9 Replies Latest reply on Feb 9, 2018 12:42 PM by Adam Kulish

    Wild displacement

    Adam Kulish

      I am doing some simulation on some basic frame rails. Trying to see what worse-case-scenario deflection is when loaded to GVWR.

      6" x 3" 316 11ga 316 SS bar.

      Fixed geometry at front edge, fixed geometry under rear axle.

      Load is applied over the entire top of bar (240lbf)

      No other components, just the rail. Has few lightening holes and cutouts.

      I have ensured everything is drawn properly.

       

      For some reason, I run the simulation and get a serious deflection out of the beam. Looks like a roller coaster. However, it shows no major stresses or strains anywhere on the part. Just a huge displacement. Even if i change the force to 1lbf there is still the same amount of deflection shown in the results, but the stresses and strains are nonexistent. I don't understand what is going on here, and would just like to be able to show an accurate representation of how much the beam could actually deflect.

       

      Thanks in advance

        • Re: Wild displacement
          Matt Peneguy

          You may get some good answers if you post screenshots.  And, you'll probably get even better answers if you post the file/s you are dealing with.

            • Re: Wild displacement
              Adam Kulish

              frame disp.png

               

              Here is a screenshot. Not sure if i can post the CAD. But this is the stress result. And I get this same result if I set the force as 0.05 lbf or even just make gravity the only acting force. I do not understand.

                • Re: Wild displacement
                  Ryan Dark

                  Can you post an image with the stress results from the 0.05 lb force?  Does the max stress go down from 5.559e+006 N/m^2 to 2.778e+005 N/m^2?

                  • Re: Wild displacement
                    Matt Peneguy

                    You posted the stress not the displacement plot.  Displacements are normally small.  So Simulation exaggerates this by default to highlight it.  I added a 1 psi load to the middle (no more than 5lbs) to the middle of this steel bar and this is what it looks like:

                    As everybody keeps telling you, look at your scale.  That's what's important.  My 2 ft long bar with about 5lbs applied to the middle is deflecting about .00007 inches.  But boy does it look like it is bending a lot.

                    • Re: Wild displacement
                      J. Mather

                      Adam Kulish

                      Your latest image attachment does nothing to resolve the issue.

                      Forget the pretty pictures.

                      Post the numbers  - magnitude and units.

                       

                      For comparison you need two sets of numbers - one for each case.

                      The pretty pictures are only serving to confuse the issue.

                  • Re: Wild displacement
                    Ryan Dark

                    Hi Adam,

                    Be default your results are visually scaled in order to better describe the behavior of the deformation.  If you would like to change this right click on your Displacement plot and go to 'Edit Definition'.  In the plot definition you will be able to change the 'Deformed Shape' from Automatic to "True Scale" or "User Defined".

                     

                     

                    This only changes the way the plot looks.  To know how much the deflection actually is you will need to refer to the plot legend.  This legend always scales between the maximum (red) and minimum (blue) deflection.  So, changing values of a loading condition visually look the same because the colors keep scaling.

                     

                    • Re: Wild displacement
                      Christopher Culver

                      Ryan is absolutely correct. The exaggerated deformation is so that you can actually visualize how a part will deform, as in most cases, especially with relatively low loads and stiff materials, the actual deflection might not be noticeable at scale.

                      • Re: Wild displacement
                        J. Mather

                        Adam Kulish wrote:

                        ..there is still the same amount of deflection shown in the results, ...

                        Are you sure about that?

                        Forget the pretty pictures - what do the numbers say?