Effect Of Elastic-plastic Contact Of Metal Machined Surface On Micro-compression Behavior

Uncder the condition of micro contact machine tool joint surface compression curve in the early performance for nonlinear rule and the degree of nonlinear is related to machine materials heat treatment and machine materials processing methods and technology,with side materials,contacting size and pre-loading and so on.Despite the pre-deformation,non-linear extent reduced,but still can not eliminate and no rules to foIlow.But this stress-strain non-linear law due to,"error copying principle" results in actual use is magnified hundreds of times or even thousands of times,seriously affecting the controllability of precision machine tools.Existing machine precision controlling is based on the linear law of elastic deformation carried out by the compensation mechanism,but the law is non-linear random variation,making the compensation mechanism difficult to execution,thereby constraining the development of the machine.This article chose 40Cr,45steel,38CrMnAlA,HT250,AZ91D magnesium alloy,316 stainless steel and CrAlYN/HSS and so sample micro compression experiments;and combined with changes of the sample surface roughness and the microstructure,the degree of hardening of the material and the 45steel tensile and flexural test results,exploring the causes and nature of nonlinear law of conta.cts formed elastic coefficient.Results show that under the micro compression condition,40Cr,45steel,38CrMnAlA and HT250 machining surface contact nonlinear change of elasticity coefficient(K)is caused by compression surface elasto-plastic contact,at the same compression process,due to the processing surface occur elasticity and partial plastic deformation,the K value is changing;Different compression under the condition of the same sample K to steady-state value Kmax corresponding to the largest nonlinear strain(?' Max)is different.Sample of epsilon 'Max size not only depends on the machining surface contact morphology;at the same time with the material of plastic deformation in the process of compression resistance change.Compression process,the material initial surface roughness,the greater the nonlinear degree,the more obvious,?' max the greater.Initial surface roughness was 1.108 ?m and 1.153 ?m of 45 steel specimen after deformation ?'max were 0.83×10-3 and 0.88×10-3;The degree of nonlinearity degree of plastic deformation of the specimen sample K showed a positive correlation.Under the same compression times,the degree of change in the surface asperity height was 15%and 11%of the samples,?'max decreased by 51.6%and 45.3%;Secondary hardening capacity of the material is stronger,Kmax samples more easily reach steady state,the compression process ?'max more rapid change.Among them,316 stainless steel,AZ91D magnesium alloy and CrAlYN/HSS samples after compression ?'max were reduced by 38.4%,1.7%and 0.9%compared with before compression.While 316 stainless steel compression times to reach steady state ?'max only 4 times,and AZ91D magnesium alloy and CrAlYN/HSS samples were compressed 10 times Kmax not yet reached steady state.The essentially reason for material nonlinear deformation in micro-compression deformation is non-homogeneous materials in the direction of the force caused by plastic deformation resistance.The greater the degree of heterogeneity,material nonlinearity is more significant.The degree of heterogeneity were 73%and 77%of the 45 samples,its composite yield strength compared to the base were increased by 8.1%and 11%.The degree of heterogeneity are 73%45 steel samples,composite tensile yield strength increased by 8.1%.The four-point bend test,as the surface of the sample contained a greater degree of bending composite yield strength increased by 23.7%.The impact caused by the elastic-plastic contact with the accuracy of the sample was ?'max workpiece thickness multiples enlarge.The thickness of the micro compression test specimens respectively of 5 mm and 5.5 mm,a difference of 0.5mm.When ?'max equal,the largest non-linear displacement of the sample were 2.34 ?m and 1.68??m,1.45 times the displacement difference.In actual use,reduce stress in the metal processing surface plastic deformation process,and the proportion of non-uniformity of deformation is controlled material micro compression stress-strain nonlinear nature of the reasons for the law.