isotropic properties 1

[mattchoo71]

Hello everyone,

I am a complete newcomer to finite element modelling and am looking at vibrations on a flat panel loudspeaker.

I would like to be able to examine a material's properties to establish whether it is isotropic (it is strongly suspected to be isotropic), but am struggling with a precise answer. I've discovered that for isotropic materials there appears to be a link between Young's modulus and shear modulus and Poisson's Ratio, perhaps by :

E = 2(1 + v)S,

with E being Young's, S being the shear and ? Poisson's Ratio. When I plug in the values I am using (below),the equation gives a close value of E (71.5x10e6), but it is not exact, as, presumably it should be.


Material properties

Dimensions : 0.63m x 0.56m x 0.018m
Mass density ro : 52 kg/m3
Youngs modulus E : 71.84x10e6 N/m2
Shear modulus S : 27.5 x10e6 N/m2
Poisson’s Ratio v : 0.3
Damping coeff. gamma : 0.05

Does anyone have a clearer method of determing a material's isotropic nature? What role does the damping coefficient play and is it related to isotropicality?


Regards,

Matt

 

[Denial]

Your theoretical relationship between E, G & v (for an isotropic material) is correct.

The apparent slight discrepancy between the formula and the values you are using is probably because the value of Poisson's ratio is given to only 1 significant figure. (If you used a value of 0.306 the formula would be satisfied exactly.)