# Define Orthotropic Material Properties

Defines the material properties for orthotropic behavior in terms of engineering constants.

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## Comments

- Orthotropic materials have three mutually perpendicular planes of
symmetry in their material properties. The stress-strain relation for
orthotropic linear elastic materials can be written as
follows.
(1) Where the compliance matrix $\underset{\xaf}{\underset{\xaf}{S}}$ is given by, The compliance matrix is symmetric and must be positive definite (real numbers for every non-zero value). This implies, from Sylvester’s criterion, that all the principal minors of the matrix are positive. Then, The above set of conditions implies that,$$\underset{\xaf}{\underset{\xaf}{\epsilon}}=\underset{\xaf}{\underset{\xaf}{S}}\underset{\xaf}{\underset{\xaf}{\sigma}}$$If the above conditions are not satisfied, an error occurs. - The thermal expansion coefficient (along X, Y, Z) and thermal properties are given if required for thermal simulations.