Effect of residual stress in low cycle fatigue for coated exhaust manifold

The exhaust manifolds are subjected to higher loads than before, due to the increasing power output, fuel consumption and exhaust gas emission. Thus, simulation and analysis of fatigue cracks is essential. The effect of residual stress on the thermal stress and low cycle fatigue (LCF) life of exhaust manifolds using strain life methods was investigated. For this purpose, Solidworks software was used to model the exhaust manifolds. Then the thermo-mechanical analysis was carried out to determine the temperature and stress distribution in ANSYS software.  Finally, the fatigue life prediction that considers residual stress effect was done. The simulated results proved that the thermal stresses and number of cycles to failure have the most critical values at the confluence region of the exhaust manifolds. The LCF results showed that the number of failure cycles for coated exhaust manifold is about 89% higher than the results obtained from the uncoated exhaust manifolds. Evaluating the residual stress, the TBC improves the number of failure cycles approximately 52% in comparison the uncoated exhaust manifold. The results of FEA proved a very good agreement between numerical simulation results and LCF analysis results, performed in references.