ショットピーニング材の疲労寿命に及ぼす複数表面き裂の分布特性の影響

抄録

Rotary bending fatigue tests were performed on annealed and shot-peened specimens in laboratory air and in salt water. During the fatigue process of a shot-peened specimen in air, many cracks are initiated but each crack growth is suppressed by work-hardening and compressive residual stresses produced by shot-peening treatment ; hence, under this condition, crack coalescence is the only possible way for crack growth to occur, and is thus one of the most important factors to decide fatigue life. On the other hand, during the fatigue process of a shot-peened specimen in salt water, especially at low stress amplitude, suppressive effects of shot-peening treatment on crack growth are lost under a strong corrosive environment. In this case, many cracks can grow to a considerable long crack size, and they distribute not only in a circumferential direction but also in a longitudinal direction of the specimen. Consequently, stress relaxation will occur in the cracked part of the specimen and crack growth rate will be reduced. This stress relaxation effect on crack growth exceeds the crack coalescence effects in a corrosion fatigue process at low stress amplitude.