PDC齿形状对破岩效果的影响机制OA

Objectives:Shaped PDC cutters are key materials for tackling the challenges of rock breaking in complex formations such as deep-earth and deep-sea environments.However,the theoretical research on their rock-breaking mechanisms remains insufficient,limiting the optimization of cutter geometry.To clarify the rock-breaking process of PDC special-shaped cutters and reveal the influence of their geometric characteristics on cutting forces and rock-breaking efficiency,this study selects four typical PDC cutter geometries and conducts laboratory single-cutter rock-breaking experiments and mechanism analyses.Methods:Firstly,a high-speed camera is used to observe the rock-breaking processes of each PDC cutter,while a triaxial force sensor records the forces during cutting.Video images and cutting force data are synchronized for the planar circular cutter to investigate the rock failure characteristics during its rock-breaking process.The rock failure zone in front of the planar circular cutter is then divided into a crushing zone,a plastic flow zone,and a rock-cutting zone,with corresponding failure modes defined.Subsequently,the rock-breaking features,tangential force,and lateral force trends of the special-shaped cutters are analyzed.The results reveal that the axe-shaped cutter breaks rock in three distinct stages,the V-shaped cutter produces stress concentration near the rock-breaking region and has a shorter contact arc length between its cutter face and the rock,and the tri-ridged cutter exhibits rock-breaking characteristics similar to those of the axe-shaped cutter.Finally,by comparing the cutting forces of the four PDC cutters,the correctness of the rock-breaking process analysis and the revealed mechanisms is verified.Results:High-speed camera observations show that the crushing zone during the planar circular cutter's rock-breaking process initiates at the cutter edge and extends toward the region near the cutter tip.As the cutter advances,the rock in the crushing zone is crushed due to compressive action,forming a clear boundary with the intact rock.Because the lowest point of the crushing zone boundary is deeper than the cutter's cutting depth,cutting produces a damaged area at the rock groove surface beneath the crushing zone boundary.When the crushing zone expands to a critical state,it applies force to the rock in front of the cutter,initiating and propagating tensile cracks and eventually causing rock chips to detach from the intact rock—a process that macroscopically manifests as rock"shearing"failure.The crushing zone expands gradually during cutting,accompanied by an increase in cutting force.During expansion,a plastic rock powder flow zone forms upward near the cutter face,and when the crushing zone reaches a critical state,it tears the rock to generate chips.Compared with the planar circular cutter,the axe-shaped cutter requires three rock fragmentation actions to complete one rock-breaking cycle,each producing a smaller rock volume,whereas the planar circular cutter requires only one action per cycle and thus fractures a larger rock chip at the same time.Consequently,the axe-shaped cutter requires lower cutting forces and achieves higher rock-breaking efficiency.The V-shaped cutter,with a smaller rock-breaking contact area,shorter cutting-edge boundary on both sides,and a sharper tip,also requires lower cutting forces than the circular cutter.The tri-ridged cutter's cutting-edge geometry resembles that of the axe-shaped cutter,but under the same back rake angle,the angle between the tri-ridged cutter's edge and the fractured rock surface is smaller,producing a larger and deeper stress zone inside the rock.This leads to larger chips but also requires greater cutting forces.The triaxial force sensor data confirm that among the four cutters,the axe-shaped cutter exhibits the smallest tangential force,followed by the V-shaped cutter,while the tri-ridged and planar circular cutters record the highest forces,consistent with the observational results.Conclusions:Differences in cutter geometry result in distinct failure modes and processes of the rock in front of the cutters,directly affecting cutting forces.Optimizing PDC cutter geometry to induce stress concentration inside the rock,subdivide the single large rock-chipping process into multiple smaller ones,and refine the cutter profile to reduce friction between the cutter and the rock can effectively reduce cutting forces during rock breaking.