A Thermoviscoplastic FE Model for the Strain Prediction in High Temperature, Thermal Cycling Applications for Silicon Molybdenum Nodular Cast Iron

The design of components for high temperature, thermal cycling situations has traditionally been a challenging problem because the analysis must compensate for the non-linear behavior of the material. One example for automotive applications is the exhaust manifold, where temperatures may reach 900°C during thermal cycling. Fatigue failure and excessive deformation of these components must be analyzed with thermoviscoplastic models. A Finite Element (FE) model is developed to simulate the material behavior at high temperature, thermal cycling conditions. A specimen of Silicon Molybdenum Nodular Cast Iron (4% Si, 0.8% Mo) is cycled between maximum temperatures of 500°C and 960°C while the stress is measured with respect to time. The model predictions for stress are compared to the experimental results for two rates of thermal cycling. The analysis is conducted with and without creep effects to understand its contribution to the overall strain. The results suggest that creep strain is essential to model predictions for thermal cycling at these temperatures. The compromise between model speed and accuracy is also discussed to understand the practical application of the model to an exhaust manifold.