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5.2 General Purpose Fatigue Model Input

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If Basquin or Basquin-Coffin-Manson or Kandil-Brown-Miller or Fatemi-Socie fatigue model is selected in the Fatigue model/code drop-down menu in Project Setup dialog box in 5.1 Data Entry and Project Setup, the Fatigue Model Input button  on the toolbar becomes activated. 


Choose Input>Fatigue Model Input or click Fatigue Model Input button.  The Fatigue Modeling Data Input dialog box appears. 



The program automatically loads default database that is shipped with software.  However, you can edit the database, add new material, delete material, and save the default database.  You can also export the database to a location of your choice and import the database later.


Click Select material dropdown menu to select material.



Then the following material properties will be retrieved from the database:



The values of the material properties can be changed.  Click Save material database button, and the following confirmation dialog displays:



The changes are saved to the material database of current project.


If you want to keep the changes in a material database to be used in future projects, you can choose to export the database and save it to a location of your choice:  Click Export material database button to save currently opened material database.  Select a folder and enter a file name.  Click Save button and the material database will be saved.



In the future for other project, if you want to use saved material database, just click Import material database to import and open the material that was previously exported.  In the pop-up dialog window, select the directory and database file, click Open button.



You can also add your own materials to the database by clicking Add new material button.  The following dialog displays.



Enter name of the material, fatigue strength coefficient, fatigue strength exponent, fatigue ductility coefficient, fatigue ductility exponent, modulus of elasticity, tensile strength, yield strength, elastic Poisson's ratio, and plastic Poisson's ratio.  Click OK button to confirm and close the dialog.  The newly added material becomes currently selected material and will be saved to the material of the current project.  If you want to use the material for future project, save the material by clicking Export material database button.


The currently selected material can be deleted by clicking Delete material button.  A warning dialog displays.



Click Yes button to confirm; click No button to cancel deletion.


The fatigue curve for the selected material can be plotted by clicking Plot fatigue curve button.  You can zoom, print or export the chart, or change the styles of the chart by clicking the buttons on the tool bar.  Click X button on the upper-right corner to close the window.



The fatigue strength reduction factor Kf is calculated by clicking Calculate button:



After clicking the Calculate button, the Fatigue Strength Reduction Factor Kf Calculator dialog pops up:



The fatigue strength reduction factor Kf is the product of Cc (corrosive environment factor), Csf (surface condition factor), Cs (size factor), Cm (mode of loading factor), Ct (temperature factor), Cr (reliability factor), Cf (notch effect factor), and Cfret (fretting condition factor).  The default values of the factors are 1.00 in the spin boxes.  Enter a value directly or click up and down arrow buttons in the spin box to adjust the number.  Pressing the UP ARROW or DOWN ARROW key can also change the value in the text box.  The resulted Kf value is displayed in the green box.  Click OK button to confirm and return to Fatigue Modeling Data Input dialog box. 


Enter safety factor for stress in the Stress safety factor box; enter safety factor on load cycles in the Load cycle safety factor box:



For fatigue life calculations, the stress is multiplied by the stress safety factor to calculate fatigue life Nf(S); in parallel, the fatigue life is calculated with stress safety factor = 1.0, and divided by load cycle safety factor to derive fatigue life Nf(L).  The final fatigue life is the smaller of Nf(S) and Nf(L).  In other words, the two safety factors are not applied simultaneously.  Note that the load cycle safety factor is typically in the range of 10s due to the large scatter of tested data on fatigue curves.


When completed, click OK button to return to the main window.






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