Fasteners
The Fasteners node is intended for a simplified modeling of fasteners like rivets or bolts. It is based on the assumption that the holes for the fasteners are present in the shell geometry. The edges of each pair of holes are joined using an elastic connection.
The actual selection of the pairs of holes to be connected is done in an Hole Selection subnode.
When one or more Fastener nodes are active in the model, three entries will be added to the list of predefined plots:
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A Fastener Forces plot group, showing the normal and shear forces at each fastener as arrows, and a label showing the identity number of each fastener.
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A Fastener Forces evaluation group, containing a table of the normal and shear forces of all fasteners.
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A Connected Region Indicator plot group, containing a line plot showing the hole edges on the destination surface where the fasteners are active. If there are other connection features in the Shell interface, all connection indicators appear in the same plots.
Note that if you change the number of fasteners in your model, and compute new results, then you must delete the Fastener Forces plots and evaluation groups, and add them again from the list of predefined plots.
Location
The sides of the shells (top or bottom) that are to be connected must be known. The information is used for two purposes: to connect to the correct set of displacements, and to compute the distance, including the shell thickness and offset. Select Connected location — Automatic or Manual. In the automatic mode, the two sides of the shells that are found to be closest to each other are connected. If you want to make another choice, or the if the automatic search for some reason does not give the intended result, select Manual.
In manual mode, the Source and Destination lists are shown. Select Top surface or Bottom surface from both lists.
There are some uncommon cases for which the automatic mode will fail. If this happen, you will get an error message. You can then either move to manual mode or, for some cases, use several Fasteners nodes having smaller selections.
Fastener Stiffness
The stiffness of the fasteners can be computed in two ways, either using analytical expressions based on that the fastener is approximated as a beam, or by direct entry of stiffness values. From the list, select Beam or User defined.
Beam
The normal stiffness, kn, and shear stiffness, ks, of the fastener are computed using the following expressions:
The four compliance contributions are defined as
In these expressions
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df is the diameter of the fastener.
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Ef, Esrc, and Edst are the elastic moduli of the fastener, the shell on the source side, and the shell on the destination side respectively.
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νf is the Poisson’s ratio of the fastener.
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dsrc and ddst are the thicknesses of the shell on the source and destination sides respectively.
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The multipliers αm are multipliers that make it possible to adjust the default analytical values.
Enter the following data for the fasteners:
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Diameter, df.
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Young’s modulus, Ef.
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Poisson’s ratio, νf.
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Bending flexibility multiplier, αb.
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Shear flexibility multiplier, αs.
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Fastener bearing flexibility multiplier, αbr.
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Plate bearing flexibility multiplier, αpbr.
User Defined
Enter the Normal stiffness, kn, and Tangential stiffness, ks.
Advanced
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog.
Select the Search method — Closest point or Manual to specify what should happen if an evaluation point in the destination boundary is mapped outside the source boundary.
The Closest point method is the default and most robust search method. The closest point in the source selection is used by the mapping operator, even if that point is far away from the destination point. This method is not as efficient as the Manual method.
The Manual method is an alternative search method that is computationally efficient, but its robustness is determined by the curvature of the boundaries, the Search distance, and the Extrapolation tolerance. Specify the maximum search distance between the source and destination boundaries and the extrapolation tolerance.
See Advanced Settings for Nonlocal Couplings in the COMSOL Multiphysics Reference Manual for more information.
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Simplified Modeling of Fasteners
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Theory for Fasteners
Location in User Interface
Context Menus
Shell > Connections > Fasteners (Boundary)
Ribbon
Physics tab with Shell selected:
Boundaries > Connections > Fasteners