Improvement of fatigue limit by shot peening for high-strength steel containing a crack-like surface defect

Purpose - The paper's aim is to investigate the effects of shot peening (SP) on the bending fatigue limit of high-strength steel containing an artificial semi-circular slit. Design/methodology/approach - SP and stress SP (SSP) were conducted on the specimens containing an artificial semi-circular slit with a depth of a = 0.1, 0.2 and 0.3 mm. Then, bending fatigue tests were conducted on the specimens. Findings - The fatigue limit was improved by SP and SSP. In the case of SP and SSP specimens, the specimens with a semi-circular slit under a = 0.2mm fractured outside the slit, and they had considerably high fatigue limits. Therefore, a semi-circular slit with a depth of under a = 0.2mm could be rendered harmless by SP or SSP. It was found that the fatigue limit of specimens with a semi-circular slit that received SP or SSP was determined by the threshold condition for non-propagation of fatigue cracks that emanated from outside the slit. Whether the semi-circular slit is rendered harmless or not is decided by the relationship between the stress intensity factor range of semi-circular cracks and the threshold stress intensity factor range. Practical implications - The proposed method can be applied to mechanical parts used in vehicles, aircraft and trains. Originality/value - There are very few examples of evaluations of fatigue limits after SP in materials containing crack-like surface defects. This study calcifies the effect of SP on the fatigue limit having crack-like surface defects.