Exporting Fiber Orientation Data from PostView

[CVidmar]

Hi all,

I am trying to model the fiber orientation of a undergoing confined compression. I created a material using the fiber-exponential power law with a Neo-Hookean ground matrix. The fibers are distributed using an ellipsoidal model where the ratios of the semi-principle axes (a, b, c values) would represent anisotropy. From my understanding, the fiber strain is found based on the changing orientation of the fibers. Is there a way to export this change in orientation or a way to back-calculate the fiber orientation? For instance, is there a way to export the semi-principal axes of the ellipsoid as a material deforms? Any help would be appreciated!


Thank you,

Chris

[maas]

Hi Chris,

I assume you are using one of the continuous fiber distribution models? We currently don't have a mechanism for defining the anisotropy for a fiber distribution (however, we are in fact working on that). Technically speaking, the ellipsoid that defines the fiber distribution never changes shape as the material deforms. Think of it as a material parameter. Although the material can behave very nonlinearly, the material parameters never change as a result of the deformation. The same is true for the ellipsoid. That said, I understand that you could define a measure of anisotropy by applying the deformation to this ellipse. In order to do that, you could apply the deformation gradient to the principle axes of the ellipse in the material frame. You would then have to fit an ellipse to these deformed vectors. Unfortunately, we don't have a lot of tools in FEBio or PostView that can help you with that. Since I assume you know the principle axes of the ellipsoid in the undeformed shape, you can export the deformation gradient from FEBio for each element. (You can have FEBio write it directly to a text file so you wouldn't have to go through PostView). You could then write some code in MATLAB or so to apply the deformation gradient to the ellipsoid's axes and fit a new ellipsoid to it. As I said, we are working on measures of anisotropy for fiber distributions, but that is still in an early stage, so I'm not sure when that would be available. I hope this helps and let us know if you find a method that works for you, since this definitely is a topic of interest to us.

Best,

Steve