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Section 4.8: Biphasic Materials Up Section 4.8: Biphasic Materials Subsection 4.8.2: Permeability Materials

### 4.8.1 General Specification of Biphasic Materials

The material type for a biphasic material is “biphasic”. The following parameters must be defined:
 Specification of the solid matrix solid volume fraction in the reference configuration ( [ ] Fluid density Specification of the hydraulic permeability Specification of the fluid supply
The <solid> tag encloses a description of the solid matrix constitutive relation and associated material properties, as may be selected from the list provided in Section 4.1.3↑. The <permeability> tag encloses a description of the permeability constitutive relation and associated material properties, as may be selected from the list presented in Section 4.8.2↓. The parameter <phi0> must be greater than 0 (no solid) and less than 1 (no porosity). The volume fraction of fluid (also known as the porosity) in the reference configuration is given by . The fluid density specified in <fluid_density> and the solid density specified in <density> within the <solid> tag are needed only when body forces are prescribed.
Example:
<material id="1" name="Biphasic tissue" type="biphasic">
<solid name="Elasticity" type="neo-Hookean">
<E>1.0</E>
<v>0.3</v>
</solid>
<phi0>0.2</phi0>
<permeability name="Permeability" type="perm-const-iso">
... (description of permeability material)
</permeability>
</material>


Section 4.8: Biphasic Materials Up Section 4.8: Biphasic Materials Subsection 4.8.2: Permeability Materials