General Mechanical

General Mechanical

Explicit Dynamics Error for Snap fit simulation

    • VJ0085
      Subscriber

      Hello, I am performing snap-fit simulation in explicit dynamics and despite everything seems OK, the solver just doesn't start at all. I first created all hex mesh and later changed to tet mesh with various settings. Could someone guide me in here? Thanks.

    • peteroznewman
      Subscriber

      What do you want the simulation to tell you about the snap fit design?


      I ask this question because I would use a Static Structural model to study a snap fit design.

    • VJ0085
      Subscriber

      Hey Peter, I would like to see the stress distribution in the snap like this one


      I know that static structural can be used but it's more time consuming and I had convergence errors popping up (maybe because of highly distorted mesh). Your advice on both types of analysis on resolving the error is highly appreciated.


       

    • peteroznewman
      Subscriber

      Don't use Explicit Dynamics. You will end up with a lot of ringing (vibration) in the solution.


      Use Static Structural analysis.


      Your model looks like it is 1/6 part of a full circle. If so, it is missing two symmetry conditions on the sides of the pie slice of the circle. That could explain why your attempt at a Static Structural solution had convergence errors.



      Even if it is not a 1/6 symmetry, the moving part does not have enough constraints on it to prevent rigid body motion.  At the same time, the moving part seems to have an unrealistic boundary condition. How is it possible that the entire face will be held perfectly flat?  I expect that when the snap starts flexing back, it will put some deformation into the flat base. Perhaps it is more realistic to apply the displacement to the cylindrical outside face of the moving part.

    • VJ0085
      Subscriber

      Hey Peter, Yes it's symmetry hence you see only sliced model. Regarding BC, I will change the displacement to -6,0,0 and apply it on the outer curved face and let's see if that solves this problem. I'll update you, Thanks.


       

    • VJ0085
      Subscriber

      Hi Peter, it's solved !! I believe in a hurry, I overlooked the boundary condition (not good for FEA guy I know) and (-6, free, free) displacement might have caused the convergence error. I changed it to (-6,0,0), created cyclic symmetry for 1/3 rd design model and applied displacement on outside face and result looks like below (it's cross-section view): 



      I am just curious about why applying displacement on the back face is not appropriate if in reality thats what the condition is...Thanks again for providing your expertise from time to time !!

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