Research On Mechanical Properties And Fatigue Life For Stator Of PCP

At present, short checking period of progressing cavity pump is one of the main reasons to restrict the promotion and popularization of PCP technology in oil extraction field. Stator rubber fatigue is one of the most important reasons to lead to the failure of PCP according to the failure statistics of PCP well. In order to improve the checking period and increase the service life of PCP, to study the fatigue life of stator rubber is particularly necessary. In this article, it uses crack propagation based on fracture mechanics and Fe-safe crack initiation based on S-N curve to study the crack extension and initiation life of PCP stator. The results not only enrich the theory of PCP, but also have great practical significance and application value in increasing oil recovery technology of PCP and economic benefits.Rubber stator of PCP is taken as the main research object in this article, to optimize the constitutive model from M-R, Yeoh, Ogden, A-B, VDW under different temperature with different stress-strain state of conventional and oil immersed rubber and determine the constructive model and model constant of dumb-bell rubber and PCP. To build finite element analytical model through setting the rotation speed of rotor and fefinementing contact seal gyids, to calculate and analysis contact stress, shear stress, equivalent stress. The dangerous position for fatigue of PCP is the middle of spirile band transition to arc near semicircle.To deduce the prediction model of fatigue crack extension life based on fracture mechanics, and to predict the crack extension life of dumb-bell rubber specimen with prefabricated notch, then contrasting with corresponding fatigue test life, the error value was 15.66%, so to predict the fatigue crack extension life based on fracture mechanics is feasible. According to the results of finite element calculation, determining the range of strain energy release rate in each dangerous position of PCP, predicting the fatigue crack extension life of rubber stator, then analyzing the prediction result, to determine the relationship between the fatigue crack extension life and chamber pressure.Fatigue tension test have been done in this article, and fatigue life prediction model that takes main strain, octahedral shear strain and strain energy density as the damage parameter have been built, then predicting the total life of dumb-bell rubber specimen according to the model. To get the S-N curve according to the fatigue tension test of stator material, to determine the fatigue crack initiation life and safety factor of dumb-bell rubber specimen and stator rubber under different working conditions using the Fe-safe for the first time. The analysis results show that the fatigue crack initiation life and safety factor of the rubber stator decline with the chamber pressure, and the most concentration position of fatigue crack forming is the middle of spirile band transition to arc near semicircle.Through the comparative analysis between the fatigue crack initiation, extension and total life of stator rubber to determine to combine the crack propagation method based on fracture mechanics and the crack initiation method based on S-N curve to predict the rubber fatigue life, and this method is feasible. The sum of predicted crack initiation life and extension life using these two methods is basically consistent with the actual life of PCP.