Add one or more Fiber nodes to add stiffness in specified directions to a solid material. The Fiber feature can be used together with Linear Elastic, Nonlinear Elastic or Hyperelastic materials. The assumption is that the volume of fibers is small when compared to the base material.

The Fiber node is only available with some COMSOL products (see https://www.comsol.com/products/specifications/).

From the Material list, select the Domain material (the default) or any other material to define the fiber’s properties. In most cases, you would use the domain material for the base material, and additional Material nodes without domain selection as the fiber material.

Enter Young’s modulus Efiber and Density ρfiber. The defaults are taken From material. Select User defined to enter other values or expressions.

Enter the fiber Volume fraction vfiber. To be consistent with the underlying assumptions, it should not exceed a few percent.

Select a Material Model — Holzapfel-Gasser-Ogden, Linear elastic, or User defined. The default values of the required model parameters are taken From material.

Select the Stiffness in tension only check box in order to make the fibers contribute to the total stiffness only when the strain in the fibers is tensile.

Select the Contribute to total stress check box if the stress in the fibers should be added to the stress tensor of the parent material in an average sense. Usually, you do not want this, since the fiber stress would then affect other material options in the matrix material, such as plasticity.

Select a Fiber orientation from the list. The available choices are the axis directions of the coordinate system selected in the Coordinate System Selection section, or User defined. For User defined, enter a Direction. The direction vector a is interpreted in the selected coordinate system.

Physics tab with Linear Elastic Material, Nonlinear Elastic Material or Hyperelastic Material node selected in the model tree: