Research On Residual Stress Relaxation Behavior For Rolled Pure Copper In Heat Treatment

During the processing of thin-walled and weakly rigid parts,the release of initial residual stress inside the part will cause deformation of the part,and finally affect the machining accuracy.To guarantee the accuracy of machining,it is great important to predict and control the deformation caused by the release of initial residual stress.For this reason,it is urgently needed to obtain the initial residual stress inside the part.In this paper,multi-pass rolling and heat treatment were used to get the thin-walled plate of copper.A novel model of stress relaxation is proposed based on the classic creep model to study the relaxation of residual stress inside the rolled copper plate during heat treatment.Then,based on the numerical model and Abaqus software,a finite element model of rolling and heat treatment was created to obtain the residual stress field after rolling and heat treatment.In addition,the plate is easily deformed during the process of clamping,especially for the part having a large flatness error.In this paper,the copper plate with large flatness error after heat treatment was pressed at high temperature to reduce this error.A finite element model was established to analyze the feasibility and obtain the residual stress field after pressed at high temperature.The detailed research is listed as bellow:(1)Copper plates with different initial hardening states were obtained through the multi-pass rolling by controlling the ratio of rolling,and then micro-hardness and dislocation density was measured to characterize the hardening states.(2)A novel numerical model of stress relaxation,considering the influence of hardening state and recrystallization,is proposed based on the classic creep model.Recrystallization experiment and stress relaxation test for the copper plates with different initial hardening states were conducted to calibrate the parameters of the model.(3)A finite element model of rolling was created to obtain the residual stress field of rolled copper plate.And the established numerical model was implemented into the software Abaqus through the creep subroutine to create a finite element model of heat treatment,which simulates the relaxation of residual stress at high temperature.Finally,the residual stress field after rolling and heat treatment was obtained.The residual stress was measured to verify the calculated accuracy of these finite element model.(4)The plate with large flatness error was pressed at high temperature to reduce this error,and a finite element model was created to analyze the feasibility and obtain the residual stress field by simulating the relaxation of residual stress.The flatness error were measured to verify calculated accuracy of the finite element model.