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That’s the problem with the carbon fiber.
Composites like that have a limited lifespan, and they’re very hard to model- there’s a lot of assumptions going into the modeling like “the fibers are all laid perfectly” and “the resin-to-fiber ratio is perfect” and similar. It’s also super hard to check for defects.
Normally, a lot of this is worked around by increasing the amount of CFC to provide a margin if error.
The problem is that you eat up that margin of error as defects expand under the cyclic stress of going down and coming back up.
Worse, they were not inspecting the pressure hull in a way that could detect the nano- and -micro-cracks so they could tell when it was time to take it out of service.
(That kind of inspection is ridiculously expensive. Like. Yeah.)
Well.
Normally this is avoided by using (very expensive) materials like titanium alloys that are “strong” enough to not fatigue after a few trips. (Strong isn’t quite the right word.
Or extremely expensive (to make) acrylic (PMMA,). It’s expensive to make because of some extremely exacting tolerances.
Incidentally, one of the reasons acrylic is used a lot is its transparency makes it super easy to see defects like cracks. (Literally you can see them with no special equipment.)
In any case while CF isn’t exactly cheap, it was less expensive than a titanium hull, or the acrylic bubble hull you see on the Triton subs; but the whole inspection thing got nixed because of greed.
Fun fact; the only reason this hearing is happening is because two of the passengers were rich. Normal people don’t get this dog and pony show.
Other fun fact: they signed liability waivers. Which makes this a very fun dog and pony show.
I dunno, it seems pretty safe to me. I've ridden the same carbon fiber bicycle for years and it has never imploded.
You, know that you’re supposed to replace the frame if you crash because of similar issues (specifically delaminating being hard to identify without destructive testing )
Just saying.
Though I do believe it’s never imploded….hehe.
I think that’s relevant info but essentially useless considering the recommended max-depth for carbon fiber subs.
They never should have gone that deep. Full stop.
I hope the judge/jury think a waiver was not sufficient to protect ocean gate from negligence.
They’re being sued my 2 millionaire estates, a liability waiver is not enough, and I’m guessing Nargeolet (the explorer,) wasn’t exactly broke.
Usually liability waivers only apply to “reasonable “ risks that are known to both parties. “We might implode because we cheated out and aren’t doing the inspections and were using materials basic material science says we shouldn’t,” likely isn’t covered- it’s reasonable to assume they’re operating a safe sub when it blatantly wasn’t.
Sure, but if it's so underdimensioned that it can only go one time, then it's seriously not good enough for passengers. If the fibre sits correctly it should be able to cycle lots of times, not necessarily having a long lifespan. But yeah this was a shitshow and I stand by the idea that they should have tested it, even several times without living beings inside.
Fot me it's all basic engineering 101 misstakes.
The issue is that carbon fibre is strong, hard, but brittle. When it fails, it fails catastrophically. It also doesn't show many/any signs of failure, till it fails.
A carbon fibre hull, under those loads, could be good for 5 dives or 100, depending on the vagaries of how it was made. It won't show the wear, until it fails. That is why most companies won't trust CF under those sort of loads.
It really is basic engineering.
Like.
Probably not even 101. We’re talking about material selection…. And the properties aren’t exactly unknown and the necessary capabilities aren’t unknown.
The only think that was really unknown is how many dived it had. (CF can be fickle. It’s almost certain there were Minor defects. That’s just something you engineer around, sure, but you never know how close those defects are to becoming not-minor, and it really doesn’t take much. A single micro crack in the wrong place and… well, it probably happened fast enough that they didn’t even know.)
It doesn't help that they drilled through the CF hull....