High temperature fatigue and creep - automotive power train application perspectives

The present paper aims to describe the engineering durability design methodology as developed by BMW of hot power train components for both the gasoline cylinder head in aluminium alloys and the hot end components in iron based alloys under thermomechanical fatigue (TMF) conditions. The deformation is described using a viscoplastic model, which in the case for the aluminium alloys is combined with an aging model. The local damage evolution is modelled based on the growth of microcracks with a parameter derived from the J-Integral. Cyclic isothermal and non-isothermal fatigue tests were conducted in order to calibrate the lifetime model. The complexity was limited to a level that the main effects were captured but the analysis of a complex structure was still feasible. The accurate prediction of the variable temperature field is crucial for the success; in the CAE environment the temperature assessment remains the largest uncertainty. An outlook to new upcoming power train components is given.