Predicting damage and failure under thermomechanical fatigue in hot forging tools

Finite element (FE) model is developed to examine thermomechanical fatigue behavior of a hot work tool steel. Experimental results for fatigue properties of 9Cr steel were used. An approach, employing a local ductile damage initiation and evolution model, using the hysteresis stress-strain energy concept combined with element removal, has been used to predict the failure. FE analysis of cyclic loading was based on a nonlinear kinematic hardening criterion employing the Chaboche constitutive equations. Parameters of fatigue damage are calculated based on experimental data at 300 and 620 degrees C. Using these parameters, simulation of high temperature low cycle fatigue behavior for standard specimens according to test conditions is carried out and the results of LCF simulation were in good agreement with the experimental. Then, a set of thermomechanical fatigue simulations for hot forging die was performed and fatigue crack initiation and growth in forging die are predicted.