11 Replies Latest reply on Aug 26, 2013 11:17 AM by Jared Conway

    SimulationXpress registers unrealistic factors of safety

    James Fiorini

      I am measuring the factors of safety for a side plate for a crane. One version of the side plate has a minimum diameter of 6.531, the "MODIFIED" is bored out to 6.534. Typically, I would expect that the factor of safety on the "ORIGINAL" plate to be greater (stronger) than the modified; however, in every case with playing around with the fixtures, force directions, etc., the plate with the larger hole has a greater factor of safety. This does not make sense to me, since there is less material in the MODIFIED model.

       

      The crane is a 94-ton crane.

      The upper hole is where I've been fixturing it.

      The force is focused on the lower bore, which is the dimension that is being modified. I've made it 94,000 lbs (since there are two plates in the assembly, I made the assumption they are equally distributing the weight), and directed downward by using the Top Plane.

       

      Any help would be great. Thanks.

        • Re: SimulationXpress registers unrealistic factors of safety
          Chris Michalski

          When you increase the diameter of that hole, you increase the surface area over which that force is distributed so the pressure acting on that face is lower.  If it is indicating compressive failure then the larger hole would have less bearing stress.

          • Re: SimulationXpress registers unrealistic factors of safety
            John Burrill

            What does the stress plot look like?  You might have to narrow your range.

            In any event, what might be affecting your factor of safety is that because your hole is the fixed face, increasing it's diametr increases the bearing surface.  So while you have a larger hole in the modified version, it actually represents a larger fraction of your surface area that can't be deformed.

            the full version of simulation has more relastic mounting scenarios, like bearing surface.  the full version also has selective mesh refinement so that you can get highly accurate results in specific areas. 

            Given how small your hole size delta is, the difference in performance between the original and modified versions is getting lost in the mesh aliasing.

            • Re: SimulationXpress registers unrealistic factors of safety
              James Fiorini

              Chris,

               

              I suspected as much with the surface area, but then why wouldn't the largest stress be on the material between the bore and the bottom of the plate? Also, I used force for the simulation, not pressure. Does that even matter?

               

              John,

               

              The hole that is being modified is not the fixture, it is the hole which has the force acting upon it. We have been looking into purchasing Solidworks Premium just for the simulation capabilities. As for the size of the delta, when I did this with the crane beam (which had a similar delta) it worked great. I believe I'm not understanding how Solidworks applies force on a cylindrical face, especially when using the direction tool. Is there any way I can find out how Solidworks does it?