Rivets
Table of contents
About
The Rivets is a load feature where so called “Rivets” are created and placed in a group folder in the current structural (or thermal) analysis. The Rivet is constructed of BEAM188 solid circular beam element for the rivet shaft and a CERIG or RBE3 remote points for the heads and intermediate sections. In thermal analysis LINK33 is used. This is the similar as the standard “Beam connection” except that rivet creates one beam element for each layer in the connected assembly. The additional features with the Rivets compared to “Beam connection” are that:
- Multiple rivets can be defined in one load object, i.e. all D12 rivets of the model.
- A point mass (MASS21 element) can be added to the rivet head to account for missing mass.
- All rivets are saved in one place, the “Rivets Group” folder.
- The rivets can have different orientation.
- Custom Behavior for the “Head” interaction can be defined in an APDL macro.
- Thermal loads on the bodies will be mapped to the rivets to account for correct thermal elongation.
- Post processing of the Rivets is done using the Rivets Result object.
Usage
Click on “Rivets” in the toolbar to insert the Rivets Group folder in the current static analysis as well as creating the first Rivets load object. To add additional rivets, right click on the Rivets Group folder and select “Add Rivets” or click on “Rivets” in the toolbar. You can also use “Duplicate” on an existing Rivets and modify the properties.
Inputs to define the rivets are:
| Rivet Holes | |
|---|---|
| Scoping Method | Geometry Selection/Named Selection |
| Geometry | Circular edges connected to non-cylindrical faces. (i) |
| Definition | |
| Material | Select material from “Engineering Data” or App default materials. |
| Nonlinear Effects | No (Default)/Yes. Use plasticity models defined in the selected material (ii) |
| Shaft Diameter | Rivet diameter that defines the circular solid section for the beam element. By default the minimum diameter from the hole selection is filled in. |
| Head Diameter | Sets the maximum size of the rivet heads. By default two times the shaft diameter is used. |
| Head Mass | Add the missing mass (optional). Default calculated to the mass of a sphere section based on steel density. The sphere section diameter, D, is the “Head Diameter” and the sphere section height, h, is D/(2√3), see the figure above. |
| Max thickness | Search distance for creating rivets, i.e. maximum part thickness along the rivet shaft. |
| Behavior | Rigid/Deformable/Custom. |
(i) Geometry
Both shell and solid bodies are supported. At least two sets of hole edges are needed to create a valid selection.
(ii) Material
The following material properties (and corresponding MAPDL MP Lab) are supported: Young’s Modulus (EX), Poisson’s Ratio (NUXY), Density (DENS), Coefficient of Thermal Expansion (ALPX), Thermal Conductivity, (KXX), Specific Heat (C), Isotropic Hardening (BISO & MISO), Kinematic Hardening (BKIN, KINH). If orthotropic properties are defined the X component is automatically used (EX, NUXY, ALPX & KXX).
Graphics
A graphic representation is created once valid inputs are given. At least two sets of hole edges are needed to make a valid selection. The Rivets load object searches to connect the holes with a distance less than Maximum thickness. Hole centroids with a distance less than 5% of the Maximum thickness are made coincident. This tolerance value can be edited in the preference file. The active hole edges are plotted in thick red lines. The head diameter is plotted as a green disc (normal to the rivet shaft) and the rivet shaft as a thick green line. Un connected hole edges are plotted in thin red lines. If the coincident edges don’t match the average centroid is used when creating the rivet so that the rivet shaft is straight. The rivet section Id number is printed at the center of each connected edge. This number is used in the result tables. The printing of Id number can be turned off in the preference file “showRivetId = False”.
A property file is also written to the solver files directory that is used by the Bolt Report feature.
Custom behavior
The Rivets connection behavior is defined in the macro file “buildRivet.mac” found in the extension installation folder. (%AppData%\Ansys\v2XY\ACT\extensions\BoltToolkit_V2XY.Z)
Edit the file in the sections “*else ! ‘Custom’” to define any type of connections using the center node on the rivet shaft (_npilot) and the selected edge nodes.
