Carbon Fiber Composites -Do they age?

Carbon fiber composites have been around for awhile, now. So if there is going to be aging problems, I would think it is about time for problems to start showing up. Has anyone noticed problems like delamination, fatigue, crazing, erosion, or embrittlement?

I dunno, maybe you could be more specific?
Yes, everything ages. Problems, depend on usage and design load cycles / build quality / actual usage vs. intended purpose...

Its a composite so there are too many variables involved to answer this generally IMHO.

My feeling is that layups have been getting lighter, especially since infusion became (almost?) mainstream but maybe not weaker in general. Boats designed for racing, with lots of carbon will have been designed on the light side to begin with. More recreational boats will take re-sale value into account as opposed to line honors...
I never heard many sailors complaining about brittle carbon, except in quite specific cases where a particular design may have saved a little too much weight in a certain year and fixed it the next.

Dennis

UV is your biggest enemy.

UV is the biggest enemy for the (epoxy-)resin, not for the carbon tissue itself.

Nevertheless unprotected black carbon/resin laminate will heatup considerably in the sun.

With carbon composites you have a few potential failure causes (with the exception of good old fashioned breaking due to higher than designed loads.

1. wrong resin: Using too stiff a reason (ie polyester) will result in the matrix breaking down and delaminating. Can be prevented by always using epoxy.

2. UV damage can cause the resin to break down and wait for it.... delaminate. Can be prevented by painting with a suitable paint, so stop posing and loose the clear carbon.

3. Getting too hot can cause the resin to soften and re-distribute itself in the matrix, so make sure the above paint is white.

4. Too much resin will make it harder and can cause it to crack as per 1. above. So worst case weigh out your resin, best case use infusion or pre-preg.

5. Not enough resin means the fibers wont be held together properly and they'll delaminate when loaded. See above for fix.

OK Capt. Semantics, carbon fiber parts aren't much use without the resin now are they?

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OK Capt. Semantics, carbon fiber parts aren't much use without the resin now are they? [/quote]

What I ment to say is that for the carbonfibre composite there isn't much difference with the good oldfashioned glass composite.

The "weak" component remains the resin: UV detoriation, critical for weight ratio tissue/resin, hardening complications (moisture,etc), after-hardening, etc.

Sometimes people forget that the only function of the resin is keeping the filaments of the glass/carbon/kevlar/orwhatever tissue together and in place.
This requires a very specific close-fitting fabrication of any composite. So from this point of view there isn't much difference between glass and carbon laminates.

A lot laymen think that Carbonfibre composites are some kind of miracle material (well it is invented in aerospace-industry), but it isn't.

It has the same usual disadvantages as all the other composites (infact even more).

For the rest, I'm all in what Scarecrow wrote above.

Hmm..., I was expecting to at least get a little controversy out of this posting. Not even one bad experience out there with carbon fiber? --All I got was a lecture from the wissened sailing elders to the ignorant masses, about the basics of boat construction. I guess that's a good sign that there haven't been any real problems specific to carbon composites.
The U.S. Airforce has to hide their Stealth airplanes in buildings, because the weather and sun damages them. Must not be a problem for sailboats. --Must be the white paint.

Has nothing to do with carbon fiber and everything to do with the RAM (radar absorbent material) used to cover the plane's skin.

Best to look at how glass and more lately carbon gliders have faired after all they have been around the longest. What started off as 3000 flight hours before being timed out, that was extended to 6000 and then I believe to 12000. As long as the resin is protected from uv and over stressing, modern composites just seem to carry on.

My carbon N20 mast has taken 12 years of abuse now. We bend the hell out of it with double trap spinn reaching. I even ease the main ALOT in the puffs to keep from driving off. It's a Southern Spars mast, which I believe is a little stiffer than the other ones. I think keeping it protected with the paint is key.

In addition to what has been said already:-

I know that at least some good quality pre pregs have UV inhibitors in the resin to protect from UV.

Also a good quality pre preg will have a relatively high cure temp and if you elevate the cure temp, in accordance with resin recommendation, towards the end of the cure cycle that can help the laminate withstand extremes of heat caused by the sun.

If you are not using pre preg get a resin with data sheets that detail the vacuum window. Weigh everything and follow the data sheets to avoid resin starvation in the laminate. Alternatively don't pull too high a vacuum.
Also post cure the laminate but I would still paint it white.

If you did not make it yourself and not privy to all the details paint it white.

#3) the heat "WILL" also cause your foam-core to melt !!
another reason for white paint. I use Nomex-Honeycomb
so i don't care about that one, UV inhibitors will work.
to protect the resin though, if Ya like that Carbon look !

#4) Weigh the resin like the man said
(1-gram of fiber TO 1-gram of resin) spread it out then
get rid of 15% of the resin with shop-towels wrapped
around toilet-paper ; Or use Peal-Ply & baby-blanket under
the vacuum bag.

Too much resin will cause the lamination's to FLOAT with
epoxy between ; this causes the Epoxy to act like a core
material so as to add thickness. NOT GOOD because the epoxy
is kinda brittle so it breaks down between the fibers.
A Quality core increases the strength by the (3) of the thickness.

Bille

UV and heat cause premature aging. The aging you cannot help is from mechanical cycling. Basically this is the number of times it cycles through its structural design or is bent from minus x to plus x. For any design you could produce a curve that relates load, cycles per hour and life

Every time you apply a full load cycle to a composite, you get some level of micro delamination. In theory the designer should determine what loads it must handle and what lifetime they want and back out the laminate. This is true for all plastic laminates and aluminum. Steel is different. Carbon and aluminum crack and fall apart. Steel gets flexy. In Engineering this usually lumped under fatigue.

I have never seen a study of the life of a catamaran. There was one published for mtn bikes. A light cross country racing carbon frame was good for about 3 years. Similar aluminum frames ranges from 4-5 years for hydoformed aluminum to ~6 years for welded tubing. Building a general purpose trail frame that is .5 to 1.5 lb heavier extends the life to 10-12 years.

Boats are different from bike frames. With one design boats there is a minimum weight. Newer designs put strength/weight where it is needed and greatly increase life. For example Lightnings and Tornados. Manufacturer one designs, at least to me, seem to have good years and bad years depending on how accurate the venders claims for their resin, fabric, core material etc was. With formula boats it's mixed, though the best built ones seem to live long enough to become obsolete. Because you have a volume production boat used for the Olympics there is some data available for Lasers. I seem to remember 5 years weekend warrior is equal to 6 months for an Olympic hopeful.

This is about as much as I know. Don't bother to ask me anymore. This is a area where I have to go ask experts and there are not many of them.

I'm too lazy to look, but can you recycle composite materials once it's past its useful life?

It doesn't melt?
Would burning it produce more problems than it's worth (for the heat output)?
Crushing/grinding? Any use for the product? (at least it wouldn't take up as much landfill space as a powder than a partially deconstructed hull/mast)

Ofcourse it melts! Below the boiling point of water, maybe 180 iirc.

20+ years ago I was warned to never anchor over a volcano!

The micro-delamination of a carbon-composite in a load-cycle, I don't quite understand. Nor the aluminium vulnerability.

If you stay with your loads far within the maximum tension values( I forgot the correct technical english for that), you don't damage the molecullar structure, aren't you????????

So, no hairline-cracks, no delamination, etc.

Besides, the aluminium fatigue I know, has often to do with outside surface-erosion (or inside; in closed tubes-constructions, like bicycles)


Is it not that this phenomenon which you describe, only applies for the situation that you pass now and then unforseenly and unwanted the stress-values of your material.?????????

Steel and Titanium behave like you described. As long as you keep the load below tbd% of yield, there is no cycle limit. Aluminum and composites have a fatigue limit. Aluminum fatigue is well documented with Airliners. (Remember the aircraft on TV that failed because they exceeded the pressurization cycles or Landing Cycles without making mods to extend their life?) Heavy flexible composite have a very very long fatigue life. The stuff from the 90's was assumed to have an infinite cycle life. Stiff light composites with only just enough of the right material in the right place have a shorter life. Composites also have a problem with crack propagation. If you hit it in a way it was not designed for, it cracks and the crack propagates until it fails.

easy to read:
http://en.wikipedia.org/wiki/Fatigue_limit
http://www.airliners.net/aviation-forums/tech_ops/read.main/91016/


Not easy to read, what the experts say to me
http://books.google.com/books?id=FW...e%20of%20carbon%20composites&f=false

http://scholar.lib.vt.edu/theses/av...Part_2_strength_and_life_predictions.pdf

Google "composite fatigue life predictions" and you will find plenty of technical articles and Conference Paper Reprints. There is a lot of information in the Public Information of the FAA.

This is not my area of expertise. I can't argue with you. Everything I have seen below the PHD level is proprietary. The only article on the subject, I know of was in, I think, Mountain Bike Action in the Fall of 2011. I showed it to 2 world class experts and they both said if their assumptions about the life of the aluminum frame is correct, it looks about right. I canceled an order for a super light carbon frame and bought a heavier aluminum one.

Thanks Carl, for this clarifying and comprehensive information you gave me.

The first and most striking eye-opener for me to read was the notice that fibre composites are by nature inhomogeneous (resin and fibres) and anisotropic (=not as strong in each direction).

This very fact alone will always create fatigue!!!

I've never realized that.

Yes, this is part of the benefit in that you can build strength vs. flexibility in particular directions in a solid laminate. America's cup teams use this to great detail. Composite spar manufactures use this function in every mast they build.

Yes, Jake , but the surprising part for me was, that there's a whole new dimension in talking about the strenght of a laminate.

I started building windsurf boards about 35 years ago and had very much to cope with the tension-strenght because of the extreme loads on a board at sea and after jumps.

When carbon and kevlar were invented and on the market a few years later, we directly started using it in strips for enforcements. (It costed a fortune that days!).

But our expectations were soon belied, because the boards broke even so. Later on when fiber-clothes were cheaper and cheaper we could use full-board covering with carbon and the breaking point was shifted in time.
But in those time we never thought about fatigue in our design considerations.

I'm still reading in this e-book which Carl mentioned and, honestly, it scares the hell out of me.

I'm now sailing three years on my homebuilt cat which has hulls of 60-70% carboncomposite. With exception of the joints of the (carbon) beams with the hulls, the fiberclothing was laid in the lenght-direction of the hulls, so no 45 degree crossed layer. I would do that differently knowing what I now learned about fatigue.

One thing I did right: I have made the beams with a full wooden core and a lot of UD carbon! (ended with 10 kg for a 260 cm beam).

So, returning to the subject of this thread, when you count fatigue under aging, then fiber composites do definetly age. I'm still reading about the carbon ones.

I'm thrown out of the site for reading this E-book: "Fatigue in composites". The computer says I reached my limit in reading for free. (book cost about 300 bugs).
So I have to live with what I found so far. Which is quite interesting.

In the book is stated that Hybrid composites ( so for instance glass layers mixed with carbon ones) are slightly more resistant to fatigue then pure mono composites.

I knew that already from my experience with carbon surfmasts. Pure 100% carbon masts break definitly earlier then f.e. 60% masts. I always thought that had to do with more vulnerability from the 100% carbon for impact accidents, but it seems to be fatigue!

So, you understand that I'm happy with my 60-70% carbon homemade cathulls.

Second remark is that they test fatigue in load-cycles with a minimum and a maximum load.
Now I've constructed my hulls (and beams) with a massive core , so the composite skins of the hulls are more fixed, they cannot move.
In a normal cathull the skin itself can bend a little when under load; hence creates a load cycle. (The old nacra's you could push in with your finger on the side)

I remember me the building of a hollow windsurfboard in the far past with only a few internal supports (like a cathull). It was made off 100% carbon and I jumped it in two halves after 3 months.

Hybrid composites also resists crack propagation. Which I would also group with fatigue. The Gougeon Bro's book on wood boat building mentioned Kevlar added to a carbon layup would resist crack propagation. You can email DuPont and ask for more information. In the past they have been quite helpful. (Be sure to ask for composite layup information on all of their products) My carbon beams have 1 layer Kevlar for each 6 layers carbon. It was the Kevlar that held the beams together long enough to get to shore when the carbon failed.

Concerning your board failure issues, research resins. Epoxy resins may not all be equal. Resin suppliers will usually give you fatigue info.

In my opinion you have a right to be concerned about fatigue. It is rarely mentioned. Builders of commercial items will provide fatigue information if asked. Consumer product builders fall back on "We offer a lifetime or 20 year or ? warranty" which leads me to believe they expect you to sell or trash whatever they sold you before fatigue becomes a factor. I suspect one reason is if you had that information and repeatably used a product near it's limits and it wore out early, you could force them to replace it under warranty. Currently it is common for companies to refuse on the grounds that you abused their product.