General Mechanical

General Mechanical

Fatigue Random Vibration Analysis : error with stress life curve

    • pierj88

      Hi all, I'm Piergiorgio, an italian mechanical engineer that is starting to learn Ansys Workbench. I just registered on this forum (a nice forum , I have read a lot of old discussion in the past weeks) and I need an help for a random vibration analysis with fatigue.

      The steps I've followed are:

      - Define material properties, including Tensile Ultimate Strenght and Alternating Stress Mean Stress Curve.

      -Import the model, reducing all to mid plane surfaces


      -Do a MODAL ANALISYS, not damped!

      -Do a RANDOM VIBRATION ANALYSIS, with constant damping ratio of 0,08. Number of modes to use: all. Output control>Calculate velocity and acceleration: yes.

      -I entered 3 PSD G Acceleration, because I've 16 hours PSD acceleration in x-axis, then 16 hours in y-axis, then 16 hours in z-axis.

      -In Solution>Fatigue Tools I've set: Method=Steinberg. Stress component=Von-Mises. Exposure duration=57600 s (because the sollecitation is for 16 hours in every direction)

      -To obtain the total fatigue damage, I entered a User Define Result with Expression=d1+d2+d3.

      Now, after all, I get and error:  An error occurred inside the FATIGUE module: Invalid or missing stress life curve.

      But the curve is set with Alternating Stress Mean Stress Curve or Bilinear S-N curve (both in attachment). There is something I'm missing?

      NOTE: Modal and Random Vibration have the green mark. Solution have the red flash symbol.

      And another question: to find the fatigue damage, with the stress that I said before (16hr for every axis), the procedure is correct, using User Define Result d1+d2+d3?

      Sorry for this long post, but I've done a lot of try and nothing worked!

      Thanks in advance


    • peteroznewman

      ANSYS staff are not permitted to open attachments. In future posts please use the Insert Image button. I have done that for you below.

      What version of ANSYS are you using?

      I will study this problem and return with more information, but maybe someone else will comment too.

    • pierj88

      Thanks a lot, Peter. I'm using Ansys Workbench 18.0. 

    • Wenlong
      Ansys Employee


      Can you check the material properties displayed in Mechanical? Does the S-N curve pass in successfully? Or does it make sense?





    • pierj88

      Solved using the stock "Structural Steel" and replacing only the properties I needed different

      Thanks all for the support!!!

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