Fatigue Process

In this step you will set parameters for the SN Fatigue Uniaxial option.

1. Select the SN Fatigue option at the top of the Fatigue Process panel and then select Uni Axial as the Method. The panel displays similar to the following image.

   
   
   Figure 6.

   Some of the parameters require selection from drop-down menus, while others require you to place a checkmark in the appropriate checkbox and then click the respective button. Make your selections according to the following table.
   Parameter definitions can be found in the OptiStruct Reference Guide.

   Parameter Name	Values
   Method	Uni Axial or Multi Axial
   Stress Combination	Max. Principal, Min Principal, Abs. Max. Principal, Von Mises, Signed Von Mises, Tresca, Signed Tresca, Signed Max. Shear, XYZ Normal, XY Shear, YZ Shear, or ZX Shear
   FE Model Units	MPA, PA, PSI, or KSI
   Mean Stress Correction	None, Goodman, Gerber, Gerber2, Soderbe, FKM, or FKM2
   Create Skin for 3D Elements	Checked or Unchecked
   Certainty of Survival	<value>
   Rainflow Type	Load or Stress
   Gate (0.0 <= Gate < 1.0)	<value>
   Seam Weld Options	Checked or Unchecked, then click button Method: Volvo Mean Stress Correction: None or FKM Certainty of Survival: <value> Thickness Correction: Yes or No
   Spot Weld Options	Checked or Unchecked, then click button Method: Rupp Mean Stress Correction: None or FKM Certainty of Survival: <value> Thickness Correction: Yes or No No. of Angles on Sheet: <value>
   Damage Model Options	Checked or Unchecked, then click button DM1 through DM4: DIRLIK, LALANNE, NARROW, or THREE
   Random Response Fatigue Options	Checked or Unchecked, then click button Upper Limit of Stress Range (FACSREND): <value> Upper Limit of Stress Range (SREND): <value> Width of Stress Ranges (NBIN): <value> Width of Stress Ranges (DS): <value> Static Subcase (STSUBID): select a subcase
   Sweep Fatigue Analysis	Checked or Unchecked, then click button NF_OPTION: checked or unchecked NF: NFREQ DF: <value> Static Subcase (STSUBID): select a subcase

2. Click Apply to move on to the next step in the process.
   The Process Manager browser will move to the Elements and Materials step and the panel displays similar to the following image.

   
   
   Figure 7.

In this step you will set parameters for the SN Fatigue Multiaxial option.

1. Select the SN Fatigue option at the top of the Fatigue Process panel and then select Multi Axial as the Method. The panel displays similar to the following image.

   
   
   Figure 8.

   Some of the parameters require selection from drop-down menus, while others require you to place a checkmark in the appropriate checkbox and then click the respective button. Make your selections according to the following table.
   Parameter definitions can be found in the OptiStruct Reference Guide.

   Parameter Name	Values
   Method	Uni Axial or Multi Axial
   Stress Combination	Set to Max. Abs. Principal by default
   FE Model Units	MPA, PA, PSI, or KSI
   Mean Stress Correction	Set to Goodman by default
   Create Skin for 3D Elements	Checked or Unchecked
   Certainty of Survival	<value>
   Rainflow Type	Load or Stress
   Gate (0.0 <= Gate < 1.0)	<value>
   Seam Weld Options	Checked or Unchecked, then click button Method: Volvo Mean Stress Correction: None or FKM Certainty of Survival: <value> Thickness Correction: Yes or No
   Spot Weld Options	Checked or Unchecked, then click button Method: Rupp Mean Stress Correction: None or FKM Certainty of Survival: <value> Thickness Correction: Yes or No No. of Angles on Sheet: <value>
   Multiaxial Damage Model	Checked or Unchecked, then click button DM1 through DM3: GOODMAN (Tension Damage), FKM (Tension Damage), or FINDLEY (Shear Damage)

2. Click Apply to move on to the next step in the process.
   The Process Manager browser will move to the Elements and Materials step and the panel displays similar to the following image.

   
   
   Figure 9.

In this step you will set parameters for the EN Fatigue Uniaxial option.

1. Select the EN Fatigue option at the top of the Fatigue Process panel and then select Uni Axial as the Method. The panel displays similar to the following image.

   
   
   Figure 10.

   Some of the parameters require selection from drop-down menus, while others require you to place a checkmark in the appropriate checkbox and then click the respective button. Make your selections according to the following table.
   Parameter definitions can be found in the OptiStruct Reference Guide.

   Parameter Name	Values
   Method	Uni Axial or Multi Axial
   Stress Combination	Set to Max. Abs. Principal by default
   FE Model Units	MPA, PA, PSI, or KSI
   Mean Stress Correction	NONE, MORROW, MORROW2, or SWT
   Plasticity Correction	NEUBER or NONE
   Create Skin for 3D Elements	Checked or Unchecked
   Certainty of Survival	<value>
   Rainflow Type	Load or Stress
   Gate (0.0 <= Gate < 1.0)	<value>
   Damage Model Options	Checked or Unchecked, then click button DM1 through DM4: DIRLIK, LALANNE, NARROW, or THREE
   Random Response Fatigue Options	Checked or Unchecked, then click button Upper Limit of Stress Range (FACSREND): <value> Upper Limit of Stress Range (SREND): <value> Width of Stress Ranges (NBIN): <value> Width of Stress Ranges (DS): <value> Static Subcase (STSUBID): select a subcase
   Sweep Fatigue Analysis	Checked or Unchecked, then click button NF_OPTION: checked or unchecked NF: NFREQ DF: <value> Static Subcase (STSUBID): select a subcase

2. Click Apply to move on to the next step in the process.
   The Process Manager browser will move to the Elements and Materials step and the panel displays similar to the following image.

   
   
   Figure 11.

In this step you will set parameters for the EN Fatigue Multiaxial option.

1. Select the EN Fatigue option at the top of the Fatigue Process panel and then select Multi Axial as the Method. The panel displays similar to the following image.

   
   
   Figure 12.

   Some of the parameters require selection from drop-down menus, while others require you to place a checkmark in the appropriate checkbox and then click the respective button. Make your selections according to the following table.
   Parameter definitions can be found in the OptiStruct Reference Guide.

   Parameter Name	Values
   Method	Uni Axial or Multi Axial
   Stress Combination	Set to Max. Abs. Principal by default
   FE Model Units	MPA, PA, PSI, or KSI
   Mean Stress Correction	Set to SWT by default
   Plasticity Correction	NEUBER or NONE
   Create Skin for 3D Elements	Checked or Unchecked
   Certainty of Survival	<value>
   Rainflow Type	Load or Stress
   Gate (0.0 <= Gate < 1.0)	<value>
   Multiaxial Damage Model	Checked or Unchecked, then click button DM1 through DM4: SWT (Tension Damage), FS (Shear Damage), BM (Shear Damage), or MORROW (Tension Damage)

2. Click Apply to move on to the next step in the process.
   The Process Manager browser moves to the Elements and Materials step and the panel displays similar to the following image.

   
   
   Figure 13.

In this step you will set parameters for the Factor of Safety (FOS) option.

1. Select the FOS option at the top of the Fatigue Process panel. The panel displays similar to the following image.

   
   
   Figure 14.

   Some of the parameters require selection from drop-down menus, while others require you to place a checkmark in the appropriate checkbox and then click the respective button. Make your selections according to the following table.

   Parameter Name	Values
   Method	Set to Multi Axial by default
   FE Model Units	MPA, PA, PSI, or KSI

2. Click Apply to move on to the next step in the process.
   The Process Manager browser will move to the Elements and Materials step and the panel displays similar to the following image.

   
   
   Figure 15.

In this step you will define SN materials. This information in this section is useful if you selected SN Fatigue in the previous Analysis Parameters step.

1. In the Elements and Materials panel, click Add.
   The Material Data dialog displays.

   
   
   Figure 16.

2. Select or type values according to the following table.
   Field name definitions can be found in the Optistruct Reference Guide.

   Field Name	Values
   Material Name	Select the material to be updated with fatigue material property
   Stress Unit	MPA, PA, PSI, or KSI
   Yield Strength (YS)	<value>
   Ultimate Tensile Strength (UTS)	<value>
   SN Curve Material Properties	check option, then fill in values in SN Curve Material Properties dialog
   Spot Weld Material Properties	check option, then fill in values in Spot Weld Material Properties dialog
   Seam Weld Material Properties	check option, then fill in values in Seam Weld Material Properties dialog

3. Click Plot SN Curve.
   Depending on the values you entered into the dialog box, you will see a plot curve similar to the following image.

   
   
   Figure 17.

4. Click Save.
   The selected material is updated with the fatigue material property..
5. Click Add Property. The Property Data dialog displays.

   Figure 18.

6. Click the Create buttons next to PFAT, PFATSPW, FATSEAM and PFATSMW to create respective solver cards depending on the type of fatigue problem you are setting up.
7. When creating a PFAT card, select or type values according to the following table. Field name definitions can be found in the OptiStruct Reference Guide.

   Item	Description
   LAYER	Region layer for shell elements
   FINISH	Material surface finish
   TREATMENT	Material surface treatment
   KF	<value>
   CRTDIST	<value>

8. When creating a PFATSPW card, select or type values according to the following table. Field name definitions can be found in the OptiStruct Reference Guide.

   Item	Description
   SPTFAIL	AUTO, or the appropriate type
   ALPHA (> 0.0>	<value>
   HEXA_D (>= 0.0	<value>
   TREF (0.0)	<value>
   TREF_N (>= 0.0)	<value>
   SF (> 0.0)	<value>

9. When creating a FATSEAM card, select or type values according to the following table. Field name definitions can be found in the OptiStruct Reference Guide.

   Item	Description
   WTYPE	AUTO, or the appropriate type
   REFEID	Reference element ID, blank or positive integer
   WLDSIDE	Weld side, text or blank
   PID	<value>
   ELSET	Flag that indicates element set follows

10. When creating a PFATSMW card, select or type values according to the following table. Field name definitions can be found in the OptiStruct Reference Guide.

    Item	Description
    BRATIO	Critical bending ratio
    TREF	Reference thickness for thickness effect consideration
    TREF_N	Exponent for thickness effect consideration
    EVALDIS	Evaluation distance in joint line method of seam weld fatigue analysis

11. Continue defining fatigue material and property definitions to the table as necessary.
12. Click Apply to move on to the next step in the process.
    The Process Manager browser moves on to the Load-Time History step and the panel displays the following image.

    Figure 19.

In this step you will define EN materials. This information in this section is useful if you selected EN Fatigue in the previous Analysis Parameters step.

1. In the Elements and Materials panel, click Add Material.
   The Material Data dialog displays.

   
   
   Figure 20.

2. Select or type values according to the following table.
   Field name definitions can be found in the Optistruct Reference Guide.

   Field Name	Values
   Material Name	automatically determined based on element material
   Stress Unit	MPA, PA, PSI, or KSI
   Yield Strength (YS)	<value>
   Ultimate Tensile Strength (UTS)	<value>
   Input Method	Slope or Estimate from UTS
   Material Type	automatically determined based on element material
   Fatigue Strength Coefficient	<value>
   Fatigue Strength Exponent	<value>
   Fatigue Ductility Exponent	<value>
   Fatigue Ductility Coefficient	<value>
   Cyclic Strain-Hardening Exponent	<value>
   Cyclic Strength Coefficient	<value>
   Cut-Off (Reversals)	<value>
   Standard Error of Log10(e) (elastic)	<value>
   Standard Error of Log10(e) (plastic)	<value>

3. Click Plot EN Curve.
   Depending on the values you entered into the dialog box, you will see a plot curve similar to the following image.

   
   
   Figure 21.

4. Click Save.
   The selected material is updated with the fatigue material property.
5. Click Add Property.
   The Property Data dialog displays.

   
   
   Figure 22.

6. Click the Create button next to PFAT.
   The PFAT dialog opens allowing you to create a PFAT solver card.
7. Select or type values according to the following table. Field name definitions can be found in the OptiStruct Reference Guide.

   Item	Description
   LAYER	Region layer for shell elements
   FINISH	Material surface finish
   TREATMENT	Material surface treatment
   KF	<value>
   CRTDIST	<value>

8. Continue defining fatigue material and property definitions according to the table as necessary.
9. Click Apply to move on to the next step in the process.
   The Process Manager browser moves to the Load-Time History step and the panel displays similar to the following image.

   Figure 23.

In this step you will import load-time history files.

Depending on the values you have input from the preceding fatigue process steps, the Load-Time History panel should look similar to the following image.

Figure 24.

1. Optional: If you want to display minimum and maximum values in the table, activate the Show Min and Max Values checkbox.
2. To define load-time history using RPC and DAC files:
   1. Place a checkmark in the Read RPC & DAC files using Assign checkbox, then click the button.
   2. In the resulting dialog, fill in the values according to your particular loadcase.
   3. Click Apply.
3. To import load-time history from a file or folder:
   1. Click either Add by File or Add by Folder.
   2. In the resulting dialog, fill in the fields according to your filename and location.
   3. Click Import to import the file(s).
   4. When you are finished, click Save.
   5. Optional: If you need to edit the file information, click Edit by File and edit the information as required.
4. To add load-time history information by value:
   1. Click Add by Values.
   2. In the resulting panel, fill in the values as necessary.
   3. Click Create.
   4. When you are finished, click Return.
   5. Optional: If you need to edit the value information, click Edit by Values and edit the information as required.
5. Optional: If you would like to delete a load-time history row in the table, select the row and then click Delete.
6. When you are ready to plot the load-time history, select the appropriate row in the table and click Plot L-T.
   You will see a Load-Time History dialog similar to the following image.

   
   
   Figure 25.

7. Click Apply to move on to the next step in the fatigue process sequence.
   The Process Manager browser will move to the Loading Sequence step and the panel displays similar to the following image.

   
   
   Figure 26.

In this step you will define the loading sequence.

Depending on the values you have input from the preceding fatigue process steps, the Loading Sequence panel should look similar to the following image.

Figure 27.

1. If you are ready to plot the load-time history based on your existing table, select a row in the table and click Plot L-T.
   You will see a Load-Time History dialog similar to the following image.

   
   
   Figure 28.

2. To add a new row of information to the table:
   1. Click Add.
      The Load Mapping dialog displays.

      
      
      Figure 29.

   2. Select the appropriate Channel and Subcase.
   3. Click the plus sign (+) to add Events.
   4. When you are ready, click Save.
      You can now plot the load-time history for this event by clicking Plot L-T.
3. Optional: Edit or Delete information from the table by selecting the appropriate row and then clicking either Edit or Delete.
4. Click Apply to move on to the next step in the fatigue process sequence.
   The Process Manager browser moves to the Submit Analysis step and the panel displays similar to the following image.

   
   
   Figure 30.