5 Replies Latest reply on Aug 9, 2010 11:10 AM by Ryan Werner

    Weldment Model is Unstable

    Scott Pratt

      I am trying to analyze a model that consists of round tubing that I am treating as beams and sheet metal sides that I am treating as shells. I applied loads and fixtures points and then welded the contact surfaces between the tubing and sheet metal. When I ran the stress study I get an error that the model is unstable. Am I treating the members correctly? Is there something I can do to figure out why my model is unstable? Thoughts?

       

      -Scott

       

      Truss Frame (08-05-10).jpg

      Truss Frame Welds (08-05-10).jpg

        • Re: Weldment Model is Unstable
          Ryan Werner

          The first thought that comes to mind is whether the sheet metal pieces are trimmed perfectly to the round tubes.  If there is any gap or interference then Simulation will not see them as connected and the weld you added may not be valid.  That is just a guess.  Seeing the model would maybe help.

           

          Ryan W.

            • Re: Weldment Model is Unstable
              Scott Pratt

              Hey Ryan,

              There aren't any gaps between the sheet metal and the tubing. Let me know if you have any other thoughts. Thanks.

               

              -Scott

                • Re: Weldment Model is Unstable
                  Ryan Werner

                  Hi Scott,

                   

                  A good way to see what parts are not connecting is to turn on the Soft Springs or Inertial Relief features and then run the anlysis.  These will help artificially stabilize the model so that Simulation can get a solution and then you will be able to see what parts are not connected.

                   

                  I will admit that I have limited experience using the shell/weld feature so I am not sure if I can really offer any more suggestions as to how you can get that working.  You may have more luck getting it to work if instead of using shells you made the sheet metal parts solids.  This would mean creating contact sets between the solids and the beams which can sometimes be quite trying.  Also, you have the option of running everything as a solid but both of these suggestions would require more computer resources and may not solve your problem anyway.

                   

                  Good Luck, Ryan W.