An Energy-Based Fatigue and Creep-Fatigue Damage Parameter

A general damage parameter for fatigue and creep-fatigue applications based on the hypothesis that damage is dependent on the internal total octahedral strain energy is derived. This general parameter is valid for isothermal mechanical cycling and inherently accounts for multiaxiality and mean stress for both nonviscous and viscous deformation response, including hold times. Forms of the parameter which correspond to laboratory test conditions under generalized states of stress and strain with nonzero mean stress are derived. The ability of these specific forms to affect data consolidation is examined using experimental fatigue and creep-fatigue life data for the corresponding conditions. It is shown that these specific forms of the general parameter affect a high degree of data consolidation.