摘要
The process of a single-tooth cutting formation is taken as the representative to analyze the fracture mechanism of the formation with natural flaws under the PDC drill bit.The modeling of the stress field distribution of the formation under a single tooth is proposed first.Subsequently,the modeling of the stress intensity factor K,T-stress and the initiation angleθof the flaw under two far-field compressive loads in two cases are presented based on the mode-II fracture.Finally,the results of theoretical calculations and simulations are given and discussed.Based on the analysis undertaken,it can be concluded that the confinement ratioλapplying on the flaw changes nonlinearly with the variation inα+φ.The relationship between the dimensionless ratioβx/βy of T-stress and the rotational polar angleφis a parabola with an upward opening.When the direction of the cutting force is consistent with the flaw,the stress intensity factor K and the initiation angleθat the tip of the flaw reach the maximum.In addition,the angle between the cutting force and the flaw weakens the T-stress and inhibits the crack initiation and propagation of the flaw.The results of numerical simulations show good agreement with theoretical calculations.
基金
The support of National Natural Science Foundation of China(No.51704074)
Youth Science Foundation of Heilongjiang Province(No.QC2018049)is gratefully acknowledged
The work is also supported by Talent Cultivation Foundation(Nos.SCXHB201703,ts26180119,td26180141)
Youth Science Foundation(No.2019QNL-07)of Northeast Petroleum University.
