6 Replies Latest reply on Mar 10, 2011 4:43 PM by Alessandro Tornincasa

    Structural Simulation of a chain

    Alessandro Tornincasa

      Hi all,

      I'm trying to perform a FEM simulation of a chain and I'm comparing results with physical testing.

       

      Physical testing occurs on the chain you see in the following picture:

       

      Pic1.jpg

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

      Test occurs with an hydraulic powered machine, and two pins are inserted in the holes you see in the picture. One pin is kept fixed, while the other pin is pulled.

      The load that breaks the chain is 100000 N.

       

      Most of the components are assembled with shrink fit, therefore I'm simulating that condition with global bonded contact:

       

      Pic2.jpg

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

      The only parts where I'm applying a different condition are those you see in the picture, where I'm applying a no penetration condition (a bonded condition doesn't work because surfaces touch only on one line):

       

      Pic3.jpg

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

      Breaking component in the inner link of the chain you see in the following picture:

       

      Pic4.jpg

       

       

       

       

       

       

       

       

       

       

       

       

       

       

      In the next picture I'm showing where exactly it breaks:

       

      Pic5.jpg

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

      In my simulation I'm keeping fixed the face of the hole where the fixed pin is in, while I'm pulling with a force the other hole where the pulled pin is in. I've also tried using a displacement instead of a force, but my problem is that I'm not getting realistic results:

       

      Pic6.jpg

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

      Just by using a 30000 N force or equivalent displacement, rhere are unreasonable high stresses on parts that have a 650 Mpa Yield stress and that are not supposed to break:

       

       

      Pic7.jpg

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

      I even had to insert some artificial fillets in order to avoid stress concentrations on edges.

       

      I tried to model this chain in a Similar way to the chain you find in the SolidWorks Simulation training manual, but I'm not getting realistic results either:

       

      Pic8.jpg

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

      Any suggestions on how to get correct results ?

      I'm attaching the chain model TEST_SIMULATION_2011.SLDASM with a few studies I tried to setup.

       

      Thanks,

       

      Alessandro

        • Re: Structural Simulation of a chain
          Anthony Botting

          Hi Alessandro:
          The contact problem is nonlinear, and notoriously difficult to model in any FEA program. Assuming failure is occuring in the link and not the pin, I would try the "Bearing Load" function on just half of one link, without using the pin at all. The Bearing Load will apply a perfect parabolic or sine load (your choice) distribution on the link's bearing surface and make it a linear problem, so it will solve much faster than using contacts. Hope that helps. -Tony

            • Re: Structural Simulation of a chain
              Alessandro Tornincasa

              Hi Antony,

              thank you, I appreciate your reply a lot.

               

              What you're saying is right, if you know in advance that the inner link is going to break, you can perform an analysis on it in order to check wether will break or not.

               

              The problem is when your chain is a brand new model, and you've never done any physical testing on it. How will you know what component will break for first, and therefore on which component make geometry optimization ?

               

              Moreover, you don't have yet an idea of the load that will yield the breaking component, and therefore you are not able to design for strength you chain in advance.

               

              In such hard cases FEM doesn't help you that much if your simulation is not set uo in a way that it can give results coincident to phisical testing.

               

              My personal idea is that the material of the pin has a tool low elasticity modulus (ifact it undergoes some thermal treatment). I imagine that a very stiff pin won't deform and force the bushing to "tear off" the hole of the inner chain.

            • Re: Structural Simulation of a chain
              Dougal Hiscock

              It appears to me that the actual failure you're looking for is tensile, yet the stresses you're currently focusing on are in compression and while likely to show up as damage in the chain aren't the source of failure.

               

              Solidworks simulation makes it difficult to distinguish between the two as it only shows magnitude of the stress, not the direction.