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

Kenny Brack's IRL incident also.......

 

A really good point. Give me good old STEEL, a durable (often repairable) material with predictable qualities.

 

Not for any flaw or foreseeable weakness of the composites, rather simply extremely poor sales exposed them to an untenable and rather mundane typical light aviation product liability and support situation easily remedied by buying up the minuscule fleet. Most of the planes were never even sold in the first place, rather being leased.

It's purely a bean-counter issue, not a materials science problem.

...Didn't someone once say the F-16 (ca 1975) is but 20,000 lbs of CRFP wrapped around a 30,000 lb-thrust engine? Never an airframe failure AFAIK.

 

...1995, too.

 

Interesting thread. I have wondered many times about how well a tub would hold up over time and stress.

 

We know about this stuff. Racers make this compromise all the time with DOM cages vs chromoly cages. We know DOM takes better wacks as it yields but does not fracture. Cro mo fractures and is brittle but has higher hardness and is lighter. No material is perfect but we each have to select our own compromises. We also know about resin/cf/glass seats in racing where FIA limits their useful life with a time limit as they know the resin breaks down. Some low level club race bodies allow them past the expiration dates by mandating added back braces. So even at my low level clubracer level we know about these kinds of materials problems . You don't need to be an engineer to know this stuff it is common knowledge.

 

Like they say when you fall from an aircraft "it's not the fall that kills you, it's the rapid deceleration as you hit the ground"

As said earlier the principle strategy in designing modern cars to be as crash-worthy as possible is to create as strong a passenger cell as possible (for intrusion prevention) with progressively deformable crumple zones at either end - you could call the latter "sacrificial deceleration zones". The idea is that the soft and very fragile human flesh (humans were only designed to crash at running speed) is cocooned in the strong tub and (relatively) gently brought to rest by the shedding of kinetic energy through the destruction of the deformable zone (front or rear as appropriate).

From this you can see that a short car is harder to make as crash-safe as a longer car and that a lighter car will have less kinetic energy that a heavier vehicle at any given speed.

Side impact, although a less common scenario, is to me the most dangerous collision to have and where the harder challenges arise. You start with 1 or 2 large openings in the tub on each side with no real ability to create a crumple zone so you are forced to strengthen the doors to reduce the effect of side impact - skinny doors give you no room to play with here.

It is incorrect to compare composites (a very broad range of materials BTW) with mild steel in terms of mass and equate that to crash-worthiness. Properly made composites have a far better ability to dissipate energy than mild steel. Simple GRP turns to dust in a collision but it absorbs far more energy in doing so than a thin piece of sheet metal does when it crumples.

These principles have always been at the forefront of my mind throughout the Monzer design process.

Give me a composite tub any day.

 

Now that's the question, plus with a $100k price tag (plus what I'm sure is a heart stopping labor number to go with it), I'm betting we're going to see quite a few cheap "supercars" for sale in the coming years (well cheap being relative).

But again, you are comparing a car that was modified vs non. Trust me, I cut your "steel" car in half and weld it back together, you will have sacrificed a lot of crash worthiness because of it, especially if the job isn't done to the highest quality (similiar to how the CF car mentioned was put together).

The failure mode for a car like the Enzo/F50/etc should NOT have the tub break in half under the drivers seat. Every other part of the car may get destroyed, but the tub is supposed to stay together.

The amount of force required to "shatter" a CF A-arm would absolutely destroy a steel arm, we're talking complete pretzel (if not outright broken).

Nobody raises an eyebrow over an Al a-arm, even in a road car. Why? Al is not a great material when it comes to strength/weight, it has a limited lifespan (Al simply wears out given enough cycles), etc.

Now of course I doubt we'll see CF suspension parts on vehicles for some time. It's a huge cost for a very small weight savings (and no bling factor), and there are some negatives to CF over steel as well, it's not the end-all be-all material out there.

 

I'm not a big fan of aluminum in critical areas because it does tend to fatigue crack more easily than steel. If you use it you should inspect more frequently and diligently.

 

For starters, composites don't simply completely shatter into a gazillion pieces...it ain't like your glassware you drink from Also, outside the cabin are metal structures that are designed to crumple.

Sheesh! Such extremists!!

 

It is interesting that we are now talking about aluminum, also. When Ferrari came out with their first aluminum chasis, I asked myself how long will these last? I was under the impression, from my knowledge of bicycles, that after a number of cycles aluminum WILL fail. That would not make me feel very good about buying an F430 to keep for 20 years. Thoughts?

George

 

They died because they were travelling at race car speeds on a race track in a car that was designed and built for the street and lacked the safety equipment and structural design for the inevitable high speed crash which race cars are often involved.

Hitting a soild wall far in excess of 100 MPH will screw up your day in any street car.

 

Some of these posts are spot-on, and some of them are completely off-base.

From a fatigue standpoint, aluminum as a general group is probably the worst of the chassis materials. Carbon fiber composites are generally the best, many show essentially no fatigue degradation. Crack propogation in a fatigue situation, for instance, is a metal issue. Are the chassis really stressed enough to fatigue at an appreciable rate? Maybe, I guess that's what they call a "worn out" race car.

Composites absorb/dissipate crash energy because of their composition - many stiff fibers held together in a tougher resin matrix. When the stiff fibers are stressed past their breaking point and fracture - Pop! - the matrix transfers the resulting load to an adjacent fiber which is then stressd until it breaks, and on and on. The energy released (transferred) with each individual failure is what we call energy absorbtion or dissipation and crash-worthiness. The failure mechanics are completely different from isotropic materials like metal.

The F1 car paic is one of my all time favorites - that was at Laguna Seca, right? It has nothing to do with this discusstion, though.

The Enzo in the first pic hit a pole sideways at high speed if I recall correctly. Metal, carbon, bubblegum, whatever your chassis is made of, you're probably going to die.

It's the force transferred to the occupant that kills in most cases, if you were driving down the street in a bank vault and hit a concrete wall, neither would deform much, but the you and the other occupants of the vault would be putty.

Unless I'm mistaken, ATR in Italy built both the Carrera GT and Enzo chassis.

 

Aluminum chassis are not designed for cars intended to be around 40 years. For what it is worth Ferrari never designed any of their cars to be around for more than a few years. The cars have always been built with current technology to be the best street cars of their day for the people that can afford such. It is intended that when a better car supercedes it, it will be replaced. Even a 250 GTO was only meant to be around a couple of years.

 

I'll also note that we've seen more aluminum 360's split in half through the passenger compartment than we've seen Enzos.

 

You need to check the pics again...the passenger compartment as Rifledriver says WAS compromised......

They died because it was their unlucky day.....nothing to do with CF.....

Fate.....kismet......karma.......a six by six hole awaits us all......

I know that's a little hard for your profession to cope with, that bad stuff just HAPPENS.....but the bumper sticker actually is correct..

Certain responsibilties and acceptance comes from dropping into the seat and turning the key 'on'!!

It's a matter of right ankle control......

 

Unless....you're driving a Porsche 928. The driver of this car hit a tree sideways at very high speed & lived (though he did break his pelvis). Note: this is a British car - the hit is on the driver side. I'll take Thyssen steel over carbon fiber any day.

More pics & info here:
http://forums.rennlist.com/rennforums/showthread.php?t=332483
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I was told they went 100-0 in ~3 feet. The car obviously stayed in one piece but your brain, spinal column and internal organs can't take that kind of force in an impact.

 

First I'm hearing of this.

Why, what's the limiting factor?

Was this disclosed at purchase?

Have any F-50 been re-tubbed?

What's the book time on swapping an F-50 over to a new tub every 10years?

...Adds a whole new dimension to 'if you have to ask,...'.

 

Both occupants only recieved minor injuries.

Hope they went out and bought lottery tickets.
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The thread you linked to said he lost it in the snow, and his speed estimate;

He was doing 69/70mph GPS, he went across 3 lanes & went 15ft down an embankment till he found the tree.
He is a very experienced 928 driver, having done many track days & the 'ring.

That is not "very high speed". Just looking at the debris field in the very first Enzo picture I'd say he was going around double what the 928 guy was (we'll just pretend the 928 didn't scrub any speed as it skidded off the road). The difference in force between a 70mph accident and a 140mph accident isn't even remotely close.

 

Back in the day, remember the E-Type, many of those ended up in two pieces in the road after a big one. As they aged, the size of the accident could be less for the same effect! And that was a steel tub with tube subframe.

Oh! Do any of you really dream about buying a 10 year old supercar? Good luck with any parts, let alone a tub! Enjoy them now while they still run.

Brian

(As said, the english wheel brigade won't be able to help, buy the muscle car era stuff, if the Feds don't ban them, they will be all that's left)