HL-T: 1080 Random Fatigue Analysis Using PSD Stresses

In this tutorial you will:
  • Import a model to HyperLife
  • Check that the FE result file contains a random response subcase with PSD stresses (Segalman Vonmises or Abs Max Principal Stresses)
  • Select the SN module with a Random (PSD Stresses) loading type and define its required parameters
  • Create and assign a material
  • Create a random response fatigue event
  • Evaluate and view results
Before you begin, copy the file(s) used in this tutorial to your working directory.
  • HL-1080\Plate_Random.h3d

Import the Model

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


    Figure 1.
  2. From the Load model and result dialog, browse and select HL-1080\Plate_Random.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.
  3. 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 Random Response Subcase with PSD Stresses

Both are needed to run this type of analysis.

  1. From the Results Browser, click the second drop-down menu and select Subcase 3 (random).
    If the Results Browser is not open, click View > Browser from the menu bar.


    Figure 3.
  2. From the View Controls toolbar, click .
    The Contour panel opens.
  3. From the panel area, select PSD Element Stresses (2D) (s) from the first Result type drop-down menu.


    Figure 4.
  4. Click Apply.
    The model is contoured.
  5. Observe the PSD element stress plot in the modeling window then select Clear Contour in the panel area.
  6. Exit the Contour panel.

Define the Fatigue Module

  1. 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.
  2. 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 (PSD Stresses) 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.
  3. Exit the dialog.

Assign Materials

  1. Click the Material tool.


    Figure 7.
    The Assign Material dialog opens.
  2. Activate the checkbox next to the part Plate.
  3. Create a new material.
    1. Click the My Material tab.
    2. Click to create a new material.
    3. Set the Elastic modulus to 200000.
    4. Change the Input method to Slope-intcept,2-seg.
    5. Set UTS to 2000.
    6. Set Yield Strength to 1800.
    7. Set Poisson's Ratio to 0.334.
    8. In the SN tab, set the Fatigue strength coefficient or Curve intercept (SR1) to 1040.
    9. Set the First fatigue strength exponent or Slope (B1) to -0.231.
    10. Set the Cyclic limit of endurance or Transition point (NC1) to 600000.
    11. Set the Second fatigue strength exponent (B2) to -0.11.
    12. Set the Fatigue limit to 10.
    13. Set the Standard error value to 0.01.
    14. Click Plot & Save.


      Figure 8.
  4. Right-click on Mat_SN("n") and select Add to Assign Material List.
  5. Return to the Assign Material Data tab and select Mat_SN("n") from the Material drop-down menu for Plate.
    The Material list is populated with the materials selected from Material Database and My Material.


    Figure 9.
  6. Exit the dialog.

Create a Random Response Event

  1. Click the Load Map tool.


    Figure 10.
    The Load Map dialog opens.

    By default, PSD Stresses is the selected Channel Type and can not be changed.

  2. Select Subcase 3 (random).
  3. On the bottom half of the dialog, click to create an Event_1 header.
    Subcase 3 is listed under the event.
  4. Activate the Event_1 checkbox.


    Figure 11.
    Note: You can only select one random response subcase per event.
  5. 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

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


    Figure 12.
    The Evaluate dialog opens.


    Figure 13.
  2. Optional: Enter a name for the run.
  3. Click Run.
    Result files are saved to the home directory and the Run Status dialog opens.
  4. Once the run is complete, click View Current Results.
  5. Use the Results Explorer to visualize various types of results.


    Figure 14.


    Figure 15.