In HyperX, Joints are entities that allow for the Analysis and Sizing of the joining mechanism between Zones. Bolted Joints contain Fasteners or Rivets which can be modeled discretely in the FEM (making them Point Joints) or simulated along Zone boundaries (in the case of Edge Joints).
Bolted Joints, like all other Joints, can be organized in Structures and Sets in the Structures Tree. As mentioned above, Bolted Joints can either be Edge or Point Joints depending on whether the connector elements are discretely modeled in the FEM. They can be classified further based on the members of the joint:
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1 Member Joints - Edge Joints with discontinuous skin over the joint.
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2 Member Joints - Edge Joints with continuous skin over the joint OR Single Shear Point Joints.
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3 and 4 Member Joints - Double and Triple Shear Point Joints, respectively.
The following sub-sections describe how to represent Bolted Joints as Edge and Point Joints (including connector modeling techniques) to help you get the most use from HyperX's joint analysis capabilities.
Edge Joints
Edge Joints are defined on the boundary between two Zones. To create an Edge Joint: select a boundary, right-click, and select "Create Joint".
From here you can select whether you want this to be a 1 or 2 Member Joint. Make your selection based on whether the skin over the joint will be discontinuous or continuous, respectively.
While this form is open, the Viewport will also show arrows pointing from the Joints based on the current selections in that form; these represent the pull-off direction of the joint. Additionally, the Zones on either side of the Joint have been color-coded to indicate which Zone will be which member.
Once the Joints are created, you can see the model updates to show them. These Joints are now Structures which can be selected in the Viewport or the Structures Tree.
Note
To learn how Edge Joints are used when extracting and processing loads, see Edge Joint Loads.
Point Joints
For a Bolted Joint to be a Point Joint, its connectors must be discretely modeled in the FEM so the process for creating them is a bit different than for Edge Joints. First, you must import the FEM ensuring that "1D Connectors" are imported.
Next, we need to create Structures for the Point Joints. Navigate to the FEM Tree, select the connector elements, right-click, and select "Create Structure".
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Organizing structures in the imported FEM with INCLUDE files can be useful for quickly selecting Joint Structures from the "Inc" view of the FEM Tree.
On the "Structure Creation" form, you will see FEM properties referenced by the elements selected, PBUSH in this case. Select "Create point joints per connector element" and "Create structures per include files" (if using INCLUDE files) and press "Create".
When done you can find the new Joints in the Structures Tree and on the model in the Viewport.
Note
To learn how Point Joints are used when extracting and processing loads, see Point Joint Loads.
Connector Modeling
To ensure the best results, it is important to understand the relationship between connector modeling techniques and HyperX Joint Load Extraction/Processing methods. Load extraction and processing differs based on whether the Joint is analyzed as an Edge Joint or Point Joint.
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Bolted Joints can be represented as Edge or Point Joints. However, when the connector elements are discretely modeled, they must be represented as Point Joints.
To make the most of HyperX's Bolted Joint capabilities, reference the image above and make the following considerations when modeling connector elements:
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CBUSH elements must be attached either directly or via RBE to different Zones on both ends. If they are not connected to different Zones, HyperX will create 0 or 1 member Joints which have limited functionality.
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RBE may be RBE2 or RBE3. RBE3 is recommended.
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The outer-most 'Grid A' represents the connection to 'Sheet 1'. For countersunk fasteners, this will be the countersunk skin.
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It is important to align 'Grid A' and 'Grid B' directions for each spring in series. However, the local shear (y-z) planes do not have to be perfectly aligned between springs - HyperX will make the proper transformations, into-sheet coordinates defined by material vectors, and shear force vector sums to compute the sheet bearing for Sheet 2.
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HyperX can handle zero-length CBUSH elements (where 'Grid A' and 'Grid B' are coincident) for single and multi-lap joints with the following considerations:
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They require a reference coordinate system, and the X-axis direction of that reference CS becomes the axial direction in HyperX.
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Zero-length CBUSH elements in multi-lapped joints must all reference the same or identical coordinate systems, or HyperX won’t recognize them as being part of the same joint.
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You can create a multi-lap joint that is a mix of zero-length and non-zero length CBUSHs, as long as the zero-length CBUSHs have a CS X-axis that aligns with the Grid A to B direction of the non-zero length element.
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Note
While specific Design Properties and Failure Criteria differ between Fastened and Riveted Joints, they function almost identically from a UI perspective. As such, the following tutorials can be used for either style of Joint as long as appropriate connector elements and Properties are used.
Initial Setup
You must assign a Design, Load, and Analysis Property to a Bolted Joint to Size and/or Analyze it. To do that:
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Drag the desired Property from the Property Tree onto the selected Joint. The assignment will be confirmed by the Joint momentarily changing color in the Viewport.
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Repeat for each desired Property.
Load and Analysis Property settings function similarly to those for Zones albeit using Joint-specific loads and criteria (see Fastened and Riveted criteria). The biggest differences between Sizing Zones and Joints comes from the Design Property settings.
Design Properties
Analysis of Bolted Joints involves assessing all objects in the joint - including the bolt, nut, fastened sheet(s), and so on. Joint Design Properties define the design space for the Joint by defining these elements. This information includes Material data for connected sheets, Fasteners or Rivets, and other variables such as sheet thicknesses, number of connector rows, etc.
When viewing a Joint Design Property, the first thing to note is the Sizing/Analysis mode.
There are 3 modes for a Joint Design Property:
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Sizing - Size the Joint in the defined design space to find the minimum weight solution.
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Advanced Sizing - Size the Joint in the defined design space with a user-defined order of operations.
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Analysis - Evaluate MS for the Joint based on the currently defined design.
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These modes are discussed in more detail in the Sizing and Results Interrogation sections.
One key difference between Fastened and Riveted Joint Design Properties is whether they feature Fasteners or Rivets - otherwise the forms look and function nearly identically. The other key difference is in the kinds of Joints that can be represented by these Design Properties:
Sizing
When "Sizing" mode is selected, Joints can be Sized by:
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Selecting the desired Joints.
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Clicking "Size".
Note
When a Joint Design Property is set to Analysis mode, Analysis will be run instead of Sizing on that Joint when you click "Size".
Advanced Sizing
The standard Sizing method for Joints will find the minimum weight design with all positive margins. However, that solution may not be easily manufactured.
A Joint in Advanced Sizing mode allows a user to specify multiple options for each variable, as well as the order of operations HyperX should use when resolving margins. This allows you to tailor the Sizing process to find the solution that works best for your situation.
A few things to notice here:
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By clicking the "Sizing" and "Advanced" buttons, we set the Design Property to Advanced Sizing mode.
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Using the "Type" and "Selection(s)" columns, we can specify one or more options for each available input. For instance, we can specify multiple Fasteners to potentially choose during Sizing.
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The "Seq..." column is how we specify the order of operations HyperX will follow when trying to resolve margins with different variables. After each change, it will re-Analyze the Joint. If the margins are still negative, it will try the next variable in the list. If margins are still negative after all operations, HyperX starts over at the next value for the first variable in the sequence.
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The "Order" column specifies the start and procedure for stepping through a range of options for a variable (i.e. start at the max or min and step down or up, respectively). In the image above, as HyperX tries different fastener spacings based on these settings, it would start at 2 inches, then try 1.75, 1.5, 1.25, and 1 inch.
Given the example above, HyperX will:
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Decrease the spacing between fasteners.
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Add a row of fasteners.
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Try the next fastener.
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Repeat from Step 1, if necessary (i.e. there are still negative margins).
After the Joint(s) have been Analyzed or Sized, HyperX features a number of visualization tools and Stress Reports to view and interrogate results:
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The Legend can be used to visualize Margins of Safety, Controlling Criteria, etc. on the model in the Viewport.
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The Probe/Label tool can be used to quickly find and label Joints with the min and max MS.
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The Analysis Watch Window provides more detail about all of the criteria evaluated for the selected Joint(s) and corresponding MS values for those criteria/objects.
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The Analysis Details Report provides even more detail on the criteria found in the Analysis Watch Window such as the controlling design load case, forces, allowables, and more.
The image above shows how to use these tools to determine why some Joints are failing Analysis:
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Using the Legend and Probe, we find the Joint with the lowest MS.
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Opening the Analysis Watch Window, we find that the negative MS in this Joint driven by Tension/Shear interaction in the Fastener.
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Diving deeper into the Analysis Detail Report, we find the strength/stress ratio for tension is over 1 meaning the Joint is critical for tension alone even though it's a tension/shear interaction.
That information informs the decision to use Fasteners with greater allowable tension.