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Forces on an object being run over?

  1. May 8, 2004 #1
    I'm currently trying to complete a Finite Element Analysis of a design i have made at uni.
    Put simply I have designed a new 'Stinger' type device for the police to use to stop pursuits with.
    I am trying to calculate the force that will be placed on my design when placed in the road and run over by cars etc.. - Obviously it must be strong enough to withstand these forces.
    The profile of the design is triangular, 35mm high and 75mm wide, with pretty much a 45 degree angle.
    I have tried to work out the force using basic impact equations, but obviously the force will not be hitting the object head on e.g. only the bottom 35mm of the tyre will hit it, the profile of the object will have some effect, etc..
    Is there any way to make this more accurate?

    With my calculations the impact force is about 2000N at a speed of 60mph.
    This does not take into account the weight of the car, should i add 1/4 of this to the impact force (to account for the 4 wheels) to get the final force so i can complete the FEA?

    Any help or pointers would be very appreciated!

    Many thanks,

    Andy
     
  2. jcsd
  3. May 19, 2004 #2
    I really expected someone else to ring in here, but i'll try and get things started.

    I think that the force needs to be calculated as the sum of two vectors of different directions. The impact will actually be less than a head on impact (as you indicate that you know) The wheel will be approaching in one direction and will strike the triangle at another angle dependant on the diameter of the wheel and the height of your gadget.

    Hopefully, this will stir some attention for your post. Good luck with your project.
     
  4. May 30, 2004 #3
    Andy,

    My concern would not be that of the initial impact of the front wheel of the vehicle running over your device but rather that of the real wheel after the front wheel tosses your device into the air and flips it over a few times...

    Just a thought...

    Cheers,
    RG500
     
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