喷丸强化对车辆传动齿轮裂纹扩展影响的研究综述

疲劳断裂是重载车辆传动齿轮的主要失效形式之一，齿轮底部疲劳裂纹的扩展将缩短车辆传动系统的服役寿命，严重时会导致车辆发生安全事故。延缓裂纹扩展的主要方法是在传动齿轮的表面引入一定大小的残余压应力。喷丸技术是一种冷加工表面强化处理工艺，该技术利用高速弹丸冲击材料表面，使零件表层产生塑性应变的同时，在表面和内部引入残余压应力，从而使裂纹闭合的能力得到强化，达到延缓裂纹扩展的强化效果。为了更好地揭示喷丸引入的残余压应力对疲劳裂纹扩展的影响，首先综述了传动齿轮表面疲劳裂纹产生的原因以及疲劳裂纹的扩展行为对重载车辆服役的影响。从强度因子、J积分以及裂纹闭合效应出发，介绍了传动齿轮表面疲劳裂纹扩展的理论以及残余压应力与疲劳裂纹扩展速率之间的关系。其次概述了目前国内外常用的新型有益于将残余拉应力转化为残余压应力的微粒子喷丸、激光喷丸、超声喷丸方法，并与传统机械喷丸技术相比较，阐述了新型喷丸表面强化技术的优缺点。此外，从数值模拟和试验结果两方面，论述了喷丸速度、喷丸角度、弹丸直径、弹丸材质和覆盖率5个工艺参数对在传动齿轮表面引入残余压应力的改善影响。最后对喷丸强化技术在传动齿轮上的多目标参数优化以及多尺度残余压应力与疲劳性能进行了展望，并结合重载车辆的使用需求，强调需要创新设计一种效率高、价格低、适用性广的喷丸技术，以进一步推动喷丸强化在延缓疲劳裂纹扩展方面的持续发展。

A Review on Effects of Shot Peening on Crack Growth of Vehicle Transmission Gears

Fatigue fracture is one of the main failure modes of the transmission gear of heavy duty vehicles. The service life of the transmission system of vehicles will be shortened due to the expansion of fatigue cracks at the bottom of the teeth, and serious accidents will occur. The generation of residual compressive stress is the main method to delay crack propagation. Shot peening technology is a surface strengthening process of cold working. When the plastic strain is generated on the surface of parts, the residual compressive stress is introduced on the surface and inside, so as to improve the crack closure effect and achieve the strengthening effect of delaying crack propagation. In order to better reveal the influence of the residual compressive stress introduced by shot peening on fatigue crack propagation, the surface of the transmission gear is usually susceptible to a variety of alternating loads, such as external thermal loads and force loads. Compared with static loads, the non-uniformity of the internal structure of the material under alternating loads has a greater influence on the fatigue damage resistance of the material. Fatigue causes tooth breakage. Based on the strength factor, J-integral and crack closure effect, the theory of fatigue crack growth on the transmission gear surface and the relationship between compressive residual stress and fatigue crack growth rate were introduced. The introduction of compressive residual stress could reduce the crack growth rate, improve the fatigue resistance index of fatigue crack, and reduce the stress intensity factor at the crack tip. The new methods of particle shot peening, laser shot peening and ultrasonic shot peening, which were beneficial to the conversion of residual tensile stress to compressive stress, were summarized. The particle shot peening was to use a smaller diameter projectile to impact the surface of a part at high speed, which could not only introduce compressive residual stress on the surface of the part, but also achieve higher surface finish requirements. Laser shot peening adopted shock wave to carry out high-speed impact, so there would be no additional mechanical damage and surface phase change on the surface of parts. The surface depth after ultrasonic shot peening was much higher than that after traditional shot peening. However, due to its high price or small applicability, it has not been widely used in the surface strengthening of vehicle transmission gears. In the future development, it is necessary to design the shot peening technology with high efficiency, high adaptability, low cost and less energy consumption. At the same time, the relationship between the new shot peening method and the traditional mechanical shot peening technology was described. In addition, based on the numerical simulation and experimental results, the influence of the selection of five process parameters including shot peening speed, shot peening Angle, shot diameter, shot material and coverage rate on the improvement of residual compressive stress introduced on the transmission gear surface was emphatically reported. The compressive residual stress did not increase with the increase of incident velocity and projectile diameter, but tended to be stable when it exceeded a certain limit. Large residual compressive stress could be introduced when the projectile vertically incident impacted the surface of the transmission component. On the other hand, the residual compressive stress increased with the increase of the projectile diameter in the range of 0.2-3.4 mm. Steel shot had a better ability to improve the fatigue strength, ceramic shot after shot peening could achieve better surface smoothness, the final residual compressive stress increased with the increase of shot peening coverage, but the surface coverage was also saturated value. Finally, the future research direction of shot peening technology in transmission gear was prospected, and the technological innovation was further carried out in combination with the use requirements of heavy-duty vehicles, so as to promote the sustainable development of shot peening technology to delay crack propagation. The special simulation of shot peening technology mainly focuses on the selection of single shot peening process parameters of gear, while the analysis of combined parameters is less. However, in practical application, it is necessary to comprehensively consider the influence of coupling effects of various parameters on the gear. Therefore, in future numerical simulation, it is necessary to combine the optimal combination of process parameters to further study the surface integrity of the gear surface after shot peening, such as corrosion resistance, wear resistance and oxidation resistance.