Fatigue Crack Growth Response of Cast Aluminum Alloys Under Hot Compressive Dwell Conditions in Engine Applications

Fatigue crack growth under Hot Compressive Dwell (HCD) conditions, a special case of creep-fatigue occurring under compressive stress, is an important failure mode in many high temperature applications, such as the combustion chamber wall of an engine.  Tensile residual stresses gradually building up at the crack root are considered a key factor contributing to crack growth under HCD conditions.  To understand and quantify this effect, both at elevated and room temperatures, a physics-based model was developed, in which the residual stress contributions are added to the elastic and plastic responses of the material to predict crack growth under HCD conditions.  In contrast with the few existing complex models, this approach is based on the simple and well-recognized Paris Law for fatigue crack growth.  Comprehensive SEM and TEM studies were also performed to understand HCD effects at the microstructural scale of a common automotive engine aluminum alloy (cast 319-T7), and recommendations will be given to optimize the alloy’s microstructure for high temperature applications.  Discussions regarding design for high temperature resistance under HCD and applying the new methodology to aerospace materials and applications will also be provided.