Fatigue Tab - Performing Assessments¶

Fatigue Material Properties¶

The limits section lists the currently loaded material fatigue limits. By default GageMap uses an internally derived limit diagram based upon the model characteristics. This is for notional use only and should not be used for fatigue evaluations. User material fatigue limit properties can be entered via the GageMap preference (.gmf) file. The format of the material properties within the preference file is provided below. A preference file is loaded within the main fatigue assessment window under the File menu. For legacy users there is also an option to import .glm files within the File menu, however, this is not the preferred method and support for this format may be dropped in a future release.

Mean Stress Alignment¶

• Project static stress tensor into the vibratory principal direction

• Storage of a single “mean stress aligned” static variable

  • Fatigue assessment task
  • Animate task

• Process

  • Select static load case

  • Select vibratory tensor for alignment

    • Stress
    • Strain

  • Select static variable for storage

    • Max prin, mid prin, min prin
    • XY, YZ, ZX shears

  • Export

    • Static / vibratory stress and strain principal directions are available for export
    • Aligned static stress and strain tensors are also available in model export

Pre-Test Fatigue Assessment¶

1. Launch GageMap and load an SDR or GMP file.

2. If gages are not already mapped, map them.

3. Load a group file and confirm the order and Booleans are correct.

4. Navigate to the “Fatigue” tab

5. On the left side panel, navigate to the “fatigue setup” tab

6. If materials have not already been loaded with the GMP file, set up the materials for the model as follows:

   1. Create a new fatigue file with the “New Fatigue File” button. The new file will appear in the “files” section of the Fatigue Setup Tab.
   2. Locate the Green “+” button towards the bottom of the panel, next to “Material:” to create a new material
   3. Name the New Material using the now unlocked text box
   4. A Temperature field and a X, Y Value field will be created automatically under the new material
   5. Change the Temperature value by selecting it in the tree in the materials box, and changing the value in the “Temperature:” field
   6. Once this is done, change the X and Y values by selecting it in the tree and changing the values in the corresponding fields
   7. Multiple values can be added to a given temperature by clicking on the green “+” button next to the X and Y value fields
   8. Add a new temperature to the Material by click the green “+” button next to the “temperature:” field.
   9. Repeat as needed

7. Materials can also be imported from Assignment files (GMM) or Legacy file formats (GMF)

8. Once materials have been defined, navigate to the “Assignments” tab in the left side panel

9. Select the active group file and define the active group in their respective dropdowns

10. Match the materials to the groups in the “Material” Dropdown

11. Select each group and confirm it is the correct material.

12. Define Static and Dynamic Stress types using their respective dropdowns

    • This can be done either on a material basis under the assignments tab or globally in the fatigue preferences panel

13. Assign stress scales and adders

    • Stress scales and adders can be used to artificially increase or decrease all of the stresses (stress type) in a group. They can be applied to both the static and dynamic stresses

14. Assign plot Identifiers

    • The plot identifiers dictate what colors & symbols to use for each group so they may be distinguished on the Goodman diagram.

15. Navigate to the “Plot Setup” tab

16. Select the Static Stresses and Dynamic Stresses for the X and Y-Axis values

17. Select the group to create the desired plot. The plot will appear in the bottom right panel

18. Navigate to the “Animate Setup” tab in the left side panel

19. Select a static load case and enter a speed in the “Static Load (RPM)” box under the “scaling” section

20. Select a mode and enter a value into the “Mode Amplitude” box under the “scaling” section

21. Besides manual scaling, mode amplitudes and static loads can be scaled by fatigue percent limit in the “Fatigue” tab of the Scaling section

    GageMap has scaled the dynamic stresses such that a single node lies at 100% of limit. The node is identified by a red “star” and the label is listed in the legend. For this mode it is in the Airfoil group. Note in the setup panel, the mode amplitude to achieve 100% of limit is listed. Also review the model window as the model has been contoured to now display “% of limit”.

    The Sensor Limit & Ratio Report is the most important report in the fatigue task. It summarizes all the sensor ratio and scope limit information for all modes in a single report. When initiated GageMap loops through each mode in sequence, determines the MSF to achieve 100% limit and reports the following for each strain gage:

    • MSF = Modal Scale Factor
    • The critical HCF node
    • The limiting vibratory node
    • Critical stress ratio
    • Vibratory stress ratio
    • Scope limit
    • Variation in limit/ratios due to sensor misplacement

22. Fatigue -> Sensor Limit and Ratio

    Note

    The stress scope limit is in model units (0-Pk). The bounds of the min/max are set in the “Optimizer” task. If NSMS sensors are present, deflection units are also computed.