The input data required for the orthotropic material model in Autodyn can be entered in two ways. The user has the option to specify the elastic engineering constants directly by selecting for the input type, or the stiffness matrix coefficients may be input by choosing . This option has been implemented since some stiffness matrix coefficients are obtained directly experimental tests. For example, depending on the application, C11 may be calculated directly from a uniaxial strain experiment such as the inverse flyer plate tests of Equation of State Properties: Inverse Flyer Plate Tests.
The stiffness matrix coefficients, in terms of the elastic engineering constants, can be calculated from the following expressions obtained by inverting the compliance matrix Equation 3–6,
 | (6–1) |
where
Table 6.1: Derivation of Orthotropic Material Elastic Properties outlines the experimental tests used to calculate values for the engineering elastic constants.
Table 6.1: Derivation of Orthotropic Material Elastic Properties
| Property | Description |
|---|---|
| E11 |
Through thickness Youngs Modulus. Not measured directly. Can be calculated from |
| E22 |
In-plane Youngs Modulus. Calculated from 0° tension tests. |
| E33 |
In-plane Youngs Modulus. Calculated from 90° tension tests. |
| ν23 |
In-plane Poissons ratio. Calculated from 0° tension tests in which strain gauges applied in 22 & 33 directions. |
| ν31 |
Out-of-plane Poissons ratio. Calculated from 90° tension tests in which strain gauges applied in 11 & 33 directions. |
| ν12 |
Out-of-plane Poissons ratio. Often unknown, can be calculated from |
| G23 |
In-plane shear modulus. Average of that calculated from 45° tensile tests using Equation 6–2. |
| G12 |
Out-of-plane shear modulus. Average value calculated from short beam shear tests. |
| G31 |
Out-of-plane shear modulus. As G12 above. |
The in-plane shear modulus G23 is calculated from the following equation [7] where EY is the modulus measured in the 45° tension test described in 45° Tension Test,
 | (6–2) |