Variable Amplitude Fatigue Life in VHCF and Probabilistic Life Predictions

Fatigue life in the very high cycle fatigue (VHCF) regime for aluminum alloy 7075-T6 in plate form is characterized in constant and variable amplitude loading using unique testing equipment that allows superposition of small amplitude vibrations on top of duty cycles [1], . Constant amplitude loading data from the current experimental effort and from literature sources are used to construct a strain-life input using a Walker mean stress correction method. Variable amplitude loading data are analyzed using the constructed strain-life input. A novel probabilistic approach based on the probabilistic framework of Castillo [2] and modified by using the proposed mean stress correction method is applied. Results are compared with experimentally obtained fatigue lives. Insights into modes of failure in very high cycle fatigue for constant and variable amplitude loading, the role of experimental scatter and interaction effects are presented.