After pneumatic shot peening, compressive residual stress is induced on the surface of the target, which will improve the fatigue life. During the process, surface roughness is also induced, which may reduce the fatigue life. To achieve the optimum compressive residual stress with the smallest surface roughness, the formation mechanism of the residual stress field and the surface topography are revealed. Then, pneumatic shot peening is simulated by using a discrete element method–finite element method coupled model. Based on the effects of four variables (the incident angle θ, the initial shot velocity v0, the shot radius R) and the mass flow rate rm on five parameters (the equivalent plastic strain, the equivalent stress, the surface compressive residual stress, the maximum compressive residual stress), the surface roughness is investigated. The results show that it induces a residual elastic–plastic strain after the impact of a single shot, which can form a crater and a hemispherical residual stress field. After the impact of many random shots, scattered craters connect with each other, therewith a rough and continuous surface topography is formed. Scattered residual stress fields couple with each other, and a constant residual stress layer with the compressive residual stress in the surface and the tensile residual stress in the subsurface are formed. All five parameters are determined by the residual elastic–plastic strain, which increases as the augment of the normal impact velocity, the shot mass, and the coverage rate. Along with the increase of θ and rm, these five parameters firstly increase and then decrease; with the increase of v0 and R, these five parameters increase. Therefore, reasonable values of θ, v0, R, and rm should be chosen to obtain the optimum compressive residual stress with as small surface roughness as possible.

中文翻译：

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离散元-有限元耦合模型气动喷丸后残余应力与表面形貌研究

气动喷丸后，靶材表面产生残余压应力，提高疲劳寿命。在此过程中，还会引起表面粗糙度，从而降低疲劳寿命。为了以最小的表面粗糙度实现最佳的残余压应力，揭示了残余应力场和表面形貌的形成机制。然后采用离散元法-有限元法耦合模型对气动喷丸进行模拟。基于四个变量（入射角θ、初始发射速度v）的影响0、喷射半径 R) 和质量流量 r米在五个参数（等效塑性应变、等效应力、表面残余压应力、最大残余压应力）上研究表面粗糙度。结果表明，单发弹丸撞击后会产生残余弹塑性应变，形成弹坑和半球形残余应力场。经过多次随机射击的撞击后，分散的弹坑相互连接，形成粗糙且连续的表面形貌。分散的残余应力场相互耦合，形成表面残余压应力、亚表面残余拉应力的恒定残余应力层。所有五个参数均由残余弹塑性应变决定，残余弹塑性应变随着法向冲击速度、弹丸质量和覆盖率的增加而增加。随着θ和r的增加米，这五个参数先增大后减小；随着v的增加0和R，这五个参数增加。因此，合理的θ、v取值0、R 和 r米应选择以获得最佳压缩残余应力和尽可能小的表面粗糙度。