22 Replies Latest reply on Jul 8, 2009 12:06 AM by Ian Hogg

    drop test-not on the floor

    oren wein
      Hi.
      How can I test the effect of droping the attached hammer to the piece (I'm trying to check if the hammer's neck will survive the impact).

      Thanks.
      Oren.
        • drop test-not on the floor
          Robert Stupplebeen
          FEA in general can not handle this accurately unless you have you materials characterized more thoroughly than E, G and Nu. If that is all that you have you need to make an assumption about how long in time it will take for the hammer to have 0 -x velocity. The force is directly proportional to the time. http://en.wikipedia.org/wiki/Impulse I hope this helps.

          Rob Stupplebeen
          • drop test-not on the floor
            Bill McEachern
            with all due respect to Rob, you can do a decent job of thisproblem with a non linear dynamics analysis available in Simulation premium.
            • drop test-not on the floor
              Robert Stupplebeen
              Bill,
              That is great that you have gotten good correlation. Roughly what velocities and materials are you using? My guess is in the background cosmos is performing a calc using the velocities, and respective moduli. It might perform very well for well behaved linear materials like steel but if it is a more complex material such as plastics or Jello (R) then it might struggle. In the end if it correlates well for a couple of similar geometries and or loadings then it is a good simulation.

              PS thanks for the respect
              • drop test-not on the floor
                Robert Stupplebeen
                I would attach the plate to a force transducer and record at a high speed the force of the impact. Then if you want to be conservative the part should be able to handle this load statically. Depending on the application fatigue allowables may be appropriate. I hope this helps.

                Rob Stupplebeen
                • drop test-not on the floor
                  Ian Hogg
                  Orien,

                  The "Drop test" study won't work for the scenario you have. It is designed for an object hitting a flat surface. In your case only a portion of the model hits something.

                  I took your model and set up a quick nonlinear dynamic run and positioned it just off contact with an initial velocity of ~4.5m/sec (based on your 1meter drop height)

                  This is a quick example of the result. The problem with the model is that it has no characteristics for the rest of the hammer used in the impact test, so there is no true momentum and response as for the full mdoel. It's not too hard to set up, but would take a little time to run.

                  If I recall, you're using SW2007, so the only option there is to use COSMOSM for nonlinear dynamics. Not a product that is easy to use, but it is fairly capable.

                  What sort of application are you looking for with respect to the hammer? There are standard tests for drop hammers that specify their dimensions, mass ,etc depending on what you're testing for.

                  Cheers,

                  Ian


                    • drop test-not on the floor
                      oren wein
                      Ian Hi again.

                      You are my God :-)
                      can you please explain how you do it????
                      I also want to run the sam simulation

                      Oren.
                        • drop test-not on the floor
                          Ian Hogg
                          Hi Oren,

                          I'm not well versed with GeoStar/COSMOSM, but in COSMOS/Solidworks Simulation (V2008 and higher), nonlinear is integrated. For your model it was extremly simple to set up.
                          Create a nonlinear time based study (end time of 5 milliseconds)
                          Apply an initial condition to the hammer (I specified an initial velocity just prior to impact)
                          Fix the body it's going to strike
                          Set gravity in the relevant direction
                          Add a restraint to keep the hammer moving in a direction towards the target (those holes in the hammer were useful for this)
                          Add mesh control to the mesh in the area of contact for accurate representation (I still used high order elements in the run since stresses are significant).
                          Run the simulation. It took just ove an hour.

                          THat's there all was to doing it. I initialyl did a longer time run to see what exact durection the collision occurred over, but I could have done some hand calcs to work that out if I really wanted to.
                          I only applied linear material properties and did focus on meshing in areas that had peak stresses, this was just a quick proof of concept for you.
                          Cheers,
                          Ian
                            • drop test-not on the floor
                              Don Vanzile


                              Hey Ian, do you do consulting work by chance?

                              Don
                                • drop test-not on the floor
                                  Ian Hogg
                                  Hi Don,

                                  No, I don't do consulting, I just enjoy providing assistance where I can so people can get the most benefit from the software (I've always had a penchant for teaching).

                                  I can highly recommend Bill McEachern if you're looking from someone

                                  Cheers,

                                  Ian
                                • drop test-not on the floor
                                  oren wein
                                  Hi Ian.

                                  Sorry for the stupid questions, but how do I specified an initial velocity
                                  I looked forit in the Cosmosworks and which type of restraint should I choose?

                                  Thanks.
                                  Oren.
                                    • drop test-not on the floor
                                      Ian Hogg
                                      Hi Oren,
                                      In 2008/2009 you will find it under forces/external loads (see image).
                                      This is for nonlinear dynamic (with time, not quasi-static) only.

                                      Not sure where it is in Geostar.

                                      Ian
                                        • drop test-not on the floor
                                          oren wein
                                          Again as usual-many thanks.
                                          I think it's about time to install solidworks 2008 :-)

                                          and as usaul you were very helpful.


                                          your admirer.
                                          Oren.

                                            • drop test-not on the floor
                                              oren wein
                                              Hello again.

                                              Finally I have Solidworks 2008 and I tried to copycat the simulation you sent me according to your instructions, but nothing.
                                              I will very appreciate if you will able to send me the simulation model you ran or send me a movie which shows how to setup the simulation or see what I'm doing wrong in mine.

                                              many many thanks.
                                                • drop test-not on the floor
                                                  Ian Hogg
                                                  Hi Orien,

                                                  The issue is you are forcing a movement downwards which is not going to give you a dynamic collision. Remove Restraint-3. Gravity and the initial velocity are going to ensure that the collision occurs.
                                                  To guide the part, add a radial restraint to each of the 2 holes (as if the hammer is sliding down 2 rods).
                                                  I do not advise fixing surfaces that are going to contact. Jsut fix the bottom face of the part being struck.
                                                  Delet the global bonded contact and define a no penetration contact between the faces that are going to hit.

                                                  With that done you should be good to go. It may take a little bit of tweaking to zero in on the time frame for just the collision and not too long after it.

                                                  Cheers,

                                                  ian