"Scott Keelan" (ScottKeelan)
01/10/2014 at 04:07 • Filed to: None
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"Scott Keelan" (ScottKeelan)
01/10/2014 at 04:07 • Filed to: None | 1
| 14 |
As passenger cars made with carbon fiber become more common, how will this effect the way damaged cars are repaired?
The use of carbon fiber to construct the chassis of the new Alfa Romeo 4C and BMW i3 is pretty exciting but what happens when one gets in a fender bender or more serious accident? A traditional steel/aluminum chassis can be bent or pulled back into place but how do you repair a carbon fiber chassis? Can new pieces of carbon fiber get glued in as replacements like a new piece of steel can be welded in? Will the entire chassis need to be replaced because of a cracked piece of carbon fiber? What thinks you Oppo?
Will repair facilities be equipped with hot glue guns instead of blow torches?
MtrRider Just Wants Doritos
> Scott Keelan
01/10/2014 at 04:18 |
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It's going to be very expensive to repair cf. Most likely bonded parts will be replaced. A damaged frame will probably be written off unless the car is extremely valuable, like a Pagani or Koenigsegg.
toadterror
> Scott Keelan
01/10/2014 at 04:18 |
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Carbon-fibre repair you say? I'm going to go out on a limb here and say it *maybe* expensive. HUGE maybe though, guys.
Seriously though, I remember reading about some carbon supercar that needed repairs (my mind says Lambo?) and they basically had to microscopically scan the stuff for superfine cracks etc.
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Scott Keelan
> MtrRider Just Wants Doritos
01/10/2014 at 04:25 |
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That's what concerns me. I imagine that eventually most passenger cars will use carbon fiber tubs but I would be outraged if a small accident that cracked the chassis totaled the car.
Have we gotten to the point where it is more expensive to repair the car than it is to just replace it with a new one?
Tentacle, Dutchman, drives French
> Scott Keelan
01/10/2014 at 04:32 |
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Materials scientist here.
Can CF be repaired? That depends on how you define "repaired". If you take it to mean "back to its original strenghth and rigidity" then you can pretty much forget it.
You may get it back to original spec, I mean it's technically possible to overlay enough material, but there is no easy way to be sure that the bonding holds properly. A weld is a lot more trustworthy than a glue bond, in comparison. I know I wouldn't trust a CF repair easily.
Then again, if it can be determined that a crack exist in a part of the structure that is not load bearing, you can easily epoxy a bit of CF cloth (or carbon-kevlar cloth) over it. However, if the car is in an accident, any damage to the CF chassis will be load-bearing.
If, say, a broken off branch hits a CF roof panel, causing a small crack, it would probably be repairable.
In practice, the panels will not be CF, but plastic or metal, and they will be easy to replace or repair. Subframes will be CF or metal, so they either have to be replaced, or they can be repaired.
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MtrRider Just Wants Doritos
> Scott Keelan
01/10/2014 at 04:36 |
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That's a valid concern, but cf is very strong (hard to break) and the cf tubs will be surrounded by crush areas to protect it in small accidents. Even if you smash a modern steel or aluminum chassis the car is most likely totaled. CF will provide an overall safety benefit.
Before the NHTSA and crash standards were a thing, people thought cars that drove away from big wrecks were stronger thus safer than cars that folded up even though the occupants almost always died. Nowadays people generally accept it is better to have the vehicle sacrifice itself to save the people inside.
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Scott Keelan
> Tentacle, Dutchman, drives French
01/10/2014 at 04:39 |
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Thank you for the input. I imagine that as the technology used to create carbon fiber subrames improves the methods used to repair it will advance as well.
PS9
> Scott Keelan
01/10/2014 at 04:48 |
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CF doesn't really deform in a bad collision. It shatters. This is why I don't think most cars of the future will be full CF. I think we'll still have some kind of aluminum or steel cage underneath.
Arch Duke Maxyenko, Shit Talk Extraordinaire
> Scott Keelan
01/10/2014 at 08:45 |
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Sinanigans
> Scott Keelan
01/10/2014 at 09:03 |
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I think the best approach is to have the chassis in 3 separate piece that are bolted together (a front, a middle, and a rear piece). If the car is hit from the front, then the front chassis piece could be replaced and bolted on. Same if it were rear ended, side impact, etc. The point is to isolate the piece that's damaged and replace it easily.
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Scott Keelan
> Arch Duke Maxyenko, Shit Talk Extraordinaire
01/10/2014 at 09:45 |
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That was pretty interesting. I would not have thought of that partnership but it certainly makes sense.
You can tell a Finn but you can't tell him much
> Scott Keelan
01/10/2014 at 14:38 |
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It depends on how they are constructed. A carbon fiber structure can be incredibly strong and rigid. If the whole car is designed as a single structure I would lean towards it being a one crash and done proposition much like a motorcycle helmet.
If the passenger cell structure is separate from the crash structures it may be possible to replace the damaged structure depending on how the different structures are bonded to the passenger cell. In the /DRIVEN video of the Pagani shop, Spinelli shows the passenger cell that Pagani used to do the U.S. crash testing. The cell itself was undamaged so they replaced the front and rear assemblies and it was crashed a total of 7 times. with no structural damage to the passenger cell.
Whether or not it would be cost effective to do that on a run of the mill daily driver type vehicle is more a question of economics than engineering. Relevant part of the video starts around 23:05 if my link doesn't jump to that. The whole video is well worth watching though.
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Scott Keelan
> You can tell a Finn but you can't tell him much
01/10/2014 at 17:55 |
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That is a pretty neat video. You brought up a good point that I was thinking about earlier. The benefit of carbon fiber is that it is so incredibly strong that with proper crumple zones the chassis of the car should be able to withstand a pretty forceful impact without breaking.
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You can tell a Finn but you can't tell him much
> Scott Keelan
01/10/2014 at 22:39 |
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As an engineering problem it is pretty easily solvable. But the liability to repair say a $40-50k car is another thing. I personally think the manufacturers will say "if it's been crashed it's totaled" for the more common cars. For a Pagani that is one of 1,000 cars ever made and costs $1,000,000+ it is worth the liability risk to repair it.
Ansel
> MtrRider Just Wants Doritos
01/10/2014 at 23:03 |
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Interesting fact: Koenigsegg was able to re-use a single carbon tub in every crash test required of them