Theory Manual Version 3.4
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Subsection 5.3.8: Fung Orthotropic Up Section 5.3: Nearly-Incompressible Materials Section 5.4: Viscoelasticity

### 5.3.9 Tension-Compression Nonlinear Orthotropic

This material model is based on the following uncoupled hyperelastic strain energy function [12]: The isotropic strain energy and the dilatational energy are the same as for the Mooney-Rivlin material (Section 5.3.1↑). The tension-compression term is defined as follows: The parameters are the deviatoric fiber stretches of the local material fibers, The local material fibers are defined (in the reference frame) as an orthonormal set of vectors . The corresponding deviatoric part of the Cauchy stress is and the spatial elasticity tensor is where .
Subsection 5.3.8: Fung Orthotropic Up Section 5.3: Nearly-Incompressible Materials Section 5.4: Viscoelasticity