Shot Peening On Torsion Fatigue

Author:  J. He, Y. Wu, Y. Yu, J. Flavenot
Source:  Conf Proc: ICSP-3, (p.619-624)
Doc ID:  1987086
Year of Publication:  1987
Abstract:  
The effect of shot peening on bending fatigue has been well documented. Compressive residual stress, work hardening and surface topography are of major factors which influence the bending fatigue strength. When a crack initiates in the sub-surface layer, surface topography will be less important and the compressive residual stress may keep the crack from going through the outer layer to the vary surface. For torsion fatigue, the loading stress is shear stress. Since the mean stress during cyclic torsion does not change the fatigue strength, naturally, the biaxial compressive residual stress induced by shot peening are thought to be of little effect on torsion fatigue strength. Most papers claimed that hardness is the only factor which influences to the torsion fatigue behaviour. But the experimental facts show that the fatigue strength of spiral spring, which is mainly under torsion load, can be greatly improved by shot peening with no much change in hardness. This paper trys to clarify the effect of biaxial compressive residual stress on reverse torsion fatigue limit. Presetting is often employed in spiral spring manufacturing, and prestrain is proved to be beneficial for bending fatigue, but for torsion it needs to be clarified. So prestrain was also carried out to examine its effect on torsion fatigue behaviour.