Flow Laws
Each plastic deformation of a material can be described by a formula in which the strain rate depends on the differential stress (σ or σD), the grain size (d) and an activation value in the form of an Arrhenius equation:
In which A is the constant of diffusion, Q the activation energy of the mechanism, R the gas constant and T the absolute temperature (in kelvins). The exponents n and m are values for the sensitivity of the flow to stress and grain size respectively. The values of A, Q, n and m are different for each deformation mechanism. For diffusion creep, the value of n is usually around 1. The value for m can vary between 2 (Nabarro-Herring creep) and 3 (Coble creep). That means Coble creep is more sensitive to grain size of a material: materials with larger grains can deform less easily by Coble creep than materials with small grains.
Read more about this topic: Diffusion Creep
Famous quotes containing the words flow and/or laws:
“To feel most beautifully alive means to be reading something beautiful, ready always to apprehend in the flow of language the sudden flash of poetry.”
—Gaston Bachelard (1884–1962)
“These are not the artificial forests of an English king,—a royal preserve merely. Here prevail no forest laws but those of nature. The aborigines have never been dispossessed, nor nature disforested.”
—Henry David Thoreau (1817–1862)