Reliability Evaluation of 0.57wt.% Carbon Steel for Springs with Different Types of Shot Peening

Springs acting as suspension systems can damaged by external collisions, such as those with stones. Corrosion pitting occurs in the damaged areas, and cracks will initiate and fracture. However, the allowable corrosion pitting size can be increased by inducing residual stresses via shot peening. In this study, residual stresses are induced through shot peening (SP) and stress shot peening (SSP). Then, the harmless crack depth (ahml), the crack depths (a25, a50) that reduce the fatigue limit of non-SP smooth materials by 25% and 50%, and the crack depths (ahml) that can be detected using non-destructive inspection (NDI) are evaluated. The residual stress affects ahml: the larger the residual stress, the larger ahml will be. The aspect ratio also affects ahml. Because both SP and SSP exhibit ahml> (a25, a50), (a25, a50) can be rendered harmless. Hence, (a25, a50) can secure the safety and reliability of the steel via SP and SSP. Because both SP and SSP exhibit (aNDI1, aNDI2) > (a25, a50), the crack depths of and cannot be detected using NDI.