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-T 6, in ambient air and in N<SUB>2</SUB> gas, and the results were compared with those in rotating bending fatigue. Fatigue strength was higher in ultrasonic fatigue than in rotating bending one. This was caused by the retardation of a crack initiation and its early propagation. 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<SUP>-9</SUP> m/cycle. The relation between an applied stress σ<I><SUB>a</SUB></I> and a crack depth at the transition of crack growth direction b<I><SUB>T</SUB></I> was expressed by σ<I><SUP>n</SUP><SUB>a</SUB>b<SUB>T</SUB></I>=constant. These results were explained from the time dependent environmental effect and texture of microstructure.
|Translated title of the contribution||Crack Growth Behavior of Al Alloy 7075-T6 under Ultrasonic Fatigue|
|Number of pages||8|
|Journal||Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A|
|Publication status||Published - Sep 25 2006|