A Methodology for Analysis of Failure Prediction Data

Reduction of design and development cycle time can be achieved by reducing the number physical and virtual prototypes. Understanding of the structural behaviour in the initial phase of design can help to reduce the number of virtual prototypes and the time taken for their evaluation. For an Engine development program, the engine Exhaust Manifold is a complex system subjected to Thermomechanical loads. The analysis of such a system is critical due to the complexity of meeting the structural and flow requirements. The use of Computational Fluid Dynamics (CFD) and Finite element analysis (FEA) are inevitable tools to achieve this. The paper deals with methodology adopted to address a failure of an Exhaust manifold during physical testing on an engine test bed. A non-linear thermo-structural strength analysis of the Exhaust manifold assembly of the four cylinder four stroke engine is carried out. The FE model consists of the Exhaust manifold assembly, Cylinder head and mounting bolts. The contact interaction between the parts is also modeled. The assembly is subjected to bolt preloads, for simulating the mechanical assembly. The thermal loads used in the simulation are computed through CFD simulations of In-cylinder combustion and coolant flow. The model considers a temperature dependency of a heat transfer coefficient on wall temperature in cooling passages. For the structural analysis temperature dependent non linear material properties and contact non-linearity is considered. A good correlation is obtained for the failure as observed in the test. The correlation and the suggested Design modification, which has been implemented is presented in this paper.