Research On The Mechanisms And Related Experimtents Of Controlling Residual Stress In Carbon Steel Based On Pulse Current Method

Based on the National Natural Science Foundation of China "Research on the pulse current method for the residual stress relief and its basic application" and the Aeronautical Science Foundation of China "Study on the Key Techniques of Stabilizing Treatment for High Precision Accelerometers",the mechanisms and the related experiments of controlling residual stress in carbon steel based on pulse current method were studied.In chapter 1,the research background,significance and contents of this dissertation were presented.First,the origins,categorizing methods,measurement methods of residual stress and its effects on the properties of workpieces were analyzed,and the significance of controlling residual stress was introduced.Secondly,the researches on residual stress control techniques and the electric pulse current applications in materials processing were reviewed.Furthermore,the present researches of pulse current method for controlling residual stress at home and abroad were reviewed emphatically,and the deficiencies of the present researches were pointed out.At last,the main contents of the dissertation were presented.In chapter 2,the mechanism of residual stress relief based on the multi-scale mechanics theory was studied.First,the continuum mechanics model of residual stress relief was built,and the relationship between the macro elastoplastic deformation and residual stress relief was established.Secondly,the relationships between crystal shear strain rate and dislocation slip or dislocation density,and the relationships between the elasto-plastic deformation of crystal grains and the residual stress relief were deduced respectively,and the problem of the mechanical scale transition from micro to macro was solved.Finally,the interaction between residual stress and dislocations was discussed based on the dislocation Newton's mechanics model,the thermodynamic model and the mechanism of dislocation density evolution.In chapter 3,the action mechanisms of pulse current on the dynamic behaviors of micro structures of carbon steel were studied.First,the electon drag force model of carbon atoms was built,and the effects of pulse current on the carbon atom diffusion and segregation in as-quenched 45 carbon steel specimens were analyzed.Secondly,the electron drag force model of dislocations was built,and the action mechanisms of electron drag force,Joule heat and microstructures on dislocation dynamic behaviors were studied.At last,the mechanical model for pulse current affecting martensite grain boundaries was built,and the mechanisms of the effects of pulse current on the martensite morphology were discussed,and the mechanisms of pulse current method for controlling residual stress by its action on the dynamic behaviors of micro structures were analyzed.In chapter 4,the influence of skin effect on pulse current method for controlling residual stress in carbon steel was studied.First,based on the Maxwell equations,the analytical expressions of electric field intensity,current density were deduced for the rectangular-cross-section conductor when the decay oscillating pulse current passed through.Secondly,the influences of skin effect on electron drag forces on carbon atoms and dislocations were analyzed,and then its influences on residual stress were also discussed.In chapter 5,the mechanisms of the pulse current method for controlling residual stress were studied using experiments.First,the experimental system for the pulse current method controlling residual stress in the metal specimens was improved.Secondly,the effects of pulse current on the mechanical properties of as-quenched 45 carbon steel specimens were studied,including residual stress,tensile property and surface hardness.Finally,the effects of pulse current on the micro structures were studied,including the distribution of carbon atoms,dislocation density and martensite morphology.According to the experimental results of the effects of pulse current on the mechanical properties and micro structures of as-quenched 45 carbon steel specimens,the mechanisms of pulse current method for controlling residual stress were proved.In chapter 6,the achievements of the dissertation were summarized,and the future research work was prospected.