Tuesday, December 16, 2014

Poisson ratio

Although Lame's constants are convinient, other elastic constants are also used. The most common are Young Modulus (E), Poisson ratio , and the bulk modulus (k). The preceding theory assumes an isotropic medium. Rocks, especially sedimentary and metamorphic rocks, are frequently not isotropic. In discussing wave propagation we generally ignore such differences and treat sedimentary rocks as isotropic media.

Poisson ratio must have values between 0 and 0.5, since both lamda and mu are positive. Values range from 0.05 for very hard, rigid rocks to about 0.45 for soft, poorly consolidated material. Liquids have no resistance to shear and hence for them mu=0 and poisson ratio=0.5 . 

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