抄録
In order to investigate the effect of frequency on the crack growth behavior, ultrasonic fatigue tests were carried out for an extruded age-hardened Al alloy, 7075-T6, in ambient air and in N_2 gas, and the results were compared with those in rotating bending fatigue. In ultrasonic fatigue, the growth direction of a crack changed macroscopically from a tensile mode to a shear one which the direction was about 35 degrees against to the specimen axis, and fracture mechanism also changed from striations to transgranular facets with voids microscopically. Crack growth rate at the transition of crack growth direction was about 3×10^<-9>m/cycle. These results were explained from the time dependent environmental effect and texture of microstructure.
