Carbon Tub Protection. - Alfa Romeo Bulletin Board & Forums

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post #1 of 20 (permalink) Old 09-26-2016, 06:37 PM Thread Starter
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Carbon Tub Protection.

Hi Guys
I don't have a 4C but having spoken to the dealers, impact damage to the tub is a major issue.
Where as most people are worried about stone chips, in the paint, the bottom of the carbon tub is quite vulnerable on Aussie roads.
Has any one considered this?
If not may I suggest a of the various films on the market one that 3M make is .5mm thick it is used on the Galley floors of Boeing and Airbus I think, and it is very strong and clear.
Just a though.

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post #2 of 20 (permalink) Old 09-27-2016, 07:43 AM
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In at least one of the review videos I watched they had the car on a lift and it looked to me like the entire underside was covered with panels.

Paul - 1972 Spider - (2)1991 164S's - 1983 308 - 2001 Discovery - 1997 F350
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post #3 of 20 (permalink) Old 09-27-2016, 10:30 AM
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That tub is pretty darn tuff. I wouldn't worry about that.

I ran my 4C into a concrete wall. Not because I wanted to, just one of those things that might happen while having to much fun. Anyway, I bent a control arm and wheel. The front sub-frame was damaged. These parts bolt directly to the carbon fiber tub. The tub is undamaged. I had the car repaired, all bolt-on parts. I've put on 20,000 miles since then.

Carbon fiber is stronger than steel, and lighter than steel. Carbon fiber can't be repaired, but, bend a steel frame and they total the car anyway.
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post #4 of 20 (permalink) Old 09-27-2016, 03:05 PM Thread Starter
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That tub is pretty darn tuff. I wouldn't worry about that.

I ran my 4C into a concrete wall. Not because I wanted to, just one of those things that might happen while having to much fun. Anyway, I bent a control arm and wheel. The front sub-frame was damaged. These parts bolt directly to the carbon fiber tub. The tub is undamaged. I had the car repaired, all bolt-on parts. I've put on 20,000 miles since then.

Carbon fiber is stronger than steel, and lighter than steel. Carbon fiber can't be repaired, but, bend a steel frame and they total the car anyway.

Guys don't get me wrong here these are great cars and it is good that there are covers on the bottom of the tub, the car I looked on a hoist didnt. Also the only place that can assess the damage is the factory, via detailed photographs, not the insurance company.
A few home truths about carbon Fibre. Its is the impact damage that is the issue even small damage let me explain
Here is the reason the only testing procedure is a very basic tap test usning a a big coin or a 6mm L shape bar and the change in audible sound is the only indicator. at this point in time that is it.
It doesn't present crack it internally delaminates. it then absorbed moisture then over periods of time in extreme cold climates and freezing the cracking gets worse and eventally brakes up.
The strength is excellent granted, but the damage it and it can be repaired I don't know where that info came from, The Aviation industry do it all the time and there are approved repair schemes for it
Admirably its a its a temperature controlled curing process.
There is no known life of carbon composites yep no one knows. I went to a presentation on this very subject. The is an international study being conducted buy Military groups around the world. Interesting part is they are not releasing any information to the Commercial world however, I recon the info will filter through, as most of the manufactures make both commercial and Military components.

Last thing if you have a bad accident and there is a a fire, the fumes and fibers are treated as Asbestos by the authorities Page 15
https://www.atsb.gov.au/media/442544...sites_2014.pdf

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post #5 of 20 (permalink) Old 09-28-2016, 12:24 PM
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The Boeing 787 fuselage is made completely of carbon fiber into which they are constantly ramming baggage loaders, galley service trucks and jetways. Look at any normal commercial airliner and you will see a number of what appear to be panels with a lot of rivets near baggage and entry doors. Those are patches over areas that were damaged by impact with service equipment. It happens virtually every day.

The carbon fiber is strong but it can be damaged which can come in the form of delamination. It's very difficult, if not completely impossible however for it to get bent, punctured, torn apart or broken in half like aluminum or steel because of the nature of it's physical properties. I wondered about these things when the 787 first came on line but obviously the Boeing engineers had already worked through all of those possible scenarios and so far I have not heard of any major issues concerning the daily abuse they receive while parked at the gates.

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post #6 of 20 (permalink) Old 09-28-2016, 02:26 PM Thread Starter
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The Boeing 787 fuselage is made completely of carbon fiber into which they are constantly ramming baggage loaders, galley service trucks and jetways. Look at any normal commercial airliner and you will see a number of what appear to be panels with a lot of rivets near baggage and entry doors. Those are patches over areas that were damaged by impact with service equipment. It happens virtually every day.

The carbon fiber is strong but it can be damaged which can come in the form of delamination. It's very difficult, if not completely impossible however for it to get bent, punctured, torn apart or broken in half like aluminum or steel because of the nature of it's physical properties. I wondered about these things when the 787 first came on line but obviously the Boeing engineers had already worked through all of those possible scenarios and so far I have not heard of any major issues concerning the daily abuse they receive while parked at the gates.
Boeing also conduct long term stress tests of wing in a special Jig and that found issues very early on that have been sorted. But the first cabin door that gets ripped off by an aerobridge will be interesting Sadly ground handelers don't report damage and that wont be picked up because you cannot see it during preflight walkarounds.

Remember that aircraft of this type are a whole now ballgame and the maintenance schedule will be under constant scrutiny by all world regulators, Time will tell.

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post #7 of 20 (permalink) Old 09-28-2016, 05:44 PM
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Actually Boeing has a strong relationship with Lamborghini and their composite department was founded by a former Boeing composites researcher. The relationship comes via the university of washington's professor Paolo Ferraboli, a world class carbon fibre specialist, one of the composite reasearchers behind the Boeing 787 dreamliner.
The head of lamborghini's research said regarding the "aventador" which has a carbon tub also, that it has 85kg of carbon fibre whereas a Boeing 787 has 19 tonnes of it but that there is common ground. He goes on to say that every piece of carbon fibre used has its properties put into their CAD data and they do simulations on each part the same as Boeing does. Indeed for their tub lamborghini use three different methods of carbonfibre production and they cure them together with tolerances of less than 1mm. Most of its tub is made using resin transfer moulding which does not require an autoclave or hand lamination with epoxy foam adding space needed to make shapes without the need for more layers of carbon fibre, which they found also served as a noise and harmonic noise dampener.
However Lamborghini's dealers do not repair damage to the carbon fibre tub. The plan was (when the article was written when the aventador was new in 2011) that dealers would solely take photos of the damage and send them to santa agata in Bologna and then carbon doctors would analyse the damage and fly out to fix the car.
As pointed out in replies on this thread carbon fibre does not bend or tear, but at the critical point will just shatter, though this point is usually higher than steel. I remember seeing a propshaft being tested in steel and carbon and the steel bent at high torque levels but the carbon fibre just shattered at a higher level of torque. I believe this is a reason the auto maker Pagani for his cars makes the tub from carbon titanium, where titanium reinforces the carbon fibres in the weave and is stronger for its weight than regular carbon fibre. It is logical to assume this mixture of carbon and titanium would not shatter so easily as regular carbon fibre if at all.
However as pointed out also there is no data on how long a carbon fibre structure by itself would take to delaminate since it is a relatively new product for long term data.
However for a 21st century sportscar a carbon tub (preferably reinforced in some way as Pagani does) is surely the leading edge for chassis in sports cars which begs the question why Ferrari do not make them apart from their specials. The Alfa 4c is surely a step up from ali chassis though not as easily repairable yet but I am sure techology will allow for this in future to make it easier.
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post #8 of 20 (permalink) Old 09-28-2016, 09:14 PM
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The nice thing about Advanced Composites structure is that there is no meaningful fatigue or corrosion problem with it, and it is pretty darn damage tolerant as well, this because the fibers act as crack stoppers in the resin. Boeing has conducted testing like this for decades, leading up to their design and fabrication of the horizontal tail of the 777, the wing of the B2 bomber, and finally to the 787. We ran many static and fatigue tests on Gr/Ep structure both undamaged and damaged and we could still achieve the required lifetimes and load levels, even several times over, with no additional damage occurring during bending or elastic deformation.

Delamination can be a problem but may not as great as one would think (Kevlar fibers used in some composite structure is much more of a problem than graphite as that material will absorb moisture causing it to swell, causing delamination and loose fibers in the matrix), because the loads in most sheet structure is in-plane tension along the various plies, where the loads don't cross many of the plies. You can have delaminated ply compression buckling, but usually that structure subject to compression is fairly stabilized by members such as frames or stringers. The structure is designed to not delaminate in ultimate load cases, including many potential impact loading situations.

It is certainly true that airlines suffer from what is called "ramp rash" caused by careless ramp personnel (although many of the doublers seen around metal aircraft door cutouts are there to repair corner cracking caused by flight fatigue loading, which were underestimated in the initial design). It will be interesting to see which kinds of repairs will be used in common ramp rash around composite structure doorways.

Perpendicular or punch loads are more of a problem if the plies are delaminated, as the stack-up of the delaminated plies is far weaker in lateral bending than the undamaged multiple ply sheet, the build-up structural moment of Inertia being much lower, until the sheet goes into tension loading, the tension capabilities of the plies then coming into play.

It is quite possible to repair most composite structure back to required capabilities, even in the field, so to speak. It does however take the proper equipment and personnel trained/experienced in the methods, which are quite different than metal repair. Sometimes metal (usually titanium to avoid galvanic corrosion) doublers are attached to reinforce the damaged area. Even then, the methods are different enough to be important (cannot use certain interference fasteners for instance).

I strongly suspect that if more composite structure is incorporated into vehicle designs, there will have to be a sea change in the make up of body repair businesses, their employees being required to attend extensive and expensive schooling for the required repair methods. Some will eventually go out of business.

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89 Milano (wife's daily driver since 1989, Shankle Sport)
91 164S (my daily driver since 1994)
94 164LS (~Q) (trip Alfa since 2000)
72 Morgan 27 (water time since 1976)

previously owned since 1964:

62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6

Last edited by Del; 09-28-2016 at 11:10 PM.
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post #9 of 20 (permalink) Old 09-28-2016, 10:15 PM
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Quote:
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...But the first cabin door that gets ripped off by an aerobridge will be interesting...
Oh don't worry, we've already done that - lol

Paul - 1972 Spider - (2)1991 164S's - 1983 308 - 2001 Discovery - 1997 F350
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post #10 of 20 (permalink) Old 09-28-2016, 10:25 PM
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Very interesting reading. Thanks to all of you.

For the purpose of education and data, I'll describe my car crash in more detail.

First, I was on the race track, so insurance didn't cover the repairs. That means an adjuster never looked at my car. My local Alfa dealer did the repairs. I did the majority of the inspection myself at their shop after they took the car apart. My dealer mechanic, service manager and two Alfa reps also inspected the car.

We never saw any type of damage to the carbon. No spider crazing, no delamination, nothing.

The left front corner took the impact. I bent the lower control arm, rim and broke (bent & cracked) the subframe. The facia, fender and headlamp were damaged also.

At first, I was pissed that AR had made the control arm so weak that it bent to easy. Then I realized that if it was stronger, it would have transferred the load into the carbon, damaging the tub. I can replace bolt on parts, but I can't replace the tub.

The control arms bolt directly to the tub. The studs are embedded into the carbon fiber tub, probably not easily replaced.

On the track, the rear end stepped out during the exit of a tight turn. I couldn't recover. I may have been doing 60 or 70 mph. I skidded sideways through the dirt scrubbing off speed. By the time I hit the wall, I was probably doing 40 mph. Hay bales lined the concrete retaining wall which was holding up a small mountain. Clearly the wall wasn't forgiving.

I hit the hay bales and the wall at about a 45 degree angle. When the car came to rest, the front had rolled up onto two bales with the left side touching the wall. The lower carbon fiber vent still has scrape marks on it.

I was in Race mode, no air bags deployed. The seat belts kept me in my seat. After fire & rescue pulled the car down and away, I drove back to the pits. It was rather obvious during that short drive that something was seriously wrong with the car.

The car was repaired, I had it aligned, and have put 20,000 hard miles on it since. That was over one and one half years ago.

Everytime the car goes into the shop for service, I take a good look around for any residual damage. I'm due for my second major service soon and will inspect it once again. No news is good news.
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post #11 of 20 (permalink) Old 09-28-2016, 11:03 PM
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Sounds like that pan was properly designed with plenty of margin. Much easier and cheaper to replace bent pieces instead of suffering traumatic damage to the composite structure.

Del

Seattle

89 Milano (wife's daily driver since 1989, Shankle Sport)
91 164S (my daily driver since 1994)
94 164LS (~Q) (trip Alfa since 2000)
72 Morgan 27 (water time since 1976)

previously owned since 1964:

62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6
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post #12 of 20 (permalink) Old 01-11-2017, 03:17 AM
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Thanks for all the learning in this thread...

Not a 4C owner (yet... may be... who knows), but aside from collision impacts and "repair-ability", do different parts of the C/F have different properties in high stress points where it meets the suspension??? I am thinking of our pothole ridden speed-bump infested excuses for a road... Is there an "extra measure" allocated to safeguard the chassis at those contact points on terrible road surfaces as we have here in Jordan???
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post #13 of 20 (permalink) Old 01-11-2017, 11:05 AM
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"do different parts of the C/F have different properties in high stress points where it meets the suspension???"

That's one of the beauties of the composite structure, as the layup directions of the various layers of the composite material can be arranged/oriented, as well as changing the number of those layers, to carry the specific loads in different areas of the built up structure. In other words, the built up structure can have the required strength in different areas such as attachment points.

This is one reason that the built up structure can be lighter than a metal version, as the structure can be tailored throughout for just the loads actually being carried at those locations in the various loading situations, such as crashes in different directions and speeds. It was determined in one early program at Boeing based on fabrication, analysis, and testing of certain composite structure (737 horizontal stabilizer inspar box), that straight replacement of metal pieces with composite pieces resulted in ~28% reduction of the assembly weight, whereas when the composite structure was redesigned to be equally efficient for the distribution of loading there would be an even greater weight saving.

The philosophy of having the tub having the strength to remain undamaged in pretty much any achievable crash, and having all other structure "breakaway and load absorbing" and replaceable is, as with F1 criteria, the proper direction to take, and clearly achievable with properly designed composite structure.
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Del

Seattle

89 Milano (wife's daily driver since 1989, Shankle Sport)
91 164S (my daily driver since 1994)
94 164LS (~Q) (trip Alfa since 2000)
72 Morgan 27 (water time since 1976)

previously owned since 1964:

62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6

Last edited by Del; 01-11-2017 at 11:19 AM.
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post #14 of 20 (permalink) Old 01-12-2017, 02:57 PM
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Great thread with lots of educational posts - thank you!

Quote:
Originally Posted by sbadaro View Post
... Is there an "extra measure" allocated to safeguard the chassis at those contact points on terrible road surfaces as we have here in Jordan???
Quote:
Originally Posted by Del View Post
"do different parts of the C/F have different properties in high stress points where it meets the suspension???"

That's one of the beauties of the composite structure, as the layup directions of the various layers of the composite material can be arranged/oriented, as well as changing the number of those layers, to carry the specific loads in different areas of the built up structure. In other words, the built up structure can have the required strength in different areas such as attachment points.

This is one reason that the built up structure can be lighter than a metal version, as the structure can be tailored throughout for just the loads actually being carried at those locations in the various loading situations, such as crashes in different directions and speeds. It was determined in one early program at Boeing based on fabrication, analysis, and testing of certain composite structure (737 horizontal stabilizer inspar box), that straight replacement of metal pieces with composite pieces resulted in ~28% reduction of the assembly weight, whereas when the composite structure was redesigned to be equally efficient for the distribution of loading there would be an even greater weight saving.

The philosophy of having the tub having the strength to remain undamaged in pretty much any achievable crash, and having all other structure "breakaway and load absorbing" and replaceable is, as with F1 criteria, the proper direction to take, and clearly achievable with properly designed composite structure.
Or, in layman's terms and associating the response back to the tub of the 4C- "yes, there is".

For instance, there are very specific lift points for the car. The front two are directly on the underside of the tub, and are marked with little squares. It isn't otherwise obvious where these points are, but clearly the weave is strengthened, or thickened (or both) in these locations to support the car, rather than just the weight of the carpet and driver's feet. That's the most obvious one, although you do note some evidence of extra structure at the suspension and sub-frame mounting points as well. Much of the structure is covered either above or below, so it is not always easy to identify if the hidden side might have thicker layers or some sort of rib in sensitive areas such as seat and seat belt mounting attachment points.

Also, this monocoque is not like a bathtub. Think more like spa tub, with lots of odd shapes to it (like bench seats moulded into a whirlpool tub). Those are, no doubt, there for strength.

The 4C tub is definitely well engineered. How that translates in to longevity is apparently an unknown. And what repeated localized loads such as pothole, or 1G cornering on the track will do to that structure and its lifespan, is also a mystery. But reading this thread does give me some pause about regularly tracking the car. At least with metal, you can usually identify a deformity when exposed to loads in excess of SLS. It seems, from the talk above, that such damage could be invisible in CF until it reaches ULS and fails. Or am I misunderstanding?

EDIT: in case these are not globally accepted terms, SLS = serviceable limit state = safe working load. ULS = ultimate limit state = max load.
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Last edited by 4Canada; 01-12-2017 at 03:00 PM.
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post #15 of 20 (permalink) Old 01-12-2017, 05:41 PM
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For those who might be interested:

Luckily, gr/ep structure is extremely damage tolerant, with no fatigue problems, as the fibers efficiently act as crack stoppers. This means that the structure can have sometimes significant damage, still meet limit loading (the max ever expected) and still not have crack growth in a fatigue environment. Many tests have been done to demonstrate this property. Plus, there are no corrosion or rust problems to worry about. In other words, I wouldn't worry much about incidental damage to the 4C structure.

Boeing tested this type of gr/ep structure to not just limit (the highest actual loading ever measure/seen) but also to ultimate loading, which is 1.5 times limit. Then the structure was damaged by saw cuts and hammer blows, and then retested to at least limit again with no problems. Then the damaged structure was fatigue tested to at least two lifetimes of expected use, with no resultant increase in damage due to fatigue. Then static tested again to limit load, with no problems.

The terms the US aerospace industry uses are: limit load, the max ever expected in real life, and ultimate load, which is 1.5 times the limit load, to provide a minimum factor of safety of 1.5. Beside meeting the required fatigue spectrum criteria, aircraft structure is sized for the ultimate loading, and static tested to ~1.07% or so of ultimate load to failure, to allow for later gross weight increases. Boeing tests an airframe to that criteria, expecting no basic structural failure below that value. At least one airframe is also fatigue tested to maybe 2 lifetimes to assess the fatigue analysis conducted for the fuselage, wing, landing gear, flap and slat mechanisms, elevator and rudder, etc.

BTW, some airframes have gone higher in the static testing. I remember witnessing the 757 airframe going to ~1.13% of ultimate before wing failure occurred. This was regarded as a problem because this represented excessive unwanted strength and weight. This resulted in another weight saving program for that airplane, lol. And, as an additional point of interest, the wingtip of the 757 wing was pulled up 28FT (!!!) before failure. What we see when we fly is absolutely nothing in comparison, a foot or two.

Having said the above, though, while I am not privy to the criteria Fiat/Alfa used in the design of the 4C, I am confident that it has been designed and tested to excessive strength for road and track use, including impacts and resulting damage. This material and it's use is well known, and common in very rigorous F1 and race car design and testing.
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Del

Seattle

89 Milano (wife's daily driver since 1989, Shankle Sport)
91 164S (my daily driver since 1994)
94 164LS (~Q) (trip Alfa since 2000)
72 Morgan 27 (water time since 1976)

previously owned since 1964:

62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6

Last edited by Del; 01-12-2017 at 07:34 PM.
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