Thermal Fatigue Design of Stainless Steel Exhaust Manifolds

The paper deals with the thermal mechanical fatigue (TMF) of stainless steels used for exhaust manifolds. A thermal fatigue test on V-shape specimen was early developed at Ugine & Alz to simulate such thermal and mechanical conditions. The examination of failed specimens indicates that cracks could be generally attributed to out-of-phase TMF. However, in specific cases, in-phase TMF may be dominant. For instance, manifolds made of austenitic stainless steel grades usually fail by in-phase TMF. Based on finite element calculation of the V-shape test, a damage criterion is proposed for out-of-phase TMF, which correlates the amplitude of the viscoplastic strain, the maximal temperature, the dwell time during the thermal cycle and the number of cycles to failure.