Numerical Simulation Of Mechanical Properties And Prediction Of Grain Size In Shot Peening

Among many surface treatment technologies,the shot peening surface treatment technology is very mature,which can improve the physical properties of metal surface.In terms of mechanical properties,metal strengthening is caused by residual stress.In terms of microscopic,metal strengthening is caused by grain refinement,dislocations,phase transitions and unit cell changes.In this paper,the effects of various factors on the residual stress and grain size in shot peening treatment are studied.The relationship between residual stress and grain size was also studied.Main tasks as follows:In order to study the deep physical mechanism of shot peening,a projectile impact mechanics model was established.Dyna software was used to study the influence of various factors on residual stress,mainly through the following methods: the variation of the maximum and minimum residual stress,the distribution of residual stress and the radiation range of residual stress,etc.It is concluded that the increase of projectile velocity,projectile radius,and number of projectile impacts can increase the residual stress;the radius of the projectile can obviously affect the radiation range of the residual stress;the distribution of residual stress can be changed by changing the projectile impact angle;the specimen size has no effect on the residual stress.And two multi-point projectile impact distributions are used for analysis,one is the multi-point matrix distribution,and the other is the superposition rate distribution.Both distributions can change the size and distribution of the residual stress,which indicates that the impact distribution of multi-point projectiles can affect the residual stress.After the simulation results are obtained,the theoretical grain size was further compute by Zener-Hollomon model and dynamic recrystallization formula,and the effects of various factors on grain size were studied.The results show that the increase of the projectile velocity and radius can make the grain size smaller,and the increase of the projectile radius will make the grain refining range larger.The results of the residual stress and grain size are fitted by MATLAB,and the fitting function is obtained.After comparative analysis,the variation trend of residual stress and grain size is similar.The results show that grain refinement is one of the factors causing residual stress of metal,but the residual stress is also related to other microstructure.