金属的切削加工工艺过程相当的复杂，其不仅与多种力学有关，还会波及到摩擦学以及材料、工艺等多种不同的学科。在多种切削加工的过程中，工件内部会形成残余应力，其会对工件造成影响，导致工件变形或断裂，从而影响到工件表面的加工质量，甚至会影响材料的抗腐蚀性、强度性等的钣金性能。
随着工艺技术的不断发展，对的应力循环数和可靠性的要求也随之增高。为了使工件的应力循环数延长，就一定要提升工件表面的加工质量，而加工表面层物理力学性能状态会对工件的应力循环数有着一定的影响。
在过程中表面所形成的残余应力会导致裂纹的形成，而且还会影响裂纹的开口、裂纹等的扩展。残余应力分成拉应力和压应力两种，在一般情况下，残余拉应力会导致已经加工表面形成裂纹，并且另其扩展，影响疲劳强度;反之，残余压应力会提升工件的疲劳寿命，借助于抵消部分拉应力，减慢疲劳裂纹的扩展。
残余应力对工件应力循环数的影响十分复杂，这与工件材料的弹性、外部应力情况和使用环境有着密切的联系，同时也与表面残余应力的强弱和分布相关。钣金加工过程中残余应力的形成原因十分复杂，包括钣金加工工艺、工作特性、刀具几何形状等多种因素。
The process of metal cutting is quite complex. It is not only related to many kinds of mechanics, but also to tribology, material and sheet metal processing. In the process of various machining, the residual stress will be formed inside the workpiece, which will affect the workpiece, cause the deformation or fracture of the workpiece, and affect the machining quality of the workpiece surface, and even affect the corrosion resistance and strength of the sheet metal.
With the continuous development of technology, the requirement of stress cycling and reliability for sheet metal processing has also increased. In order to prolong the stress cycle of the workpiece, it is necessary to improve the machining quality of the workpiece surface, and the physical and mechanical properties of the machined surface will have a certain influence on the number of stress cycle of the workpiece.
The residual stress formed on the surface during sheet metal processing will lead to the formation of cracks, and will also affect the expansion of cracks, cracks and so on. The residual stress is divided into two kinds of tensile stress and compressive stress. In general, the residual tensile stress will lead to the formation of cracks on the machined surface, and the other expansion will affect the fatigue strength. On the contrary, the residual compressive stress will improve the fatigue life of the workpiece, and help to counteract partial tensile stress and slow the expansion of fatigue crack.
The effect of residual stress on the stress cycle number of the workpiece is very complex, which is closely related to the elastic, external stress and the use environment of the workpiece material, and it is also related to the strength and distribution of the surface residual stress. The cause of residual stress in sheet metal processing is very complicated, including sheet metal processing technology, working characteristics, tool geometry and so on.
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