HL-T: 1090 Random Fatigue Analysis Using FRF Stresses and Power Spectral Density of Loading Versus Frequency (Input PSD)

In this tutorial you will:

Import a model to HyperLife
Check that the FE result file contains a frequency response function (FRF) subcase with element stresses
Select the SN module with a Random (Input PSD with FRF) loading type and define its required parameters
Create and assign a material
Create a random fatigue event with Input PSDs
Evaluate and view results

Before you begin, copy the file(s) used in this tutorial to your working directory.

HL-1090\Antenna_Vibration_Fatigue.h3d
HL-1090\Input_PSD.csv

Import the Model

From the Home tools, Files tool group, click the Open Model tool.

Figure 1.
From the Load model and result dialog, browse and select HL-1090\Antenna_Vibration_Fatigue.h3d for the model file.
The Load Result field is automatically populated. For this tutorial, the same file is used for both the model and the result.
Click Apply.

Figure 2.

Tip: Quickly import the model by dragging and dropping the .h3d file from a windows browser into the HyperLife modeling window.

Check That the FE Result File Contains a Frequency Response Function Subcases with Element Stresses

From the Results Browser, click the second drop-down menu and select Subcase 1 (Load_X).
If the Results Browser is not open, click View > Browser from the menu bar.

Figure 3.
From the View Controls toolbar, click .
The Contour panel opens.
From the panel area, select Element Stresses (2D & 3D) (t) (c) from the first Result type drop-down menu.
Select XX from the second Result type drop-down menu.

Figure 4.
Click Apply.
The model is contoured.
Observe the element stress plot in the modeling window.
Select Subcase 2 (Load_Y) from the second drop-down in the Results Browser.
Observe the updated element stress plot in the modeling window then select Clear Contour in the panel area.
Exit the Contour panel.

Define the Fatigue Module

Click the SN tool.
The SN tool should be the default fatigue module selected. If it is not, click the arrow next to the fatigue module icon to display a list of available options.

Figure 5.

The SN dialog opens.
Define the SN configuration parameters.
1. Select Uni Axial as the method.
2. Select MPa for the FE model units.
3. Enter a value of 0.5 for the certainty of survival.
4. Select NONE for the mean stress connection.
  
  Note: Mean stress correction is only applied if a static subcase is to be added in the Event.
5. Select Worst for the layer selection.
6. Select Random (Input PSD with FRF) for the type of loading.
  von Mises is automatically selected as the stress combination.
  Note: For Random Fatigue with the SN module, Abs Max Principal is also available from the drop-down. For EN, only the von Mises stress combination is supported.
7. Accept the default random response values.
  
  Stress Range Upper Limit (Calculated): Calculates the upper limit of the stress range. This is calculated as 2*RMS Stress*factor (Default factor = 8). The RMS stress is output from the random response subcase. The stress ranges of interest are limited by the above calculated stress. Any stresses beyond the calculated value are not considered in random fatigue damage calculations. Upper stress range can also be input directly via the User Input option.
  
  Stress Range Width (Calculated): Calculates the width of the stress range for which the probability is calculated. The default is 100 and the first bin starts from 0.0 to the calculated width. The width of the stress range is calculated as the upper limit of the stress range / Stress Range Width (Calculated). The stress range width can also be input directly via the User Input option.
Figure 6.
Exit the dialog.

Assign Materials

Click the Material tool.

Figure 7.

The Assign Material dialog opens.
Activate the checkbox next to Plate.
Select a material.
1. Click the Material DB tab.
2. In the Search field, enter 189 and press Enter.
3. From the search results, right-click Steel 1005, HR Sheet, Su = 359.0(189) and select Add to Assign Material List from the context menu.
Return to the Assign Material Data tab. Using the Material drop-down menu, select Steel 1005, HR Sheet, Su = 359.0(189) for Plate.
The Material list is populated with the materials selected from Material Database and My Material.

Figure 8.
Exit the dialog.

Create a Random Response Event

Click the Load Map tool.

Figure 9.

The Load Map dialog opens.
From the Channel Type drop-down menu at the top of the dialog, select Input PSD: Real & Imaginary.
Load PSD vs Frequency data (input PSD that is to scale the FRF stresses).
1. Click in the Choose File field and browse for psd_X.csv, psd_Y.csv, and psd_Z.csv.
2. Click to add the load case.
Optional: Click to view a plot of the loads.
Select Subcase 1 (Load_X), Subcase 2 (Load_Y), and Subcase 3 (Load_Z).
On the bottom half of the dialog, click to create an Event_1 header.
The possible correlations of Subcase 1, Subcase 2, and Subcase 3 are listed under the event.
Select the three psd files and drag-and-drop them into the Event header.

Note: Any blank correlations are not considered in the calculation.
The following pairs are created:
- Subcase 1 with psd_X
- Subcase 2 with psd_Y
- Subcase 3 with psd_Z
The remaining correlations are left blank.
Activate the Event_1 checkbox.
Set the Exposure Time for the event to 18000.

Figure 10.
Exit the dialog.

Note: If Mean Stress correction is to be applied, a static subcase, if present in the result file, will be listed in the Subcase window and can be drag and dropped onto the event (no channel is required to be paired).

Evaluate and View Results

From the Evaluate tool group, click the Run Analysis tool.

Figure 11.

The Evaluate dialog opens.
Optional: Enter a name for the run.

Figure 12.
Click Run.
Result files are saved to the home directory and the Run Status dialog opens.
Once the run is complete, click View Current Results.
Use the Results Explorer to visualize various types of results.

Figure 13.

Figure 14.