quattro digest, Vol 1 #3897 - Crash Testing (mAC) long

[Larry C Leung]

Okay, tried to stay out of this, but this thread is getting old.

GENERALLY speaking, mass is the greatest factor when
it comes to accident survival. It stems from Newton's
2nd Law, i.e. F=ma. Recast as a = F/m and you should
note that the higher the mass for a given force
(the collision, and from Newton's 3rd Law, action/reaction, the
force is the SAME on both colliding vehicles), the lower
the acceleration (okay, DE(a)cceleration) of the colliding
vehicle. This goes back to the Force on the occupants
of the car. The less the acceleration of the car, the less
force it imparts on the passengers. This is the job
of the crush zones, to prolong the TIME of the crash,
thus decrease the acceleration, thus the force on
the occupants. Procon Ten (mAC) and airbags do their part
by increasing the time of head/torso to steering wheel.

Now, since a lighter car experiences greater accelerations in
a crash, the force on the occupants is higher. Engineering
does as much as possible to imrpove the crush zone distance
(thus time) on the smaller cars as much as possible, but in the
long run it will fail. Think of even a large car vs. a tractor and
trailer
combo. In most cases, I'd rather be in the slower (de)accelerating
truck, which will continue to travel in it's original direction for a
period after the crash, hence a long period of deceleration. The car,
OTOH will probably reverse direction (get carried along with the
truck) giving a much larger acceleration, hence have high forces
within the passenger compartment.  Truck wins.

Also, case in point. As most of us know, a deer hit with a car usually
wrecks the car quite severely, i.e. usually disabled. The deer's mass
will significantly slow the car's nose, while the rest of the car piles
into
the stopped front of the car + deer. Car/Deer wrecks are usually found
on the side of the road. Tractor trailer combos often hit deer too (where
I used to live in Central NY, I saw the results EVERY day during deer
season. The deer accelerate in the direction of the truck soooo severely
that they often, well, become multi-piece deer. The trucks usually
motored
on, with at most a broken headlight, some trim or paint damage, and
fur in the grille.

You figure,

the Physics Teacher



> Date: Fri, 30 Aug 2002 08:32:36 EDT
> To: quattro at audifans.com
> Subject:  ncap
>
> I don't agree with your summary dave, few engineers would.  The
> BIGGEST
> difference to crash survival is MASS.  The stiffness of the larger
> vehicles
> isn't for the testing, it's for the weight/design of the vehicle vs
> occupants
> of that vehicle.  The occupants of the "other" vehicle really aren't
> a
> design
> parameter (well the rear crash bar on the 18 wheelers might be an
> exception),
> too many variables to figure that out.  In house testing usually
> assumes two
> identical vehicles.  The "independent" lab tests that do the tests
> for
> public
> consumption is a vehicle and a wall, not another vehicle.  Doing
> tests with
> 2
> different vehicles would create fear in a lot of folks, and we'd all
> be
> driving Excursions.
>
> The offset test isn't really the *main* focus of engineers.
> Statistically,
> replicating that scenario in real world is a tough argument to make.
>  The
> head on is a different story, and many a engineer has had toyota
> trucks in
> the war room (they do really well).  I also remember too, on a
> in-law visit
> to Auburn Hills, a laser diced A4 at D-Chrysler.
>
>
> Scott J
>
>
> D. Eaton writes:
> however, due to the ncap insistence on only 2 tests (offset and
> side), and
> the public's addiction to the "star" scoring system, they virtually
> obligate
> engineers to build cars focused on the magic 5-star metric, at the
> penalty
> of other, arguably more important, safety measures.  for instance,
> the
> heavier the vehicle, the more difficult it is to get good ratings on
> the
> offset test, so engineers are increasingly making their large
> vehicles very
> "stiff" to get the good scores.  this is causing considerable
> concern
> because, in an impact with a lighter vehicle, this will almost
> certainly
> result in greater chance of injury in the other vehicle, where a
> "softer"
> impact structure wouldn't..