n.
Slow change in the dimensions of a material from prolonged stress .
Most common metal s exhibit creep behaviour. In the creep test, loads below those that ordinarily cause plastic flow or fracture are applied to the material, and the deformation over a period of time (creep strain) under constant load is measured, usually with an extensometer or strain gauge . Time to failure is also measured against stress. Once creep strain versus time is plotted, various mathematical techniques are available for extrapolating creep behaviour beyond the test times; thus, designers can use thousand-hour test data, for example, to predict ten-thousand-hour behaviour. See also testing machine .