| On account of the excellent mechanical properties and fatigue strength,2024 aluminum alloy is widely used in the shear rib,wing skin,web,engine blade and other metal components with high strength requirements,and plays an extremely important role in the aircraft manufacturing industry.Due to the severe working conditions and subjected to cyclic loading,fatigue failure has been the main failure form of 2024 aluminum alloy and other metal components.In order to improve the fatigue life of 2024 aluminum alloy,engineers and technicians often introduce some residual compressive stress into the metal components by shot peening.However,the research shows that the residual stress of shot peening is not stable,and it will relax or even relax reversely under large load.if the instability of residual compressive stress is not considered,the expected life will deviate from the reality,and the fatigue state of components cannot be evaluated accurately.Therefore,it is of great significance to study the relaxation effect of residual compressive stress and evaluate the fatigue state of metal components based on residual stress.Based on the research status of relaxation effect of residual compressive stress and fatigue life model based on residual stress,this paper proposes a modified fatigue life model based on residual stress and establishes a fatigue state evaluation method based on residual stress.The main research work are as follows:(1)This paper studied two kinds of classical fatigue model based on the residual stress of metal components,them are the logarithm linear model of Kodama and power function model of Omar respectively.And this paper also studied two methods about unknown parameter estimation,NLS(Nonlinear Least Squares)and BM(Bayesian Method)based on the physical model respectively.The modified Omar model was proposed and the Kodama model was proved to be still applicable after the residual compressive stress became the residual tensile stress by combining the results of simulation analysis,theoretical analysis and experimental analysis.(2)based on the distribution of residual stress introduced by shot peening,ABAQUS software was used to establish the simulation model of tensile fatigue,change the load strength,cycle times,initial residual stress and other factors that have an effect on fatigue to study and analyze the variation law of residual stress in the fatigue loading process,and obtain the evolution law and redistribution law of conventional relaxation and reverse relaxation of residual stress.(3)The specimens of 2024 aluminum alloy was carried out fatigue test with fatigue testing equipment,and the changes of residual stress during fatigue loading tracked by the residual stress detector.The fatigue state evaluation model was established according to the residual stress detection results of the full life fatigue test and periodic fatigue test,and the accuracy of the fatigue state model was evaluated by the residual stress detection results of periodic fatigue test.(4)Considering the influence factors of the experiment process,small data samples,material differences and other factors,this paper hold that the full life of all 2024 aluminum alloy specimens has probability,and the life distribution range of the whole specimens was obtained by combining the fatigue life simulation analysis and fatigue test.On the basis of the optimized physical model,the fatigue state assessment based on residual stress of the 2024 aluminum alloy metal components in small specimens was realized. |
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