2 Replies Latest reply on Sep 4, 2013 6:25 PM by Jerry Steiger

    Stress analysis of a press fit insert

    Dinesh Sharma

      Hello All,

       

      I am trying to simulate a press fit assembly, in which boss amde of PC is press fitted with a threaded insert made of brass. I simulated it using shrink fit connections in solidworks simulation. i find out the hoop stresses and VM stresses.

      The insert outer surface has serrations to prevent rotation. at the location of the serration (on inner surface of the boss) i am getting stress values which are far higher than the material break strength of boss. these stresses reduce both circumferentially as well radially outwards and reach values less than the yield stress.

      My question is regarding the results interpertation, how can i get stresses at which the crack will initiate on the boss inner surface and propagate to the outer surface.

      Physically, the part sometimes develops crack, but most of the part are correct. If the analysis is correct then all the parts should fail in actual.

       

      Please suggest what can be considered as failure stress in this case.

       

      Thanks for your valuable time,

      Dinesh Sharma

        • Re: Stress analysis of a press fit insert
          Jared Conway

          have you considered mesh size?

           

          are you using static or nonlinear analysis?

           

          you may want to post your model or some pictures of your models and then show some of your back end calculations that show what you're comparing against.

           

          overall, i could potentially see some high stresses happening in the area of a shrink fit just because of how the software handles them. but similar to other high stress areas, you may need to interpret the results a few elements away to understand exactly what is happening. some research on singularities and mesh convergence would be good. here's an article we wrote awhile ago:

           

          http://www.hawkridgesys.com/blog/solidworks-simulation-achieving-convergence-of-results/

          • Re: Stress analysis of a press fit insert
            Jerry Steiger

            Dinesh,

             

            You would have to run a non-linear material to get a better feeling for what is going to happen. The material has to yield and flow to form around the insert.

             

            You are going to have very small radii (probably 0 in your model, if not in the real parts) at the serrations.

             

            Knit lines are often a reason why some bosses fail and some don't. Bosses which have weak knit lines will fail much more often than bosses with strong knit lines. Processing differences can cause knit lines in a given location to be much weaker than normal.

             

            Cracking can also depend on how the inserts are inserted. Are you doing it with heat or with ultrasonics? Using too low a temperature or too low ultrasonic energy can cause cracking.

             

            The "right" way to run the analysis would be to run a multi-physics analysis combining thermal and mechanical analyses. Even then, how would you account for knit lines?

             

            Jerry S.