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Fatigue analysis in LS-Prepost for cyclic loading

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Posts: 3
Topic starter
(@error-k)
Unpaid Intern
Joined: 9 months ago

Hi everyone,

I am trying to do a fatigue analysis on a bicycle handlebar and stem to predict points of failure. The handlebar is loaded on either end with a 270N 5 Hz (assume sinusoidal input) in-phase load for 100k cycles, followed by 100k cycles out-of-phase loading.

I've previously done something similar using the "fatigue tool" for a static structural analysis in Ansys Mechanical, but I no longer have access to the Uni licences, unfortunately. I'm still very much a novice Dyna/PrePost user and slowly but surely getting to grips with it.

I've read in the user manual that there are several *Fatigue keywords available. How would you go about setting up the simulation for cyclic loading and using for example the Goodman or Soderberg mean stress correction methods? For now I just want to do 100k cycles in-phase loading.

I currently have the model set up with bolts modelled with beam elements and pre-load to 6 kN using *INITIAL_AXIAL_FORCE_BEAM. Applied loads are defined using the *LOAD_NODE_SET keyword. The load is by *DEFINE_CURVE keyword.

Are there any reference material or YouTube tutorials that you could recommend?

Cheers,
Jaco

 

 

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2 Replies




Posts: 1
(@dennis_chen_88)
Barista
Joined: 8 months ago

Look up Mat_add_Fatigue_(option) in the Dyna vol 2 manual. 

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Posts: 3
Topic starter
(@error-k)
Unpaid Intern
Joined: 9 months ago

Thanks Dennis, that's always a good place to start. 

 

For any others interested in this type of analysis, I reached out to the guys at Dynamore to ask for advice. Attached is a very nice workflow summary of how to use the relevant fatigue keywords. 

In short, you will build two input decks. Deck 1 is a regular implicit analysis for one cycle of loading. Important to output ELOUT data or use *DATABASE_HISTORY_SOLID/SHELL data for the elements of interest. 

Thereafter, copy Deck 1, remove the element history keywords and add the fatigue keywords. You only need to add one *Fatigue keyword to "invoke" the fatigue analysis. They recommend using *FATIGUE_ELOUT with RESTART=1 and the binout file as input file. Remember to add the material S-N data via the *MAT_ADD_FATIGUE keyword and *DATABASE_D3FTG to be able to plot the fatigue results in post.  

First run Deck 1 and save all the binout files to a separate folder. Reference this file path in Deck 2 *FATIGUE_ELOUT keyword. 
Then run Deck 2 with the relevant fatigue keywords. Open the D3FTG file in post to see the result. 

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