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Measuring impact force on rubber spacers

  1. Dec 15, 2014 #1
    I need to find the impact force that can be absorbed by these spacers as shown in the image. The spacers are radially distributed over the shell, and they are supposed to dampen any external impact loads to reduce the effective stress inside the inner shell. Since the FEA model is not showing results, I thought of attempting it by hand to get an approximate value. A curve relating the impact load and stress at the inner shell would be enough.

    However, I cannot figure out how to account for the distribution of these spacers, since depending on the load some of these will be in tension, compression and/or shear. The shell is polycarbonate and the spacers are silicon rubber.
     

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  3. Dec 15, 2014 #2

    Simon Bridge

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    Why would you need to know the impact force that can be absorbed?
    Surely you just need to know that the spacers can take a prescribed maximum impact?
    In which case you need only measure for impact with only one.

    Note: it is not the sort of thing you calculate: drop it on something hard (or drop something hard on it) with an accelerometer inside.
    That sounds drastic I know - to et an idea of what to expect, you set up a test rig to work out how each spacer behaves.

    The overall impact profile will be very complicated - the thingy may initially strike 1, or 2, or 3 at once - probably just one at a glancing blow - then would bounce and roll, maybe also deforming, to bring other spacers in contact. There is no what to predict the exact results.

    You could model specific impact profiles by treating the device as two spheres separated by damped springs.
     
  4. Dec 15, 2014 #3

    Danger

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    This doesn't help with the question, but I'm curious: How does it work with the 2 intermediate shells? Do the spacers just go through holes in them, or are they also attached?
     
  5. Dec 16, 2014 #4
    Thanks Simon. I guess I'll keep trying and see if the simulation works. Can't set up an experiment where I work. I could just do this with a single spacer, but a spherical surface helps distribute the forces all over, so my calculation would just be an approximation for a flat surface.

    Danger, The spacers have cones with flats on both ends, which mate with flats on the shells.
     
  6. Dec 16, 2014 #5

    Danger

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    Okay, I think that I can sort of see that now. Thanks.
     
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