Research On Mechanical Model Of Polycrystalline Diamond Composite Bit Based On Bottom Hole Shape

Bottom hole shape is an important factor affecting PDC bit cutting mechanics model.It is affected by the crown shape of the drill bit,and different parts of the bottom hole shape correspond to different cutting stress distribution,i.e.different rock breaking difficulty degrees in different parts lead to different reverse forces on cutting teeth in different parts during the working process of the drill bit,thus affecting the overall stress and motion state of the drill bit.In the past,when experts and scholars at home and abroad studied the cutting mechanics model of PDC bits,they usually believed that the degree of rock breaking difficulty in different parts of the bottom hole shape was the same,and the non-uniformity of rock breaking stress caused by different bottom hole shapes was not considered,which could not truly reflect the stress situation of cutting teeth in different parts of PDC bits.Therefore,this paper focuses on the distribution of rock breaking stress in different parts of the bottom hole shape,studies the influence law of various factors including the bottom hole shape on the force of PDC bit cutting teeth,and establishes the cutting mechanics model of PDC cutting teeth.In this paper,two cutting force prediction models including the influence of bottom hole shape will be established by indoor simulation tests and theoretical derivation.In the laboratory simulation experiment part,circumferential cutting experiments are carried out on cylindrical rock samples and cylindrical rock samples with different lithology and specifications to study the influence of cutting depth and bottom hole shape on cutting force,and an empirical relationship model of cutting force including the influence of bottom hole shape is established.In the part of theoretical derivation,the static equilibrium relation of cutting unit is used to carry out theoretical derivation,and the theoretical model of PDC cutting tooth force including the influence of bottom hole shape is obtained.The model takes bottom hole shape,cutting area,rock shear strength and other influencing parameters of cutting force.The research in this paper will help to expand the research ideas of PDC bit cutting mechanics model and promote the development of bit dynamics and rock breaking theory.