Influence Analysis Of Cutting Parameters On The J-C Constitutive Coefficients Of IN718 Alloy And Research On Its Optimization

The Johnson-Cook(J-C)constitutive model is widely used in the finite element simulation of machining to describe the plastic stress-strain behavior of materials.The J-C constitutive model reflects the relationship between material stress and strain(?),strain rate((?))and temperature(T)through five coefficients(A,B,n,C and m).In view of the shortcomings in the application of J-C constitutive model coefficients in cutting simulation at present,the thesis formed an optimization method with good applicability by applying the law of influence of J-C constitutive coefficients of IN718 alloy on turning simulation results under low-high cutting conditions,and solved the problem that it is difficult to determine J-C model coefficients under large range of cutting parameters.On this basis,an influence link model of cutting parameters on J-C model coefficients was established,which was used to reveal the influence relation of cutting parameters on J-C constitutive coefficients and provided a new solution for improving cutting simulation accuracy.The research content of this thesis specifically includes the following four aspects:1.Carried out basic analysis of the J-C constitutive model of IN718 alloy.Through the adjustment of the parameters in the J-C constitutive model,the analysis of the influence of the five coefficients on the flow stress curve and the description of the dynamic mechanical properties of IN718 alloy were obtained.These conclusions laid the foundation for the following research contents.Based on the literature review,the existing problems of J-C constitutive model in cutting simulation application are summarized,such as the coefficients are difficult to determine and can be affected by cutting parameters.2.Established and verified a high-speed cutting simulation model.A three-dimensional finite element turning simulation model that accurately describes the high-speed cutting of IN718 alloy was established.The reliability of the model was verified by comparing the residual stress and chip thickness in the turning experiment and the simulation results.3.J-C model coefficients optimization method based on the impact analysis of simulation results.Through variance analysis of L¹⁸(2×3⁶)mixed orthogonal test,the sensitivity analysis and influence trend analysis of 5 coefficients and friction coefficients on cutting force,cutting heat,residual stress distribution and chip morphology in J-C model under low-high cutting conditions were realized.The results showed that the yield strength A,strain hardening index n and thermal softening coefficient m of the material in the J-C model have more significant effects on the residual stress and chip thickness.And as the cutting parameters increase,the impact of each coefficient on the simulation results will change significantly.According to the influence analysis of J-C model coefficients on simulation results,a general optimization method was formed to solve the problem that it is difficult to determine and improve J-C model coefficients under low-high cutting conditions.The error of cutting simulation prediction could be greatly reduced.4.Established the influence relation model of cutting parameters on the coefficients of J-C model.According to the above optimization results,combined with the relevant metal cutting theory,a relationship model between cutting parameters and J-C constitutive model coefficients was built.Then,to verify the above relationship model,on the basis of sensitivity analysis,the optimal J-C model coefficients under low-high cutting parameters were determined through the reverse identification method.The results prove that the cutting conditions have a decided influence on the J-C model coefficients.Different cutting conditions should use the corresponding J-C model coefficients for cutting simulation.