3 Replies Latest reply on Feb 13, 2010 6:26 AM by Devi Prasad Samal

    Buckling Analysis Questions

    Chuck Lob

      See attached jpeg.  I'm trying to do a buckling analysis of an assembly consisting of a rod and identical clevises and cross pins on either end - five parts total.  I've attached a hinged contraint to the middle of the lower pin (I used split lines to define a center of the pin) and have assigned bonded contacts between the pins and their respective clevises and between the clevises and the rod.

      My question is in regard to how to apply the load and constraints at the upper end because the analysis, although it runs fine, doesn't produce a symmetrical "bowing" shape with the loading/constraints I'm using.  The upper clevis - where the load is applied - stays relatively in plane.  I don't think this is correct.

      I've applied a vertical load to the center section of the upper pin and applied constraints such that the pin can only move vertically, but I don't want to inhibit the clevis from rotating about the pin and I don't think I have, but it appears to be stuck in-plane.  SW Sim only allows bonded and free contact elements in buckling mode so every contact point between the parts is bonded - I have no choice.  Also, there doesn't appear to be any vertical displacement of the upper clevis - it doesn't move down.  I did some really simple models of just a flat plate and the results are similar - no vertical movement of the upper portion.  Any help is greatly appreciated.

        • Re: Buckling Analysis Questions
          Devi Prasad Samal

          hi lob,

           

          i just want to know which type of restraints you have applied in the upper portion of the pin....to restraint it , so that it will actually move in vertical direction only.

           

          from the figure i think you can apply a reference plane restraint which allows the rod to only move in vertical direction & stop it in other direction...

           

          but in the picture it assumes that you pin is restaint to move in vertical & goes any other direction freely.....

           

          if you can attach the part it will be easy for me to work on it.........

            • Re: Buckling Analysis Questions
              Chuck Lob
              Devi, thank you for your help.  I have attached the parts and assembly file.  Also, there is a closer jpeg image that shows the load and restraints at the upper clevis pin.  You can see that I have constrained it along the pin axis and transverse to it.  The downward force is 1000 lbs.
                • Re: Buckling Analysis Questions
                  Devi Prasad Samal

                  Sorry for the late reply.......

                   

                  from the analysis file i  find that you have given one roller sliding & one reference geometry mate with respect to a line....

                   

                  so i think the restraints are ok.....

                   

                  i think you just worry about the animation which you see in buckling analysis is not behaving properly......

                   

                  dont worry about that because you will never find any other animation than bending (buckling of beam) in buckling analysis.

                   

                  one thing i just want to share whenevr you are going to create a buckling analysis it will show only the bending of the beam...

                   

                  so upper clevesiss will not be going to move downward in animation of buckling analysis.

                   

                  if you are going for buckling analysis then 1st create a static analysis of the same assembly so that you will know from the animation that is it your restraints are perfect or not.....

                   

                  another thing is check that factor of safety for static & buckling which is greater....depending upon the high value you should go for that analysis....

                   

                  if buclikng factor of safety is higher than a staic then no need to worry for the buckling analysis.....

                   

                   

                   

                  also see the attachments for the animation of different analysis ....