collision engineering 3

[tecnos]

hello

anyone involved in automotive collision engineering?

I would like to know:

1) do we have the materials/design/technology etc to create a totally unbreakable capsule or car body ? under velocities that todays car can achieve, like 100mph etc

2) do we have the materials/design/technology etc to create a capsule/car body that when the human inside will not have serious injuries in a collision under velocities that todays car can achieve, like 100mph etc

where are we now exactly?

thanks!

 

[tecnos]

by unbreakable, I mean that will not bend either or in general change its shape

 

[hydroman247]

The capsule is not the issue. Slowing the human being inside from 100mph to 0mph without their brain getting squished is the bit that kills you.

 

[tecnos]

what if the head is secured in a point of the capsule?
or if during deceleration, it touches a soft material, that will absorb its momentum?
will the damage be the same?

 

[tecnos]

can we put an egg inside a capsule that is properly designed (with hydraulic mechanisms or anything) and with the right materials in its walls, and then play football with that capsule and the egg won't break?

 

[Dougt115]

Un-bendable no. All that kinetic energy has to go somewhere. Either the structure deforms and absorbs the energy or the structure will have to bounce, which means you are now going 100mph in reverse and you had to survive the acceleration twice

Survivable most of the time. As hydroman says depends on the collision. 100 to 0mph in a distance equal to the front of the car to the driver gives a deceleration of about 33g's. Humans have survived 100MPH crashes with only 2 feet to stop resulting in 178g's but that was a race car.

Hitting a pole, a fence, a cement wall, another car all have different impact profiles so...

The best advice is to prevent the collision in the first place and that device is between your ears.

 

[dhengr]

Tecnos:
Yes we can make a capsule so that the egg shell doesn’t break, but the egg will still end up scrambled. That’s the same as Hydroman247's statement.

 

[msquared48]

Securing the head to the frame does nothing to secure the brain. Deceleration will still cause the brain to move forward in the cranial cavity, imparting a concussion if not a blackout from the high G forces.

Mike McCann, PE, SE (WA)

 

[1gibson]

Collisions, like with another vehicle? Sure, make it 3x as heavy as anything it will hit. Semi truck covered with a few inches of steel plate should do it. Hard to really call that technology, even calling it design is a stretch.

 

[zdas04]

technos,
You can do a simple experiment to show yourself exactly how impractical the whole zero bending thing really is. Buy a helium balloon and tie it to the passenger seat belt in your car with the balloon extending over the head rest. Accelerate and see where the balloon goes. That is your brain and internal organs. If you fix a body to an unbendable frame ad accelerate it from 100 mph to zero to negative 100 mph in a couple of milliseconds you'll find that all the firm bits of your body floating in squishy fluids will be broken. Things like brains, heart, lungs, liver, kidney, etc would look pretty much like hamburger in the autopsy. The unbendable frame would still be perfect, but the result is not survivable.

If your goal is to build a frame that would protect an egg shell during a football game, then it isn't all that difficult (as long as you don't care about what the inside of the egg looks like in the end). This stuff is the reason that cars have "crumple zones" to spread the change in velocity over seconds instead of milliseconds.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[tecnos]

1)
if you fall with 100mph in this:

http://www.youtube.com/watch?v=lb4cItFJ9vg

it is apparently not the same as if you fall with 100mph in a cement wall
I was thinking of a material like that
I understand that there will be still damage, but I wonder if it is the g's that are responsible for the damage or the crashing into a solid surface

2)
so the best model to minimize damage would be a spring that will gradually absorb all the collision energy and then it will release it gradually or somehow store it?

 

[msquared48]

2 is correct. That's why the vehicles are designed to absorb rather than transmit energy.

Mike McCann, PE, SE (WA)

 

[drawoh]

tecnos,

There was a lovely response on the Straight Dope to the question 'If aircraft "black boxes" are indestructible, why can't the whole plane be made from the same material?'

The quick and dirty answer to your question is that we can do just about anything, if you are willing to pay for it. The cost is not just money. Your time and convenience are involved. Modern racing cars almost completely restrain the driver's head, for the reasons noted above. The front and backs of most modern cars are designed to come apart, dissipating energy that otherwise would be available to harm the people in the car. Would you as a pedestrian wish to be hit by one of these indestructible cars?

--
JHG

 

[MintJulep]

The term used is "Crash Energy Management".

When there is a Crash there is Energy to deal with and you need a design that Manages where that energy goes.

In wheeled vehicles typically the energy management is by deformation of carefully designed structural elements that will collapse in a predictable and controlled way.

 

[KENAT]

If you want to get an idea of what can be achieved look at the ratings for mine resistance for naval ships and the equipment there on.

They are designed to survive a shock loading that will most likely kill/incapacitate many if not most of the crew.

Idea being that at least you can then sweep off the afore mentioned 'hamburger' that results and replace with a new crew.

(At least that's what we used to say when I worked in that field.)

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(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[BrianPetersen]

There is another aspect of this which hasn't really been touched on yet.

I think it is already clear that you have to create a controlled deceleration at a rate that the human body can survive. In modern cars, this is done by engineering deformation into certain parts of the bodyshell. Those parts are designed to collapse and absorb energy in the process. The amount of force that it takes to deform those elements is pretty much defined by the yield stresses of the various materials involved - so it is more or less "fixed".

Now, let's say that you have 2 feet of available crushing space in the bodyshell and another 1 foot for the seat belts and air bags to allow the person's body to move inside the vehicle before they start striking undesirable things like the steering column, etc.

If you crash it at 30 mph into a solid obstacle, and you perfectly select the various deformations so that you get uniform deceleration (which is nigh-on impossible in the real world, but "suppose we could"), the deceleration will be about 10 g's. Almost all people survive.

If you crash it at 60 mph into a solid obstacle, and you perfectly select the various deformations so that you get uniform deceleration, the deceleration will be about 40 g's. It is potentially survivable but not everyone will.

If you crash it at 90 mph into a solid obstacle, and you perfectly select the various deformations so that you get uniform deceleration, the deceleration will be about 90 g's. Almost no-one survives.

But ... you are not able to know in advance which of the above collision scenarios will occur. If you design the vehicle with very strong crush zones and seat belt restraints for the 90 mph collision then the same forces will be applied at 60 mph (it will simply deflect less). But now, with this design change, no-one survives the 60 mph collision because the forces are too high, and there are more casualties in even the 30 mph scenario because the forces are too high. How many real world 30 mph impacts are there compared to 60? Compared to 90? Do we want to sacrifice a rather large number of victims of 30 - 60 mph victims in order to maybe, possibly, theoretically protect a scarce number of 90 mph victims? It's not worth it. It's a better statistical scenario to protect the large number of people in the lower-speed impacts and let those in truly high-speed impacts be pretty much on their own ...

So the result is that you design for a lower impact speed (in reality it is in the 50 - 60 km/h or 30 - 35 mph range) because impacts of this magnitude are far more common in the real world. The person who has an impact at 90 mph will blow through all of the crash structures and doesn't survive ... but it wouldn't have been practical to design something survivable at that speed anyhow.

The other thing is that this assumes a full frontal impact. Now take the same vehicle and offset the impact so that it only happens over half of the width (an "offset" impact). Now all the crash structures that you designed for the 60 mph impact are only deformed on one side of the car. What happens now? (The real world is that there are few truly square-on frontal impacts - most of them are offset)

This video illustrates how impractical it is to protect vehicles at the top speeds that they are capable of ...

https://www.youtube.com/watch?v=6dI5ewOmHPQ

 

[tecnos]

mmm so what can we think of?
maybe energy-absorbing hydraulic cylinders (like train buffer stops) or springs inside the car that will absorb the energy?
or ejection seats for cars?

 

[zeusfaber]

I think probably not ejection seats. In an aeroplane, they can be quite useful post-collision (bearing in mind that there, once the mid-air impact is over, your problems have only just begun) provided the initial collision was survivable.

On a ground vehicle, you'd need to preempt the collision if you wanted to do much more than just add a load of accelerations in additional directions to the already lethal mix - and probably preempt it by quite a long time considering the time it usually takes to discard inconvenient bits of structure before you can fire the main gun. This is time that might be better spent avoiding the collision in the first place.

Then you have a mid-air with the poor guy who's coming the other way - both of you inconveniently senza crumple zones. Take a few milliseconds to shake your fist and yell abuse at him as he approaches - you won't get a lot longer.

And that's before you worry about all that malarkey with safety pins. Horrible, horrible things.

A.

 

[tecnos]

ok, maybe not ejection seats but a mechanism that will move the seat to the top of the car and let the left of the car crash beneath and absorb the whole energy?

 

[LittleInch]

Not to mention a crash in a tunnel....

tecnos, I'm not sure what you anticipate from a forum like this that motor manufacturers, government research institutes, racing car designers etc haven't come up with after spending billions of dollars on research, testing, crash tests, investigations of accidents (Mercedes were reported as sending an investigation team to any Mercedes crash within an hour of their plant to gather real life data

http://www.daimler.com/dccom/0-5-1501757-1-1476107-1-0-0-1460121-0-0-135-0-0-0-0-0-0-0-0.html

)....

The HANS system you see on racing drivers nowadays is the result of research into deaths and paralysis where the head plus helmet was being shocked and jerked to the extent that drivers necks were being broken when they hit very hard things (concrete walls , crash barriers etc). The result was the fixing of the helmet to the body , not the car, within a certain amount of movement so that relative to the torso the head is prevented from extending so much that the neck can't take it anymore.

http://en.wikipedia.org/wiki/HANS_device

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Also: There's usually a good reason why everyone does it that way