How To Implement Correction Factors on Composite Allowables

To enable Tabular Correction Factors, Database settings must allow for tabular input. To do that:

The Corrections Factors Form is available for any Composite Material. To access that form:

On this form, you can see all of the properties for this Material and any Correction Factors applied to it. The default value is 1. As Correction Factors are added, that spot in the form will be highlighted orange.

Tabular Correction Factors will be labeled with "TABLE". To see the tabular correction data, right-click on the cell and select "Correction Data Definition" from the dropdown.

This tutorial will use the Open Hole Compression laminate strain allowable as an example.

First, locate "Compression, OHC" in the "Laminate Strain Allowables" section. Right-click the cell in the first column for that property and select "Correction Data Definition" from the dropdown.

Next, select "Tabular" from the "Type" dropdown.

The form will update to show two (currently empty) tables and a new dropdown option. First, identify which independent variables the OHC allowable should be corrected with respect to. Do this by selecting them from the "Add Variable" dropdown". Let's start with a "%0" variable.

After selecting a value from the dropdown, the tables in the form will update to include that variable.

The next step is to populate the bottom table with data. Simply enter your data and new rows will be added as you go. You can also right-click a row and select "Delete Selected Rows" if you want to remove one.

Interpolated Variable

You must select one of your variables to be the interpolated variable. The values for this variable will be linearly interpolated with respect to the Correction Factor values to create a curve. As you add more variables, more curves are produced, and all other variables will be "snapped" to these curve(s).

By pressing the graph button at the top-right of the form, you can view the data from the bottom table graphically. The graph will use the interpolated variable as the x-axis, plotting all other data relative to it.

Selecting another variable from the dropdown will add a new column to the table. Let's add a variable for "%45" to model various knockdowns based on relative percentages of \(0\) and \(45^{\circ}\) plies.

On the graph, the interpolated variable determines the X-axis, so values for the second variable are represented by different coloring. Below the graph is a key that maps those colors to their associated values.

Changing the interpolated variable changes the graph and key accordingly and re-sorts the values table (bottom).

When done, you can save this correction data and apply it to all Design Properties which use this Material by pressing "Apply" on the Correction Data Definition, Correction Factors, and Composite Material Forms.

Adding more variables to a Tabular Correction Factor doesn't fundamentally change how that Correction Factor is applied. One variable is interpolated, and the others are "snapped". However, once you have three or more independent variables, the graph settings in the Correction Data Definition Form change.

To account for the extra dimensionality of three or more variables in a two-dimensional display, the form will feature a "Curve Variable" dropdown and additional dropdowns for each variable beyond the interpolated and curve variable.

The "Curve Variable" dropdown allows you to select which value to snap to the interpolated variable to produce the Correction Factor curve(s). The other dropdowns allow you to select a value for the associated variable to view the curve(s) relative to.

For this example, let's add a "Temperature" variable and set all of our existing rows to 72. Then, copy the table and paste it below. For the copied rows, change the temperature to 100 and change the Correction Factors (k). In the graph view, make sure the "Curve Variable" is "%45" and change the "Temperature" dropdown between 72 and 100 to see the different curves.

If you wish to add any more variables, the form will add another dropdown for non-curve variables.

The Composite Strength Plugin (included with the HyperX install) extends the functionality of Tabular Correction Factors in a couple of ways but it must be enabled first. If the Plugin is already enabled, you may skip ahead to the other sub-sections that detail additional functionality.

Enabling the Plugin

First, press the "Plugins" button on the Analysis tab of the Ribbon.

In the Plugins Form, press the "Add" or "..." button to browse for Plugin Packages.

Navigate to the location of the Plugin. This will be "{HyperX_Install_Directory}/Methods/". Select the "HS_CompositeStrength.dll" Plugin Package and click "Open".

That will populate the form with more information about this Plugin. You can review the specific Failure Criteria added and the Analysis Settings provided. When done, click "Ok" to enable the Composite Strength Plugin Package and close the form.

Snapping

For Correction Factors comprised of multiple curves (like we have in this tutorial), one column is interpolated while the others are “snapped.” As Structures are Sized, their dimensions and attributes change and may not match up with a particular curve generated by a Correction Factor Table.

For example, consider the values in this tutorial and Sizing indicated one of our Structures should have around 30% 0-plies and around 20% 45-plies. It would fall somewhere in the blue circle in the image below.

To determine the Correction Factor to apply in this case and others like it, HyperX must determine which curve to "snap" those values to. The snapping behavior is defined by the “C.F. Snapping Behavior” Analysis Setting.

There are two snapping behaviors:

1. Snap to Closest (default)

   • Snap to the nearest curve regardless of which curve will produce the most critical result.

2. Snap to Critical

   • Snap to the curve with the more critical result. This is more conservative and matches the native analysis methodology.

To make a change to this Analysis Setting, return to the Composite Strength Failure Mode we created in the last sub-section. Expand the "Laminate Allowables" section of the Settings and select an option from the "C.F. Snapping Behavior" dropdown.

Out of Bounds Behavior

When the target value is outside of the Correction Factor curve bounds, it is considered Out of Bounds (O.O.B.). This can occur with any curve but especially when multi-variable curves aren't "packed out" - meaning the curves don't have the same length.

The curves we created in this tutorial are already packed out, but removing one of the rows can provide an example of what not to do. The non-packed-out graph is on the left, and if we were starting from there, we would want to add another row to extend that curve to match the length of the other. In a normal case of "packing out", you would just extend the curve horizontally, like below.

Out of bounds behavior is defined by the "C.F. O.O.B Behavior" Analysis Setting and there are two possible settings:

1. Truncate to nearest available point (default)

   • When a target value is out of bounds, the nearest available value is used.

   • A warning will be printed in the Analysis Detail Report describing which value is out of bounds.

     

2. Throw error and stop sizing

   • Sizing will end, and an error message will pop up described the out of bounds value.

     

   • This is similar to the native HyperX behavior where Sizing will end and warnings are logged in the Process Monitor.

     

To make a change to this setting, return to the Composite Strength Failure Mode. Expand the "Laminate Allowables" section of the Analysis Settings and select an option from the "C.F. O.O.B Behavior" dropdown.