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 Material, Nonlinear Elastic Material, or Hyperelastic Material. The assumption is that the volume of the 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
Linear Elastic Material or Nonlinear Elastic Material
Select a Material Model — Linear elastic or Uniaxial data.
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. This selection will be overridden if you use the User defined option for a certain material property.
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For Linear elastic enter the Young’s modulus Efiber and Density ρfiber. The defaults are taken From material. Select User defined to enter other values or expressions.
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For Uniaxial data enter the Uniaxial stress function σax,a and Density ρfiber. The defaults are taken From material. Select User defined to enter other values or expressions. The default user defined expression for σax,a is the linear function 210[GPa]*<item>.eea, where the variable <item>.eea is the elastic strain in the fiber direction, and <item> corresponds to the tag of the Fiber node, for example solid.lemm1.fib1. See Fibers for Linear and Nonlinear Elastic Materials in the Structural Mechanics Theory chapter for details and more options.
Enter the fiber Volume fraction vfiber. To be consistent with the underlying assumptions, it should not exceed a few percent.
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.
Hyperelastic Material
Select a Material Model — Holzapfel–Gasser–Ogden, Linear elastic, Uniaxial data, or User defined. The default values of the required model parameters are taken From material.
From the Material list, select the Domain material (the default) or any other material to define the fiber 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. This selection will be overridden if you use the User defined option for a certain material property.
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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 or Uniaxial data to describe the fiber stiffness. See Linear Elastic Material or Nonlinear Elastic Material for details.
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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 isochoric 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.
For the Holzapfel–Gasser–Ogden model, select the Use isochoric deformation check box to account for the fiber incompressibility. See Compressible Fibers in the Structural Mechanics Theory chapter for details.
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