Research On The Theory And Key Technology Of Residual Stress Relief Based On Electriopulsing Method

Considering the limitation of traditional residual stress relief technologies, a method based on electropulsing stress relief was presented in this dissertation, and its theory and several key technologies were investigated.In chapter 1, the research significance and contents of this dissertation were presented. First, the generating model and categorizing method of residual stress were analyzed, and the hazard of residual stress and the significance of eliminating residual stress were pointed out. Secondly, the present research status of residual stress relief technologies and measurement methods at home and abroad was reviewed, as well as the electropulsing treatment technology. Finally, a new method was advanced which used electropulsing treatment to remove residual stress, and the primary contents of this dissertation were generalized.In chapter 2, the microscopic mechanism of the electropulsing stress relief method was researched based on electro-dislocation dynamics. First, the microscopic resistance force to actuate baffled dislocation was calculated by analyzing the basic configuration of dislocation and its influence on residual stress; in addition, the flow stress of material strengthening was derived. Secondly, the instantaneous thermocompression stress and the electron wind force of high-energy electropulse which drove dislocation were obtained. Finally, the microscopic acting condition of electropulsing stress relief method was established based on electro-dislocation dynamics.In chapter 3, the finite element numerical calibration technique for the calibration constants in the hole-drilling method and the measurement technique of the incremental hole-drilling method for constructing non-uniform residual stress were researched. First, the calibration process of mechanical tensile test was simulated with the finite element numerical analysis technique; and an agglutinate 3-D model of a workpiece and a strain rosette was built up in ANSYS; furthermore, the influence parameters on the calibration constants a and-b was analyzed, including the specimen's pasting-plane side length, the workpiece thickness, the hole diameter and the drilling depth. Secondly, the incremental hole-drilling method was used to measure non-uniform residual stress, and the calibration constants matrix ani, and-bni were calculated by a dividing-layer loading method; moreover, a practical measurement technology of five-step incremental hole-drilling method was established. Finally, the residual stress in Cr12MoV quenching specimens was measured contrastively by the direct hole-drilling method and five-step incremental hole-drilling technology.In chapter 4, an electrical pulse generating device was developed for electropulsing stress relief method. First, the RLC equivalent circuit of the capacitor discharge loop was established, and the generating condition of pulse current was analyzed, as well as the influence of each circuit parameter on characteristic of the pulse current. Secondly, the master control unit was developed based on MCU which controlled the charge and discharge switches for automatic operation, then the electrical pulse generating device was built up. Finally, the pulse current produced by the electrical pulse generating device was tested.In chapter 5, experiments were carried out to study the electropulsing stress relief method. First, the experimental system was constructed with the developed electrical pulse generating device, and the hole-drilling method was used as quantitative evaluation standard; furthermore, experiments were carried out to study the influence of four electrical parameters on residual stress relief effect, including the peak of pulse current Im, the pulse widthτ, the pulse recurrence frequency f and the electropulsing stress relieving times p. Secondly, based on the metallographic analysis and microhardness testing techniques, the impact of the electropulsing method on the micro structure configuration of the specimen was investigated. Finally, the temperature rise of the specimen and the change of pulse current were investigated during the process of electropulsing stress relief.In chapter 6, the quantitative evaluation technique of electropulsing stress relief method was investigated based on electrical-parameter rule. Based on the multivariate function approximation model, the quantitative evaluation model X(Im,τ,f,p) was established considering the current peak Im, the pulse widthτ, the pulse recurrence frequency f, and the electropulsing stress relieving times p. According to the constructed evaluation model, the impact of each electrical parameter or their combination on the residual stress relieving effect was investigated. In chapter 7, the achivements of this dissertation were summarized, and future research work for further study was prospected.