Creep is often considered one of the modes of material failure and it is typically defined as the tendency of a solid material to deform permanently under the influence of stresses. It is usually the result of long-term exposure to high levels of stress that are below the yield strength of the material.
Creep rate is a function of the material properties, exposure time, exposure temperature and the applied load. Depending on the magnitude of load and duration, the deformation may become so large that a component can no longer perform its function — for example, creep behavior in a turbine blade will cause the blade to contact the casing, resulting in the failure of the blade.
Creep properties are of concern to engineers and metallurgists when evaluating components that operate under high stresses and temperatures. Creep is a deformation mechanism that may even initiate a failure mode. In certain cases, such as creep in concrete, it can relieve tensile stresses that might otherwise lead to cracking. In biological materials, creep is often characterized to understand how certain tissues respond to biomechanical loading in both normal and sports-related activities.
Creep response can also occur in polymers and metals which are considered viscoelastic materials. When a polymeric material is subjected to an abrupt force, the response can be modeled using the Kelvin-Voigt model. In this model, the material is represented by a Hookean spring and a Newtonian dashpot in parallel. See the stress relaxation page for further discussion.
Bose® ElectroForce® test instruments are used to study a variety of creep behaviors and response for engineered materials and a variety of biological specimens. Contact us to discuss your particular application.