3 Replies Latest reply on Feb 16, 2012 2:54 AM by Mikael Martinsson

    Buckling analysis

    Mikael Martinsson



      I have a long ejector pin for a mold and I have done a static study to evaluate displacement and stress. No problem there.

      Since the ejector pins are very long and slender I also want to do a buckling analysis.

      The ejector pin is radially fixed 30 mm in the tip and 30 mm in the back end.

      There are also 150 mm below the tip where there are a clearance of about 0,5 mm


      The first thing that i notice when copying fixtures, loads and contacts is that "no penetration" is not available. Why is it so?

      This contact was used on the static study to simulate the 0,5 mm radial clearance that we have thru the insert and die holder.


      I exclude this "no penetration" contact, and run the analysis. The BLF is above 0 but below 1 so buckling can be a problem.


      I then exchange the contact with a radial fixture similar to the one for the 30 + 30 mm.

      The BLF is even lower now. Shouldn't this affect the result in a positive way since the "free length" of the pin is shorter?


      Perhaps stupid questions and to my defence I have not yet attended the course for this module.

      Thank you for your answers.

        • Re: Buckling analysis
          Wayne Matus

          The no penetration option would make this a nonlinear buckling analysis and that is only available in the Simulation Premium package.


          I too would have thought that your second test of adding a radial fixture for what was the contact region would increase the BLF not lower it.


          I do not have my hands on Simulation right now to test myself.

          • Re: Buckling analysis
            Paul Kellner

            What does your hand calculation say the buckling load should be?


            How does the stress in the pin compare to yield stress?

            • Re: Buckling analysis
              Mikael Martinsson


              I did something wrong in the setup yesterday, probably with the fixtures.

              Windows decided to not let me save the file with the study, so I had to do it again this morning.

              Now the results are as expected.



              Ok, that explains it. I only have the Simulation Professional so nonlinear is not possible for me.



              Hand calculation for this load case gave F = 1672 N compared to the actual load 3924 N. BLF = 0,42. My result yesterday was 0,13 but today, with the same 3d  i got BLF = 0,42. 

              If I add a fixture on the 0,5 mm clearance (150 mm length) hand calc gives F = 3489 N, BLF = 0,89. Simulation gives BLF = 0,88.


              Stress in the pin is only about 1/4 compared to yield stress.


              Thank you both for your time.