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collision engineering
3

collision engineering

collision engineering

(OP)
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!

RE: collision engineering

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

RE: collision engineering

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.

RE: collision engineering

(OP)
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?

RE: collision engineering

(OP)
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?

RE: collision engineering

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.

RE: collision engineering

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.

RE: collision engineering

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)


RE: collision engineering

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.

RE: collision engineering

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

RE: collision engineering

(OP)
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?

RE: collision engineering

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

Mike McCann, PE, SE (WA)


RE: collision engineering

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

RE: collision engineering

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.

RE: collision engineering

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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RE: collision engineering

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

RE: collision engineering

(OP)
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?

RE: collision engineering

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.

RE: collision engineering

(OP)
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?

RE: collision engineering

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... )....

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

My motto: Learn something new every day

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

RE: collision engineering

(OP)
it's frightening that it took many years and deaths for HANS device to be accepted

RE: collision engineering

Not as many deaths, injuries and years as seatbelts in "normal" motor cars.... It has taken legislation in most countries to both require front and back belts to be fitted and to force people to wear them...

My motto: Learn something new every day

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

RE: collision engineering

"Hydraulic cylinders" ... "Springs" ...

Even if this were somehow feasible (did you watch the video that I posted), which way do you point them? Collisions can come from any angle and speed.

How about the air bag systems and pretensioned seat belt systems that cars already come with? Doesn't help the bodyshell, which does the job that it's designed to do by crumpling, but it helps the occupants.

RE: collision engineering

(OP)
we can position them to protect from both frontal and side collisions (placed perpendicularly)

as for improving the air bag systems, I would like to know if there is still a big fatal factor the fact that passengers get smashed in rigid parts of the car, like the cockpit, the front window, etc
if yes, then we can introduce whole body airbags
and maybe fill them with some kind of foam, instead of air, to increase their elasticity

as for improving seatbelt systems, we can introduce a system that will encapsulate the passenger in in the seat, like some arms extending from the seat and seal him to the seat (not sure if you get what I mean)

RE: collision engineering

Quote (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?

I cannot remember my source for this, but I read somewhere that four out of five people thrown clear in car crashes are killed. Generally, particularly in modern cars, you want to stay inside the vehicle during a crash.

Ejection seats are for when you discover a supervillain in the seat next to you.

--
JHG

RE: collision engineering

"we can position them to protect from both frontal and side collisions (placed perpendicularly)"

The Insurance Institute for Highway Safety (IIHS) spectacularly demonstrated the fallacy of such as design requirement more than 20 years ago by having a car impact a typical access restriction post and showing the degree of damage that would cause to the car and occupants. While the auto companies bitterly complained about the test being outside of the federal standards, almost all cars designed since then can survive such a crash without serious injury to the occupants, and at fairly high speeds. The federal standards were designed with the collusion of the car makers, so that minimal damage to the cars would occur, but the IIHS has a different mandate from equally well funded special interests.

"as for improving the air bag systems, I would like to know if there is still a big fatal factor the fact that passengers get smashed in rigid parts of the car, like the cockpit, the front window, etc
if yes, then we can introduce whole body airbags
and maybe fill them with some kind of foam, instead of air, to increase their elasticity

as for improving seatbelt systems, we can introduce a system that will encapsulate the passenger in in the seat, like some arms extending from the seat and seal him to the seat (not sure if you get what I mean)"

There are very specific reasons why airbags are the way they are, which is due to the fact that they have to fully deploy in less than 100 milliseconds. And, they have to essentially provide nothing solid to hit the occupant as they impact the airbag. Given those constraints, there is almost nothing else that will do the job. And, that's why higher end cars have a multitude of airbags specifically to protect the occupant from impacting other obvious parts of the compartment. Other reasons for NOT using mechanical structures is the degree of difficulty in extracting the occupant from the vehicle after the crash and before they burn or bleed to death. Having to cut through a deformed car frame is bad enough, but to then have to cut through additional metal to get inside is just more deaths waiting to happen.

TTFN
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RE: collision engineering

Modern airbag systems are already coming pretty close to "encapsulating" the passengers. Modern interiors are designed to minimize occupant impact with hard structures ... provided that they wear their seat belts. Biggest problem nowadays is people that don't wear them. They are (almost) on their own, with regards to the possibility of being ejected.

Side impact is a big problem. It is impossible to build sufficient "crush zone" into the side structures of a vehicle while keeping the vehicle at a practical width. The modern approach is to make the side structures as rigid as possible and then rely on the crush zone of the impacting vehicle. It does not help the person who goes off the road and then sideways into a tree.

There will always be impact scenarios that we can't realistically help. Commonly heard ... "I hit something in my car and the air bag did not go off!" Well, guess what, that statement is coming from someone who survived! The "smart airbag" controller took into account the magnitude of the impact and the weight of the person and the status of their seat belts and decided that it was not necessary to fire the air bags. And there is good reason for this. Suppose you have a double impact - a minor glancing impact with (say) a small deer, followed by the car going off the road and a blunt impact with a large tree. Airbags can only protect once! If the airbags went off at the slightest provocation, they would fire unnecessarily at the minor impact when they weren't really needed, followed by not being there for the second impact when they were really needed.

Some of your suggestions are completely off the wall. "Foam, instead of air"? Riiiight. How do you propose to inflate that in milliseconds as required?

Honestly, the best direction for vehicle safety going forward is to prevent the collisions in the first place. If you prevent the collisions, you don't need the crash protection. Realistically, the collision protection is going to stay, but further development is heading in the direction of preventing collisions.

RE: collision engineering

"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. "

If the ballon is on a string I believe it will curioiusly lean "into" corners or forward on acceleration due to its bouyancy and the stratified air sloshing in response to gravity.

RE: collision engineering

Filling the doors with foam doesn't increase the amount of crush distance. The existing steel structures in the doors already include anti-intrusion structures. Foam doesn't magically make the need for a controlled deceleration pattern go away. No, you cannot inflate foam in milliseconds as required. I'd like to see what your proposed "elastic polymer compressed and let it loose" would look like and function.

How about you store a small amount of reactive chemicals inside a folded plastic bag and ignite it to inflate the plastic bag to cushion the occupants from impact?

RE: collision engineering

Well, star for that one BrianPeterson.

RE: collision engineering

Or you could use an embedded C4 shaped charge to counter the impact force... Or not.

Mike McCann, PE, SE (WA)


RE: collision engineering

"I don't know if you can inflate a foam airbag in milliseconds, I would need to calculate it, maybe with the correct (higher) amount of pressure, you can"

You can't, that's why current airbags are essentially tailored explosions. No chemical reaction, other than an explosion, and no pressurized gas can achieve the deployment speeds; they've already spent the money to prove that other approaches aren't fast enough.

TTFN
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RE: collision engineering

(OP)
Thank you all for your input.

RE: collision engineering

You may wish to start with the requirements of the Federal Motor Vehicle Safety Standards: http://www.nhtsa.gov/cars/rules/import/fmvss/

You may wish to explore Youtube for videos of crash tests by IIHS on existing vehicles. Here is an example of the new "small overlap" frontal impact for a new vehicle that was designed with this test in mind. Note that although there is plenty of destruction to the front of the vehicle, the driver's door remained pretty much intact (the skin was damaged but the underlying A-pillar kept its general shape - visible in the photo after the door was removed to show it - there is some deformation, which is hard to avoid in this type of test), and the windshield didn't even break. The driver's head was cushioned. In the video, the driver's seat headrest had been removed for visibility, but in reality the rebound of the driver's head would have been contained by the headrest.

Think you can do better?

RE: collision engineering

"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"

Ignoring ALL of the other engineering impossibilities inherent in this, it would take something like 500 g's of acceleration and deceleration, which is NOT survivable. And now you are outside of that nice, strong, metal container that was specifically modified to protect you from injury, with just a seat flying through the air, and very likely to be bouncing down the road, unprotected, at 65 mph because your car is now 50 ft behind you, having been stopped by its collision.

TTFN
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