# Difference between revisions of "Creep"

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where the left hand side is the strain rate due to creep, ''Q'' is the activation energy of creep, ''d'' is the grain size, <math>\sigma</math> is the stress in the material, ''T'' is the temperature, and ''m'' and ''b'' are constants that depend on the mechanism of creep. | where the left hand side is the strain rate due to creep, ''Q'' is the activation energy of creep, ''d'' is the grain size, <math>\sigma</math> is the stress in the material, ''T'' is the temperature, and ''m'' and ''b'' are constants that depend on the mechanism of creep. | ||

− | For a general visco-elastic material, | + | For a general visco-elastic material, such as a polymer, |

==See also:== | ==See also:== | ||

## Revision as of 21:08, 8 December 2011

Started by Lauren Hartle, Fall 2011.

## Definition

Creep is the time dependent change in Strain of a material subject to a constant Stress. Creep is distinct from Plastic flow, which is often defined as time-*independent* permanent deformation. A Creep test and Stress relaxation test attempt to quantify the same material behavior: the timescale and functional form of molecular and/or atomic rearrangement that occurs when a material is irreversibly deformed. The mechanism of creep differs depending on the material. In a crystal, mechanisms for creep include the movement of dislocations and the diffusion of atoms along grain boundaries or through grains.

The general equation for describing creep is:

<math> \frac{\mathrm{d}\varepsilon}{\mathrm{d}t} = \frac{C\sigma^m}{d^b} e^\frac{-Q}{kT}</math>

where the left hand side is the strain rate due to creep, *Q* is the activation energy of creep, *d* is the grain size, <math>\sigma</math> is the stress in the material, *T* is the temperature, and *m* and *b* are constants that depend on the mechanism of creep.

For a general visco-elastic material, such as a polymer,

## See also:

## Keyword in references:

Homogeneous flow of metallic glasses: A free volume perspective

Stress Enhancement in the Delayed Yielding of Colloidal Gels