# Difference between revisions of "Creep"

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<math> \frac{\mathrm{d}\varepsilon}{\mathrm{d}t} = \frac{C\sigma^m}{d^b} e^\frac{-Q}{kT}</math> | <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. In dislocation creep, m = 4 to 6 and b = 0. In Nabarro-Herring creep, m = 1 and b = 2. In Coble creep, m = 1 and b = 3. | + | 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. In dislocation creep, m = 4 to 6 and b = 0. In Nabarro-Herring creep, m = 1 and b = 2. In Coble creep, m = 1 and b = 3. Depending on the mechanism being modeled, the exponents m and b can be tuned. |

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

## Revision as of 21:31, 9 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. A Creep test attempts to quantify the relevant timescales and functional forms of molecular and/or atomic rearrangement that occur when a material creeps. The mechanism of creep differs depending on the material. In a crystal, mechanisms for creep include the movement of dislocations (Dislocation Creep) and the diffusion of atoms along grain boundaries (Coble Creep) or through the bulk (Nabarro-Herring creep).

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. In dislocation creep, m = 4 to 6 and b = 0. In Nabarro-Herring creep, m = 1 and b = 2. In Coble creep, m = 1 and b = 3. Depending on the mechanism being modeled, the exponents m and b can be tuned.

## See also:

## Keyword in references:

Homogeneous flow of metallic glasses: A free volume perspective

Stress Enhancement in the Delayed Yielding of Colloidal Gels