What do you mean by creep and creep curve.

 In material science, creep ( sometime 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 gene rally increases as they near their melting point.

The rate of deformation (strain) 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 became so large that a component can no longer perform its function. 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 when evaluating components that operate under high stress or high temperatures. Creep is a deformation mechanism that may not constitute a failure mode. For example, moderate creep in concrete is sometime welcomed because it relives tensile stresses that might otherwise lead to cracking.

Classical Creep Curve:

The rate of deformation is called the creep rate. It is the slope of the line in a creep strain vs time curve.