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How can I figure Crush on a vehicle accident?

  1. Sep 21, 2010 #1
    My truck was rear ended. It has a steel and chrome bumper, the vehicle that hit it has a soft bumper, and was travelling at 15 miles per hour.
    My bumper showed deformation by being bent in 1.27 cm and bent up 1.5 cm. The truck which was with the brakes on, also moved forward 6 inches. The soft bumpered bullet vehicle, showed the same amount of crunch ; I am assuming....

    My question is what is the actual Crunch that I can input into the Acceleration, Velocity , Crunch formula???? In centimeters or inches.??
     
  2. jcsd
  3. Sep 22, 2010 #2

    brewnog

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    Acceleration Velocity Crunch formula?
     
  4. Sep 22, 2010 #3

    Danger

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    All that I can suggest is what we have told others in similar situations: you pretty much have to hire a professional accident reconstructionist. These things are far too complex to try solving over the net.
     
  5. Sep 22, 2010 #4

    What I meant is Acceleration = (Velocity Square) / (2 x crush)

    the other posibility is the formula G force= Change in velocity / time
    applied to the actual moment when the crush occurs.

    My problem is if the forward movement of the vehicle with brakes on, has to be added to the crush damage distance.
     
  6. Sep 22, 2010 #5
    Too many variables in a real crash to even attempt to make a formula for it. See danger post.
     
  7. Sep 22, 2010 #6
    After a few hours of reading on this, I realized the following :

    The bullet vehicle travelled for 45 ft before hitting, and it did this in 4 seconds, that changes my closing speed to 7.67mph ....

    I can get the Delta V by using

    Delta V: Vc x [(1+e)/(1=(Wt/Wb))]

    Vc =closing velocity = 7.67mph=11.24 fps
    e= Veh to veh coeff of restitution , bounce, = from .1 to .4, so I'll take the average=.2

    Wt= weight of the truck=2842 #, plus 3 persons, 120, 150 and 200, plus fluids 20#=3332#
    Wb= weight of Altima=2875#, plus 120, plus 20#=3015#

    Delta V=11.24 x (1.20/2.11)

    Delta V= 11.24 x .57

    Delta V= 6.41 fps

    next I got to figure the actual distance the vehicles moved in the crash time.

    somebody check me on the delta V evaluation !!!
     
  8. Sep 23, 2010 #7
    The crush distance=

    Truch damage, 1.27 cm and 1.50 cm, average= 1.38 cm =.5 inch

    Altima damage , let’s assume the same, 1.38 cm,

    The truck travelled 6 inches further.

    Then the change in distance would be .5+.5+6=7 inches=.583 ft

    Wow, so it travelled .583 ft , if I divide it by the average velocity , I should get
    The time ….

    Starting velocity 11.24 fps, ending velocity 11.24- Delta V=11.24-6.41= 4.83 fps
    Average velocity then is 4.83 fps + 11.24= 16.07 fps/2= 8.03 fps

    T= D/V = .583/8.03= .07 seconds


    G= Delta V/ Time= 6.41/.07= 91.57 fps^2/32.2= 2.84 G

    The other way

    A= V^2/ 2xD= (8.03x8.03)/ 2x.583=64.48/1.17=55.11/32.2= 1.71 G

    WHY THE DIFFERENCE , SHOULD NOT THE TWO G’S BE THE SAME?????

    CAN SOMEONE SEE A MISTAKE??
     
  9. Sep 23, 2010 #8

    Danger

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    What tread pattern does the target vehicle have? What rubber compound in the tires? Of what material, and in what state, was the road surface? What angle were the steering wheels of both vehicles at? What gear was the target vehicle in?—even if the brakes were applied, that makes a difference. What was the ambient temperature? That can help to determine the tire temperatures of both vehicles, as well as that of the road surface. How far at at what speed had the vehicles been moving within the prior 10 minutes or so? (Also in furtherance of determining tire temperature.) What were the weight distributions of both vehicles? Are you starting to get the picture?
    And I'm not even getting into the complicated stuff yet...
     
    Last edited: Sep 23, 2010
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