Step 2: Create and assign materials

Create and assign materials

Next we will create the two materials used in this model: Elastosil (for the elastomeric tube) and Kevlar (for the fibers).

To create the first material, double click on Materials in the model tree. Name the material ‘Elastosil’. This is a nonlinearly elastic material, so we assign it the property Mechanical->Elasticity->Hyperelastic. We will model it using a neo-Hookean strain energy potential. Choose ‘Coefficients’ as the input source, with C10=0.12MPa and D1=0.0. Click OK.

For a bending actuator, instead of defining the Elastosil material, define the materials Smooth-Sil 950 and Dragon Skin 10, as follows:
Double click on Materials in the model tree. Name the material ‘DS10’. This is a nonlinearly elastic material, so we assign it the property Mechanical->Elasticity->Hyperelastic. We will model it using a neo-Hookean strain energy potential. Choose ‘Coefficients’ as the input source, with C10=0.0425MPa and D1=0.0. Click OK.
Make a second material and name it 'SS950'. Again, we will model it using a neo-Hookean strain energy potential. This time set C10=0.34MPa and D1=0.0.

To make the material for the fibers, we double click on Materials again. Name this material ‘Kevlar’. We model it as a linearly elastic material, with properties Mechanical->Elasticity->Elastic. Enter 31067 MPa for the Young’s modulus and 0.36 for the Poisson’s ratio. Click OK. 

Double click on Sections in the model tree. Name the section elastosilSection. Click Continue, choose Elastosil as the material, and click OK.  For a bending actuator, instead of defining the section elastosilSection, use the materials DS10 and SS950 to define DS-section and SS-section.

Double click on Sections again and name this section kevlarSection. Select Beam as the Category and as the Type, and click Continue.

In the ‘Edit Beam Section’ dialog box that appears, click on Create Beam Profile.

Name the profile fiberProfile, and select ‘Circular’ as the shape.

Click Continue, enter 0.0889 as the radius ‘r’ and click OK. This models the fiber as a beam structure with a circular cross section.

In the ‘Edit Beam Section’ dialog box, select ‘Kevlar’ as the Material name and enter 0.36 as the Section Poisson’s ratio. Click OK.

Now we need to assign a material to each of the parts. Expand Merged_Actuator under Parts and double click Section Assignments. Select the actuator and click Done.

Click OK in the ‘Edit Section Assignment’ box.

For a bending actuator, assign SS-section to the caps and the bottom half of the actuator. Assign DS-section to the top half of the actuator.

Expand fibers under Parts and double click Section Assignments. Select the fiber and click Done.

Click OK in the ‘Edit Section Assignment’ box.

In the main toolbar, click Assign->Beam Section Orientation. Select the fiber and click Done. Accept the default n1 direction of (0,0,-1) by hitting enter. Click OK.