2007 年 2007 巻 52 号 p. 9-13
Effects of shot peening on the bending fatigue strength of spring steel specimens (SUP9A) containing an artificial small hole were investigated. Shot peening (SP) and stress shot peening (SSP) were carried out with the specimens containing an artificial drilled hole 0.2, 0.4 and 0.8 mm diameter. Then, bending fatigue tests were carried out with the specimens. The fatigue strengths of specimens containing an artificial small hole were increased by shot peening. Stress shot peening (SSP) was effective in improving fatigue strength. The specimens containing an artificial hole 0.2 mm diameter which received shot peening fractured elsewhere the hole, and they had considerably high fatigue strengths almost equal to those of the shot peened smooth specimens. It was found that the fatigue limit of specimens having an artificial hole of under 0.2mm diameter determined by the threshold condition for non-propagation of fatigue cracks emanated outside the drilled hole. From these results, it can be concluded that an artificial drilled hole under 0.2 mm diameter could be made acceptable by shot peening.