Constant and Variable-amplitude Loading of Aluminum Alloy 7075 in the VHCF Regime

The aim of this study is to quantify the influence of VHCF cycles on fatigue life of 7075-T6 Al-alloys using both constant and variable amplitude loading. Constant amplitude loading tests with and without superimposed mean levels were performed to characterize the material behavior with minimal effect of load interactions. The effects of combined cycle fatigue loadings were studied by using a spectrum composed by a low frequency carrier wave at 0.01, 0.4, 2 and 5 Hz and a superimposed high-frequency wave at 20 kHz. The low frequency wave is sinusoidal or rectangular, the high-frequency wave has constant and variable amplitudes, and the effects of different loading sequences are investigated. Correlating the measurement results with microscopic surface observations allowed identification of fatigue crack initiation and propagation.