10 Replies Latest reply on Dec 5, 2011 12:57 AM by Mikael Martinsson

    see max stress and deflextion in shaft

    Pascal M

      hi i have access to sw premium 2010.

       

      my shaft is supportred on both sides.  i want to see min max deflexion and stress at different stages of deflextion (1,2,3,4,5mm)  since in dont know how to do this, i put a physical support in the point of interest, with contact mate but only for positioning...  same for the 2 extremities.  works out fine if the supports are in contact but when i try to put a 1 mm play in the middle (2 extremidies still being in contact) the shaft goes righ thru them as is they wherent there.

       

      anyone could help?

       

      i think solution lies in component contact, just dont know how to handle it so far

       

      i made the supports .200 wide... in reality, they are normal 10 in wide and because of deflextion of the shaft, it will bend and only touch on the inside part of the 2 extremity supports... i couldnt model those and the shaft would be glued to the whole support.  with th support being .200 wide, the can bend and not affect the result... 

       

      please please please help me

       

      thanks ALOT

        • Re: see max stress and deflextion in shaft
          Per Engberg

          I don't think that SW FEM supports stress as function of deflection. You might try to simulate by adding a force on the middle of the shaft and adjusting it until you get the desired deflection. You may have to split the face of the shaft to be able to place the force where you want it. Be careful when evaluating the results, preferably check by manual calculations that they are in the correct order of magnitude.

            • Re: see max stress and deflextion in shaft
              Pascal M

              maybe i miss explained...  loads are defined, supports are defined : 2 fixed supports at eache end, 1 support un the middle that i wild adjust with 0mm gap, 1, 2, 3...  for each gap, i want do be able to measure von misses and the point in the shaft with most deflection. 

               

              simulation works out with no middle support or middle support being in contact with shaft.

               

              when i put 1mm play between middle support and shaft (or any other play), the shaft bends right thru the middle support as if it wasnt there

               

              amy idea on how to make it stop on the support so i can calculated shaft von misses and max deflection with play on middle support. (to simulate if the middle support was not adjusted to proper height)

               

              thanks!

                • Re: see max stress and deflextion in shaft
                  Jerry Steiger

                  Pascal,

                   

                  I'm not at all familiar with how SW Simulation handles this kind of problem, but I suspect you may be running into the same types of difficulties that I have had in ANSYS. I think what happens is that the contact has a distance (called the pinball radius in ANSYS) within which it checks to see if it might be in contact with something. If there isn't a mating contact surface within the pinball radius, then it ignores the possibility of contact. If you have large load increments in your analysis, then the mating contact may be outside the pinball radius in one direction on a step and outside the pinball radius in the other direction on the next step. The two parts pop through one another. The fix is to use smaller load increments. In ANSYS I could set up the load with large increments until it got close, then smaller increments as it established contact, then larger increments to get to my maximum load.

                   

                  This is a non-analyst ME explanation of what I think I see when the software runs. I don't actually know what is going on in the software.

                   

                  Jerry Steiger

                  • Re: see max stress and deflextion in shaft
                    Bill McEachern

                    Hello Pascal,

                     

                    Since you did not supply a picture it is hard to tell what is really going on. I am assuming you have the central support in there to somehow aid in your limiting the deflection. If you are trying to calculate the stress vs. displacement that occurs with a support at various distances then the following is not going to work. If that is the case there are otherways to get it done. You need to supply a picture of the load case with or without the supports depending on why they are there.

                     

                    If the load is applied at a vertex (single node) you can rplace it with a displacement in the desired direction and get the stress versus deflection by doing a number of runs.

                    If the load is not so convenient and is applied over some goup of nodes as is likely, the easiest way to get what you want which is the stress vs displacement at some node is to, assume the structure is linear as may be the case, and just calculate the values of the stress as simple linear ratios of the case you did run. If the sturucture is non linear you can just use the Premium version of the software for this and  can get what you want directly.

                    If you don't absolutely need contact don't put it in.

                      • Re: see max stress and deflextion in shaft
                        Pascal M

                        IMG_0983.jpghere is a pic...  shaft always rest on extremity supports...  i want max delfection and von mises based on the center support play... to simulate that it wouldnt be set at the right height.

                         

                        maybe it makes a difference.. i would like stress AND deflection... i dont want to impose displacement as i dont know where it will be maximum :S

                         

                        in the first mail i sent is my model... 

                  • Re: see max stress and deflextion in shaft
                    Mikael Martinsson

                    Hello.

                    I'm new to simulation, and I'm not sure if I understand what you want to do. If the statement in your first post is what your looking for, to see stress with different displacement, you should follow the advice that Bill gave earlier. Induce a displacement by 1, 2 or 3 mm (no other force needed) and you'll find the stress for each number.

                     

                    If you want to have central supports, as in your 3d, you need to add contact sets. By default the global contact set is "bonded". That only works if the parts are in contact, and they'll behave as if they where welded together. You can change the global set to "No penetration" but the calculation can take a long time. Instead you add 2 contact sets between half round surfaces on the middle supports and the shaft diameter. The shaft will move freely until it hits the support and after this continue to deform but with contact to the supports. Important to know is that even with "no penetration", the visual result if you have a high deformation scale, will still look as if it didn't work. The result will be correct any way.

                     

                    Please see some pictures on a similar situtation (deformation scale is 1) with large deformation.  Gap between shaft and support is 1 mm. In pic 1 you see the result with only the global bonded contact. The shaft moves as is if it hangs free without support.  In pic 2 you see the same result with a local No penetration contact.

                    Bonded Displacement.JPG

                    No Penetration Displacement.JPG

                    • Re: see max stress and deflextion in shaft
                      Pascal M

                      yes, i found the contact trick the night before he had replied    seems to work...

                       

                      i have 2 load points and the support/loads and they are not symetrical, so deceiding where to apply the deflection is easy...

                       

                      one of you know how to find the force applied on each support (in the event for example that the middle support would happen to be lower? 

                       

                      thanks

                      • Re: see max stress and deflextion in shaft
                        Pascal M

                        is there a trick to find max load on supporting points?

                         

                        thanks