The shear modulus, sometimes called the rigidity modulus, refers to the change produced by a tangential stress, and provides a measure of how stiff the material is.
The thermo-mechanical property calculation for fiber-filled composites are based on the orthotropic assumption, that fiber-filled material properties are different in three orthogonal principal directions. Under this assumption, there are 9 independent mechanical constants and three independent thermal expansion coefficients.
The option (found in the Fiber Orientation Solver Parameters dialog under ) selects the 9 mechanical constants (E1, E2, E3, v12, v23, v13, G12, G23, G13) and 3 CTE's (thermal expansion coefficient in first/second/third directions) all at once. In a Fiber analysis, the complete set of thermo-mechanical properties with orthotropic assumption is necessary for a Warp analysis using 3D analysis technology. These properties are element-based, so each tetrahedral or beam element has its own orthotropic set of properties.