This paper presents a method for the assesment of thermal and vibration fatigues in integral exhaust manifold/turbine housing system. Most of failures on turbine housing are observed by thermal cyclic loads. In order to predict thermal failures by finite element analysis, we considered the temperature-dependent inelastic materials and transient temperature histories based on the thermal shock test. The results showed that the plastic strains of localized critical regions such as valve seat coincided well with crack locations from an endurance test. But, some failures around neck areas of turbine housing could not predict from thermal stress analysis. These cracks were originated due to the vibration excitations near resonance frequencies within engine operating ranges. The stress results of neck areas, which divided by temperature dependent yield stresses, from harmonic analysis showd a good agreement with experimental results.

Thermo-mechanical fatigue cracks on the turbine housing of turbochargers are often observed in currently developed gasoline engines for them to adopt lightness and higher performance levels. Maximum gas temperatures of gasoline engines usually exceed 950℃ under engine test conditions. In order to predict thermo-mechanical failures by simulation method, it is essential to consider temperature-dependent inelastic materials and inhomogeneous temperature distributions undergoing thermal cyclic loads. This paper presented the analytical methods to calculate thermal stresses and plastic strain ranges for the prediction of fatigue failures on the basis of motoring test mode, which is commonly used for accelerated engine endurance test. The analysis results showed that the localized critical regions with large plastic strains coincided well with crack locations from a thermal shock test.