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Turbine housings for automotive turbochargers are complex castings that are subjected to transient thermal stress from exhaust gas temperature and flow variation under complex duty cycles. A fatigue model based on a cumulative damage approach (Chaboche model [1]) is used to predict crack initiation. As the stress varies with temperature, a modified Chaboche model based on a normalized stress is proposed. To determine the transient stress and temperature distributions due to the high rates of convection from the gas, and the complexity of the design, conjugate heat transfer CFD simulation is performed. The tongue of the turbine housing is a critical region in which cracks initiate within a short time. Heat transfer coefficients ( HTC ) and bulk temperature predictions from CFD, in general, can be validated by thermal measurement. But because of the geometry and the location of the tongue, it is impossible to measure the metal temperature. For this work 2 methods were presented: HTC calibrated by thermal measurement and HTC from CFD heat transfer Conjugate method, steady state analysis. Heat transfer Coefficients and bulk temperatures obtained with those 2 methods are different. The heat transfer from CFD analysis with 15 layers has an important HTC which is 3000 W/ m2 °C, it is equal to 1200 W/m2 °C for the calibrated method, but the bulk temperatures are not the same. A sensitivity study on predicted life shows that this difference results in no more than a 2 hr change for a total predicted life of 50 hrs. In the industrial approach this difference is quite acceptable. The design of a turbine housing is optimized based on this TMF methodology and shows very good results in testing, as presented here.

Many critical components in turbocharger are subjected to rapid temperature changes during operations. Thermal gradient within these components produces internal stresses and the repetition of these thermal cycles may cause a component to fail due to Thermal Mechanical Fatigue (TMF). Turbine Wheel, Turbine Housing and Manifold are subjected to TMF; these are the most expensive components of the turbocharger and have very complex geometric shapes. The maximum exhaust gas temperature could reach 1050°C. To assess TMF failure, it is very critical to accurately estimate metal temperature of these components subjected to complex duty cycles where exhaust gas temperatures vary significantly with time. Evaluating metal temperature and stress components from finite element analysis for complex duty cycles is a very time consuming process, particularly for complex geometries and approximately requires more than 3 weeks of time to complete analysis for different field complex duty cycles (driving conditions: city, highway and road). Several of these analysis cases are required to consider the impact of the real driving condition. In the present work we have developed an analytical methodology that is accurate and faster to predict the metal temperature and stresses in turbocharger components for complex duty cycles. This method was applied to evaluate the fatigue damage of turbine housing under actual condition.

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