A novel perspective to study rock failure characteristics during single PDC cutter tests: Based on the combined cutting and penetration

Polycrystalline diamond compact (PDC) cutter tests have been extensively conducted to shed light on the rock failure mechanism, thus further enhancing the performance of PDC bits. However, most of these studies primarily focus on the cutting process. Specifically, the cutting depth is pre-set rather than calculated based on rock penetration process. In the present paper, a physical model is developed to examine the combined effects of cutting and penetration on rock breaking. Experimental and theoretical analyses are also performed to study the individual impact of cutting and penetration. Based on rock failure characteristics under varying back rake angles and penetration forces, cutting parameters are recommended. The findings indicate that the back rake angle should not exceed 40 degrees to prevent cutter breakage. Increasing the back rake angle simultaneously improves penetration efficiency and limit cutting efficiency. For rocks with high strength and it is challenge to load the weight on bit (WOB), a back rake angle of 20-30 degrees is advised for efficient cutter penetration. However, the smaller the back rake angles, the more obvious the enhancement in penetration depth and rock-breaking volume with the further increase of penetration forces. At an equivalent cutting depth, larger back rake angles yield higher rates of penetration (ROP), while smaller angles enhance drilling efficiency. The determination of drilling parameters should further depend on field requirements. The present study provides an in-depth understanding of the rock failure process and the arrangement of PDC bits.