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. 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. | 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. | ||
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| + | For viscoelastic materials like many polymers, a number of models can be used. An uncross | ||
==See also:== | ==See also:== | ||
Revision as of 22:00, 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.
For viscoelastic materials like many polymers, a number of models can be used. An uncross
See also:
Keyword in references:
Homogeneous flow of metallic glasses: A free volume perspective
Stress Enhancement in the Delayed Yielding of Colloidal Gels
