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Fatigue properties of age-hardened Al alloy 2017-T4 under ultrasonic loading frequency (20 kHz) were investigated and compared with the results under conventional loading of rotating bending(50 Hz).The growth of a crack retarded at about 500μm in surface length under ultrasonic loading,while at about 20μm under rotating bending.Although striations being a typical fracture mechanism were observed under conventional loading,most of fracture surface was covered with many facets under ultrasonic loading.These facets were also observed under rotating bending in nitrogen gas.The difference in growth mechanism depending on the loading frequency and the retardation of a crack growth under ultrasonic loading may be caused by the environment at the crack tip due to high crack growth rate under ultrasonic loading.
Fatigue properties of age-hardened Al-alloy 2017-T4 under ultrasonic loading frequency (20 kHz) were investigated and compared with the results of conventional loads of rotating bending (50 Hz). The growth of a crack retarded at about 500 μm in surface length under ultrasonic loading, while at about 20μm under rotating bending. Though striations being a typical fracture mechanism were observed under conventional loading, most of the fracture surface was covered with many facests under ultrasonic loading. difference in growth mechanism depending on the loading frequency and the retardation of a crack growth under ultrasonic loading may be caused by the environment at the crack tip due to high crack growth rate under ultrasonic loading.