4 Replies Latest reply on Jan 29, 2012 12:36 PM by Wayne Matus

    URES Displacement

    S. H

      Hi all,

       

      I am new to SolidWorks and have been designing some parts to be milled. I am using SimulationXpress to analyze whether a part I am designing can handle a load.

       

      I am trying to figure out if the below part can hold 150lbs in the downward direction on the front face. The analysis produced the following results.

       

      I am not a qualified engineer and, as such, trying to understand the results. Is this suggesting then at the top of my model, with 150lb, it will be displaced by 28.16mm?

       

      Screenshot on 1.27.2012 at 6.36.54 PM.png

       

      Many thanks.

        • Re: URES Displacement
          Kevin De Smet

          One of the things to realize about finite element analysis, even in SolidWorks with its straight-forward easy to use interface, is that it is still very dependent on mathematics that date to way back; meaning there are plenty of things you should be aware of when doing analyses and interpreting the results, or you will be deceived by the software!

           

          Firstly, whenever you get large displacements you can no longer assume a linear static analysis, which is what SimulationXpress is capable of doing. That is because it can not account for the stress softening or stiffening of the stucture as it takes this big deformation.

           

          Secondly, I see you have a simple load and fix restraint. Finite element analysis is very sensitive about loads and restraints, meaning you really should not idealize it to be very simple (like hand calcs are) unless maybe you're using beam elements, again not available in SimulationXpress. Think about how your load is actually distributed, it is really all on that tiny top face? is the fixed restraint really holding the entire bottom completely rigid? remember, if you tell it to be fixed it won't move at all. generating a large reaction force. Think of the fixed restraint as another load in that way, just an indirect load. Compare it to a sound wave (load) and the bounced sound wave off of a wall as a restraint, it can still carry a big punch.

           

          I would suggest you try to go through all of the Cosmos Companion papers, they are very great and explain a lot of fundamentals in using Solidworks Simulation and it is written in a way it is understandable for a layman: http://www.eng.uwo.ca/designcentre/FEA%20resources/default.htm

           

          To end, you really should think about at least using SolidWorks Premium to get the full static analysis capability. SimulationXpress is useless (sorry but that's what I think about it)

            • Re: URES Displacement
              S. H

              Thanks for that Kevin. I understand that SolidWorks is using a linear static analysis. I am just trying to get a basic understand of if this model can hold the load (150lbs) and acknowledge it will not take all complexities into account.

               

              The load is being applied on the front face in a downward direction (imagine something is hanging/bolted onto the front face), rather than on the small top face. The bottom face will not necessarily be fixed but be sitting flat on a surface so all forces will essentially be in that direction.

               

              However, going back to my question regarding the URES and deformation scale, is this analysis suggesting that the model will be displaced 28.16mm at the top in the x direction at max load (150lbs)?

                • Re: URES Displacement
                  Kevin De Smet

                  Hmmm. I'm not sure. Another thing to take into account is your mesh settings, make sure you have at least 3 to 4 elements through the thickness of the model. In a perfect world you would use a Shell mesh (surface model) but Xpress won't do it.

                  • Re: URES Displacement
                    Wayne Matus

                    Several comments.

                     

                    If the real part was  loaded exactly like you have it modeled and the mesh was of proper size, then yes, the max deflection would be approximately 28.16 mm. But the model is not loaded and constrained like the real world part.

                     

                    The fixed constraint is like the piece is full penetration welded to what it actually sets on.

                     

                    If something is bolted to it, then what is bolted to it is going to be stiffening it.

                     

                    Finally, the most critical mistake you are making. URES is the Resultant Displacement, not the displacement in the X direction. URES is square root of (delta X squared + delta Y squared + delta Z squared). You can see from the image that most of the deflection is in the Z direction, which may be stiffened in by the piece this part is holding.