OS-T: 6050 Dang Van Criterion (Factor of Safety)

The Dang Van criterion is used to predict if a component will fail in its entire load history.

The conventional fatigue result that specifies the minimum fatigue cycles to failure is not applicable in such cases. It is necessary to consider if any fatigue damage will occur during the entire load history of the component. If damage does occur, the component cannot experience infinite life.

The following file found in the optistruct.zip file is needed to perform this tutorial. Refer to Access the Model Files.

Spring-link.fem

or

A copy of the model file used in this tutorial is available on <install_directory>/tutorials/hwsolvers/optistruct.

A spring link loaded by vertical force of 5000N, longitudinal force of 20000N and radial force 2000 is used (Figure 1). Further Torsional Fatigue Limit (TFL) and Hydrostatic Stress Sensitivity (HSS) is introduced for the Dang Van FOS calculation.


Figure 1. Spring-link for Fatigue Analysis Model

Launch HyperMesh and Set the OptiStruct User Profile

The model being used for this exercise is that of a control arm (Figure 6). Loads and boundary conditions and two static loadcases have already been defined on this model.

  1. Launch HyperMesh.
    The User Profile dialog opens.
  2. Select OptiStruct and click OK.
    This loads the user profile. It includes the appropriate template, macro menu, and import reader, paring down the functionality of HyperMesh to what is relevant for generating models for OptiStruct.

Import the Model

  1. Click File > Import > Solver Deck.
    An Import tab is added to your tab menu.
  2. For the File type, select OptiStruct.
  3. Select the Files icon files_panel.
    A Select OptiStruct file browser opens.
  4. Select the Spring-link.fem file you saved to your working directory. Refer to Access the Model Files.
  5. Click Open.
  6. Click Import, then click Close to close the Import tab.
    The outline of the Fatigue Analysis setup to be achieved in the following steps.


    Figure 2. Fatigue Setup - FOS

Set Up the Model

Define TABFAT Load Collector

The first step in defining the loading sequence is to define the TABFAT cards. This card represents the loading history.

  1. In the Model Browser, right-click and select Create > Load Collector.
  2. For Name, enter TABFAT.
  3. For Card Image, select TABFAT from the drop-down menu.
  4. For TABLEFAT_NUM, enter 2.
  5. Click on the Table icon table_pencil next to the Data: field, enter 1 in row1 and enter -1 in row2 as the y values.
  6. Click Close.

Define FATLOAD Load Collector

  1. In the Model Browser, right-click and select Create > Load Collector.
  2. For Name, enter FATLOAD_Vertical.
  3. For Card Image, select FATLOAD.
  4. For TID(table ID), select TABFAT from the list of load collectors.
  5. For LCID (load case ID), select Vertical from the list of load steps.
  6. Set LDM (load magnitude) to 0.01.
  7. Set Scale to 1000.0.
  8. Repeat the process to create 2 additional load collectors with TABFAT cards named:

    FATLOAD_Longitudinal with FATLOAD as the Card Image.

    FATLOAD_Radial with FATLOAD as the Card Image.

  9. Set LDM to 0.01 and Scale to 1000.0.

Define FATEVNT Load Collector

Create an event to assign the fatloads created.

  1. In the Model Browser, right-click and select Create > Load Collector.
  2. For Name, enter FATEVENT_1.
  3. For Card Image, select FATEVNT.
  4. For FATEVNT_NUM_FLOAD, enter 3.
  5. Click on the Table icon table_pencil next to the Data field and select FATLOAD_Vertical, FATLOAD_Longitudinal and FATLOAD_Radial for FLOAD in the pop-out window.

Define FATSEQ Load Collector

  1. In the Model Browser, right-click and select Create > Load Collector.
  2. For Name, enter FATSEQ.
  3. For Card Image, select FATSEQ.
  4. For FATSEQ_NUM enter 1, as 1 FATEVENT has been created.
  5. For FID (Fatigue Event Definition), select FATEVENT_1 and N as 1.
    Tip: Right-click on N and select Status to edit.
    Defining the sequence of events for the fatigue analysis is completed. The Fatigue parameters are defined next.

Define Fatigue Parameters

  1. In the Model Browser, right-click and select Create > Load Collector.
  2. For Name, enter fatparam.
  3. For Card Image, select FATPARM.
  4. Verify TYPE is set to FOS.
  5. Set MAXLFAT to Yes.
    FOS Type shows DANGVAN.

Edit Material Data Card

This step instructs on how to add torsional fatigue limit and hydrostatic stress sensitivity.

TFL and HSS are required for calculating the FOS by Dang Van Criterion.

  1. From Materials, select Mat1_FOS.
  2. Activate MATFAT.
  3. For UTS, enter 600 MPa.
  4. Scroll down and activate FOS.
  5. For TFL, enter 102.0.
  6. For HSS, enter 0.424.
  7. Click Close to exit the material card.

Define PFAT Load Collector

  1. In the Model Browser, right-click and select Create > Load Collector.
  2. For Name, enter pfat.
  3. For Card Image, select PFAT.
  4. Set LAYER to TOP.
  5. Set FINISH to NONE.
  6. Set TRTMENT to NONE.
  7. Set Kf to 1.0.

Define FATDEF Load Collector

  1. In the Model Browser, right-click and select Create > Load Collector.
  2. For Name, enter fatdef.
  3. Set the Card Image to FATDEF.
  4. Activate PTYPE and PSOLID in the PTYPE Entity Editor.
  5. Edit FATDEF_PSOLID_NUMIDS to 1.
  6. Select spring_link for PID and pfat for PFATID.

Define the Fatigue Load Step

  1. In the Model Browser, right-click and select Create > Load Step.
  2. For Name, enter Fatigue.
  3. Set the Analysis type to fatigue.
  4. For FATDEF, select fatdef.
  5. For FATPARM, select fatparam.
  6. For FATSEQ, select fatseq.

Submit the Job

  1. From the Analysis page, enter the OptiStruct panel.
  2. Click save as following the input file field.
    The Save As dialog opens.
  3. For File name, enter the name spring_link_fatigue.fem.
  4. Click Save.
  5. Click OptiStruct to submit the analysis.

Review the Results

  1. From the OptiStruct panel, click HyperView.
    HyperView is launched and the results are loaded. A message window appears to inform of the successful model and result files loading into HyperView.
  2. Go to the Results tab.
  3. In the Results tab, select Subcase 4 (Fatigue) from the subcase field.
  4. On the Results toolbar, click resultsContour-16 to open the Contour panel.
  5. Set Result type to FOS and click on Apply to contour the elements.


    Figure 3. Dang Van Contour Plot