Research On Residual Stress Relaxation Based On Dislocation Density Evolution For Pure Copper

The residual stress is one of the factors affecting the machining accuracy for extreme manufacturing of weakly rigid components.The stress relief annealing is one of the most effective method to release the large tensile stress in controlling the deformation of the product.A novel residual stress relaxation model is proposed to predict the change of residual stress during annealing process by considering the dislocation evolution mechanism and the plasticity theory.When this novel model is used,only one state variable was necessary to be determined,which was more accurate and efficient to reveal the residual stress change mechanism in the annealing process.Hole-drilling experiments combined with electrical speckle pattern interferometry were conducted to measure the residual stresses for calibrating the proposed model.The calibrated model was then used to predict the change of residual stresses during annealing process.The results showed that the initial work hardening of components had a great effect on the residual stress relaxation.High initial dislocation density hindered the residual stress relaxation during the annealing process.The results provided guidance on optimizing the annealing conditions for residual stress reduction.The detailed research is listed as follows:(1)The pure copper plates were cold rolled with different rolling ratios.The workpieces were then annealed with different annealing parameters to control the residual stresses.Holedrilling measurement combined electrical speckle interferometry were conducted to obtain the change of residual stresses.(2)The novel model combining the dislocation density evolution theory and plasticity theory was proposed and then calibrated with the experimental measurements.The effects of initial hardening condition on residual stress relaxation was then studied,and the mechanism of residual stress relaxation was revealed.(3)The novel model was used to predict the residual stress change in the annealing process.A FE model was also established combined with this model to simulate the residual stress change in the workpieces.