Modelling and design of an exhaust manifold under thermomechanical loading

Abstract

In the early stage of designing an exhaust manifold, a designer usually has to perform the fatigue analysis of each candidate of the exhaust manifold, and to decide whether or not it is satisfactory. In each case, elastoplastic stress analysis by the finite element method (FEM) is required, which is very time consuming considering the preprocessing and post-processing of the FEM data. In this study, a thermal stress index is proposed for a practical application to the early stage of designing the exhaust manifold. Although this index (the ratio of the elastic effective stress to the yield stress) does not predict quantitatively the expected fatigue life, it is believed that it can be easily evaluated, and its merit lies in the quick estimation of the effect of the design parameters at the development stage without performing complete non-linear analysis of fatigue.