切削摩擦加工材の疲労特性に及ぼす負荷形式の影響

Abstract

Aiming for a result to improve fatigue strength, “cutting and rubbing process” which is a kind of surface treatment was used for forming a round-bar smooth-specimen, showing drastically enhanced rotating-bending fatigue strength. On the other hand, actual machine components and structures invariably contain geometrical irregularities, such as fillets, keyways, screw threads, and holes. Fatigue cracks initiated from such stress raisers, indicating that the validity of the cutting and rubbing process on fatigue strength of specimen with a stress raiser should be examined. In this study, fatigue tests of smooth and notched specimens finished by the cutting and rubbing process were conducted under some loading types including rotating-bending, tension-compression and torsion loading. Results showed that fatigue strength of notched specimens was significantly enhanced compared to that of smooth specimens under rotating-bending and tension-compression loads. In other words, the cutting and rubbing processing was more effective in stress raisers than the smooth surface. The physical background on the effect of loading type on the fatigue strength of the cutting and rubbing processed specimen was discussed based on the fracture origin, microstructure in the surface layer, stress gradient caused by both loading type and notch.