4 Replies Latest reply on Apr 16, 2018 3:26 PM by Simon Yang

    Solidwork Bolt Connector Problem

    Jasper Liu

      Hi everyone,

       

      I started to study solidwork bolt connector and its applications recently. However, there are some doubts that I could not figure out by finding answers online by myself. I appreciate if anyone can offer me little bit help here. Please see below as my question:

       

      1. No penetration contact: What is the function of "Friction Coefficient" under the no penetration contact properties? Imagine there is a clamp on a tube. The bolt holes on the clamp provides the clamp force or fiction to avoid the tube from slidding. In solidwork simulation, regardless of whether I check the friction option and input the friction coefficient, I get nearly 0 displacement for the tube or clamp. This would not make sense as if we did not check the friction option, friction is 0, thus the tube should slip from the clamp.

       

      In solidworks, is there a way to test if the bolt will loose or the tube will slide away due to insufficient of friction?

       

      2. Pretension of bolt connector: I am confused about how much torque i should put in the pretension of bolt connector. Apparently we can get this valve by either hand calculation or just grabbing it from website by googling standard bolt torque. We know that for different bolt (Grade 8.8 and grade 10.9 for example)(But size are all M8), they have different standard bolt pretension even they share same properties apart from yield strength. (I know the pretension is a function of yield strength.). Please see my confusion below:

       

      Lets still take the clamp and tube scenario for example. if the we use M8 (Grade 8.8), standard torque to tighten the bolt is around 25 N.M. If we use Grade 10.9, the standard torque will be around 36N.M. Apparently the latter will provide more clamping force. However, they perform the same function or serve the same purpose here which is to provide the clamp force to the clamp. If 25N.M is already enough for this purpose, can we use grade 10.9 bolts with a torque as 25N.M? I check some online videos, it seems that the torque they put as pretension is pretty random. They put 500 N preload (Axial) for a M16 bolt and the result indicates that the bolt passes under the safety factor of 2. However, I would seriously doubt that if they put the standard pretension which is 213 N.M or around 72570N in axial. The plate beneath the bolt will definitely failed (because of too much axial load).

       

      Thank you very much for everyone's help!

        • Re: Solidwork Bolt Connector Problem
          Ryan Dark

          Hi Jasper,

          I have been pondering your questions and have some (partial answers):

          1. I ran a quick test case to confirm how friction is behaving in SOLIDWORKS Simulation.  The result was, if the friction setting is not turned on a zero value friction coefficient is being applied to the model.  I have attached my test setup here with two studies.  One with no applied clamping force and one with an applied clamping force.  The study with no friction value is unstable and will not solve (the rod is slipping through the clamp).  The study with applied friction value does solve to a solution.  If your own setup is not behaving the same way I'm not sure what it may be.
          2. This seems more about the philosophy of design rather than how the program behaves.  It looks like you may have answered your own question though.  If the goal of the bolt and its preload is to apply a clamping force to create friction and prevent a tube from moving then both bolts will work for that with varying success.  It comes down to what applied load you have that is trying to pull the tube through the clamp.  If that overcomes the friction produced from the smaller bolt a larger bolt will be needed.  It seems like this is where you ended up though.
            • Re: Solidwork Bolt Connector Problem
              Jasper Liu

              Good afternoon Ryan,

               

              Thank you very much for you help with my inquiry. Now I know much better about the this friction coefficient!

               

              Another question is related to the bolt connector under compression external force. Is it true that solidwork cannot do this job very well and a real model of bolt would be needed for simulation?

              Please see the information mentioned in solidwork help: "In loading scenarios where the bolts are under compressive forces, the axial forces of bolt connectors may not be accurate. In such cases, a decrease in preload bolt force can result in a "loosening" of the bolt and loss of contact between the bolt and the components. This behavior cannot be captured by the bolt connector formulation. For these cases, model the actual bolt and define no penetration contact sets between the bolt and the components."

               

               

               

              With regards to my second question, I have a doubt: what would be the difference between Grade 4.6 M8 with 8.5N.M as preload and Grade 8.8 M8 8.5N.M as preload? For example, the requirement for the bolted connection in a hypothetical scenario is that a pretension of 5000N has to be applied. As we can see, for both options, we can achieve that 5000N preload(Axial). Grade 4.6 bolt reaches 65% of Proof Load but grade 8.8 does not. Is there any advantage of using grade 4.6 bolt over grade 8.8 bolt or vice versa? Grade 4.6 bolt reaches its 65% of its Proof Load but grade 8.8 bolt doesnt. Does this mean that Grade 8.8 tends to loose compare with Grade 4.6 bolt?

               

              Thank you very much Ryan.

                • Re: Solidwork Bolt Connector Problem
                  Ryan Dark

                  Jasper,

                  Bolt connectors could not be used in a case where the preload is overcome and the bolted connection becomes loose.  The formulation for bolts is only valid for a tight connection with some preload preserved.

                   

                  As for your questions on bolt grades, I will have to defer to an expert.

                  • Re: Solidwork Bolt Connector Problem
                    Simon Yang

                    To reduce the cost usually selecting the bolts depends on the work load range.

                    Always using the right bolt for engineering. Such as using Grade 4.6 bolt if it works well, other wise using Grade 8.8, or Grade 10.9. Do not using higher grade if the lower grade bolt works well.

                    By the way, higher grade bolt works will well if the lower grade bolt works well.