FEBio Tutorial 5: Biphasic unconfined compression

The model for this tutorial is the unconfined compression of a porous biphasic material.

An axial direction prescribed displacement is applied to a cylinder model.

The displacement is held constant after loading and the interstitial fluid flow through boundaries induce the material relaxes in the radial direction.

 

Creating the geometry

Creating a cylinder (radius 1 and height 1).

Meshing with the following parameters

Meshing type = Wedged center, Slices = 30, segments = 30, stacks =1, R-bias = 0.9

To reduce the computational time using the symmetry condition with the quarter model.

Similar to tutorial 4, delete elements of 3/4 model.

1. Convert the mesh to the editable mesh.

2. Mouse right-click for top view.

3. Click select elements tool at the bottom toolbox.

4. Click Edit at the Main menu bar and Delete selection

Setting up the boundary conditions

Applying the symmetry boundary conditions at the planes of y-z, x-z, and x-y.

1. Click Boundary Conditions.

2. Select Fixed displacement.

3. Click x displacement at the Properties.

4. Select the surface at the y-z plane.

5. Add the selected surface.

Repeat the above procedures for the planes x-z and x-y.

All steps are the same as the previous setup except Properties part.

For x-z plane

Constrain y displacement.

For x-y plane

Constrain z displacement.

Setting up Fixed fluid pressure boundary condition at the outer surface of the cylinder.

1. Click Boundary Conditions.

2. Select Zero fluid pressure.

3. Click pressure at the Properties.

4. Select the surface at the outer curved surface.

5. Add the selected surface.

Applying a prescribed displacement (z-direction) to the top plane.

1. Click Boundary Condition.

2. Select Prescribed displacement.

3. Select z displacement at the Degree of freedom and set scale as 1.

4. Select the top surface and add it to the Selection.

5. Setting up Curve Editor under Tool menu bar.

6. Setting up the first point: 0, -0.01.

7. Setting up the first point: 2000, -0.01.

Setting up material properties.

1. Click Add Material

2. Select multiphasic at the Category.

3. Select biphasic at the Material.

4. Select isotropic elastic at the solid Material.

5. Select perm-const-iso at the permeability.

6. Setting Young’s modulus (= 1) and Poisson’s ratio (= 0.15) for the solid materials.

7. Setting permeability (= 0.001).

Setting up the analysis.

1. Click Add Analysis step at Steps.

2. Select Biphasic.

3. Setting up parameters for the step.

Time steps = 20000, Step size = 0.1, Max step size = 100, Min step size = 0.001

Auto time stepper = checked, Optimal iterations = 40.

Running simulation

Please see the previous posting.

Result: select effective fluid pressure

Reference

Tutorial 5 from https://help.febio.org/PreView/PreView_2_1/index.html