Damage Analysis in Multiple Impact Rear-End Collisions

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MSI
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Damage Analysis in Multiple Impact Rear-End Collisions

Post by MSI »

Q: Does anyone know of publication which address the reduction in delta v in a multiple vehicle rear-end collision scenario. I have reviewed SAE 2010-01-0055 but was hoping that there might be others out there as well.

A: You ask about “reduction in delta v in a multiple vehicle rear-end collision scenario” and “whether or not there would be enough energy coming into the system after all the movement and damage to even get to the fourth vehicle's crush damage”

Multiple vehicle impacts on the structure of a vehicle presents many complexities.
  • First because data/research related to damage analysis on the reloading of vehicle structures is limited…
    However…
    if you look up Prasad and the NHTSA "reformulation" you will see a lot of multiple barrier impact tests on vehicle structures and they did many on rear impacts. You might find some good data points for rear impacts with multiple impacts.
I have not read SAE 2010-01-0055 (I will add to my list). I hope/expect they referenced Prasad’s NHTSA tests as a baseline? In the reports related to the crash tests the damage and accelerations were measured for each vehicle being crashed multiple times and that might provide some indication of the ‘residual crush stiffness’ of a damaged vehicle. Obviously these were not multiple low speed impacts however provide some indication of what type of loading in multiple impacts (each test report should include the acceleration time histories)

I’m not sure I understand what another response to this meant by “Crush energy is mostly related to the restitution between the vehicles”
  • the main amount of crush energy is due to the structural loading. I expect he meant in low speed impacts once you damage the vehicle the restitution on subsequent impacts will be lower since the bumper/structure is damaged.
In CRASH type damage analysis the energy and increase in deltaV due to restitution is ignored.
  • Damage analysis equates the barrier impact speed to the residual crush which is a ‘virtual crush stiffness’ relationship. Restitution is the energy feedback which is a source of problem with simple damage analysis since as we have said many times
    Restitution acts to reduce the residual damage while increasing the impact speed change

Here’s information on restitution What is Restitution?

I expect no information on relative impact and rest positions? From that you might be able to run some form of simulation to do a trajectory analysis?
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MSI
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Re: Damage Analysis in Multiple Impact Rear-End Collisions

Post by MSI »

Another posting clarified the actual problem, and here's my response:
  • I agree that the problem would make an interesting simultaneous equation/spreadsheet analysis investigation.
    • My first (incorrect) impression of the question was that it was about a vehicle struck 4 times in the rear!
      • and rethinking about that I'm like 'how would that happen??
    Its about evaluating 4 cars in a line since some are front and some are rear collisions!
    • And the question was on analyzing the 4th vehicle in line rear impact!
    In cases we have evaluated these types of multi vehicle impacts we included the ability to vary (or have known) the relative positions/distances at rest and then vary the relative assumptions for distances/positions at initial impact
    • how far apart and whether any had secondary contact after the first, etc.
    If no vehicle sustained enough damage to impair wheel rotation there should be relatively little drag in between vehicles
    • or include some allowance for damage induced or driver produced drag occurring between collisions

    Has some interesting variables to consider to investigate and analyze.
    And as suggested in another response assume plastic collisions then you have a great starting point.
    Restitution would simply slow the striker and increase the struck vehicle at separation in each impact.
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Re: Damage Analysis in Multiple Impact Rear-End Collisions

Post by MSI »

And for an amusing sidelight...
  • I had posted
    • My first (incorrect) impression of the question was that it was about a vehicle struck 4 times in the rear!
      ....and rethinking about that I'm like 'how would that happen??
    and INCR member posted:
    • How could the same car get hit several times? You may want to check out this film excerpt:
LOVE IT!! hahahahaha!
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