Visualizing fibers and fiber stretch

[adgomez]

Hi,

Has anyone found a simple way to visualize fibers, or fiber stretch in PostView? Normally use a wrapper script that takes the symmetry vectors from the model, tensor data from the solution, and writes a .txt file with the information, then add it to PreView as a data field (vectors for fibers, and scalars or fiber stretch).

It never occurred me to ask if there was a built-in way to do this...

Thanks,

Dave.

[maas]

Hi Dave,

If you add the following to the plotfile section in your feb input file:

<var type="fiber vector"/>

FEBio will export the fiber vectors to the plot file. In PostView you can visualize them using a vector field.

To visualize fiber stretch, you can add

<var type="fiber stretch"/>

Cheers,

Steve

[adgomez]

That is perfect.

Thanks,

Dave.

[ntjacobs]

I'm not sure I'm getting this to work correctly. As a simple example, for a 20% uniaxial stretch along the X axis, I am getting a fiber stretch in postview of 1.2 whether I align the fibers in the x direction or the y direction. I thought maybe I had incorrectly assigned fiber alignment, but I checked that for the Y direction the effective stress was equivalent to the same test with no fibers present, and with fibers aligned in the x direction the stress is orders of magnitude greater. I am using a solid mixture material, is it possible this feature is not available for solid mixtures, or am I doing something else wrong?

Thanks!

Nathan

[ntjacobs]

I dug a little deeper on the forum and found a post from Gerard that explains the situation better. I've copied his answer here for reference for anybody that reads this thread later:

Displaying the fiber direction using <var type="fiber vector"/> will only show the x-direction of the material axes' xyz-coordinate system. The parameters theta and phi represent fiber directions relative to these local material axes. Unfortunately, you will not be able to visualize these theta-phi directions directly in PostView using this command. (Also keep in mind that the user is free to add any number of fiber materials in a solid mixture, yet the <var type="fiber vector"/> command can only plot one such direction.)

I agree that it would be nice to visualize fiber directions as a material deforms. In practice, I believe it would not be easy to implement that feature, but you could submit a feature request and Steve and I could discuss it to decide what could be done.

[apaz]

Hi,

I am using FEBio Studio 1.0, FEBio 3.0. And these variables (fiber vector and fiber stretch) are not being plotted. I was able to see them using FEBio 2.9.1 and PostView 2.5. What could be the cause of this?

Kind regards,
Alex

[maas]

Hi Alex,

In FEBio3, fibers are defined as an explicit material property. This is different in FEBio2, where the fiber direction was usually the first column of the local material axes. This means that the "fiber vector" and "fiber stretch" plot variables are only stored if the material has this fiber property. Currently, only the top-level (elastic) material is checked, so if your fiber is embedded in a solid mixture, it will also not work. If you can send me your input file, or at least your material definition, I will look into this a little more and try to come up with a solution.

Cheers,

Steve

[apaz]

Fibers07.feb

Hi Steve,

This is an example of input file, I am trying to use different families of fibers. It would be nice to visually verify the orientation of fibers, especially when user-defined distributions are used. Thank you for your time.

Alex

[maas]

Hi Alex,

I have this working now in the development version of FEBio3. Since multiple components of the solid mixture can have fiber properties, you need to specify which component you want to get the fiber vector from. The syntax is:

<var type="fiber vector['solid[1]']=fiber1"/>

The square brackets allow you to provide a filter. In this case, the filter is the name of the material component, which is solid[1]. The text after the equal sign (fiber1), is the name of the plot variable as it will show up in FEBioStudio. If you'd like to try this version out, please send me an email (steve dot maas at utah dot edu), and I'll point you to our development version.

Cheers,

Steve

[apaz]

Hi Steve,

Yes, I am interested in trying this version and this feature. I am sending you the email. I appreciate your commitment.

Regards,
Alex