Analysis of Hysteresis Damage Accumulation and the Effect on Fatigue Life

In order to validate an existing energy-based fatigue life prediction understanding, the strain energy accumulation for interrupted loading cycles was analyzed. The life prediction method being validated was developed based on the understanding that strain energy density accumulated during monotonic fracture is a physical damage quantity that is equal to total cumulative hysteresis strain energies in a fatigue process. If this understanding is true, it is possible to suspend cyclic loading for long periods during a fatigue procedure, and then resume the procedure to failure, resulting in the same fatigue life as if the fatigue test was conducted continuously to failure. This assumption, along with critical analyses such as surface roughness and loading frequency, is tested empirically on Titanium 6Al-4V (Ti64) axial tension-compression specimens in the lifetime regime of 5x103 and 6x104. The failure results are compared, with encouraging results, to the aforementioned energy-based prediction method, thus validating the theory and the prediction capability.