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

Abstract

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 ¼ 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 ¼ 0.2 mm fractured outside the slit, and they had considerably high fatigue limits. Therefore, a semi-circular slit with a depth of under a ¼ 0.2 mm 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.

Effects of laser peening on the fatigue strength and defect tolerance of aluminum alloy

“…Takahashi et al clarified that the fatigue strength of spring steel specimens with artificial surface defects could be improved with SP by the same level as that attained in the cases of defect-free steel specimens subjected to the same SP. 14,15 Similar effects of SP and needle peening have been reported in various other materials for the rendering of harmless surface defects. [16][17][18] Specifically, Takahashi et al clarified that semicircular slits with depths of 0.1 mm in the aluminum alloy A7075-T651 could be rendered harmless by performing SP.…”

Fatigue assessment and failure analysis of shot‐peened leaf springs

“…Therefore, surface treatment methods providing an enhanced surface strength are gaining increasing importance in many fields of applications. Shot peening 3–8 is a well‐known mechanical surface treatment process improving the surface strength of engineering components by creating compressive residual stresses in the specimen's surface. Thereby, small spherical media (shots) bombard the surface of the component (peening) by means of turbines fixed in the near of the component's surface.…”

Increase in Strength of Partially Stabilized Zirconia After Shot Peening

“…Compressive residual stress is generated by the localized plastic deformation of the surface layer. SP can increase the fatigue strength of metals because the compressive residual stress prevents fatigue crack initiation and propagation [3][4][5]. Takahashi et al carried out bending fatigue tests using high strength steel specimens containing surface cracks subjected to SP, and reported that a surface crack that reduced the fatigue limit by 50% could be rendered harmless by SP [3].…”

“…SP can increase the fatigue strength of metals because the compressive residual stress prevents fatigue crack initiation and propagation [3][4][5]. Takahashi et al carried out bending fatigue tests using high strength steel specimens containing surface cracks subjected to SP, and reported that a surface crack that reduced the fatigue limit by 50% could be rendered harmless by SP [3]. Fernández-Pariente reported that SP was able to improve the fatigue strength of low-alloy steel specimens with pre-existent defects, regardless of the defect type [4].…”