Rapid prediction of fatigue life based on thermodynamic entropy generation

Abstract

The present paper is devoted to rapid prediction of fatigue performance of materials for medium- and high-cycle fatigue based on the thermography approach. During cyclic loading, the temperature of specimens or components increases due to both anelastic and plastic deformation, while only the plastic strain energy contributes to fatigue damage. Therefore, in this work, a model is proposed to estimate the damaging (plastic strain energy) and non-damaging (anelastic energy) parts of the dissipated heat during the cyclic loading. It is also shown that by taking advantage of the concept of fracture fatigue entropy (FFE), one can rapidly generate a stress-life diagram by conducting a stepwise test and only one fatigue experiment until failure. Further, it is shown mathematically that the dissipating energy is directly proportional to the steady-state temperature. Therefore, in situations where determining the dissipation energy is difficult, the fatigue performance can be readily predicted only by measuring the steady-state temperatures during stepwise testing. The predictions of the proposed models are verified by comparison to a series of experimental results for different materials.