A Model for the Determination of Residual Fatigue Life of a Nickel-Based Superalloy

In this paper, both the dissipation of the plastic-strain energy and the exhaustion of the static toughness during high-temperature low-cycle fatigue of GH4145/SQ superalloy were investigated. Together with the analysis of the microscopic aspects of the material, an energy-based damage mechanics model was developed for the prediction of the residual fatigue life of the high-temperature fastened parts in power plant. Experimental results show that the static toughness is a parameter that is highly sensitive to the fatigue damage process. The deterioration of the static toughness during fatigue process reveals the exhaustion of the materials’s ability to absorb energy, which is essentially associated with the irreversible energy dissipation process of the fatigue failure. Based on the dissipation of the plastic-strain energy and the exhaustion of the static toughness during fatigue, a damage variable is defined that is consistent with the fatigue damage mechanism. The variable is sensitive to the fatigue process and can be measured with a simple experimental procedure. A fatigue damage evolution equation is derived on the basis of Lemaitre’s potential of dissipation in the framework of continuum damage mechanics. Furthermore, an equation for the determination of the residual fatigue life is deduced. The fatigue damage mechanics model is verified by comparing the predicted results with the experimental observations. The fatigue damage mechanics model developed may provide a feasible approach to determining the residual fatigue life of the high-temperature fastened parts in power plant.