| Petroleum is an important strategic resource in China.Electrical-submersible-motor-driven progressing cavity pumping system has been widely used as petroleum lifting equipment in the petroleum industry.Progressing cavity pump consisting of a metal rotor and a rubber stator is an important component in the electrical-submersible-motor-driven progressing cavity pumping system.The rubber stator will produce fatigue cracks under the action of high temperature and high pressure and alternating load,which will lead to its failure.Therefore,studying the fatigue damage mechanism,finding out the location of fatigue crack initiation,and predicting the fatigue life of the rubber stator are of great significance to the safe operation of the progressing cavity pumping system.Based on the theory of fracture mechanics,this paper establishes a model of rubber fatigue crack life prediction.The finite element software was used to calculate the stress and strain of the rubber stator in the working state,and its fatigue life was predicted.The main contents of this article include:The expressions and characteristics of various hyperelastic constitutive models are introduced in detail.According to the tensile and shear tests,the stress-strain curves of multiple models were fitted.The Mooney-Rivlin model with better accuracy was selected as the constitutive model of nitrile rubber in this paper,and the relevant material parameters were calculated.Based on the theory of fracture mechanics,the relationship between the tearing energy and the fatigue crack growth rate was found,and the complicated multi-directional stress was converted into the uniaxial equivalent stress.A fatigue life prediction model of nitrile rubber was established.The fatigue life curve of nitrile rubber was obtained through accelerated fatigue test,and the related fatigue parameters were calculated.The geometric model of metal rotor and rubber stator is established,and the finite element analysis is carried out by applying different interference and pressure load to the working characteristics of the rubber stator.Through the stress cloud diagram to explore the influence of interference and oil pressure on the contact stress and equivalent stress of the rubber stator.The location of the hazardous unit is determined based on the peak stress.Analyze and calculate the tearing energy of the hazardous unit and its variation.By means of numerical analysis,the fatigue life of the rubber stator is calculated using a nitrile rubber fatigue life prediction model.The software simulation method is used to calculate the fatigue of the rubber stator using simulation software.Comparing the two results,it is found that their ratio is within the interval of 1.34-1.74,so the accuracy of the model is considered ideal.Finally,the possible reasons for the deviation of life prediction are analyzed. |
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