| Cast aluminum alloy is widely used in the automobile industry due to its excellent high thermal conductivity,workability,low thermal expansion coefficient,low density,wearresistance,and high corrosion resistance,and is often used in the casting of gasoline engine pistons with complex geometries.In recent years,to pursue the overall goal of high output capacity and low fuel consumption,the gas pressure and temperature in the engine cylinder have been greatly increased.In such a high temperature and high pressure working environment for a long time,the cast aluminum alloy material for the piston will not only cause fatigue damage but also creep damage.The complex nonlinear coupling between the two damages will cause the piston creep-fatigue failure phenomenon.This paper studies the creep-fatigue nonlinear coupling characteristics of cast aluminum alloy materials for pistons from three aspects: experimental testing,theoretical analysis,and numerical simulation.The main purpose is to establish a creep-fatigue life prediction model based on the creep-fatigue behavior of cast aluminum alloy materials for the characteristic loads of the reliability test of the piston bench and apply the new model to the calculation of the piston's creep-fatigue life.The main research contents and conclusions of this paper are as follows:(1)Study on creep-fatigue behavior of the cast aluminum alloyThe high-temperature tensile mechanic's test of cast aluminum alloy materials has been carried out.The test results show that the temperature has a greater impact on the mechanical properties of the material,and the ultimate tensile strength of the material at high temperatures is significantly reduced.In addition,the high temperature creep deformation behavior of the cast aluminum alloy material is studied by the high temperature creep test of the cast aluminum alloy material,and through the secondary development of the ABAQUS commercial finite element software,the creep constitutive model is introduced into the strength calculation of the piston structure.Creep-fatigue tests are carried out on cast aluminum alloy materials to obtain the number of life cycles of the materials under cyclic loading under variable conditions.(2)Research on the creep-fatigue life prediction modelBased on the theory of continuum damage mechanics and fully considering the characteristic loads of the piston bench reliability test,a new creep-fatigue life prediction analysis model for the calculation of cast aluminum alloy materials is constructed.The model parameters are determined by numerical fitting of the experimental data through the established new model.Then,the model is used to predict the life of cast aluminum alloy under specific load conditions.The prediction results of the new model are all within a scatter band of factor two of the creep-fatigue life of the material,indicating that the new model established in this paper has a good ability to predict the creep-fatigue life.(3)Research on creep-fatigue life prediction of piston structure under characteristic load of bench reliability testAiming at the characteristic load of the bench reliability test of the piston structure of a gasoline engine,an analysis process and method for predicting the creep-fatigue life of the piston are proposed.The creep-fatigue life of the piston structure under the cyclic load of idle speed and calibration conditions is predicted.The results show that under the characteristic load of the reliability test of the piston bench,the lowest point of the piston's creep-fatigue life is at the joint between the piston pin boss and the reinforcing rib.Among them,the creep damage accounts for 53.9% of the total damage,and the creep-fatigue life is4290 cycles.In this paper,a new creep-fatigue life prediction model based on the creep-fatigue properties of cast aluminum alloy is established.The model is successfully applied to actual engineering cases,and the creep-fatigue life of the piston structure of the gasoline engine is calculated.The series of creep-fatigue analysis procedures and methods established in this paper from the basic performance analysis of materials to the actual engineering application of structures can provide references for piston design and structural creep-fatigue life prediction. |
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