General Mechanical

General Mechanical

Fatigue analysis in APDL

    • matthias.zeller
      Subscriber

      Hey,


      I'd like to solve a fatigue analysis in APDL 19.0. I did a tutorial on how it works, but even if I do the same steps like in the tutorial I can't find the button "Fatigue" under "General Postproc". The tutorial was made in APDL 15.0. Is there a change in the software or is there something which has to be set necessarily to set the the fatigue?


      Thank you very much

    • Rohith Patchigolla
      Ansys Employee

      Hi, 


      From v17.0, this is an legacy feature. Hence, this option cannot be seen in the APDL GUI under "General Postproc". 


      Please go through this link in ANSYS v19.0 help documentation for further reference. 


      This link gives further information on fatigue evaluation in v19.0 in APDL.


      Best regards,


      Rohith

    • matthias.zeller
      Subscriber

      Thank you very much! This helped a lot.


       


       


       


      Is it possible to analyse the fatigue for every node and to output the maximum number of cycles graphically?


      Another question: I want to do a fatigue analysis of a plastic part which has got a highly temperature dependent strength and a certain temperature distribution. Is it possible to consider the temperature dependent strength/ S-N behaviour in APDL or Workbench?


       

    • Sandeep Medikonda
      Ansys Employee

      [EDITED]


      Hi,


      The Mechanical Fatigue Tool automatically calculates the fatigue damage for every node.


      MAPDL can use temperature dependent S-N curves, but it only does ASME Code fatigue.  It cannot really be used with plastic materials at the moment but hopefully this will change in one of the next releases.


      Note that while using metals, after selecting the S-N curve option, you need to choose the Temperature Field Variable from the Toolbox.The fatigue behavior of the material can be accurately captured with a S-N curve, then it will work fine. If the fatigue behavior cannot be captured with a S-N curve, the results will be inaccurate.  The fatigue behavior of some plastic materials can be captured with a S-N curve.  For many it cannot.  You have to verify if the S-N approach is applicable to your material.  If yes, you can use the Mechanical Fatigue Tool.  If not, then you need to use another tool.  DesignLife has some tools for analysis of plastic materials, but not much.  The issue is that fatigue behavior is often very dependent on the specific plastic material. 


      Also, The S-N approach in the Mechanical Fatigue Tool is not limited to any particular material type. It just uses the calculated elastic stresses and the defined stress vs cycles (S-N) curve to predict the fatigue damage.  It is a simple approach.Traditionally, however, it is applied to metals.


      Hope this helps.


      Regards,


      Sandeep

    • matthias.zeller
      Subscriber

      Hi Sandeep,


      thank you very much for your detailed answer. How can I visualize the damage in every node at the same time? I only know how to see the result for one node at a time with the FSNODE command.


      Thanks


      Maddes

    • Sandeep Medikonda
      Ansys Employee

      Maddes,


      FSNODE is part of the MAPDL Fatigue Module.  It is an "archived" feature.  It only does ASME Code fatigue.  It is not a general purpose fatigue tool. 


      The short answer to your question is I don't know of a way to do this at every node, but why aren't they using the Mechanical Fatigue Tool?


      Regards,
      Sandeep


       

    • matthias.zeller
      Subscriber

      Okay, do you mean the Mechanical Fatigue Tool in Workbench? This would be another good possibility.


      Is it possible to apply the loads in APDL and do the fatigue analysis in workbench?

    • Sandeep Medikonda
      Ansys Employee

      Yes, you should be able to write the database using CDWRITE and carry out the analysis in Mechanical.


      Also, you can bring it in with the External Model.


      Regards,


      Sandeep

    • matthias.zeller
      Subscriber

      Thank you very much for your help! :-)

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