Structural Integrity of Carbon Monocoque chassis like the Enzo Porsche GT? Dangerous?

After seeing pics of the disintegrated Enzo in Milan I couldn't help but wonder about the disadvantages of a carbon fiber monocoque. Example: carbon fiber driveshafts are said to be a good thing because they are extremely strong and because when they fail the became hazardless flimsy material. Now, I'm thinking that's NOT a good thing for a passenger compartment. Super strong and light but when it fails it really fails big time? E.g., metal will bend, carbon fiber will shatter. What are people's thoughts and/or experience in this regard?
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It absorbs enormous energy.

Many F1 drivers are walking on their own legs and a number more are still alive because of it.


The Enzo's problem is big time race car performance in the hands of drivers that have a hard time getting a drivers license.

 

What did the front of the Enzo look like after that crash?

 

"Many F1 drivers are walking on their own legs and a number more are still alive because of it."

Yes, but when it fails, then what?

 

Many F1 drivers are walking on their own legs and a number more are still alive because of it."

Yes, but when it fails, then what?
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In a race application, where you're able to x-ray and ultrasound inspect the chassis, and have the budget to throw it away if it becomes damaged, carbon and kevlar composites are great.

On the street, in my opinion, not so much for structural forms. The problem with carbon is that it's too rigid in some cases, so instead of flexing with impact, it develops stress fractures in the resin. Usually, this happens inside the various layers of material, so it's next to impossible to detect without an x-ray or ultrasound. Hence, parts can become stressed, and eventually fail, and you'll never have any warning before it happens. And in most cases it's impossible to fix.

For a street car, when it comes to structural material, I'll stick with good 'ol steel and aluminum.

Those who don't think composites can fracture internally and eventually fail should take a look at the various happenings with Airbus' A300 series aircraft. Those would be the ones that randomly like to lose parts of their rudder and control surfaces. They've since had to internally inspect all of the composite parts on their aircraft at regular intervals in order to detect fractures in the material.

In the case of the Enzo crash(es), it's more an issue of silly people stuffing them into things at high rates of speed than a failure of any material. Metals will come apart as well if you subject them to enough force, however, the properties of those failures are entirely different as most are not brittle and won't completely sheer off or snap when subjected to massive loads.

 

Thanks SIMBA! Excellent points. If I recall correctly, the National Geographic Channel had a story on the Airbus that crashed in NYC shortly after 9/11. Apparently rudder broke clean off the plane! Must have been a horrible experience for the passengers as the plane spun around its axis.

Those are my thoughts on the carbon tub for the street. Also, what happens with resins or glues with age? I've read some NASA stuff (found through google) where they indicate the long term integrity of such materials is not known. E.g., what happens when you (God forbid) crash an Enzo in fifty years, say at a vintage race event. Or will she crack hitting a good old pothole?

More thoughts on this subject would be of great interest! Any structural or composite engineers out there?

 

this got me thinking, carbon composites will absorb tremendous amounts of energy, but energy from where? i'll explain, the mass of itself the carbon is much much less than say the same steel/aluminum part, so with less mass comes less energy to dissipate. I've seen them crash test the nose cones on F1 cars and the cone sits on a sled and is driven into the barrier.

now on the street the carbon monocoque isn't up against other carbon bodies but steel ones, can it dissipate the energy from them as well? has that type of testing been done? if you've seen an older American car from the 50's thru the 70's plow into a newer model car, it's amazing how much damage is done to the new car vs the older one. more mass more energy.

good question...

 

And seat belts kill because they trap people in the car.


There is also evidence that that tub failed because of a modification.

 

F50 tubs have a life of 10 years. I suspect Enzo is the same.

 

That's not a fair comparison, newer cars are design to absorb as much as energy as possible while transferring the least amount of energy to the occupants of the vehicle. This means that an accident that happens in a car from 1950 vs one from 2007 could mean the difference between skipping your evening workout because you're a little sore and getting a free ride in a coroner van.

As for the rest, you're kinda-sorta on the right path, CF isn't going to "give" like steel/AL, but there is still more to it than that. In a car you want the tub/occupant area to be as strong as possible, in an ideal world that "cocoon" should never break/bend, the rest of the car breaks/bends in order to dissipate the energy, that's true regardless of the material used to make it.

CF that is properly “made” is orders of magnitude stronger than steel (which is quite a bit stronger than Al) for any given weight (hence why you can make something out of CF that is lighter but still much stronger). The amount of force needed to break it is usually enough to break steel/Al if that force happens in the right way (steel and Al can crack and sheer), and even if it doesn’t outright break it will be bent to the point it is not repairable. If the above Enzo were made out of steel, you’d likely see the same result (car broke in half), if not the car would be U shaped.

 

I wasn't comparing the safety of the new vs old, but the energy released when the two collide. composites have less mass and hence less energy to disperse, it seems that they can also take the mass and energy from other components, but how much?

 

SMG2 raises a very interesting point. E.g., a smart car on smart car accident versus a smart car on SUV accident. The smart car is very stout for its mass. However, it can only absorb so much energy given that specific mass. At least, that's what would make sense to me.

Personally, I'd rather have my car bend then have my passenger cell shear in half with CF! Gulp!

I didn't know the tub for an F50 was good for only 10 years. Is this true? What's the cost, not just to purchase, but to replace, the TUB? Ironic, Porsche started offering something like 12 year chassis/body (i.e., anti-corrosion warranties) 10-20 years ago. The F50 chassis needs to be replaced after a similar amount of time? And now the big question: WHY?

While on this subject: What would be the ideal construction of a high performance passenger cell?

 

Last I heard tub was $94,000. Parts only.

 

Long term life for composite materials is definitely a question. Beechcraft built the Starship, an absolutely awesome composite aircraft. They have bought most of the planes back and sent them to the boneyard.

Eventually replacement parts for these CF cars may not be available. A TIG and an English Wheel won't help you then.

 

Was there ever any "official" determination of what was afoot in the Kroyman's incident?

 

The official cause was determined by the same people that built it, modified it and maintained it.

Kind of like a govenment official investigating himself.

It broke where it was stretched and did so in a very minor accident.

 

That NY plane crash was the result of the pilots mis driving the plane...the tail DID fail but they rewrote flight manual and/or retrained the operators, IIRC....

You can break anything if you try hard enough!

I obviously weigh in with the steel tube frame guys...LOL!

And fly VERY rarely!

Out to Portland OR in '04 ....#22641
Up to Chicago IL last week....#20405

 

Forgive my naivety, I gave up on this story years ago from informational deprivation: Ferrari stretched it?

...I thought that one was ex-Corsa Clienti.

 

yes, they did....any normal dimensioned person would not fit the cockpit, so they put in a glued 'extension ring'...that's where it broke...

Yes, this was all done under the CC program.......

They didn't know he was gonna test it to Silverstone standards....

 

From personal experience I have no doubt CF tubs are incredibly safe. I am actually most worried when I'm in a metal chassis even with roll cage.

If given the choice, I'll take alive with crunched CF tub over dead with repairable metal chassis anyday.

 

How tall is this guy? (I'd need mine "Mansellized".)

 

It's not a generic answer, it depends on the construction, the materials used, the amount of material used, the construction of other components, etc. As has been pointed out, look at the death rate of race car drivers today vs 40-50yrs ago (you don't have to look at just F1 either), look at the various GT classes around the world, it's pretty rare for a driver to be killed these days, back in those early days drivers were killed at every other race on the calendar (averaged out).

That's correct, at least in a "general" sense, tonnage rules. That doesn't account for other safety items in place of course, nor the design of the vehicle, a smart car was designed to be very safe, an SUV may be old school body on frame and not built to be the safest thing around, that's why you see safety ratings on some SUV's be very good, and others are rolling death traps (heads slapping into B-pillars, poor side impact, front crush zone that extends into the passenger compartment).

Sure, but you're comparing an apple to an orange now as the car in question was modified. A quick google search will yield you plenty of pictures of steel cars broken in half for various reasons.

 

Most F1 jockeys are fairly small.....about "Danika Patrick' size.......

Mansell these days would need to split the car lengthwise!

 

If you want to see how a CF tub will protect a driver watch the Road America crash of Katherine Legge. She lost her wing as she was entering a turn. Car was disintegrated, she walked away.