A simple life prediction method for 304L stainless steel structures under fatigue-dominated thermo-mechanical fatigue loadings

Thermo-mechanical fatigue (TMF) tests of 304L stainless steel were performed in the temperature range in which creep and oxidation effects can be considered negligible. Four different phase angles between mechanical strain and temperature cycles (in-phase (IP), out-of-phase (OP), clockwise-diamond-phase (CD), and counter-clockwise-diamond-phase (CCD)) with three different mechanical strains were performed to elucidate the effects of the mechanical strain and phase angle on the fatigue life. IP and CD induce longer life in general compared to OP and CCD, which could be related to the difference of the mean stress in each condition. Ultimate tensile strength values from tensile tests were used to consider the effect of varying temperature during a TMF cycle on the fatigue damage and material resistance. The effects of specimen geometry (solid versus hollow) on the fatigue life were considered. A simple life prediction model that utilizes the plastic strain energy density, ultimate tensile strength, and mean stress is suggested; this model can predict the TMF fatigue life within a 2× scatter band and explain the difference between different phase angles. The model used one new term to consider the mean stress effect, in addition to the two parameters that are used in the conventional Morrowʹs model.