Stress-Life (S-N) Approach

In this tutorial you will:
  • Import a model to HyperLife
  • Select the SN module and define its required parameters
  • Create and assign materials
  • Assign load histories for scaling the stresses from FEA subcases
  • Evaluate and view results

Prior to running through this tutorial, copy Models-h3d.zip from <HyperWorks_installation_directory>\tutorials\hl to a local directory. Extract Ibeam.h3d, load1.csv, and load2.csv from Models-h3d.zip..

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 Ibeam.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.

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 3.
    The SN dialog opens.
  2. Define the SN configuration parameters.
    1. Select Multi 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 GOODMAN for the Tension Damage Model.
    5. Select NONE for the Shear Damage Model.
    6. Select Worst for the layer selection.


    Figure 4.
  3. Exit the dialog.

Assign Materials

  1. From the Setup tools, click the Material tool.


    Figure 5.
    The Assign Material dialog opens.
  2. Activate the checkboxes next to the parts Flange and Web.
  3. Create a new material.
    1. Click the My Material tab.
    2. Click to create a new material.
    3. Name the material Mat_SN_multiaxial.
    4. Set the Elastic modulus to 200000.
    5. Set the Input method to Slope-intcept,2-seg.
    6. In the SN tab, set the Fatigue strength coefficient or Curve intercept (SR1) to 1203.
    7. Set the Fatigue limit to 10.
    8. Set the Standard error to 0.334.
    9. Click the Other tab and ensure the Yield Strength is set to 250 and Poisson's Ratio is set to 0.333.
    10. Accept all other default settings then click Plot & Save.


      Figure 6.
  4. Right-click on Mat_SN_multiaxial and select Add to Assign Material List.
  5. Return to the Assign Material Data tab and select Mat_SN_multiaxial from the Material drop-down menu for both Flange and Web.
    The Material list is populated with the materials selected from Material Database and My Material.


    Figure 7.
  6. Exit the dialog.

Assign Load Histories

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


    Figure 8.
    The Load Map dialog opens.
  2. From the Load Type drop-down menu, select Time Data.
  3. Click and browse for load1.csv.
  4. Click to add the load case.
  5. Repeat steps 3 and 4 for load2.csv.
  6. Optional: Click to view a plot of the loads.


    Figure 9. Load 1


    Figure 10. Load 2
    Tip: Expand the width of the dialog to view a clearer picture of the plot.
  7. On the bottom half of the dialog, set the radio button to Auto for event creation.
  8. Select both the Block 1 channel under load1 and Subcase 1, then click to create the first event.
  9. In a similar manner, create a second event by selecting Block 1 under load2 and Subcase 2.
  10. Activate the checkboxes for the two events.
  11. Set the Scale to 8.0 for subcase 2.


    Figure 11.
  12. Exit the dialog.

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 History dialog opens.


    Figure 14.
  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.

    The life expectancy for the worst element is 64,660 cycles.