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> OceanGate’s submersibles are the only known vessels to use real-time (RTM) hull health monitoring. With this RTM system, we can determine if the hull is compr
by hn_throwaway_99 3y ago
> OceanGate’s submersibles are the only known vessels to use real-time (RTM) hull health monitoring. With this RTM system, we can determine if the hull is compromised well before situations become life-threatening, and safely return to the surface. This innovative safety system is not currently covered by any classing agency.
> No other submersible currently utilizes real-time monitoring to monitor hull health during a dive. We want to know why. Classed subs are only required to undergo depth validation every three years, whereas our RTM system validates the integrity of the hull on each and every dive.
Completely, completely bizarro in my opinion. I'll take the hull that is proven to actually withstand the pressures it was designed for over some system that gives me a heads up before I get crushed to death.
Related question for those more knowledgeable. I always thought the primary benefit of carbon fiber was tensile strength. I don't even understand how it could sufficiently resist the compressive pressures at the bottom of the ocean - it is a fiber after all. Edit: After seeing the comments below about James Cameron, apparently I'm not alone. From James Cameron's Wikipedia page: "He was also critical of the use of carbon-fiber composite in the company’s Titan submersible, stating that the material has “no strength in external compression” when withstanding the pressure in deep sea environments."
- cbzoiav 3y agoThe craft survived several launches - that proved it can do it. Whether it can do it reliably / survive fatigue accross repeated cycles is a different question. Imagine we'll find out as the investigation progresses.
- jfk13 3y agoWe already found out, I think.
- someweirdperson 3y agoMaybe some orcas played with it.
- hn_throwaway_99 3y ago> The craft survived several launches - that proved it can do it. Exactly, that's my point. I didn't realize that (this present catastrophe notwithstanding) that carbon fiber could even begin to have such compressive strength. How is the fiber formed in such a way to maintain that strength?
- jackmott42 3y agoalign layers of fibers in different directions and you can get strength in different directions. But it is tricky! The glue holding the metal end caps to the carbon tube is also a possible failure point. Imagine a metal ring slid over a carbon tube held on with glue. If pressure deforms the metal differently than the carbon, you get a gap at the interface and BOOM or if sea water degrades the glue, or if the carbon fiber degrades after each trip and eventually isn't strong enough any more, etc.
- Alupis 3y agoA point raised by James Cameron (and others) was the titanium bands mated to the carbon fiber hull. Apparently in the material science community, that's a huge no-no, and a well known one to boot. Galvanic corrosion or something like that...
- zarzavat 3y agoIt’s a dumb idea for numerous reasons. The titanium and carbon fibre will expand and contract in relation to temperature and pressure at different rates, they are two different materials with totally different material properties. So you’ve added a second force on the vehicle which is the pulling and pushing of the carbon fiber and titanium from one another. And all you have to hold that together is fancy glue, the glue is taking all that force. A 5 year old could do better.
- oofbey 3y agoIt’s counter-intuitive, but the so-called hoop stress on a cylinder being compressed from the outside actually results in tensile stress not compressive. This is because the material as it resists shrinking to a smaller radius is being pulled apart.
- Alupis 3y agoJames Cameron gave an interview where he claimed the carbon fiber hull concept was tested by a team competing to get down to Challenger Deep at the same time his team was - and the concept failed in testing. He also claimed many within the deep submersible community wrote letters to OceanGate warning them their plan was flawed and would result in catastrophic loss. Specifically, the failure mode was delamination. I can't vouch for how credible this all is - but, given how much disregard the OceanGate team had for safety, it doesn't seem too far fetched. https://www.youtube.com/watch?v=e9YB31ElEFQ https://www.youtube.com/watch?v=e9YB31ElEFQ
- hn_throwaway_99 3y agoThat was a great interview IMO, thanks for posting. I think some people might find it hard to both convey sympathy and compassion for the deceased and their families as well as being adamant that the submersible design was nuts (especially since the man primarily responsible died), but I think Cameron in particular did that very well.
- cbzoiav 3y agoChallenger Deep is exponentially more difficult than this - 10km Vs 4km so over double the pressure. While it may still be an entirely unsuitable material for 4km, not being suitable for 10km doesn't prove that.
- AdamJacobMuller 3y agoAs far as I'm aware, and please correct me if I'm wrong, they had never dove to this depth before. So, sure, it was launched before and recovered, but it never experienced the same conditions which caused the failure.
- mjb 3y agoThey did: http://web.archive.org/web/20200814020351/https://www.oceangate.com/our-subs/titan/titan-4000m-validation-dive.html http://web.archive.org/web/20200814020351/https://www.oceang... (At least twice, and probably more times).
- sitic 3y agoApparently it's at least 13 dives since 2021: https://www.geekwire.com/2022/beyond-the-titanic-oceangates-founder-contemplates-future-deep-sea-frontiers/ https://www.geekwire.com/2022/beyond-the-titanic-oceangates-...
- larrywright 3y agoI saw someone on Twitter suggest that this was probably WHY it failed this time. Each dive would weaken it.
- deleted 3y ago[deleted]
- distrill 3y agoi think we found out when it imploded
- ineedasername 3y ago>Whether it can do it reliably / survive fatigue accross repeated cycles is a different question. Imagine we'll find out as the investigation progresses. Seems like we already found out the answer is “no”. The overall ship design failed.
- deleted 3y ago[deleted]
- AdamJacobMuller 3y agoTruly bizarre. Failures like this happen in milliseconds, it doesn't matter how realtime your realtime monitoring is. I'm not arguing in favor of the classification system, but, I think if you went to them and framed things as simply as they are here "you require validation every 3 years, we're doing it on every single dive" they would say "that's more than once per 3 years, APPROVED!" so the situation is clearly far more complicated than they are indicating.
- _yb2s 3y agoYes, I don't understand this acoustic monitoring concept... I'm curious what the logic behind it was. It just doesn't seem like there would be enough time to take action once the monitor starts to detect failure.
- jnwatson 3y agoIt depends on the material. It might work for certain tours of steel, since the failure state is gradual. Carbon fiber, however, is not known to gradually fail.
- mustacheemperor 3y agoIt seems they felt this was one of the novel innovations that enabled this design - that the monitoring system was so good, they'd never be at risk in the pressure hull at depth. James Cameron said it looks like they had dropped their emergency ascent ballast before the implosion, so they may have gotten enough warning to take action. But I would guess that system was never tested to failure in real life. It will be interesting to see which of the novel innovations supposedly enabling this unconventional design failed, if it can be determined. Rush also lampshaded the fact that his company had "successfully" bonded the titanium endcaps to carbon fiber despite that being contradictory to conventional materials science wisdom, reading the patent for the monitoring system it looks like it may have been intended to provide warning about those bonds failing too.
- _yb2s 3y agoIt seems like it would be trivial to test how much early warning such a system gives by bringing smaller/cheaper test hulls to failure, either in the ocean, or in a pressure testing chamber. I wonder if they did that?
- learn_more 3y agoI too am perplexed. Perhaps the compressive strength is all derived from the epoxy not from the carbon fiber.
- _yb2s 3y agoYes, this doesn't make sense to me either. I suppose it could help prevent bucking and crack propagation, because as the walls of the sub started to bend, one side would have to suddenly be in tension? Still, I wonder if a pure plastic/epoxy hull would have actually been stronger than composite in this situation.
- marcosdumay 3y agoFrom the design they published of it, I do really think they intended to have the carbon fiber tensioned between a pair of titanium rings. I understand epoxy doesn't deal well with that, but with the right plastic, I believe it could work very well.
- _yb2s 3y agoIt is a carbon fiber tube with a hemispherical titanium cap on each end. The caps push inward under pressure putting the carbon fiber hull under compression, not tension.
- johnwalkr 3y agoThat would only be possible if the rings were fixed relative to each other, which they are not.
- marcosdumay 3y agoYeah, you are right. It's not tensioned between the rings then.
- ReptileMan 3y agoconst int well_before_in_milliseconds = 50;
- hotpotamus 3y agoHonestly, the "real time health monitoring" felt like almost every tech "innovation" over the last decade or so - a half-baked excuse not to do things correctly. And when you can't switch your lights on because the cloud is down, it's inconvenient, but clearly the results of applying this thinking to critical safety are self-evident.
- ummonk 3y agoThe epoxy in carbon fiber makes it stiff. Stiffness helps reduce buckling loads.
- johnwalkr 3y agoI think the confusion about tensile strength comes from imagining a single carbon fibre. It very obviously has little strength in compression, like a bicycle spoke. But the fibres don't act alone. Even under tension, you need the epoxy to transmit loads between fibres, or else the carbon fibre is pretty useless which is why the finished material CFRP (carbon fibre reinforced plastic) is used. Unlike metals which are generally equal strength in compression and tension, CFRP is roughly half as strong in compression. But it's very light so from a strength point of view it's not automatically the worst material choice. I get Cameron's point but if it really had "no strength in external compression" then it would be a useless material in general. Regardless of material the main failure mode of a tube with external pressure is buckling, so the strength in compression is much lower than what you expect from a hand calculation that doesn't consider buckling anyway[1]. But CFRP is a risky choice for at least 4 reasons: analysis is not as straight-forward/easy-to-trust, signs of fatigue are harder to detect, delamination is difficult to control[2], and interface to other materials is tricky, especially when temperature changes and water are involved. [1] You can use hand calculations to check buckling as well but they depend on analytical models which, if they even exist for CFRP, would be quite difficult to trust because there are so many more variables compared to metals. [2] Delamination must be really nasty when coupled with buckling. Local weaknesses greatly affect buckling, and a even a small void between plys is a local weakness where the plys don't transmit load to each other.
- dm319 3y agoWhen I heard Cameron speaking about this recently, I thought he was referring to two different materials being used, rather than the carbon fibre per se.
- hn_throwaway_99 3y agoThanks! Very informative reply, greatly appreciated.