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Compare 2 mechanical shock scenarios with different magnitude and time

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  1. Apr 14, 2017 #1
    For example, How does one compare 100 g's for 6 milliseconds to 45 g's for 11 milliseconds. These are two different shock scenarios with different magnitudes and times, so how can I compare them? If I have something that is shock rated at 100 g's for 6 ms does this imply that it will withstand 45 g's for 11 ms?

    I have tried finding a "shock equivalence" chart or a metric for comparing two shock scenarios but I haven't found anything.

    I was thinking it may depend on the mass of the equipment that is being shock rated. We have:

    F=ma
    v=at
    Power, P = Fv

    An energy metric like power may give me a reasonable estimate to compare, but I am just guessing here. Is there a standard way to compare two scenarios? A chart or equation would be nice..

    Thank you for the help!
     
  2. jcsd
  3. Apr 14, 2017 #2

    berkeman

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    Staff: Mentor

  4. Apr 14, 2017 #3

    berkeman

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    I suppose that some systems may have trouble with the extra energy in a wider shock pulse, but in my experience with shock and vibe testing of electronic assemblies, it's usually the peak amplitude of the shock that does the damage...
     
  5. Apr 14, 2017 #4

    JBA

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  6. Apr 14, 2017 #5
    Last edited by a moderator: Apr 15, 2017
  7. Apr 14, 2017 #6
  8. Apr 15, 2017 #7

    JBA

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    This raises an issue I have not previously considered of the actual shock profile vs the effective profile vs the rigidity of materials involved in the shock contact, i.e. will high modulus material collisions tend to be more of a saw tooth wave vs low modulus materials resulting in more of a sine wave effect.
     
  9. Apr 15, 2017 #8

    berkeman

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    It is my understanding that the number is the peak of the half-sine shock waveform (at least in mechanical shock testing of assemblies at our local test labs). The waveform is directly off of the accelerometer that is attached to the falling assembly.
     
  10. Jun 28, 2017 #9
    hi,
    if we look at a half sine shock and try to integrate it we would get a value of velocity that can be observed like energy.
    so same shock amplitude (A) lets say, 10g@1ms and 10g@100 at different integration times will have different energy.
    I think the greater the integration time the more area you get that is more energy from the ∫f(A)dt ...
    hope that helps.
     
  11. Jun 28, 2017 #10
    can it be that from both 10g@1ms and 10g@100ms we would get same amplitude of equivalent force?
     
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