Shear Modulus
Enter positive values for the shear moduli of the material. You can define this property or assign a parameter to the property. You can either type a value or right-click to assign a Parameter as appropriate.
For orthotropic material properties, enter values for:
G12
G13
G23
These values represent the shear modulus in each of the three material directions.
For transversely isotropic material properties, enter a value for the shear modulus of the material in two of the three principal planes of the material. The Material Definition dialog box shows the following shear modulus values:
G12 = G13
G23 = E3/(2 X (1 + Nu32))
Enter a single positive value for the 21 and 31 planes. Structure automatically calculates the value for the 32 plane, using the equation shown on the dialog box.
* 
For both orthotropic and transversely isotropic, G21 is also denoted as G12, G31 as G13, and G32 as G23.