The parameter "density" of Neo-Hookean material

[wxy0901]

Hello everyone,

I'm a using FEBio and Gibboncode to model the growth process of the human brain. I calculate the density (W), the Young's Modulus (E) and the Poisson ratio (v) on Matlab, so I wish customize the Neo Hookean material which I apply differentially to each mesh tetra. I'm taking a look to the NeoHookeanPI plugin, but I don't see the definition of the density.

In addition, the parameter "density" of Neo-Hookean in FEBio is or not the volumetric strain energy density? How does FEBio calculate Cauchy stress based on this density?

Thank you.

Xiaoyu

[maas]

Hi Xiaoyu,

The "density" parameter in FEBio is the initial (or reference) material density (i.e. mass per volume). It is not the strain energy density and it is only used for dynamic analyses. Since the strain energy density is calculated from the deformation gradient and material parameters, you don't need to add another parameter for the strain energy density. I hope that answers your question.

Cheers,

Steve

[wxy0901]

Hi Steve,

Thank you. So if we want to define our own strain energy density calculation formula, do we have to use the plugins?

Cheers,

Xiaoyu

[maas]

Hi Xiaoyu,

Yes, you will need to implement this is as a plugin. To be more specific, you will need to implement a new material plugin and write a stress and tangent function. In this new material you can then also implement a strain energy density and allow that to influence your stress and tangent.

Cheers,

Steve