Fasteners
The Fasteners node is designed to enable simplified modeling of fasteners such as rivets and bolts. It assumes that the corresponding fastener holes are already defined in the geometry. Typically, two plates are connected using an elastic connector. Two types of such connections are available:
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The edges of matching holes are connected.
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Boundaries surrounding the matching holes are connected. Such boundaries should typically match the size of the rivet heads or washers.
The latter type of connection offers greater accuracy and helps reduce local stress concentrations, especially when bolts are modeled. Creating such connections requires a more detailed geometric representation, in which the fastener holes are enclosed by appropriate, typically annular, boundaries.
The actual selection of the pairs of holes to be connected is done in the Hole Selection subnode.
When one or more Fasteners nodes are active in the model, five entries will be added to the list of Result Templates:
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A Fasteners Forces plot group that shows the normal and shear forces at each fastener and a label for the identity number of each fastener. The fasteners forces have to be evaluated first in the Fasteners Normal Forces and the Fasteners Shear Forces evaluation groups. The coloring can be affected by the addition of a Safety subnode.
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A Fasteners Normal Forces evaluation group that contains a table of the location, the normal forces, and the damage index of all fasteners. Evaluate this table to display the forces in the Fasteners Forces plot group.
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A Fasteners Shear Forces evaluation group that contains a table of the location, the shear forces, and the damage index of all fasteners. Evaluate this table to display the forces in the Fasteners Forces plot group.
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A Fasteners Forces Magnitude evaluation group that contains a table of the normal and shear forces magnitude of all fasteners.
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A Connected Region Indicator plot group that contains a line plot or a surface plot showing the hole edges or hole surrounding boundaries, respectively, on the destination surface where the fasteners are active.
You must evaluate the Fasteners Normal Forces and Fasteners Shear Forces evaluation groups to update the Fasteners Forces plot group if you change the number of fasteners in your model and compute new results.
Also, you need to remove the Connected Region Indicator plot group and replace it by a new one if you change the hole selection type between edge or boundary.
Fastener Properties
Enter
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Diameter, df for the fasteners diameter.
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Plate thickness, destination tdst for the plate thickness on the destination side.
From the Plate thickness, source list select Same as destination or User defined to reuse the thickness as tdst or to enter a different value for tsrc.
The stiffness of the fasteners can be computed in two ways:
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Use analytical expressions when the fastener can be approximated as a beam.
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Enter the shear and normal stiffness values.
From the Fastener model list, select Beam or Spring.
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, and νf are the elastic modulus and Poisson’s ratio of the fastener, respectively.
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Esrc, and Edst are the elastic moduli of the shell on the source side and destination side, respectively.
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tsrc and tdst are the thickness of the plate on the source and destination sides, respectively.
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The multipliers αm make it possible to adjust the default analytical values.
Enter the fasteners data:
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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.
Select Include pretension to add a load to the fastener normal force definition.
Pretension
This section is only visible when Include pretension is selected.
When pretension is included, the normal stiffness, kn, is corrected to include an estimated head stiffness by the following expression:
Enter the Pretension force, Fpre.
The Grip stiffness can be specified in two ways: either by using analytical expressions based on the simplified pressure-cone method or by directly entering stiffness values.
From the list, select Shigley’s frustum, 1 material; Shigley’s frustum, 2 materials; or User defined.
Select Shigley’s frustum, 1 material when the plates have the same Young’s modulus. Select Shigley’s frustum, 2 materials when the Young’s moduli are different.
When both plates have the same material, the grip stiffness is evaluated as
For Shigley’s frustum, 1 material or Shigley’s frustum, 2 materials enter
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Washer diameter, dw.
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Hole diameter, dh.
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Frustum angle, αsh.
For User defined enter values or expressions for the Grip stiffness, kg
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Simplified Modeling of Fasteners
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Theory for Fasteners
Location in User Interface
Context Menus
Solid Mechanics > Fasteners
Ribbon
Physics tab with Solid Mechanics selected:
Global > Fasteners