Multiaxial and Thermomechanical Fatigue of Materials: A Historical Perspective and Some Future Challenges

Many engineering components in aircraft gas turbine engines, reusable space propulsion systems, and automotive engines must endure cyclic mechanical forces and deformations in multiple directions and non-isothermal conditions. For the design and safety of such engineering components, durability needs to be estimated with robust multiaxial fatigue life prediction models that are validated under such non-isothermal conditions. In this paper, a historical review is presented on the evolution of uniaxial fatigue (thermal, isothermal, bithermal, and thermomechanical) and isothermal, multiaxial fatigue leading to multiaxial, thermomechanical fatigue with several examples on testing techniques and fatigue life prediction methodologies. The necessity for multiaxial, thermomechanical fatigue testing of structural and engine materials, additional cyclic hardening and reduction in fatigue life observed under such service conditions, and ramifications of estimating multiaxial, thermomechanical fatigue life with isothermal multiaxial fatigue data at the greatest temperature of the cycle are discussed. Finally, some of the potential future challenges associated with experimental characterization of materials and fatigue life estimation under these complex but realistic service conditions are highlighted.