Training Module #10: Stiffened Panels - Stiffener Laminate Families (Click-Along)

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Project: Stiffener Laminate Families

Before getting into Stiffener Laminate Families, let's briefly review standard Laminate Families. Open the Library and double-click on the "Laminate Families" section.

In the resulting form, double-click or right-click and "Edit" "LF Skin - 7".

In the resulting form, there are a couple things to notice:

Close the "LF Skin - 7" Laminate Family form and double-click "LF Stiffener - 1 - New 2".

This is the Editor version of the Stiffener Laminate Family form; there is a Generator version we will use in the next part of the tutorial. There are a lot more features to this form than the general Laminate Family form we will go into later. For now, let's focus on four things:

If you would like to view a diagram to understand what these sections of the table correlate to in a physical stiffener, you can view this by clicking the blue "i" QuickHelp button in the top-right corner of the form.

This diagram and the table layout will change based on the stiffener concept used. In the next part, we will primarily work with a SLF for a corrugated/hat stiffener but will briefly review an I-stiffener to highlight some of those differences.

When you're done reviewing the form, you can close it and the "Laminate Families" form.

From the Composite tab of the Ribbon, select the Laminate Family button.

From the popup, select "Generate Stiffener Laminate Family" and from the dropdown select "Corrugated".

This opens the Generator version of the Stiffener Laminate Family form. It starts with only a single layer so let's add a few more to define the MSS for this Stiffener Laminate Family in the next step.

In the Stiffener, the Base laminate continues throughout the entire Stiffener without any ply drops. Ply drops throughout a stiffener only come from Charges. It's also important to note that the Base is mirrored for analysis. These concepts are illustrated below.

The Main Stacking Sequence is defined in the Base section of the Generator version of the Stiffener Laminate Family form. To define one, we need to add a few layers to the Base laminate. Do this by clicking the "Add Row" button a few times to add more layers/rows to that section of the table.

Now let's update the "Angle" values. The values in this column define the MSS. We'll go for a quasi-iso laminate.

Now that the MSS is defined, we need to actually create the Base laminates to add the first Family members (or Candidate Laminates) to this Stiffener Laminate Family. To do this, press the "Regenerate" button in the top-right corner of the form.

This will regenerate the MSS and Sublaminates (i.e. the Base and Charges/Planks) based on user-defined ply counts and ratio filters. The latter will be explained when we create Charges in the following steps. After clicking it, you will notice a few changes to the form.

First, we see that there are new columns in the table. These are the Base laminates - the first members of this Laminate Family - and they are all subsets of the MSS like we see in standard Laminate Families. We call these Laminate Family members, "Candidate Laminates" which you can now see are counted next to the "Regenerate" button in the top-right corner of the form. For now, we have an equal amount of "Candidate Laminates" and "Filtered Candidate Laminates". This won't always be the case as we will see later in this part of the tutorial.

Adding 0° plies, such as Charges, to "extreme" parts of the stiffener, such as the Cap and Foot, greatly improves the efficiency of the stiffener. These objects act like beams - meaning that stiffening them improves things like the buckling efficiency of the panel. With that in mind, let's add a Charge to the Foot of the Stiffener.

To add a Charge or a Plank, you have to do three things:

After regenerating, you can see that we have added 5 Foot Charges. The first thing to notice is how these use the ratio you defined. The "Max Ratio" is 1 so the thickest Foot Charge will be as many layers as the MSS (4 in this case). The "Min Ratio" is 0, so the "thinnest" Foot Charge is 0 plies, i.e. we wouldn't use a Foot Charge in that case. The next thing to notice is our "Candidate Laminate" and "Filtered Candidate Laminate" counts.

In the last step, we saw these values matched the number of columns we had in the table, but now we see that they correlate with the number of columns in a different way. We also see that the "Candidate Laminates" count is greater than the "Filtered Candidate Laminates" count.

That's because the Stiffener Laminate Family is produced from a full factorial combination of the Laminates in each section. The "Candidate Laminates" count is the count of all Laminate combinations we could make with the Laminates defined, i.e. 4 Base x 5 Charge = 20. The "Filtered Candidate Laminates" is the count of all possible laminates that satisfy the ratio rules we've set.

As we'll see more easily in later steps, the Charge thickness in a Candidate Laminate must fall within the thickness ratio we set relative to the Base laminate for that Candidate. In other words, if a Candidate Laminate is using Base laminate #3, which is 2 layers thick, it is only a valid Candidate if it uses Foot Charge laminate #7, 8, or 9 because a Charge or Plank can't be thicker than the Base in any given Laminate.

Adding Charges to the Web and Cap follows the same procedure as adding them to the Foot section. So, check the "Allowed" checkbox in each section, set the same 0:1 ratio, and "Regenerate".

As expected, our table expands with more columns for the new Charges and our Candidate Laminates have increased significantly.

We've been using a corrugated/hat stiffener concept for this tutorial because it is a simpler example than other concepts, such as an I-stiffener. This is because the geometry of a hat stiffener allows for continuous charges throughout the whole stiffener. We can see that in the image below where a charge is added in the web, continues through the cap into the web on the other side.

In terms of the Stiffener Laminate Family form, the potential for continuity between parts of the stiffener means we can keep all of the charges in the same rows of the table. Alternatively, in an I-stiffener, we do not have the ability to continue charges between parts in the same way. For instance, a web charge cannot continue into a cap charge because we can't split a ply in half. Similarly, you can't have cap charges continue into a web because you can't "zip" them together.

The discontinuity is represented in the Stiffener Laminate Family form for I-stiffeners. Let's create one with the same inputs as the hat stiffener we used before.

We see the difference in potential continuity between these concepts in the layout of the table and the number of "Filtered Candidate Laminates". The geometrical differences between concepts changes what kind of valid Candidate Laminates can be generated based on the input Laminates we define. This is also illustrated by a different table layout.

Additionally, you'll notice that the QuickHelp diagram is different than before as it reflects an I-stiffened panel now.

Each stiffener concept will have a slightly different version of the Stiffener Laminate Family form based on the level of continuity afforded by its geometry. Hat and I-stiffeners are on either end of that continuity spectrum, so other concepts' forms will appear to be somewhere in the middle of these.

For now, let's return to the corrugated concept we've been working with. You can close the I-stiffener SLF form without saving.

To summarize some key Stiffener Laminate Family concepts so far: 

Candidate Laminates are generated by a full factorial combination of the input Laminates the user defines in the Generator version of the Stiffener Laminate Family form. A Candidate Laminate is only valid if the thicknesses of the Charges fall within a defined ratio based on the thickness of the Base laminate for that Candidate. For instance, if a Candidate Laminate's Base Laminate is only 2 layers thick, and the Charges have a 0:1 min/max ratio, the Charges can be no thicker than 2 layers while still being considered "valid".

To see that a bit more clearly, let's change the max value for our Charge ratios to .5. Instead of regenerating after, just press the "Update Count" button. That will show us how these changes will affect candidate filtering without regenerating the MSS and all input laminates (which saves time for larger, more complicated SLFs).

Changing the ratios and updating the counts significantly reduces the number of valid candidates we can generate. To see all of the filtered candidate laminates, we need to open the Editor version of the Stiffener Laminate Family form. To do this, we first have to save the SLF:

Once you've saved the SLF, you will notice that the "Edit" button that's next to the Candidate Laminate counts in the top-right of the form is now clickable.

Clicking that button will switch the form to the Editor mode that has a different look and some additional features.

A few things to notice:

The Editor version of the form is a handy way to visualize the valid Candidate Laminates contained in a Stiffener Laminate Family. Before moving on let's review some other features of the form in the next step.

To round out the basics of Stiffener Laminate Families, let's review a few functions of the Editor version of the Stiffener Laminate Family form.

We'll start with the "Cross-Section" view, to open that:

That opens a new window showing a cross-section of a stiffener based on the selected Laminate.

This view allows you to visualize the relationship between the layout of the table and the geometry of the stiffener it represents. For instance, we can see in the image below where the two layer charges in the feet and webs drops to one layer in the cap of Candidate Laminate 2.

The other noteworthy features of this form relate to editing the SLF directly. These are mostly self-explanatory, so we'll quickly summarize them below.

Manually creating an SLF has provided us a good opportunity to learn more about them and the Generator and Editor forms. However, there are a couple of methods of automatically generating them based on different kinds of Sizing results that are more practical. We'll review two of these methods in the following parts of the tutorial.

Using Set Variables is a way to use Rapid Sizing to generate inputs for Detailed Sizing which, in our case, includes generating a Stiffener Laminate Family.

To begin using Set Variables, we need to create a Design Property and assign it to the Stiffened Panels in our model. To create the Design Property: open "Designs - Panel" in the Property Tree, right-click "Stiffened Panel - Closed Sections", and select "Create Hat Bonded" from the dropdown.

In the resulting form:

Next, we need to assign this to the stiffened panels in the model. We've already organized the Zones that represent those into a Set for you. To assign the Properties to the Set:

Now that we've created and assigned the Design Property to the stiffened panels, we can set up our Set Variables.

To get started, we need to set our stiffener spacing:

Next, we can press the "Set Variables" button to open up the corresponding form. In that form, we are setting inputs (such as material, stiffener height, etc.) that will be used to Rapidly Size the stiffeners. Per the definition of “Set Variables,” the Rapid Sizing solutions will be converted into representative min/max/step inputs for inputs for Detailed Sizing. This also includes a skin and Stiffener Laminate Family.

All we are going to change is the "Ply Material". Click the "Select tape or fabric" button, select "Collier Tape" from the resulting form, and click "Ok" to confirm.

After that, press the "Set Variables" button. As HyperX processes the Set Variables, HyperX determines the per-Zone optimal design for geometrical dimensions of the stiffener as well as thicknesses of each object in the stiffener. HyperX then uses that quick and dirty solution to create a broader set of Laminate Families for the skin and stiffeners.

When done, you will notice quite a few changes to the Design Property form. The first thing to notice is that many of the variables (those highlighted with green) now have Dimension Overrides. These have been set based on the Set Variables results. The main thing to notice is that a new Stiffener Laminate Family ("LF Stiffener - 8") has been generated and applied.

Double-click the SLF to review it in the Editor version of the form.

This SLF was generated from the Set Variables results based on the per-Zone optimal design for geometrical dimensions of the stiffener as well as thicknesses of each object in the stiffener. The next step is to use these results as inputs for Detailed Sizing. Ultimately, this process allows us to get to higher fidelity Sizing results more quickly than manually creating Laminate Families for the skin and stiffeners ourselves.

To run Sizing, select the "Stiffened Panels" Set, right-click the selection, and choose "Size".

Now that Sizing is complete, let's review one of the stiffened panel Zones to see which Candidate Laminate was selected for it.

Click one of the Zones that are a part of the "Stiffened Panel" Set. Then right-click and select "Design Result" from the dropdown.

Then double-click one of the "Material" entries that uses the "LF Stiffener -8" Stiffener Laminate Family.

That will open the Editor version of the Stiffener Laminate Family form, show the selected Candidate Laminate, and its metadata. From that form, or from the View tab of the Ribbon, you can view the cross-section the skin and stiffener Laminate in that Zone.

Generating Stiffener Laminate Families with Set Variables is a great way to get high fidelity Sizing results based on those SLFs quickly. However, the recommended method of generating SLFs from Effective Laminates leads to even higher fidelity results. That process is covered in the next part of the tutorial.

Effective Laminates are a homogenized representation of a Laminate making them effective for preliminary sizing. They are a smeared stiffness representation that captures the overall laminate ABD stiffness terms without having to track individual plies in a stack. While maintaining good accuracy, they reduce the number of variables needed to size stiffened panels so they're a good starting point.

To begin this process, we will need a Design Property that uses Effective Laminates. We have already created and included one for this tutorial. Let's review it before assigning it.

In the Property Tree, under "Designs - Panel" > "Stiffened Panel - Closed Sections", right-click "Hat Bonded - Effective Laminates" and click "Edit".

The first things to notice are that we already have some Effective Laminates selected and the stiffener's geometric variables have already been refined. If you were to start from scratch, you would have to generate Effective Laminates, manually set bounds for the stiffeners' geometric variables, and iterate on those bounds to reduce the number of laminate candidates.

We have already taken care of that setup work so let's look at the Effective Laminates we have selected so far. Right-click on the stiffener's "Material" entry and choose "Select Effective Laminate(s)" to review the selection.

These were generated based on the default Effective Laminate generation settings. Basically, just a collection of laminates with a varying degree of bias in the 0, 45, and 90° directions.

To summarize, under normal circumstances, you would generate Effective Laminates and then use those to refine non-laminate related variables. Since we've already done that, we just need to assign this Design Property to the "Stiffened Panels" Set.

Select the Set in the Structures Tree and click the "Assign" button on the Design Property form.

Once the Effective Laminate Design Property has been assigned, you can close the Design Property form. Select the "Stiffened Panels" set (if it was un-selected) when closing the form, right-click, and select "Size" from the dropdown.

When Sizing is complete, select one of the Zones in the Set, right-click, and select "Design Result".

Main things to note here are we have updated dimensions for the Zone and have selected an Effective Laminate for the skin and each part of the stiffener. Close the form when you're done reviewing it.

The next step is to use these Sizing results to generate a Stiffener Laminate Family.

While the "Stiffened Panel" Set is selected, open the Stiffener Laminate Family Generator form from the Composite tab of the Ribbon.

Unlike when we opened this form in Part 2 of this tutorial, we can now see several Zones selected on the left side of the form; these correspond to the Zones in the Set. The next thing we'll do is click the "Main Sequence" button which will generate the Main Stacking Sequence (MSS) for the Base laminate using the Sizing results from the selected Zones.

In our case, the generated laminate is pretty close to quasi-iso but slightly biased in the 0° direction, as we would expect for a stiffener. The MSS also has 10 layers but recall that they will be mirrored during analysis.

HyperX takes the Sizing results we have for the selection and finds the best compromise for all Zones to use as the MSS. Ultimately, this allows us to replace the Effective Laminates we used for preliminary Sizing with this Stiffener Laminate Family so we can achieve higher fidelity results on the next Sizing run. We will do that soon, but first we need to define some Charges for the SLF.

Before setting up a Design Property to use this Stiffener Laminate Family, let's add Foot, Web, and Cap Charges. Enable each of these, set the ratios from 0 to .5, and click "Regenerate".

When done, make sure to click "Apply" to name and save the SLF. You can close the form after that.

To use the generated Stiffener Laminate Family, we need to reference it from a Design Property that's assigned to the Set. Let's start by making a copy of the "Hat Bonded - Effective Laminates" Design Property.

Right-click and "Edit" the copied Design Property. Rename it and click "Apply" to save.

To use the SLF we just generated, we need to assign it as the stiffener's Material. To do that:

Once the Stiffener Laminate Family Design Property has been assigned, we can re-size the selection by right-clicking it and selecting "Size".

Unlike the "smeared" laminate representation we had with Effective Laminates, HyperX will now size the Set by treating the laminate in each object as a Discrete Laminate.

When it localizes loads, HyperX gets the strains and stresses in each object (foot, web, and cap) and then does an ABD calculation with those object loads. It's also doing that for the Laminate itself and, if you have ply-based criteria active, it does that for each ply in each object as well. Then calculations for things like local buckling use that refined ABD calculation based on the Discrete Laminate in every object.

When Sizing is complete, select one of the Zones in the Set, right-click, and choose "Design Result" from the dropdown.

In the resulting form, you can see the candidate laminate chosen for each stiffener object. Double-clicking any of them will open the Editor version of the Stiffener Laminate Family form and highlight the selected Laminate. Additionally, you can use the "Cross-Section" view to see a 2D representation of the Laminates in the stiffener for the Zone you selected.

Generating SLFs from Effective Laminates does take longer than generating them from Set Variables. However, the Sizing results from Effective Laminate generated SLFs are much more detailed and accurate. The increased fidelity provided by this method makes it the recommended method for generating Stiffener Laminate Families.