Vibratory stress relief equipment is to apply equal amplitude alternating cyclic excitation force to the residual stress concentration of the component by vibration excitation equipment, and the component can obtain larger excitation stress under resonance state. The combined stress in a certain direction exceeds the yield limit of the material, where the yield deformation will occur, causing the residual stress relaxation and release, so that the residual stress is evenly distributed . This method can not only effectively reduce the peak residual stress, but also reduce the overall residual stress.
In order to eliminate or reduce the residual stress in the workpiece, the following conditions must be met:
(1) The total stress after the superposition of the residual stress inside the component and the vibration stress exerted by the exciter should exceed the yield limit of the material. That is s residual + s dynamic > SS, where s residual is the internal residual stress of the component, s dynamic is the induced vibration stress, and SS is the yield limit of the material.
(2) With the increase of vibratory stress relief equipment time, the residual stress will decrease due to plastic yield. When the residual stress is reduced to the new yield limit after superposition with the vibration stress, the internal stress will reach equilibrium and the dimensional stability of the component will be improved.
(3) The residual stress decreases with the aging vibration, and finally reaches equilibrium. If we want to continue to reduce the residual stress, we must increase the residual stress, otherwise the vibratory stress relief equipment is invalid.
From the micro point of view, the essence of residual stress reduction is the gradual release of elastic strain energy through some micro or local plastic deformation. There are a lot of dislocations in the crystal. Under the cyclic strain, the dislocations overcome the resistance to produce slip, which makes the crystal produce micro plastic deformation. The peak value of residual stress decreases, which makes the original internal stress field of the component change, and the internal stress decreases and redistributes, so as to achieve equilibrium. Under the continuous excitation of vibration alternating stress, the dislocation will be excited continuously. With the continuous cyclic stress applied to the component, the dislocation will become more uniform. The movement of dislocation, that is, the beginning of crystal yield, at this time the material begins to plastic deformation. The above process will reduce the stress in the stress concentration area and the peak value of residual stress.
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