5 Replies Latest reply on Sep 23, 2013 11:57 AM by Jared Conway

    Modelling a pre-loaded stud, with additional forces

    Doug Rawlings

      Hello all,


      I'm trying to model a situation where a stud runs through the centre of a cylindrical boss, holding that boss onto a fixed support. At the end of the boss a load is applied acting in the radial direction with respect to the stud axis. I'm trying to find when the joint between the boss and the support starts to come apart.


      So far I've been trying to do this by putting some interference between the nut and the top of the boss, then defining this as a shrink fit contact.


      The fixed component is fixed pretty well with fixed geometry constraints.


      Then I apply a load at the edge of the boss.


      When I run this with very low forces then it looks fine but it only takes a very small amount of force for the joint to come apart, much less than my spreadsheet calcs suggest. And then it shows much greater deflection than is expected.


      So my question is: does this sound like a valid way of modelling the preload on the stud? My concern is that it is getting confused with the deflection occuring due to the external force.


      Any help would be appreciated,

        • Re: Modelling a pre-loaded stud, with additional forces
          Jared Conway

          linear static analysis or nonlinear analysis?


          how exactly are you determining the force to pull the joint apart?


          your method seems reasonable. if you could post some screenshots of the results and the files it might be helpful to understand what is going on.


          other options would be things like modeling the study and applying a temperature to shrink the part to create the "preload". or using a bolt connector.

            • Re: Modelling a pre-loaded stud, with additional forces
              Doug Rawlings

              Linear static analysis. I expect the joint to come apart before any non-linear issues such as yield.


              To determine the force required I'm running a design study, with the force applied as the variable. I'm not looking for an exact figure and I'm not trying to "optimise"; I'll just change the ranges manually.



              So there's a section view of the model. I've not saved an image of the results, I'll post what I can tomorrow, after the study has run overnight.


              I'd thought about fiddling the temperatures but haven't tried it yet. Maybe I should, but I was put off a bit by some of the comments on another thread Non-linear Analysis of Bolt Preload.


              Edit: Sorry, forgot about the connector suggestion. Although not much to report because I haven't tried one. I've no experience with connectors. I'll investigate if I get some time tomorrow.


              Message was edited by: Doug Rawlings

                • Re: Modelling a pre-loaded stud, with additional forces
                  Jared Conway

                  what part is the nut?

                  what kind of contact do you have defined?


                  what do the results look like?


                  i didn't go over that other thread completely, it seems to bounce around between a few topics, what specifically concerns you?

                    • Re: Modelling a pre-loaded stud, with additional forces
                      Doug Rawlings

                      OK, I think I've found what was going wrong but I've attached a screenshot of the bad results just so you can see.




                      It looks like there were typos in the materials definitions that had been corrected in SolidWorks but those corrections hadn't worked through into Simulation. Which is irritating. irritating that I'd made the mistakes in the first place and irritating that they were still there in Simulation, despite having used the right-click and "Update All Components". It seems it updates geometry but not material definitions? That's quite frustrating and misleading.


                      I've found this issue mentioned in various discussions so I'm not the first to be tripped up by it. I wonder if they can change "Update All Components" so that it updates all aspects of all components?


                      having stripped the studies out of the assembly file, de-activated Simulation, re-activated Simulation and then recreated them I get results that look sensible. for completeness I'll post one of those when I get a chance.


                      To answer your questions the - nut is a seperate part, bonded to the stud and shrink fit to the boss. I agree that the other thread jumped around a lot but I thought that one of the more authoritative posts suggested that using thermal expansion to create the preload was not the best way of doing it, but maybe I misunderstood.


                      Thanks to all those who've looked at this. Sorry it was such a trivial error,