this post was submitted on 26 Jun 2023
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From my limited experience with laying up carbon fiber, I know there's the raw carbon fiber cloth and there's liquid resin that you spread into the cloth. It's also very common to see carbon fiber cloth that is "pre-impregnated" - the resin is already applied to the cloth. Everyone calls this "pre-preg".
So I've seen a lot of folks online scratching their heads about "how can carbon expire?" or "my carbon fiber (bike/boat/etc.) is N-years old, is it expired?" but I think the most likely thing to expire is the resin. Once the resin is cured it is much more stable.
Any materials folks or structures engineers who want step in and correct me, please do.
Also most bikes aren't under enough pressure to cause them to implode
Not with that attitude.
Relevant IT Crowd: https://www.youtube.com/watch?v=elrV-oHeSjE
STRESS
Lmao
Actually CF road bikes only have a safe lifespan of about 10 years - https://icancycling.com/blogs/articles/lifespan-of-road-bike-frame
<insert yo mama joke here>
Different loads, different failures, but still a valid safety concern.
I would not want my bike frame or fork to be made with expired resin. But the age of the bike after the CF is cured is a different matter.
Well it would have an expiry if purchased from Boeing. All materials used in aircraft have stringent performance requirements. Resin is a plastic and like all plastics it degrades over time. It can lose strength and fail to meet materials ratings. Now if you wanted to make something like a regular boat hull out of the stuff it would probably last a lifetime, but if you want to make something like an airplane wing, that's a different story.
Anyway carbon fiber composite is stronger and lighter than steel, but the wonderful thing about metals is they can have good properties for supporting all kinds of loads. But even then you have to inspect for fatigue on a regular basis when loads cycle repeatedly. Carbon fiber doesn't do as well with that.
I agree with all of that. My intuition is that prior to curing, the polymers are less stable and may change in unpredictable ways depending on subtleties in the storage environment and handling. After curing, the polymers are much more stable and durable.
Metals definitely are more forgiving, and we have better tools for testing, especially non-destructive testing. Whether the CF flaws are due to fatigue or workmanship, it's easy to miss them in inspection.
I'm also curious what the sub designers saw as the advantage of CF for this application. Is light weight really all that advantageous for a submersible? Generally no one chooses CF if they are prioritizing cost.
I don't see where it fits as a good solution either. Typically it's used where weight is the main consideration, such as in aircraft. CF is more expensive, has higher maintenance cost, and more difficult to produce than metal. Was it more about doing something different than doing it better? Well the tried an true method for deep sea submarines is a titanium sphere and that's quite expensive so it probably was a lot cheaper.
In his scenario weight was a factor.
They were trying to get the sub to be as light as possible so it could be operated from nearly any vessel. The goal was to have the sub and a launch sled that could be launched and recovered aboard a rented ship. This was all to save money; they didn't want to have to purchase and outfit a special purpose support vessel.
I think the design was flawed from the start, proper stress testing would have revealed it. From what I understand they basically sent it down a few times and said all good, we're done.
The sub did have titanium front and rear bulkheads. If their goal was to make it cheap and light, they might have done better hatching together a train of CF spheres. A cylinder is not strong enough.
Though to be fair, even the best design with the most rigorous testing can fail catastrophically. If that weren't the case space flight would carry no risk. And space is easier to deal with than the pressure at 4km ocean depth. Still that doesn't change my opinion of Rush, he was a hack.
Even worse, in the only third party testing that was performed, by the University of Washington, they rated the original iteration of the Titan only up to 9800 ft. As far as I can tell, Oceangate never redesigned the sub after that, and still decided to take people to 13,000 ft.
Also, given that Rush would brag about how cheap the original hull was, I doubt they fully replaced it when they noticed cyclic fatigue in the sub later. To me it looks like they did some kind of shoddy repair. And that's the Titan everyone ended up with.
I've seen some short interview clips with him and it seemed like he was proud of how cheaply and recklessly he was doing shit. I'd only have to talk to the guy for five minutes and make up my mind I'm not getting near anything he's doing. Those ill-fated tourists had conversations with him a lot longer than that.
Reminiscent of these clowns and their deadly water slide
At 169 feet tall, Verrückt was the tallest waterslide in the world. Riders plummeted down the nearly vertical 17-story chute—taller than Niagara Falls—at speeds up to 70 miles per hour. German for “insane,” Verrückt was designed to challenge the laws of physics. Visitors flocked to Schlitterbahn Water Park in Kansas City, Kansas, to experience its thrill.
That is, until August 7, 2016, when the raft that 10-year-old Caleb Schwab was riding went airborne and hit a metal pole supporting a safety net, resulting in his decapitation and instant death.
Nathan Truesdell, a filmmaker from nearby Missouri, heard about the devastating incident on the news. “My first thought was that it must have been a freak accident—what a horrible, horrible story,” Truesdell told me. “But once I took a closer look, I started to realize how complicated this story really was, and how this could have happened to anyone who went down that slide.”
The story, it turned out, was one of gross negligence, lax state regulations, and the consequences of hubris. Truesdell’s chilling short documentary The Water Slide, premiering on The Atlantic today, uses news and promotional footage to depict the ill-conceived project and its tragic fallout.
The design was definitely flawed from the start. The carbon fiber is not a good material to use for repeated stress cycling. Each time the carbon fiber compresses it causes tiny fractures in the resin. They basically made a one-time use sub as each time it was used the carbon fiber became weaker. There was no way to test how weak it had become because testing it would further weaken it.
I'm seeing a lot of misconceptions in the replies. You have it mainly right from a very high level.
The reason why prepreg "expires" is simply that the resin system is mixed before being impregnated into the fibers, so it starts the curing reaction immediately. These resin systems are usually designed to cure properly at high temperatures, typically 250-400F depending on end-use, but they'll still slowly react at lower temperatures. To further slow the reaction, prepreg is kept frozen. Prepreg also has two types of expirations: "shelf life" and "out life". Shelf life is how long it can last frozen. Out life is how long it can last at room temp.
Theres a few issues that can happen when using expired prepreg. It can be harder to laminate since it will be too stiff and not as sticky. It won't cure correctly causing failures in the resin.
Expired prepreg can be recertified by testing the material for those types of failures. Check if the prepreg can fold over a certain radius and stick to a certain angle without sliding off. Cure a sample and test it.