Carbon Fiber Longevity

[Ventucky Red]

Anyone hearing of any fatigue issue with carbon fiber composites in GA?

I know that some of the gliders out there have had the age lifted.

 

[ClimbnSink]

Composite airframes last longer then metal. All composite airframes have been around almost as long as all metal airframes.

 

[thezoolityre]

Greg is right, but the difference with composites versus metal is the visual effect of wear and tear... Metal will have the cracking, rusting, and bending of surfaces as they age/ get hit by things... but composites, on the other hand, most often wear from the inside out... So there may be 7 layers of composite coating for a surface like a wing, and 4 layers are cracked to ****, but on the surface it looks fine... Just something to keep in mind... more info in the PHAK under aircraft structure...

 

[BiffJ]

I think the jury is out on composite aging right now. I've seen stuff that was built in the 60's that looks great and I've seen stuff built in the 90's that looks like crap. It depends on a lot of things like how they were stored and how much sunlight they received. Composites can have issues with UV light which breaks down the resin binder. The carbon fiber itself is pretty much unlimited life but if the resin breaks down the fiberlife is meaningless. Another thing that can affect the structure is water. Not just liquid water but vapor as well. I've seen gliders that were kept in trailers which had delaminations on the wings both in the skins and spars due to water that got between layers and forced them apart physically. Look up osmosis.
Gelcoat is not waterproof and many resin systems are permeable membranes rather than waterproof barriers. I worked in one composite shop where we were not permitted to bring any type of silicone into the shop. It was found that molecules of silicone could migrate along fiber/binder boundries and cause delaminations. At the time silicone vacuum bags were used by many composite companies and work was done to see which caused issues and which didn't.

I've been out of the composite industry for some time but I built or worked on a number of 15m racing gliders, homebuilts both molded and moldless and mostly drones and RPV's (which was the original term for them). I learned a lot about making and repairing these things and the one thing I can tell you is that the biggest problem is finding problems. Composite structures can look perfect and feel fine but have flaws that can cause serious problems. Look up the crash of Rick Massagees Sukoi. The spars that were supposed to be tested to 20g or so failed at somewhere in the region of 9? It was found that the spar layup had some delaminations or discontinuities. (at least this is the story I got). I knew Rick and he was a very good pilot. It was tough to see this happen and was one of the things that changed me from a composite fan to a less fanatical user.

At the other end of the spectrum I worked on Indy Cars for 15 years. In 1992 I watched the carbon fiber and aluminum tub of a car hit the turn 4 wall at Indianapolis Speedway. It was travelling at 220 mph and hit head on with Nelson Piquet at the wheel. The tub was crushed back to about where his knees were but he survived the crash and had his legs rebuilt. I saw him at the speedway 2 years later looking for a ride. Over the years of racing I watched a goodly number of crashes and piled debris into the race trucks all too often. The composites of the cars after 93 was all carbon and aluminum or phenolic honeycomb which is what a lot of the commercial aircraft use now. It is great for energy absorbtion in the crashes and seems to hold together well. Lifetime is anyones guess though. Maybe not much of an answer to your question but only because your question is hard to answer. It needs to be more specific......


Frank