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This appears to be the vessel in question: https://oceangate.com/our-subs/titan-submersible.html https://oceangate.com/our-subs/titan-submersible.html Pressur

• bubblehead8780 3y ago
  The failure of the carbon fiber is a repeated theory of what could have happened to OceanGate Titan. Is there any information on the difference expansion and contraction of titanium versus carbon fiber. The seal between the end-caps and the carbon fiber hull would have to be very flexible and would be susceptible to failure. Any thoughts on the seals being the failure? I'm a US submarine veteran.
• engineer_22 3y ago
  The structural problems for space vessels vs submersibles I might believe to be quite different. In space the main issue is containing internal pressure - so the skin is all in tension. While a submersible the pressure is from without - so the skin is all in compression.
  • the__alchemist 3y ago
    Also of note, the pressure differences are much higher in submersibles.
    • vrosas 3y ago
      Professor: Good Lord! That's over 150 atmospheres of pressure! Fry: How many atmospheres can the ship withstand? Professor: Well, it’s a spaceship, so I’d say anywhere between zero and one…
      • ajessup 3y ago
        I love this line - one of my favorites of the show. Thanks for sharing.
        • jonathankoren 3y ago
          And then JJ Abrams put Enterprise underwater, ostensibly to hide it from a stone age civilization. Such a hack. Ruined both of the biggest and beloved scifi franchisee. smh
          • wombatpm 3y ago
            I still have problems with Voyager and Enterprise landing at all. Besides the maxim that everything is airdroppable at least once.
            • fnord77 3y ago
              I had problems with their hulls absorbing 75 megaton equivalent torpedoes and only having a minor breech
            • jonathankoren 3y ago
              Voyager I’ll allow since it’s small and pointy, and came with landing gears. The Enterprise is too big. You only get to “hot drop” that saucer section once. (Galaxy class only. Any other saucer sep is apocryphal.) I hate that Rogue One had Star Destroyers hovering in atmosphere. That’s just dumb, and destroyed the lore about Victory versus Imperial class Star Destroyers.
              • hef19898 3y ago
                I loved Rogue One for all the EU hardware they used. And the new TIEs they introduced were cool, too, the TIE Striker is the new canon version of the Scimitar in my head. If they had parked a VSD over the city so, that would have been the crown!
          • 3y ago
    • jaclaz 3y ago
      Yes, but not only, there is number of pressurizing/de-pressurizing cycles to be taken into account (that lead to fatigue), this is more known for hulls of (pressurized) planes. They esperience at least two full cycles per flight, a submarine has as well at least two of them, but with much larger pressure values, for each immersion. Some reference: https://navalpost.com/how-deep-can-a-submarine-dive/ https://navalpost.com/how-deep-can-a-submarine-dive/ AFAICT, steel is still preferred to titanium because (besides the costs) this latter tends to become (after a certain number of cycles) more brittle than the particular kind of steel used in submarines.
• kortex 3y ago
  I'm not really an engineer (general hobbyist, former chemist) but I have built and worked with pressure and vacuum vessels. Positive pressure (tank vs exterior) is much easier to deal with than negative pressure (vacuum vessel at 1 atm, or bathyscape with 1 atm inside and high pressure exterior). In positive pressure, your stress is mostly in the hoop mode, which is stable. This is why aluminum cans can be so thin. In negative pressure vessels, you have a buckling mode, which is inherently unstable. As soon as it goes, it goes all at once. I've had a 2L glass vacuum flask implode on me. There is no warning. All it takes is a tiny defect, and once you hit a certain pressure delta, kaboom. Composite is similar in that it's mostly brittle failure vs ductile. I've also imploded a 55 gallon steel vessel. That goes a lot more gradually (though still fast) - maybe enough to detect and abort the trip. The other main advantage of steel vs composite is you can inspect with X-ray imaging to find defects.
  • readams 3y ago
    Also space pressure difference is much less. A fuel tank might have just a few atmospheres inside, and of course a human pressure vessel will have a bit under 1 atmosphere inside, compared to the outside which is at ~0 atm. At 4000m, the outside pressure is _400_ atmospheres compared to just one inside. It's way, way harder.
    • krisoft 3y ago
      > A fuel tank might have just a few atmospheres inside Not quite. The composite overwrapped pressure vessels (COPV) we are talking about are easily pressurised up to 5000 psi [1]. That is about 340 atm. They use these tanks to contain helium as a pressurant, and nitrogen for the life support systems. Elon talked in a tweet about higher numbers. 6k psi and 10k psi in this tweet[2] but it is unclear if he is talking about design works or actual pressures they have flown. All in all you are right that the difference between the people tank and space is only 1 atm, but that is not where the challenge is in terms of space exploration and pressure vessels. 1: https://ntrs.nasa.gov/api/citations/20110015972/downloads/20110015972.pdf https://ntrs.nasa.gov/api/citations/20110015972/downloads/20... 2: https://twitter.com/elonmusk/status/1501673373813907464 https://twitter.com/elonmusk/status/1501673373813907464
• floxy 3y ago
  Carbon fibers are strong in tension. That's why it is good for pressure vessels that are trying explode. Your wrap the fibers on the outside of the pressure boundary. Same concept that you can only pull on a rope, not push it. I'd be interested to see how they are using carbon fibers in compressive applications like deep sea vessels. Is that more of a marketing thing? "Carbon fiber" sounds sexy, so we'll advertise that we're using it, but it is really for non-load bearing applications?
  • marksmithhfx 3y ago
    Carbon fibre is horrible in compression as just demonstrated, unequivocally by the submersible Titan from OceanGate.
  • deleted 3y ago
    [deleted]
  • materials2023 3y ago
    It is basically a composite material. Carbon fibers bonded with resin compound. The fibers need resin to keep them all together and create a non pours barrier for the fluid contained. The fibers are in tension under the application of internal radial pressure. without the fibers, the resin, having brittle properties cannot handles the tensile hoop stress.
  • materials2023 3y ago
    One disadvantage of Carbon fiber/composite material is that the surface can get electrically charged and cause an arc. It could be that inside the Titan there was an electric short circuit (DC short circuit can produce enough energy) and a Flash fire originated in which flames engulfed the entire capsule rapidly, consumed all the oxygen, decapacitated all the crew. due to the heat generated and the negative pressure created inside, resulted in an implosion of the vessel.
  • pge 3y ago
    The CBS news article referenced in another reply says the body of the sub is 5-inch thick carbon fiber with titanium used in the rounded ends. I am surprised it’s just carbon fiber in the body.
• zabzonk 3y ago
  > 13,000 ft titanic is at about 12500, according to wkikipedia - a bit close?
  • ghaff 3y ago
    Not really. Numbers like that have some safety margin built in.
    • jacquesm 3y ago
      Time will tell on that one.
  • michaelt 3y ago
    Given that it's named the "Titan" and described as "the world's only privately owned manned-submersible capable of reaching Titanic depths of 4000 meters" [1] I suspect this was designed with the Titanic in mind. You would hope that would include a substantial safety margin. [1] https://www.youtube.com/watch?v=vNHXqOUtxgw https://www.youtube.com/watch?v=vNHXqOUtxgw
    • BoryAlis 3y ago
      "Titan" - an ominous omen.
• moralestapia 3y ago
  >The most significant innovation is the proprietary real-time hull health monitoring (RTM) system. [...] provides early warning detection for the pilot with enough time to arrest the descent and safely return to surface. Interested to know more about what happened.
• zh3 3y ago
  I imagine the search and rescue effort have checked the seismograph/ocean sounds/other networks, AIUI an implosion at depth makes quite a bang, so not detecting one would be a positive.
  • ra 3y ago
    Yeah, and you would have thought that in calm weather there would have been something to see on the surface. I hope they're OK.
    • mannykannot 3y ago
      It is a notoriously foggy area. I hope it at least has a radar reflector.
• carabiner 3y ago
  Titanium Titan for the Titanic, carrying business titans. You had to have some Ti in there.
• mechhacker 3y ago
  I've had some work in designing vessels to take external pressure. It's fundamentally a nonlinear problem. A lot of new(and some not so new) engineers don't understand the process of solving it properly For instance, euler buckling is the simple eigenvalue problem of solving a column in compression. But, it misses: initial defect because nothing is truly straight, material nonlinear effects if the part approaches yield strength, etc. I've seen it overestimate compressive capacity as much as 3-10 times depending on how geometry and material. You have to use more advanced techniques than just force over area. Metallic vessels are difficult enough. You have to set up the problem properly and run nonlinear solves in the right way, and account for the right (or at least bound it conservatively) initial imperfections and analyze. And provide margin. Lots of compute time for a realistic analysis. And you probably still want to test. And you want to know your material very well, as the higher it's loaded, the more nonlinear that behavior could be too. And that's with the simplicity of metal. Composites are different. And that's not accounting for complexities of this problem. A lot of things get brittle at lower temperatures. Steel does, and I'm not sure about this particular material but at depth I would want to know specifics of temperatures and material behavior and select the right material for the job. Matrix and fibers themselves. Either failing would be fatal. I don't know enough here to say anything other than there are a lot of variables and I'm far enough away from the problem that it would take a lot of data to convince myself that I understood what could possibly happen.
  • Exuma 3y ago
    That’s sounds crazy complicated. In engineering is it like software design where you can get very far just being bad? Like do companies hire just crap engineers who don’t know all this stuff and call it a day? (Kind of like hiring offshore to build mvp for cheapiest crappiest quality possible)
    • mechhacker 3y ago
      You can do that but you'll spend a lot of money breaking things. If you're in a non-safety critical field then that is a possibility. But, you really need good engineers, or to make them through these mistakes, to figure out what is really going wrong.
• userbinator 3y ago
  I wonder if it has an adaptive pressurisation system, similar to airplanes but in the opposite direction, where the internal pressure is allowed to increase up to a certain point as it descends to reduce the pressure differential.
• foobar1962 3y ago
  > Can any engineers comment on whether that task is easier for a vessel exposed to compression (under sea) as opposed to vacuum (space)? I believe the pressure where the Titanic lays is 300 atmospheres. The pressure differential for the submarine is 300 - 1 = 299 atmospheres. A vessel in space will be have a pressure differential of 1 atmosphere to contend with.
  • wnc3141 3y ago
    I too am interested in this question, may I piggyback and add a question about whether the basic capsule shape is as efficient in negative pressure as it is in positive pressure
    • foobar1962 3y ago
      The design of pressurised aircraft is probably a good example to study.
• oneTbrain23 3y ago
  I think Titan imploded killing the crews instantly. This would explain sudden lost of contact and subsequently unable to find them. Those fiber has been confirmed to buckle from cyclic pressure. The take away from this incident is OceanGate should have pursue Edison manual ways of repetitive testing. It would be very expensive but the knowledge gather from those test will enhance material science of carbon fiber use in that kind of scenrios and design specs. Instead they prefer to fire the engineer whistleblower who try to save them. Such irony.
• 32faction 3y ago
  My background is in aerospace and while I’m not an expert on COPVs, I’m familiar with their design. Carbon fiber overwrap is really good for internal pressure applications or in other words, the typical pressure vessel due to carbon fiber’s very high tensile strength. Think of those videos where folks put rubber bands on watermelons to make them explode; the concept is similar to a COPV in that the rubber bands (carbon fiber) “compress” the watermelon (pressure vessel) to “contain” the pressure. COPVs can take high internal pressures of 6000 PSI (which is the same internal pressure of the ISS NORS tank used to recharge oxygen and nitrogen on the ISS and coincidentally is the same *external* pressure experienced at the depths of the Titanic. (Some helium bottles have higher internal pressure). While in aerospace applications there are some load cases where the COPV has an external pressure load on them like a helium bottle stored in a propellant tank on a SpaceX Falcon 9, those pressures are nowhere near deep sea pressures. The reason why I don’t think COPVs are a good design for an external pressure application is the load direction; carbon fiber tow doesn’t really do well maintaining an external load. Think back to the watermelon example; apply an increased external pressure and the rubber bands really don’t help with withstanding that increased pressure. Carbon fiber itself is very difficult to verify that you have the correct properties once they're wound onto the tank. The properties are anisotropic meaning depending on the direction of the fiber you’re gonna get different mechanical properties. Defects like delamination (when a wind unwraps) or voids between the tank wall and fiber are common if you don’t have a qualified winding operation and really really good procedures. In short, while not needing software, repeatability in manufacturing a COPV is incredibly difficult. Part of the reason SpaceX switched to metal tanks is that the mechanical properties of stainless actually increase in a cryogenic environment so there’s an added benefit. In 2016, SpaceX’s Falcon 9 carrying AMOS-6 exploded during a routine static fire due to a buckled liner of a COPV on the 2nd stage LOX tank. The liner buckled which created a void between the liner and the fiber overwrap which then developed solid oxygen (or an ingress of LOX) that initiated an explosion due to friction. Falcon 9 had been flying for 6 years at that point so I’d consider that a pretty mature or at least an “operational” vehicle so for it to explode on the pad like that is how tricky COPVs can be. EDIT: Spelling and clarification on delamination
• skibsky 3y ago
  There's a formula for designing the strain on pressurized vessels especially when the strength characteristics of the material used is known The thicker the material used for the vessel the more pressure It will take That's obvious & simple so far They used carbon fiber and titanium fiber probably interwoven and then glued there is a procedure for this There's also a nominal, working, and burst value after these vessels are manufactured. Basically established by testing There was no testing on this vehicle non-destructive or destructive That was bypassed Also I believed it was planned to be a 7-in thick vessel this one for some reason was 5-in thick Two of the employees from oceangate were sued and dismissed for making issues of the safety of this vessel particularly about the thickness and particularly about the gluing process (That isn't even that strange in any industry where there is engineers) Especially in R&D situation like this So you have a material which the mechanics of that material are not fully understood Being used to manufacture a vessel that's going to withstand unimaginable pressures because of its size every square inch of that vehicle had 4,000 per square inch on it It's of a certain configuration (shape) Needs to be tested The other thing I would bring up is I wonder if the gasket failed they're almost at full depth Maybe they didn't change the gasket or they change the gasket and it was of a different physical characteristics The gasket is used on the hatch which was bolted shut The gasket surface design is very critical at that pressure also I think you can rule out fatigue because carbon fiber and titanium for that matter have really high fatigue resistance LJK
• nickocrates 3y ago
  For those looking for more detail on the engineering of the vessel, refer to this brief walk-through from Rush himself filmed by a Mexican travel blogger back in July of 2021: (Skip to 18:05 for Rush's explanation of the sub) https://www.youtube.com/watch?v=uD5SUDFE6CA https://www.youtube.com/watch?v=uD5SUDFE6CA