Fatigue Life Prediction Of Friction Stir Welding Ladders With Magnesium Alloy

Friction stir welding is the British Welding Institute in 1991 invented a solid state welding technology.However,with the deepening of the research of friction stir welding technology,it is found that the hook defect occurs in the overlapping area.This defect is inevitable,and it is also a crucial factor affecting the fatigue strength of the lap joint.Also affect the fatigue strength of the lap joint hook height of the hook,hook tip radius and the hardness of the weld area distribution.In particular,when the lap joint is subjected to the load,its stress state is very complicated,it is difficult to use the experimental method to analyze it,so this paper uses the finite element simulation method to simulate the analysis of the weld zone stress and strain,and based on The results show that the fatigue life of overlapped joints is predicted by local stress-strain method.The research content of the paper has the following aspects:Firstly,the finite element model is established according to the size of the weld specimen and the defect shape of the hook,and the material properties of the weld area are assumed to be consistent with the upper plate.This is to determine the fatigue life prediction model.It is found that the stress concentration and strain concentration occur at the hook area of the weld joint area of the joint joint,and the area of the high stress area formed around the tip of the hook increases with the increase of the load.In addition,the stress and equivalent plastic strain amplitude of the weld will reach the peak in this area.The local stress-strain method is used to predict the life of the lap joint and compare the predicted results with the experimental results.When the fatigue damage equation SWT The error in the life prediction of the lap joint is twice that of the fatigue failure equation,and the fatigue error of the overlapped joint can be predicted by the SWT fatigue damage equation.Secondly,the effect of the effective thickness on the lap joint is studied.It is found that the distribution of the stress and the equivalent plastic strain amplitude in the weld zone are the same as the effective thickness decreases.The fatigue life of the lap joint increases with increasing effective thickness.Then,the influence of the tip radius of the hook on the fatigue strength of the lap joint was studied.It was found that the stress distribution of the weld zone and the distribution of the equivalent plastic strain amplitude gradually decreased with the increase of the tip radius of the hook,and the fatigue life The tip radius increases and gradually increases.Finally,by analyzing the influence of hardness on the fatigue life of the overlapped joints,it is found that the stress distribution and the value of the stress are very close to the stress distribution considering the hardness distribution and the hardness distribution,but the equivalent plastic strain amplitude is in the numerical value The gap on the larger.Through the comparison of the results of life prediction,it is found that the error between the predicted value and the real life is within two factors,but the prediction error of the hardness distribution is smaller.