Thermo-mechanical fatigue analysis of ferritic stainless steel STS444LM for exhaust manifold application

This work presents thermo-mechanical fatigue (TMF) life analysis of ferritic stainless steel STS444LM recently developed to enhance the durability of the automotive exhaust manifolds. To determine cyclic material properties, isothermal tensile and low cycle fatigue (LCF) tests at temperature ranging from 200 degrees C to 900 degrees C under two different strain rates of 0.1 %/s and 0.01 %/s are performed. Based on these tests, the unified Chaboche visco-plasticity model is determined. Then, the TMF test using the V-shaped specimen subjected to the temperature cycle from 250 to 850 - 950 degrees C with three different dwell times at the maximum temperature is performed. An energy-based model based on the Morrow model is determined using TMF test data by incorporating effects of the dwelling time and maximum temperature.