the rock-breaking performance by creating a combined tensile-shear crack propagation zone with larger rock fragments. As compared to SL mode, the crack area, number of failure elements and crack fractal dimension in A-TCPL mode grow by 22, 18 and 10%, respectively, which are significantly greater than those in single axial and torsional percussion modes. For A-TCPL mode, there is an optimal axial-torsional ratio, which is 1:3 in both impact amplitude and frequency. Compared to conventional sinusoidal wave, linear impact waveforms, i.e., triangular, trapezoidal, rectangular waves, benefit to enhance rock-cracking performance, but the effect is relatively limited (< 5%). Current works are expected to provide theoretical insights for optimizing rock-breaking capacity of percussive drilling in deep earth.