In materials science, creep (sometimes called cold flow) is the tendency of a solid material to move slowly or deform permanently under the influence of mechanical stresses. It can occur as a result of long-term exposure to high levels of stress that are still below the yield strength of the material. Creep is more severe in materials that are subjected to heat for long periods, and generally increases as they near their melting point.
The rate of deformation is a function of the material properties, exposure time, exposure temperature and the applied structural load. Depending on the magnitude of the applied stress and its duration, the deformation may become so large that a component can no longer perform its function — for example creep of a turbine blade will cause the blade to contact the casing, resulting in the failure of the blade. Creep is usually of concern to engineers and metallurgists when evaluating components that operate under high stresses or high temperatures.
|dϵ||creep strain (dimensionless)|
|C||constant dependent on the material and the particular creep mechanism (dimensionless)|
|σ||applied stress (dimensionless)|
|m||exponents dependent on the creep mechanism (dimensionless)|
|d||grain size of the material (dimensionless)|
|b||exponents dependent on the creep mechanism (dimensionless)|
|Q||activation energy of the creep mechanism (J)|
|T||absolute temperature (K)|