4 Replies Latest reply on Oct 21, 2008 11:14 AM by Anthony Moulton

    Boss and shaft analysis

    Anthony Moulton
      Hello all,

      I am new to COSMOS so please bear with me, I am sure there is a simple solution to my problem that I am not aware of. I am attempting to perform an analysis on a boss with a threaded shaft inserted into it. Once the shaft is inserted, fillet welds are created around were the boss and shaft meet on both the front and back of the boss. I have constructed models with accurate threads and also with semi-accurate thread approximations but neither model will mesh. Is there a simpler way to perform this test i.e. a simpler way to inform COSMOS the boss and shaft meeting is threaded without actually constructing helical threads? I have also constructed multiple solid parts without threads but when I perform the analysis it appears that the front fillet weld is under stress but not the rear fillet weld. If anyone has any suggestions please let me know. Thank you for your input.

      Anthony
        • Boss and shaft analysis
          Steven Dinsdale
          Could you post some pictures of what you are trying to accomplish? What loads are you applying?

          To get it to mesh you are going have to apply fine mesh control in the thread area. You could also try "automatic transition" under Options when you mesh.

          I don't know if it would help but you might also want to look into bolted connectors under loads/restraints->connectors.

          Steven

          Edit:
          Also, modeling contact between threads usually requires nonlinear analysis. From COSMOS help:

          Contact Nonlinearities
          A special class of nonlinear problems is concerned with the changing nature of the boundary conditions of the structures involved in the analysis during motion. This situation is encountered in the analysis of contact problems.

          Pounding of structures, gear-tooth contacts, fitting problems, threaded connections, and impact bodies are several examples requiring the evaluation of the contact boundaries. The evaluation of contact boundaries (nodes, lines, or surfaces) can be achieved by using gap (contact) elements between nodes on the adjacent boundaries.


            • Boss and shaft analysis
              Anthony Moulton
              I have attached screenshots which will hopefully paint the picture more clearly. I have fully restrained the back of the boss because it is only the welds and threads I am concerned about. The load is a 1500 lbf load applied normal to the top plain applied at the end section of the shaft approximately 17 inches from the back of the boss.

              I have tried to apply fine mesh control and I was successful but only the threaded areas appeared and I could not figure out how to apply fine mesh control locally. When I tried to apply fine mesh control over the entire model SW stated that I ran out of memory and then shut down (apparently 3 gigs of ram is not enough to handle that). I tried your automatic transition option to no avail. I have yet to look into bolted connectors, that is my next plan of action.
                • Boss and shaft analysis
                  David Anderson
                  this is not good application for FEA. this can all be done using closed form solutions that will give excellent results and take less time.

                  stress in a cantilever s=M/C*I

                  give that this shaft is welded on the front and back, you can ignore the threads and simply look at the crossectional area of the weld joint under stress and to determine if it is strong enough.