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Homework Help: Impact Device

  1. Feb 11, 2008 #1
    1. The problem statement, all variables and given/known data

    I am creating a device to provide 250 to 300 g's of impact force to an electrical device in a plastic housing. I would like to lift a steel plate approximately 16" x 16" X thickness "T",, to a height of "Y" and release it. It would fall at the rate of gravity, impacting a steel base plate and come to rest. The goal is to determine the weight of the plate based on it's thickness and set the height required to create the desired impact force of 250-300 g's. The test must be able to be repeated with consistent results. I have designed the tool, but lack the information requested above.

    2. Relevant equations

    F=Ma ?

    3. The attempt at a solution
    I am not a physics student,, I am a product designer trying to test the impact forces placed on a device. Thank you.
  2. jcsd
  3. Feb 11, 2008 #2


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    You can't work it out from that.
    You can calculate how much energy/momentum a falling block will apply quite easily but to know what force it will apply to the object you need to know how quickly the block will stop - which depends on how the test object will deform.

    It's a bit like dropping something on the floor, the same mass dropped on a concrete floor will experience much greater shock than one dropped on wood - becuase the wood deflects to slow the object down over a longer time and so has less accelearation.
  4. Feb 11, 2008 #3

    Thank you for the reply.

    The base plate of the testing device will be 16" x 16" x 2" thick steel plate. The device will rest on a concrete floor to run the test. 4, 1/2" diameter steel rods will be mounted into the base plate and slide through the mounting plate to guide the mounting plate up and down.

    Is there anything else I can provide to assist you?
  5. Feb 11, 2008 #4


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    There is no practical way to calculate this - without doing CFD modelling of the part and for such a high force over a short time this wouldn't be remotely accurate.
    The problem is that G force will peak over a very short time - it doesn't take a very big change in the design to give you 100g for 2.5us rather than 300g for 1us.

    The best I can suggest is to get some accelerometers, attach them to the plate and experiment with the peak shock - this has got a lot easier since fast digital storage scopes were invented!
  6. Feb 11, 2008 #5
    thanks for your help,,, I'll work on it from that angle
  7. Feb 11, 2008 #6
    Call Bruel & Kjaer. Ask for a sales engineer to drop by. They'll sell you what you need.
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