Rendered Harmless Of Surface Crack With Different Crack Aspect Ratio In Ultrasonic Peened Sts316l Steel

The effect of ultrasonic peening (UP) on tension fatigue limit of Ni 12% STS316L steel with a surface crack was investigated. UP was conducted on the specimens with a surface crack of aspect ratio, a/c=1.0 and 0.4, where a denotes the crack depth (a=0.1, 0.2, 0.3, 0.4 and 0.5 mm), and c denotes the half-length of surface crack. Tension fatigue tests were conducted under stress ratio, R=0.1. The result showed that the fatigue limit of the UP specimens having the crack below 0.3 mm in depth was almost same as that of the UP smooth specimens. Thus, the maximum depth of crack with various aspect ratios that can be rendered harmless was less than threshold stress intensity factor of the material. The estimated values were in good agreement with experimental values. According to the estimation method, a harmless crack assessment diagram was proposed.