creepfatigue

Creepfatigue is a damage and failure mechanism that occurs when a material is subjected to cyclic loading at elevated temperatures, such that time-dependent creep deformation interacts with fatigue processes. The result is accelerated damage accumulation and shorter life than would be predicted by high- or low-temperature fatigue alone.

Creepfatigue typically arises in components that experience repeated load cycles at high temperature, often with hold or dwell periods during which the material remains under load. This situation is common in power generation and aerospace equipment, such as turbine blades, combustors, and steam or gas turbines, where temperatures are high enough for creep mechanisms to be active over service timescales.

Mechanisms of creepfatigue involve the coupling of cyclic plasticity and creep deformation. During load cycles, creep strains accumulate, while dwell periods promote diffusion and time-dependent damage such as cavitation and grain boundary sliding. These processes can interact to initiate cracks at stressed regions (often grain boundaries or inclusions) and drive rapid crack growth once propagation begins. The result is a deterioration of strength and life that depends on temperature, peak stress, strain range, and hold time.

Testing for creepfatigue uses specialized experiments with controlled temperature, loading amplitude, and dwell times to measure cycle life and observe damage evolution. Life prediction generally combines a fatigue damage fraction with a creep damage fraction, sometimes with interaction terms, and relies on material-specific data. More advanced models aim to describe the microstructural evolution under coupled loading.

Materials prone to creepfatigue include nickel-based superalloys and high-temperature steels. Mitigation focuses on improving creep resistance, reducing dwell times, and applying protective coatings or design changes to lower peak stresses.