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Fibersim 101: (5 of 14) Core

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Welcome to Fibersim 101, a step-by-step series of articles meant to familiarize new users with the key concepts of the software. We recommend starting with Part 1 and downloading the “” file at the bottom of that page in order to follow along with these exercises. If you need to go back to Fibersim 101: (1 of 14) Model Setup click here.


Core objects in Fibersim are used to represent insert components of a composite layup, such as rigid foam panels or honeycomb slabs. These Core objects are defined using a laminate surface and 3D boundary, at a minimum, and sequence and step values are used to specify each Core’s order in the laminate stackup. There are four types of cores: 

  • Modeled Core 
  • Virtual Core 
  • Virtual Step Core 
  • Virtual Variable Core 

Modeled Core objects in Fibersim are typically used when designers are already aware of what the final “as flown” shape of the finished part will be. Since geometry is pre-determined, users must create an additional laminate in conjunction with a Modeled Core object. This laminate—a child of the main outer mold line (OML) tool surface—will often represent either the direct over-core tool surface or the actual final inner mold line (IML) shape.  

The advantage to using Modeled Core is that accurate producibility and flat pattern data can be generated for over-core plies. For Modeled Core objects, users define only the boundary, or footprint, of the core, while Fibersim determines the core’s 3D shape based on the over-core laminate’s layup surface geometry. Producibility analysis for all plies created as children of the over-core laminate will be performed using its layup surface, while core sample and laser projection data will be calculated by measuring the distance between the over-core surface and the parent OML laminate’s layup surface. 

An example of the “create Modeled Core” form is shown below: Cores1.jpg

Virtual Core objects in Fibersim are often used when the final part (or core) shape is not known beforehand, or otherwise when the core shape is to be determined analytically based on parameters defined by the user, rather than measured based on surface geometry. For Virtual Core, users define the boundary, or footprint, of the core on the 3D layup surface, as well as the cross-sectional shape of the core, using numeric values for thickness, bevel angle, and blend radius. 

  • In our example model, please create a Virtual Core by clicking on “Core” in Fibersim’s left-hand Applications tree, right-click in the main right-hand window, and choose Create New > Virtual Core as shown below: 


The “create Virtual Core” form should then appear. The goal is to set up the form as follows: Cores3.jpg

  • First, fill out the Name, Sequence, and Step as shown above. For the Parent, please click the pull-down arrow and select our “DUCT” laminate.
  • For the Material, please click the database link button and choose “Honeycomb” from the list of materials, as shown below:  


  • Next, under “Geometry”, click the link geometry button for Origin and select the core origin point as shown in the images below:  




  • Finally, click the link geometry button for Boundary, and select the curves shown below: 




  • Under “Core Top”, the default values for Thickness and Bevel Angle can be used. Please note that the Thickness value entered on the Virtual Core form will override the selected core Material’s thickness value from the database. Click OK to save the Virtual Core object. 

Virtual Step Core and Virtual Variable Core objects in Fibersim operate in very much the same way as Virtual Core. Again, no over-core or IML laminate is required, and the shape of the core is determined analytically based on user-defined parameters, rather than by CAD surface geometry (as in the case of Modeled Core). 

What makes Virtual Step Core and Virtual Variable Core unique is the way they are parameterized. A Virtual Step Core assumes that there is a core-bottom with a 90-degree bevel angle. On top of this constant-thickness “step”, there is a core-top section with the more-familiar bevel angle. An example of a Virtual Step Core form can be seen below (note that the same core geometry can be defined by a Virtual Core with a Core Bottom defined with a specified Thickness and a Bevel Angle of 90): 


Virtual Variable Core, on the other hand, is useful for more exotic core geometries, where the bevel angles may not be consistent or known ahead of time. Instead, CAD curves representing boundaries must be selected for the main footprint, as well as the footprints for the Core Top and Core Bottom. An example of this form can be seen below: 



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