Creep

The dimensional change with time of a material under a mechanical load. The flow or plastic deformation of metals held for long periods of time at stresses lower than the normal yield strength. Plastic deformation that proceeds slowly and continuously when stress is applied at elevated temperatures. In steel, creep is negligible below about 300°C (572°F). Methods of creep testing involve the determination of strain/time curves under constant tensile load and at constant temperature.