| Metallic components tend to fatigue fracture when subjected to alternating loads,while shot peening is a surface strengthening process that can substantially increase the fatigue strength of structural members.The residual compressive stress on the shot peening surface can partially offset the external load,which is the main strengthening factor recognized by now to improve the anti-fatigue performance.However,the surface of the shot-peening due to the impact of the projectile becomes uneven,the roughness tends to increase,resulting in increasing stress concentration factor or the appearance of surface microcracks,which is considered as a weakening factor to reduce fatigue strength.Therefore,the overall goal of this research is based on the new modeling theory or method,from the positive and negative aspects of the comprehensive exploration of the mechanism of shot peening to optimize the shot-peening process parameters to improve the effectiveness of shot peening for providing technical support for the reasonable choice of shot peening parameter in actual industrial production.The scientific significance of carrying out the above research lies in comprehensively analyzing the effect of surface roughness and residual stress of shot peening on the fatigue life.But most of the existing studies only study the strengthening effect of residual stress of shot-peening while ignoring the weakening effect of surface roughness of shot-peening,Or only to study its weakened effect without the combined effect of the two points.In this paper,the effect of different pellet parameters on residual stress,surface topography and fatigue life of shot peening was analyzed through experiments and simulations,in order to obtain an optimized parameter with the goal of improving fatigue life.In the simulation research,the mechanism of reducing the fatigue life of shot-peening surface roughness and the inhibition mechanism of the residual stress field on crack propagation were revealed.The main contents of this paper are as follows:(1)Firstly,the surface of the aluminum alloy was treated by different shot-peening processes,and then the surface morphology and residual stress distribution of the samples were analyzed by optical profiler and X-ray stress diffractometer.The three factors and two levels orthogonal test was conducted to study the influence of the size of pellets,projectile material and shot-peening method on the fatigue tensile properties from a statistical point of view.The experimental results show that the enhancement of the fatigue property of 2024 aluminum alloy by shot-peening is mainly caused by the combined effect of residual compressive stress and surface roughness.(2)This article is proposed a method for calculating the surface roughness of shot-peening and predicting the crack initiation life by numerical simulation.Firstly,the numerical model of multi-shot peening was established by using ABAQUS finite element software.Then an orthogonal experiment was carried out to study the effects of pellet size,pellet material,impact speed and the number of projectiles on the surface roughness,which chose R(?)and Rsm as the surface roughness parameter,and then analyze the effect of surface roughness on stress concentration factor and fatigue crack initiation life.The results show that the fatigue notch coefficient is affected by the surface morphology parametersR(?)andRsm of the shot peening specimen.The fatigue crack initiation life is not dominated by a single surface topography parameter but closely related to the fatigue notch coefficient.(3)According to the theory of crack propagation,the finite element software ABAQUS and the fatigue analysis software MSC.fatigue were used to establish a simulation model.The feasibility of the simulation was verified by the fatigue test.From the statistical point of view,using the parametric model of shot-peening and the orthogonal simulation test to study the effects of impact velocity,pellet diameter,pellet material on the crack propagation performance under alternating tensile load.The results show that:the crack growth life by shot-peening mainly in two aspects:Increase in crack termination size,and decrease in crack growth rate.The diameter of the pellet is almost linearly correlated with the crack propagation life;the increase of shot-peening speed has a gain effect on the crack propagation life,but the gain effect gradually decreases with the increase of the velocity to a certain degree;the material of the pellet also has a significant effect on fatigue life,The harder the material,the more significant the impact. |
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