| Oil extraction progressing cavity pump(PCP)is an important lifting equipment in oil field,which has many advantages that can't be replaced by other oil production equipments.The fatigue failure of the rubber stator of PCP due to the influence of alternating load,working temperature and underground medium is an important reason for the failure of PCP.This paper aims at the fatigue failure of the stator of PCP under different working conditions,and carries out life prediction and simulation test study,which provides a theoretical basis for structural optimization of oil extraction PCP,development of fatigue-resistant stator rubber and improvement of the service life of PCP.Uniaxial tensile and plane shear tests are carried out on the stator rubber treated by oil immersion and water immersion at different temperatures.The Yeoh model and the modified Arruda-Boyce model are used to predict and evaluate the uniaxial tensile stress-strain,the modified Arruda-Boyce model with strong characterization ability is selected as the stator rubber constitutive model,and the parameters of the constitutive model are determined.According to the temperature expansion and swelling test of the stator rubber,the temperature equivalent method is applied to determine the swelling equivalent temperature under different working conditions,the finite element model of oil extraction PCP is established under the conditions of different temperatures,different medium and different interference,the distribution laws of contact stress,shear stress and equivalent stress of the rubber stator is obtained,and the dangerous position for fatigue is determined under various working conditions.Accelerated test methods such as Demesia are used to perform fatigue tests on specimens of stator rubber under different temperatures in water immersed and oil immersed,the parameters of fatigue crack propagation characteristics of stator rubber and the equivalent crack size of potential critical damage are determined,analysis the variation of the two parameters changing with temperature and medium,and the relationship between the two parameters and temperature is determined;At the same time,fitting to obtain the elongation ratio of stator rubber-fatigue life curve established the fatigue crack initiation life prediction model of stator rubber based on the strain damage parameters,and the model parameters under different working conditions are determined.Combined with finite element analysis results of various working conditions of PCP,a unified fatigue crack growth life prediction model for the stator of PCP with interference,temperature and medium as variables is established;Application of the theory of continuous damage mechanics,based on the fatigue crack initiation life model of rubber with strain as fatigue damage parameter,the fatigue crack initiation life prediction model of stator of PCP with equivalent strain range as fatigue damage parameter is established.The fatigue crack propagation life and fatigue crack initiation life of stators under different working conditions are predicted,the analysis determined that the fatigue life of the stator of PCP mainly depends on the fatigue crack growth life.According to the working characteristic of PCP,an accelerated fatigue test device for the stator rubber of the simulated PCP is developed.This paper takes the static stiffness loss rate as the criterion of fatigue failure,and takes temperature,interference and medium condition as variables to perform the accelerated fatigue test.Modification of fatigue crack propagation life prediction model based on fatigue test results,using the modified fatigue life prediction model,predicting the fatigue life of the stator of PCP under actual conditions,the ratios of predicted life to actual life are 1.23 and 0.93,model prediction accuracy is higher,The reliability of the modified fatigue life prediction model is verified. |
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