Mechanism-based thermomechanical fatigue life prediction of cast iron. Part I: Models

In the present paper, mechanism-based models are developed to describe the time and temperature dependent cyclic plasticity and damage of cast iron materials. The cyclic plasticity model is a combination of a viscoplastic model with kinematic hardening and a porous plasticity model to take the effect of graphite inclusions into account. Thus, the model can describe creep, relaxation and the Bauschinger-effect as well as the tension-compression asymmetry often observed for cast iron. The model for thermomechanical fatigue life prediction is based on a crack growth law, which assumes that the crack growth per cycle, da/dN, is correlated with the cyclic crack-tip opening displacement, Delta CTOD. The effect of the graphite inclusions on crack growth is incorporated with a scalar factor into the crack growth law. Both models can describe the essential phenomena which are relevant for cast iron materials.