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

  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-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.
  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 Frequency Response Function Subcases with Element Stresses

  1. From the Results Browser, click the second drop-down menu and select Subcase 1 (Load1).
    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 Element Stresses (2D & 3D) (t) (c) from the first Result type drop-down menu.
  4. Select XX from the second Result type drop-down menu.


    Figure 4.
  5. Click Apply.
    The model is contoured.
  6. Observe the element stress plot in the modeling window.
  7. Select Subcase 2 (Load2) from the second drop-down in the Results Browser.
  8. Observe the updated element stress plot in the modeling window then select Clear Contour in the panel area.
  9. Exit the Contour panel.

Define the Fatigue Module

  1. From the Setup tools, 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.
    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.
      • Mean Stress Correction is only applied if the static subcase is to be added in the Event.
    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. From the Setup tools, click the Material tool.


    Figure 7.
    The Assign Material dialog opens.
  2. Activate the checkboxes next to the parts ND, Antenna, and 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 220000.
    4. Set UTS to 488.
    5. In the SN tab, set the Fatigue strength coefficient or Curve intercept (SR1) to 1203.
    6. Set the First fatigue strength exponent or Slope (B1) to -0.123.
    7. Set the Cyclic limit of endurance or Transition point (NC1) to 1000000.
    8. Set the Standard error value to 0.3.
    9. Click the Other tab.
    10. Set Yield Strength to 355.
    11. Set Poisson's Ratio to 0.3.
    12. Click Plot & Save.


      Figure 8.
  4. Create a second material.
    1. Click in the My Material tab.
    2. Set the Elastic modulus to 70000.
    3. Change the Input method to Slope-intcept,1-seg
    4. Set UTS to 288.
    5. In the SN tab, set the Fatigue strength coefficient or Curve intercept (SR1) to 462.
    6. Set the First fatigue strength exponent or Slope (B1) to -0.119.
    7. Set the Cyclic limit of endurance or Transition point (NC1) to 1000000.
    8. Set the Standard error value to 0.3.
    9. Click the Other tab.
    10. Set Yield Strength to 155.
    11. Set Poisson's Ratio to 0.3.
    12. Click Plot & Save.


      Figure 9.
  5. Select both of the created materials then right-click and select Add to Assign Material List.
  6. Return to the Assign Material Data tab. Using the Material drop-down menu, select the first material for the parts ND and Plate and the second material for Antenna.
    The Material list is populated with the materials selected from Material Database and My Material.


    Figure 10.
  7. Exit the dialog.

Create a Random Response Event

  1. From the Setup tools, click the Load Map tool.


    Figure 11.
    The Load Map dialog opens.
  2. From the Channel Type drop-down menu at the top of the dialog, select Input PSD: Real & Imaginary.
  3. Load PSD vs Frequency data (input PSD that is to scale the FRF stresses).
    1. Click in the Choose File field and browse for Input_PSD.csv.
    2. Click to add the load case.
  4. Optional: Click to view a plot of the loads.
  5. Select both Subcase 1 (Load1) and Subcase 2 (Load2).
  6. On the bottom half of the dialog, click to create an Event_1 header.
    The possible correlations of Subcase 1 and Subcase 2 are listed under the event.
  7. Drag and drop the Input_PSD channel onto the Input PSD field of Subcase 1 - Subcase 1.
  8. Similarly, drag and drop the Input_PSD channel onto Subcase 2 - Subcase 2 and Subcase 1- Subcase 2.
  9. Activate the Event_1 checkbox.
  10. Set the Exposure Time for the event to 1800000.


    Figure 12.
  11. 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 13.
    The Evaluate dialog opens.


    Figure 14.
  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 15.


    Figure 16.