An elastic parameter: the ratio of transverse contractional strain to longitudinal extensional strain. In other words, a measure of the degree to which a material expands outwards when squeezed, or equivalently contracts when stretched (though some materials, called auxetic, do display the opposite behaviour).
Expressed in terms of acoustic velocities, assuming the material is isotropic and homogenous:
In this case, when a material has a positive it will have a ratio greater than 1.42.
Expressed in terms of Lamé's parameters:
For incompressible material, ν is approximately 0.5. Cork has a value of about 0, meaning that it does not expand radially as it is compressed. Most rocks have ν between about 0.1 and 0.4.
Materials with negative Poisson's ratio, meaning that they get thinner as they are compressed, do exist. They are called auxetic and include the mineral α-cristobalite.
Required: a table of common (and relevant) values.
- Poisson's ratio — Wikipedia article
|Conversion formulas — edit|
| The elastic properties of homogeneous isotropic linear elastic materials are uniquely determined by any two moduli. Given any two, the others can thus be calculated. Key reference: Mavko, G, T Mukerji and J Dvorkin (2003), The Rock Physics Handbook, Cambridge University Press.
| P-wave velocity
| S-wave velocity
| Velocity ratio
| 1st Lamé parameter
| Shear modulus
| Young's modulus
| Bulk modulus
| Poisson's ratio
| P-wave modulus