Influence of superimposed VHCF loadings in cyclic fatigue of 7075-T6 aluminum alloy

Abstract

The influence of very-high-cycle-fatigue (VHCF) cycles on fatigue life of 7075-T6 aluminum alloy have been quantified for newly designed superimposed loading conditions in this research. Ultrasonically generated 20 kHz stress waves of different amplitudes have been superimposed to specimens undergoing low cycle fatigue testing at 5 Hz. The resulting fatigue lives, given by the interaction of the two superimposed loadings have been obtained, along with fractographic examination of the surface, and of the initiation sites. The influence of the 20 kHz cycles was found to be highly significant, starting form an amplitude of superimposed loading of only 3 ksi. Fatigue life calculations have been compared with experimental results, revealing in the majority of cases very conservative predictions. Preliminary fractographic examination of the surface of the specimen was performed to obtain crack growth rate measurements, and results are compared with data from literature. These results opened the way to a more intensive experimental program and examination of combined cycle fatigue effects in structural alloys. Nomenclature LCFLow Cycle Fatigue HCF High Cycle Fatigue V HCF Very High Cycle Fatigue