Research On The Law Of Rock Damage Under The Action Of PDC Teeth

The rock-breaking process by PDC cutter is a complex and transient issue which involves the tool-rock interaction,the fracture of rocks and the progression of fractures,for which the relative theory about rock-breaking mechanism has been known scantily by researchers.Even though research on rock-breaking mechanism it the key to improve rock-breaking theory and bit design technology,there's no a systematic rock-breaking mechanism theory widely approved by researchers now.So it is necessary to break through the restriction of the influence of single cutting structures on bit performance and capture the law of rock-breaking damage under the alternately mixed of cutting loads.Therefore,it is necessary to study the damage law and crushing process of PDC tooth during the cutting process beyond traditional cutting parameters.By consulting a large number of literature,the paper summarized means,methods and theoretical results which was studied by the domestic and foreign scholars on the PDC cutter rock-breaking theory.Next,the stress state and rock breaking process of PDC cutter under load was analyzed.Based on the display dynamics method and the dynamic damage constitutive model,numerical simulations of rock crack development,stress states,fracture modes and damage laws during the rock breaking of PDC teeth were performed and,at the same time,the feasibility and rationality of numerical simulation were analyzed.The main content of this article is as follows:(1)Breaking the traditional Drucker-Prager,Morh-Coulomb constitutive model to simulate the rock damage limitations,this study developed a finite element procedure for the PDC tooth rock breaking process by selecting the continuous cap model of rock combined with the plastic damage parameters and unit erosion plan.(2)Based on the results of numerical simulation,the process of rock crushing is divided into four stages:crack initiation,chip nucleation,crack propagation and block collapse according to the theory of rock-breaking theory,and damage law and stress states are also analyzed by phases.Then,the mechanism of PDC rock-breaking under load is summarized.Through the simulation model,the influence of the "adjacent effect" between cutting teeth on the rock damage and the theoretical verification of the PDC tooth shear rock breaking mechanism are analyzed.(3)Through multiple sets of numerical simulation plan,this paper studies the influencing regularity of experimental parameters(including the back rake angle,cutting depth and rock hardness etc.)on the rock-breaking efficiency together with cutting force,crack growth and damage model,it provides theory for optimizing the design of PDC bit.This paper was aimed at breaking through the experimental research on the difficulties of transient rock-breaking process by means of numerical simulation and,at the same time,providing fundamental basis to improve the rock-breaking theory and bit design technology.Lastly,the research achievements are conductive to providing technology for drill companies with independent intellectual property rights.