Thermo-Mechanical Fatigue Simulation of Exhaust Manifolds

Exhaust manifolds bridge the gap between the cylinder head and the catalytic converter. Loading conditions and complex geometry have led the exhaust manifolds heads to become the most challenging parts of diesel engines. Thermal fatigue failure of the engine components easily happens due to excessive temperature gradient and thermal stress. Modern exhaust systems must withstand severe cyclic mechanical and thermal loads throughout the whole life cycle. This study focuses on the Thermo-mechanical Fatigue (TMF) analysis for exhaust manifolds. During recent years, with the constantly advancing progress of high performance computer technology, many finite element software codes provide the ability to solve finite element analysis coupled problems have been developed. The three-dimensional model of the exhaust manifolds was simulated in abaqus software and a chaboche model was utilized to investigate the elastic and plastic behavior of the exhaust manifolds. This model makes the cyclic stress-strain behavior of the material predictable. The numerical results showed that the temperature and thermal stresses have the most critical values at the confluence region of the exhaust manifolds. This area was under the cyclic tensile and compressive stress and then is under low cycle fatigue. thermo-mechanical fatigue was the main reason for exhaust manifolds failure. After several cycles the fatigue cracks will appear in this region. The lifetime of this part can be determined through finite element analysis instead of experimental tests. Computer aided engineering (CAE) plays an important role to find the weakness of an exhaust manifold layout at the early stage of the engine development.