Term: Creep (deformation)
– Definition of Creep (Deformation):
– Creep is slow deformation in solid materials under persistent mechanical stresses.
– It occurs below the material’s yield strength due to long-term stress exposure.
– More severe in materials exposed to heat for extended periods.
– Deformation rate depends on material properties, exposure time, temperature, and load.
– Creep can cause components to fail if deformation is significant.
– Factors Influencing Creep:
– Material properties, exposure time, temperature, and applied load affect creep.
– Creep increases as materials approach their melting point.
– High stress levels and duration can lead to excessive deformation.
– Creep is a concern for components operating under high stress or temperature.
– Creep can relieve tensile stresses in materials like concrete, preventing cracking.
– Creep in Engineering:
– Engineers and metallurgists evaluate components for creep under high stress or temperature.
– Creep is a deformation mechanism that may not always result in failure.
– Creep can compromise component function, such as turbine blades contacting casings.
– Understanding creep is crucial for designing reliable high-stress components.
– Moderate creep in concrete can be beneficial in certain applications.
– Comparison with Brittle Fracture:
– Creep deformation is gradual, unlike sudden brittle fracture.
– Creep does not occur immediately upon stress application.
– Brittle fracture and creep are different failure modes in materials.
– Creep is a concern for materials operating near their limits.
– Engineers must consider both brittle fracture and creep in component design.
– Importance of Creep Analysis:
– Creep analysis helps predict material behavior under long-term stress.
– Crucial for assessing component reliability in high-stress environments.
– Creep testing is essential for materials used in elevated temperature applications.
– Understanding creep behavior aids in preventing unexpected failures.
– Creep analysis guides material selection and design considerations.
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In materials science, creep (sometimes called cold flow) is the tendency of a solid material to undergo slow deformation while subject to persistent 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 generally increase as they near their melting point.
The rate of deformation is a function of the material's properties, exposure time, exposure temperature and 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 could cause the blade to contact the casing, resulting in the failure of the blade. Creep is usually of concern to engineers and metallurgists when evaluating components that operate under high stresses or high temperatures. Creep is a deformation mechanism that may or may not constitute a failure mode. For example, moderate creep in concrete is sometimes welcomed because it relieves tensile stresses that might otherwise lead to cracking.
Unlike brittle fracture, creep deformation does not occur suddenly upon the application of stress. Instead, strain accumulates as a result of long-term stress. Therefore, creep is a "time-dependent" deformation.
Creep or cold flow is of great concern in plastics. Blocking agents are chemicals used to prevent or inhibit cold flow. Otherwise rolled or stacked sheets stick together.