2010 年 2010 巻 55 号 p. 31-38
In recent years weight reduction of suspension springs has been increasingly required from the viewpoints of improvement in fuel efficiency of automobiles and global environmental concerns. To realize further weight saving of the suspension spring, it is important to increase its fatigue strength and it is imperative to understand shot peening techniques, which affect improvement in the fatigue strength. However, the relation between surface roughness, residual stress distribution, which affects the fatigue strength, and shot peening conditions has yet to be sufficiently clarified while it is qualitatively comprehended. Moreover, the quantitative relation between the surface roughness, the residual stress distribution, and the fatigue strength has also not been fully understood. If the fatigue strength can be predicted quantitatively from the shot peening conditions, shot peening can be used as a tool for the optimal design of the suspension spring. This quantitative prediction will also be very useful in knowing processing conditions to improve the fatigue strength. In this study, various shot peening conditions, such as shot size and spring steel hardness, were examined to obtain a regression formula to estimate the residual stress and the surface roughness. Further, a method to predict the fatigue limit from the regression formula and the fracture mechanics was examined, and its practicality was verified.