Creep
The slow, time-dependent permanent plastic deformation of a solid material subjected to long-term mechanical stresses below its yield strength, accelerated at elevated temperatures.
Governing formula
ε_creep = A σ^n e^(-Q / (R T)) (Power law creep)
SI unit
s⁻¹ (Creep Strain Rate)
In depth
Creep occurs via thermal stress-assisted dislocation climb and vacancy grain boundary diffusion (Coble and Nabarro-Herring creep) at temperatures T > 0.4 T_melting.
Examples in the real world
Jet engine turbine blades or high-pressure steam pipes expanding permanently over thousands of hours of high-temperature service.