Experimental evaluation of fatigue damage in two-stage loading tests based on the energy dissipation

Heat energy dissipation is a manifestation of damage accumulation in fatigue-loaded components. Once recognized that some mechanical energy has to be expended to fatigue a material, energy partition into heat and stored energy is thought of as a material property in the present testing conditions. However, most of the mechanical input energy is dissipated as heat; therefore, the stored energy is difficult to estimate as difference between the expended and the dissipated energy. In this article heat energy is assumed as an index of fatigue damage. Since it reflects the material response to external loading, heat energy was seen to reduce the scatter of constant amplitude fatigue test results with respect to the use of the stress amplitude. Moreover, two-level fatigue test results could be interpreted with a higher level of accuracy when Miner's rule was applied in terms of energy rather than stress amplitude.