Study On Fatigue Life Prediction Method For Notched Metal Material Parts

There are countless safety incidents caused by metal fatigue,and fatigue fractures often occur without any precursors,laying a major safety hazard to the actual engineering structure.Therefore,it is especially important to accurately predict the fatigue life of components and structure.To this end,based on the previous research,this paper improves the existing fatigue life prediction model,aiming to obtain a life prediction model closer to the real life of components and structure.The specific work of the study is as follows:(1)This paper combines the advantages that the stress field strength method can reflect multiaxial stress and the critical distance theory calculation is simple.Replacing the maximum principal stress with equivalent stress,replacing the average value of the maximum principal stress with the average value of the equivalent stress as the effective stress for controlling the fatigue behavior,New model for fatigue life prediction that can reflect the multiaxial stress of the root of the notch and is relatively simple to calculate is created.(2)Based on the basic assumptions of the existing life prediction model,the hypothesis of the fatigue damage equivalent relationship between the notched and smooth parts is given.Starting from this basic assumption,the method for determining the characteristic length of fatigue damage zone in the new model is created.Combined with finite element analysis,the characteristic length of fatigue failure zone of different notched parts of 2A12 aluminum alloy was determined.Mathematical expression of the power function form of S-N curve of 2A12 aluminum alloy material obtained by least square method.The new model predicts the fatigue life of the 2A12 aluminum alloy center circular hole notched plate,the central waist hole notched plate and the double U-shaped notched plate specimen.The new model prediction results are compared with the nominal stress method,the stress field strength model,and the test results.(3)The problem of size factor is not considered when predicting fatigue life by local stress-strain method.Based on the previous research,the paper also considered the influence of stress gradient and size factor,and makes a simple correction to the fatigue strength coefficient.The relevant performance parameters and fatigue test data of 45# steel(tempered and tempered)double-sided U-shaped notched parts and double-sided semi-circular notched parts are quoted,calculating the corrected fatigue strength coefficients and analyzing fatigue life prediction results before and after correction.