Study On Prediction Method Of Fatigue Life For 2A12 Aluminum Alloy Notched Specimen

2A12 Aluminum Alloy is important for aviation aluminum,safety of the fatigue strength of the aircraft plays an important role in the process of high altitude flight,aircraft landing will be continuously circulation force,if the actual fatigue strength is much lower than the predicted results,which is likely to cause the aircraft fatigue fracture.However,the prediction method of high cycle fatigue life could not predict the high cycle fatigue life of the 2A12 aluminum alloy notched parts well in the present,and the flight safety of the aircraft will not guarantee.Therefore,optimization and improvement of prediction methods make it stable in prediction process,high accuracy in life prediction,moderate in computation scale and convenient for application in engineering field.The main research contents and achievements of this project are as follows:(1)The prediction process of the nominal stress method and the stress field strength method,as well as the analysis and optimization of the related parameters.The important parameters in the life prediction process of the nominal stress method depend on the empirical formula or look-up table,which results in the instability of the prediction process and the poor prediction accuracy.In order to reduce the dependence,the elastoplastic finite element method is used to solve the theoretical stress concentration coefficientK_T.The solution path is different and the value ofK_T is different.It is applied to the life prediction process,and the effect of prediction is compared.(2)Compared with nominal stress method,the stress field strength method can comprehensively consider the effect of maximum stress,stress gradient and stress state on fatigue strength,and quantitatively explain fatigue size effect and fatigue notch coefficient.The field strength method limited by the stress criterion,and it is considered that the multi point stress interaction in the small damage zone?leads to fatigue damage.It is required that the gap root mesh of the finite element model is very accurate and the calculation cost is great.If the grid precision reduce and the computing resources are saved,it does not follow the general law of the fatigue damage mechanism of material and the elastoplastic finite element.According to Saint Venant principle,adopt sub model technology.Firstly,for the overall model of rough grid and analysis,and then build cover the damage zone?model and precision mesh,and finally to the analysis results in sub model boundary,using APDL language programming to measure the field strength,fatigue strength.(3)In order to verify the prediction effect of the optimized method,three notched2A12 aluminum alloy notches were designed,and the fatigue test under different stress states was carried out on the electro hydraulic servo fatigue tester.The test life compared with the method used in this paper and the predicted life of the original method.The predicted result of the optimized nominal stress method is much better than that of the original nominal stress method.The predicted result of the optimized field strength method is no less than that of the original field strength method,which saves computing resources.The optimized method of fatigue life prediction provides a new method and idea for the fatigue life prediction of practical engineering.