Research on Mechanistic Interface Laws of Impregnated Diamond Bits under Fixed Depth-of-Cut Drilling

Summary Impregnated diamond (ID) bits are widely used for coring in hard and abrasive formations, yet the underlying bit/rock interfacial mechanisms under controlled drilling conditions remain insufficiently understood. To clarify the rock-breaking behavior of ID bits under fixed depth-of-cut (DOC) conditions, we develop a mechanistic framework based on the cutting mechanics of a single diamond particle. Under simplifying assumptions regarding interfacial friction stability, applicability of the cutting model, and uniform random distribution of diamond particles, microscale force relations for individual diamond particles subjected to frictional and cutting interactions are derived. A dual-mechanism description distinguishing friction-dominated and cutting-dominated rock breaking is established. Through macro-micro linkage, mechanistic interface laws (IL) are formulated to relate macroscopic drilling responses, including weight on bit (WOB) and torque (T), to the DOC per revolution. A series of fixed DOC drilling experiments were conducted using an S46 ID bit on concrete-simulated formations. Experimental results show that, with an increasing DOC, the drilling process can be clearly divided into three characteristic stages: a friction-dominated stage, a stable cutting stage, and a repeated-crushing stage. Each stage exhibits distinct WOB- and T-response patterns, reflecting fundamental transitions in the bit/rock interfacial interaction mechanism. Further analysis indicates that, when the DOC is controlled, variations in rotational speed have a limited influence on the mean levels of WOB and T, confirming that DOC is the dominant parameter governing the interfacial interaction state. The proposed interface laws show good agreement with experimental observations over different DOC ranges and provide a physical basis for understanding the rock-breaking behavior of ID bits under fixed DOC drilling conditions.