Fiber
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/). The Fiber subnode is available for 3D, 2D, and 2D axisymmetry.
Fiber Model
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.
Linear Elastic Material or Nonlinear Elastic 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.
Hyperelastic Material
Select a Material Model — Holzapfel-Gasser-Ogden, Linear elastic, or User defined. The default values of the required model parameters are taken From material.
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The Holzapfel-Gasser-Ogden model defines an exponential strain energy density Wfiber. The values for the Fiber stiffness k1, Model parameter k2, and Fiber dispersion k3 are as a default taken From material. Select User defined to enter other values or expressions.
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Select Linear elastic to use a linear elastic material to describe the fiber stiffness. 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.
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If User defined is selected from the list, select a Material symmetry — Isotropic, Transversely isotropic, or Anisotropic.
Depending on the choice, different stretch invariants are available to define the Fiber strain energy density Wfiber. The default expression for Wfiber is the function 0[Pa]*(item.IaCIe-1), where the variable <item>.IaCIe is the stretch invariant in the fiber direction, and <item> corresponds to the tags of the Fiber node, for example solid.hmm1.fib1. See Fibers for Hyperelastic Materials in the Structural Mechanics Theory chapter for details and more options.
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.
Orientation
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.
See also Distributed Fiber Models in the Structural Mechanics Theory chapter.
Location in User Interface
Context Menus
Solid Mechanics>Linear Elastic Material>Fiber
Solid Mechanics>Nonlinear Elastic Material>Fiber
Solid Mechanics>Hyperelastic Material>Fiber
Ribbon
Physics tab with Linear Elastic Material, Nonlinear Elastic Material or Hyperelastic Material node selected in the model tree:
Attributes>Fiber