Training Module #12: Joints - Point Joints (Click-Along)

Path: C:\HyperX\Training\[Version#]\

Database: Training Module #12 - Joints - Point Joints_[Version#].hdb3

Project: Point Joints - Crew Module

On the left side of your screen, navigate to the FEM Tree.

Press the "Inc" button to look at the entities imported via INCLUDE file. Since the FEM contains a well-structured series of INCLUDE files, this view shows which entities belong to which parts of the vehicle. This allows us to quickly hide/show these parts and more easily turn them into HyperX Structures.

In this exercise, we are focusing on joint fittings which are located underneath the aeroshell and heat shield. We're also going to hide the 1D Elements. Let's hide those parts to have a better view of the underlying Structures.

The quickest way to hide the aeroshell and heatshield is hiding them from the "Inc" view. To do this:

To hide the 1D Elements:

Tip

You can also improve visibility by hiding additional FEM entities (like the coordinate systems) and/or changing model appearance. You can hide the shadows cast by the model by going to the View tab of the Ribbon, pressing the "Appearance" button, and selecting "Shadows" from the dropdown.

In addition to quickly hiding/showing parts of the model, we can use the INCLUDE view to quickly generate HyperX Structures directly from imported FEM elements. To do this:

By creating these Structures from INCLUDE files with "Assign Designs" selected, HyperX will check the property definition in the FEM for all of the parts you're creating structures for. It will attempt to match the material IDs from the FEM with corresponding Materials in the Database. When HyperX finds a match, a Design Property will be created, the Property will be added to the Property Tree, and assigned automatically to the proper Zones. 

When the Structure Creation process is complete, you can review the new Structures and automatically created/assigned Design Properties in their respective Trees.

Review Plate Design Property

By selecting the aluminum plate Design Property, you may notice it is primarily used on the main parachute fittings.

You can review the Design Property by right-clicking it and selecting "Edit". You can see that this is an aluminum plate with a generic .2 in. thickness. You can also see that overrides are in use.

By clicking the overrides button, you will open the Dimension Overrides form where you will see that the thickness for each Zone using this Design Property has overridden the thickness. These values were automatically applied when we selected the "Include Metal Overrides" option when creating these Structures. This was similarly done for the Laminate Design Properties, although their Ply counts were overridden.

Tip

Dimension Overrides allow us to use a single Design Property for all these Zones despite their different thicknesses. Without Dimension Overrides, we would need to define and assign a separate Design Property for each possible thickness to all of these Zones.

The previous step involved defining the fitting panels, which are the sheet objects in the Joints. The next step is to translate CBUSH FEM elements into Point Joints by creating additional Structures. To create the Point Joints that reference the Properties from the last step:

Improving Joint Visibility

If you're struggling to see the Joints on the model, you can increase the rendering size. To do this, go to the View tab of the Ribbon, select "Viewport Settings", increase the "Joint Size" setting, and press "Apply".

Additionally, you can remove the mesh lines from the model by clicking the "Mesh Lines" button on the View tab of the Ribbon.

You can also change the Color Mode to color by Joint to further highlight them.

By expanding the Joint Structures in the Structures Tree, we see there are two kinds: "2 Member" and "3 Member". These represent single and double shear joints, respectively.

Notice that the Joints say they're unassigned. That means that they don't have a Design Property assigned to them.

To assign a Design Property, it has to be in the Database's Library. We could create one by going to the Design tab of the Ribbon and clicking one of the "Joint Designs" buttons.

Using these buttons we can create Edge-Allowable, Fastened, Riveted, or Bonded Joints. However, in this case, program-accepted joint designs have already been created and defined in the Database Template. Therefore, we can expose our Joint Design Properties from the Library.

To import these Properties:

After you close the form, you can see the imported Design Properties in the Property Tree.

Now that we've imported Design Properties for our Joints, we need to assign them. Let's start with the 2 Member Joints. To assign their Design Properties:

Then, repeat the above process for the 3 Member joint with the "HL10-16_Double-Shear" Design Property.

Now that we've imported and assigned our Joint Design Properties, let's review them to understand how we will use them. Right-click the "HL10-12_Single-Shear" property in the Property Tree.

In the resulting form, notice a few things:

Before we can Analyze these Joints, we need to assign the other required properties: Load and Analysis.

Let's start by creating and assigning a Load Property:

Finally, let's import an Analysis Property and assign it to the Joints to prepare them for Analysis.

Now that the Analysis Property is imported, we can see it in the Property Tree and review it. Locate the Property, right-click, and select "Edit".

In the resulting form, we can review the Failure Modes that make up this Analysis Property. Structures assigned this Analysis Property will be evaluated against the criteria defined in these Failure Modes. Let's review the "Fastener Default" Failure Mode by right-clicking it and selecting "Edit.

In the "Criteria" section we can see all of the potential Fastener-related criteria that will used for evaluation. They can be enabled or disabled via checkbox, the required MS can be customized, and they can be set to Limit or Ultimate.

In the "Settings" section, we can view the inputs that are used to determine pretension for these Fasteners.

When you're done reviewing, close the form. Next, we can review the "Fastened Sheet Strength Default" Failure Mode by right-clicking it and selecting "Edit" from the dropdown.

Here you can see we will be using "Bearing-Bypass" criteria. For more info, you can select the blue "i" quick help button or view the help center articles here. When you're done with reviewing these Failure Modes, close all of the forms.

Finally, assign the Analysis Property to all (both 2 and 3 Member) Joints.

With our Structures and Joints created and Properties assigned, we are now ready to Analyze the Joints.

To Analyze the Joints, select them all in the Structures Tree, right-click, and select "Size".

After Analysis is complete, we can use the Legend to view the results. You can open the Legend from the Result tab of the Ribbon.

After opening the Legend, we can see the Margins of Safety on all of the Structures that we Analyzed.

Looks like quite a few of these Joints have negative Margins of Safety. Let's look at the controlling criteria to understand why. To do that:

After investigating the model, we can see where our Fasteners are tension-shear critical. To determine how to address these negative margins, let's take a deeper look at each Joint membership type - starting with 3 Member Joints.

To focus on the 3 Member Joints, let's hide the 2 Member Joints for now. In the Structures Tree, use the dots to the right of the 2 Member Joint structures to hide those Structures.

Let's switch the Legend back to showing Margins of Safety and use the Probe/Label tool to find the minimum and maximum MS.

The Min/Max label will automatically label the minimum and maximum MS for our visible Joints. That allows us to quickly locate the Joints with negative margins so we can interrogate them further.

Next, let's select that min MS Joint, right-click, and select "Analysis Results" from the pop-up menu.

Doing so opens the Analysis Watch Window. Locate the negative MS in the window to see this Joint is Tension/Shear driven. You can also right-click the negative MS and select "Analysis Details..." from the dropdown to view the Analysis Details Report.

The Analysis Detail Report will open in Excel. It gives us a lot more information about this entity, the controlling Design Load Case, forces, and allowables for this entity.

By scrolling all the way over to the right, we can see that the strength/stress ratio for tension is over 1. This means this Joint is critical for tension alone even though it's a tension/shear interaction. We can address the tension failure by changing the Fastener.

To change the Fastener we're using for 3 Member Joints, we need to update the corresponding Design Property for these Joints.

After Analysis is complete, we can see that the previously failing Joint now has positive margins by using the Legend.

By using the Plot/Label tool to find the min and max MS, we can see that the minimum MS is now positive.