A new energy-based fatigue damage parameter in life prediction of high-temperature structural materials

A new life prediction model has been developed with the energy-based fatigue damage parameter of a non-dimensional plastic strain energy density (PSED). Tensile tests and low cycle fatigue tests of 316L austenitic stainless steel and 429EM ferritic stainless steel have been performed at elevated temperature for the prediction. While the cyclic stress response of a material is not stabilized during fatigue deformation, it was found that PSED is stabilized at the early stage of fatigue life and nearly invariant through the whole cycles. Hence, PSED can be regarded as a suitable fatigue parameter for the materials. The Morrow model using PSED gave a good correlation on low-cycle fatigue under isothermal conditions for both stainless steels. A fatigue damage parameter, which is defined as the PSED non-dimensionalized by material toughness, was proposed to account for temperature effect on the fatigue life. The developed model, in which the fatigue exponent is obtained from the universal slope method and the true toughness measured from the tensile test is used as a temperature-compensating parameter, provided a good prediction on the fatigue behaviors of both stainless steels over the temperature range.