A Total Strain Energy Density Theory for Cumulative Fatigue Damage

A unified theory based on the cyclic strain energy density criterion is presented first. It is shown that the fatigue failure in both low and high-cycle regimes, and cumulative damage and loading sequence, can all be expressed in terms of a single damage parameter. The damage criterion is based on the total strain energy density per cycle (sum of the plastic and tensile elastic strain energy). Both the crack initiation and propagation phases of the fatigue life are embodied in this approach. A systematic investigation into the cyclic, fatigue and cumulative damage behavior of the pressure vessel steel, A-516 Gr. 70, is subsequently presented. The comparison between the predicted and experimental results is found to be good.