An Energy-Based Approach to Determine the Fatigue Strength and Ductility Parameters for Life Assessment of Turbine Materials

Abstract

An energy-based framework is developed to determine the fatigue strength parameters of the Basquin equation and the fatigue ductility parameters of the Manson–Coffin equation to predict high cycle fatigue (HCF) and low cycle fatigue (LCF) life of a steam turbine rotor base and weld materials. The proposed framework is based on assessing the complete energy necessary to cause fatigue failure of a material. This energy is considered as a fundamental material property and is known as the fatigue toughness. From the fatigue toughness and the experimentally determined fatigue lives at two different stress amplitudes, the cyclic parameters of the Ramberg–Osgood constitutive equation that describes the hysteresis stress–strain loop of a cycle are determined. Next, the coefficients and the exponents of the Basquin and the Manson–Coffin equations are computed from the fatigue toughness and the cyclic parameters of a material. The predicted fatigue life obtained from the present energy-based framework is found to be in a good agreement with the experimental data.