Nummerical Simulation Of Microdynamic Fatigue Crack Initiation Of Ultrafine Crystals Based On Crystals Plastic Mechanics

As a nonferrous metal material closely related to human beings,pure copper has been widely used in the electronics industry,transportation,machinery,aerospace and other fields due to its excellent electrical conductivity,ductility,and wear resistance.Under actual service conditions,pure copper components are constrained by different boundary conditions such as bolts.Under service fatigue loads,pure copper will undergo small reciprocating deformations.This small reciprocating deformation will interact with the external boundary constraints,resulting in wear and damage to the contact surface of the component,causing fretting fatigue failure.Therefore,in order to ensure the service safety of pure copper components,it is extremely necessary and urgent to understand and master the fretting fatigue failure mechanism and life prediction.This article takes ultrafine crystal pure copper as the research object,it has higher strength and hardness than pure copper,and has a broaderapplication prospect.In order to promote the potential industrial application of ultrafine-grain pure copper,it is an important task to comprehensively understand the fatigue failure mechanism of this material to carry out fretting fatigue research on ultrafine-grain pure copper.First,in order to describe the mechanical behavior of ultrafine-grain pure copper,the constitutive model of ultrafine-grain pure copper was established based on crystal plasticity theory,and the fretting fatigue behavior of ultrafine-grain pure copper was analyzed;Based on this,a grain orientation rotation method is proposed to predict fatigue crack initiation.Finally,the mature fatigue indication parameter method is used to verify the prediction results of the grain orientation rotation method.The main research contents and related innovations are as follows:1.Consider the microstructure and mechanical properties of ultrafine-grain pure copper,use crystal plasticity theory to establish the constitutive model,combine the experimental data to fit the ultrafine-grain pure copper constitutive model parameters,and apply the set of parameters to the fretting fatigue.In fatigue simulation,the crack initiation of ultrafine-grained pure copper under fretting fatigue was explored.2.Based on the theory that the plastic deformation of the metal material will cause the rotation of the lattice,it is proposed that by analyzing the rotation angle of the grains on the surface of the test piece and the surface unit of the grain surface,it is believed that the grain unit with a large change in the rotation angle of the grain is prone to crack initiation.This method is named as theorientation update deviation method,and its prediction result is compared with the mature fatigue indication parameter method,and the result shows that the prediction accuracy is good.3.Detect the influence of different loads and surface microstructure on the crack initiation position of the specimen.Firstly,by controlling the load of the specimen to be unchanged,then the orientation change amplitude method and the fatigue indication parameter method are used to predict the crack initiation of the surface grains of the specimen with different initial orientations.Both methods predict the same grain,the orientation change amplitude method predicts that the increment of the rotation angle of the grain unit with the largest change increases by 0.5229°,and the maximum cumulative plastic slip P value predicted by the fatigue indicator parameter method is 0.5834.Finally,by controlling the position of the grains on the surface of the test piece unchanged,the comparison between the two methods of predicting crack initiation under different load conditions was explored.The results show that the grain position predicted by the orientation change amplitude method is consistent with the fatigue indicator parameter method.