Effect of compressive creep on fracture toughness: application to thermomechanical fatigue (TMF) life prediction

An experimental procedure is developed to identify and quantify a connection between compressive creep and the evolution of fracture toughness. Specifically, it is determined that an accumulation of compressive creep leads to a reduction in fracture toughness. Insight into the mechanism responsible for this observed behavior is pursued. Fractography performed following the fracture toughness tests shows a transition from ductile to brittle failure caused by the presence of residual creep. The quantified effect of compressive creep on fracture toughness is applied in a thermomechanical fatigue (TMF) model to simulate crack propagation in the single crystal nickel-based superalloy PWA 1484. Considering the coupling between compressive creep and decreased crack resistance led to significantly improved TMF life prediction. Further application of the developed experimental procedure to fully quantify the evolution of fracture toughness as a function of creep accumulation will lead to greater TMF and structural life predictive capabilities. This finding has implications for a wide variety of materials and applications involving high temperature dwell fatigue including in the aerospace, energy, and manufacturing sectors.