Creep
“In materials science, creep is the tendency of a solid material to slowly move or deform permanently under the influence of stresses. It occurs as a result of long term exposure to high levels of stress that are below the yield strengthof the material. Creep is more severe in materials that are subjected to heatfor long periods, and near melting point. Creep always increases with temperature.”
“The rate of this deformation is a function of the material properties, exposure time, exposure temperatureand 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 failureof the blade. Creep is usually of concern to engineersand metallurgistswhen evaluating components that operate under high stresses or high temperatures. Creep is a deformation mechanism that may or may not constitute a failure mode. Moderate creep in concrete is sometimes welcomed because it relieves tensile stresses that might otherwise lead to cracking.”