Bolt Thread Contact
Use the Bolt Thread Contact node to define a simplified model for the contact between two mating threads. The boundary between the internal and external thread is assumed to have a cylindrical shape. This feature is available for 3D and 2D axial symmetry only. One Bolt Thread Contact node is required for each bolt.
The Bolt Thread Contact node is only available with some COMSOL products (see https://www.comsol.com/products/specifications/).
Pair Selection
From the Pair selection list, choose the contact pair which defines the thread connection for this bolt. The contact pair should be created so that the source boundary is the internal thread, and the destination boundary is the external (bolt) thread.
Bolt Geometry
Enter the Half thread angle, α. The default angle is 30[deg], which is used in for example the ISO and UTS standards. For 2D axial symmetry, this is the only input required to describe the bolt geometry. For 3D, you need also to provide the following settings:
Enter the Lead, l. This is the axial distance a single thread travels after one full revolution of the bolt.
Select a Handedness — Right-handed or Left-Handed. Most bolts are right- handed.
Select a Bolt geometry — Automatic or User defined. If the mesh on the boundaries selected for the contact between internal and external thread give a good representation of a cylinder, the diameter and centerline of the bolt can be determined automatically. If this is not sufficient, you can instead enter the data manually.
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When using Automatic, the computed orientation of the beam axis, ea, is indeterminate with respect to its direction. If needed, you can control the direction by selecting the Direction adjustment check box. Then, enter a vector giving an Approximate orientation, ea,approx. The positive orientation of the bolt axis will be chosen so that .
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For User defined, enter the bolt diameter, dp. Then enter the Orientation of the bolt axis, ea, and a Point on axis, P.
Select a Contact orientation — Both, Up, or Down. In most cases, it is obvious that only one side of the thread will come into contact. It is then possible to decrease the size of the contact problem by considering only that direction. For a prestressed bolt, having the bolt axis orientation vector ea pointing toward the bolt head, it will usually be sufficient to check contact in the Up direction.
Contact
Enter a value or an expression for the Penalty factor, p. A smaller value will increase overclosure and sliding, but is in general more stable. The default value, (2*solid.btc1.Eequ)/solid.btc1.rd, is intended to supply a stiffness which gives a small elastic slip. This slip is related to the estimated bending stiffness of the threads.
Enter a value for the Friction coefficient, μ.
In order to specify contact conditions like this, one or more Contact Pair nodes must be defined in the Definitions branch of the component.
When a contact feature is present in your model, all studies are geometrically nonlinear. The Include geometric nonlinearity check box on the study step Settings window is selected and cannot be cleared.
See also Simplified Modeling of Bolt Threads in the Structural Mechanics Modeling chapter for a complete description of how to model bolt threads.
Location in User Interface
Context Menus
Solid Mechanics>Pairs>Bolt Thread Contact
Ribbon
Physics tab with Solid Mechanics selected in the Model Builder tree:
Pairs>Bolt Thread Contact