Fiber
Add one or more Fiber nodes to add stiffness in specified directions. The Fiber feature can be used together with a Linear Elastic Material. The assumption is that the volume fraction of the fibers is small when compared to the shell volume.
You can include the effect of thermal expansion of the fiber by adding a Thermal Expansion subnode (see Thermal Expansion (Fiber)).
Fiber Model
Select an Approximation — Wire or Beam. In the wire approximation, only the axial stress in the fiber is taken into account. When using the beam approximation, there will also be a contribution to the bending stiffness, based on the diameter of the fibers. In either case, the fiber will contribute to the bending stiffness of the shell as long as it is not placed at the midsurface.
Select a Material Model — Linear elastic or Uniaxial data. The uniaxial data model is only available when the wire approximation is used.
From the Material list, select the Boundary material (the default) or any other material to define the fiber’s properties. In most cases, you would use the boundary material for the base material, and additional Material nodes without boundary selection as the fiber material.
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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 σa is the linear function 210[GPa]*<item>.emela, where the variable <item>.emela is the elastic strain in the fiber direction, and <item> corresponds to the tag of the Fiber node, for example shell.lemm1.fib1. See Fibers for Linear and Nonlinear Elastic Materials in the Structural Mechanics Theory chapter for details and more options.
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.
Orientation and Placement
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 in-plane directions of the selected coordinate system.
For a Linear elastic material, select the Fiber placement — Top surface, Midsurface, Bottom surface, Volume distribution, or User defined. Fibers represented by a Uniaxial data material model are always assumed to be placed at the midsurface.
For User defined, enter a value or expression in the zrel_offset field for the relative fiber offset. It is given as the ratio between the offset distance and half the shell thickness. A value of +1 means that the center if the fiber is located on the top surface of the shell, and a value of −1 means that the center of the fiber is located on the bottom surface.
Unless Volume distribution is used, enter the Fiber diameter dfiber and the Fiber spacing sfiber. To be consistent with the underlying assumptions, the diameter−spacing ratio should not exceed a few percent. When a beam assumption is used, the fiber diameter is used to compute the bending stiffness.
For Volume distribution, enter the fiber Volume fraction vfiber. To be consistent with the underlying assumptions, it should not exceed a few percent.
See also Distributed Fiber Models in the Structural Mechanics Theory chapter.
Location in User Interface
Context Menus
Shell>Linear Elastic Material>Fiber
Plate>Linear Elastic Material>Fiber
Ribbon
Physics tab with Linear Elastic Material node selected in the model tree:
Attributes>Fiber