Study On Mechanism Of Precrack Propagation In Stator Rubber Of Screw Pump During Wear

Rubber material is widely used in oil exploitation because of its excellent oil resistance and wear resistance.The screw pump composed of rubber stator and metal rotor plays an important role in the exploitation of heavy oil sand well.Through the analysis of the stator of the screw pump,it is found that the main cause of the damage is fatigue wear.When the fatigue crack initiate on the surface,the crack growth rate and the direction of propagation will directly determine the service life of the rubber stator.At present stage,the research on this aspect is mainly focused on the experimental study and theoretical analysis under the effect of tension-compression or shear,and very few people study the mechanism of crack propagation during the wear process.Therefore,in this paper,we firstly used ANSYS finite element analysis software to study the crack propagation of rubber samples with different crack angles under the stretching,and performed the tensile tests for prefabricated rubber samples with different crack angles to verify the correctness of the finite element analysis results.Secondly,the wear tests of nitrile rubber samples with different crack angles were carried out by reciprocating wear tester to observe the crack propagation path in the wear process.Meanwhile,the wear model was constructed by ANSYS finite element analysis software to calculate the stress values at the crack tips of the nitrile rubber samples with different crack angles under the wear conditions,and the results were compared with that from the wear tests.Finally,the finite element analysis of the screw pump stator rubber was performed to extract the equivalent stress and strain value of the hazardous unit for predicting the service life of the screw pump,combined with the life of hazardous unit calculated by the theoretical formula of fracture mechanics.The results show that the crack propagation path has the deflection of a certain degree in the tensile fracture process of the rubber samples with different prefabricated crack angles,and the final expansion direction of cracks is always along the direction perpendicular to the load.With the increase of the prefabricated crack angle,the stress value at the crack tip of the rubber sample increases gradually under the tensile action,meaning that the large angle cracks are most prone for crack propagation.During the wear process,the small angle cracks are more prone to crack and crimp due to the shearing force.The crack propagation path firstly extends along the direction of the initial prefabricated crack angle,and then it changes and turns into the rapid expansion phase along the horizontal direction,and finally it curls fracture after deflecting a certain degree to form a tongue shape.Finally,the finite element analysis of screw pump stator rubber shows that the hazardous unit is mainly distributed in the contact surface between the stator concave and the rotor of the screw pump.Moreover,the maximum equivalent stress is much smaller than the rubber tensile strength,and the predicted life of the stator rubber is less than the actual life.The research of this paper not only promotes the development of the crack propagation mechanism of rubber wear,but also has practical significance to improve the performance and fatigue life of rubber under practical working conditions.