표면 상태를 고려한 표면균열재의 하한계응력확대계수 및 피로한도의 평가

Abstract

Abstract

This study evaluated the threshold stress intensity factor and fatigue limit of surface cracking materials according to the variation of stress ratio and aspect ratio with reference to fatigue limit of gentle grind specimen, severe grind specimen and shot peened severe grind specimen. Surface cracks in the gentle grind specimen, severe grind specimen and shot peened severe grind specimen could evaluated the threshold stress intensity factor and the fatigue limit according to stress ratio and aspect ratio using the equivalent crack length. As the surface crack length increased, the fatigue limit decreased rapidly as a small stress ratio and a large aspect ratio. On the other hand, the depth of surface cracks decreased rapidly as a small tress ratio and aspect ratio. As the surface crack length increased, the threshold stress intensity factor rapidly increased at a small stress ratio and a large aspect ratio. On the other hand, the surface crack depth rapidly increased at a small stress ratio and aspect ratio. The reduction ratio of the fatigue limit at the surface crack length of the same stress ratio is more larger than 0.4 in aspect ratio 0.1. However, the surface crack depth is larger than 0.1 in aspect ratio of 0.4. On the other hand, in the surface crack length of the same stress ratio, the rate of increase of the threshold stress intensity factor is smaller than 1.0 in the aspect ratio 0.4, but the surface crack depth is larger than 1.0 in the aspect ratio 0.4. This is because, when the aspect ratio became large, crack propagates in the depth direction than the surface direction, and propagtes at the same time when it becomes similar to the surface crack length.