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Titanic tourist submersible goes missing with search under way

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Re: Titanic tourist submersible goes missing with search under way

#641

Post by marksmithhfx »

CarVac wrote: post #114
floxy wrote: post #95

Earlier quoted context omitted.

Here is an article with a few more details on the construction of the Cyclops vessel: https://www.compositesworld.com/articles/composite-submersib... ...still not seeing what the carbon fiber is buying here, other than historical reasons / "that's how we do composite pressure vessels". Maybe it adds some slight rigidity when it is being raised up out of the water?

Carbon fiber is used because it is rigid. The failure mode for a member in compression is buckling, which is resisted by stiffness, not strength. It's also a lot easier to make a huge thick tube out of composites than out of titanium. That's why only the spherical ends are titanium, and the middle tube part is CF.

Poor design choice. Too many materials expanding and contracting at different rates leads to friction stress and ultimate material failure. Maybe not at first, but over repeated compression and expansion cycles.

Re: Titanic tourist submersible goes missing with search under way

#642

Post by marksmithhfx »

patrec wrote: post #309
jacquesm wrote: post #292

Earlier quoted context omitted.

Air.

True, although fortunately the air supply is meant to last for 4 days. As a passenger I would probably be more alarmed about the apparent absence of some kind of distress beacon than the inability to open the hatch without help.

There was a distress beacon… it’s called a transponder. It is in a separate pressure chamber controlled by a separate battery. It is a completely separate and isolated system. It failed at the same time as regular comms leading some to conclude the vessel was gone. Kaput. Is no more.

Re: Titanic tourist submersible goes missing with search under way

#643

Post by marksmithhfx »

pomian wrote: post #244
ohazi wrote: post #237

Earlier quoted context omitted.

Here "in practice" actually means "in sheets." If you have a flat sheet of concrete / carbon fiber composite supported at both ends, and then you apply a downward force in the middle, the top of the sheet will be in compression while the bottom of the sheet will be under tension. In a negative pressure vessel that's a cylindrical shell, all of the force is being applied uniformly inward from the outside surface of th…

Interesting. There must be interior bulkheads(walls), your idea of shear could very well happen where the bulkheads prevent tension of the inside surface.

This makes me think, why didn’t they build in composite reinforced bulkheads every 12 inches or so. That definitely would have had substantial impact on compressing the cf hull and preventing delamination. So obvious.

Re: Titanic tourist submersible goes missing with search under way

#644

Post by marksmithhfx »

pomian wrote: post #244
ohazi wrote: post #237

Earlier quoted context omitted.

Here "in practice" actually means "in sheets." If you have a flat sheet of concrete / carbon fiber composite supported at both ends, and then you apply a downward force in the middle, the top of the sheet will be in compression while the bottom of the sheet will be under tension. In a negative pressure vessel that's a cylindrical shell, all of the force is being applied uniformly inward from the outside surface of th…

Interesting. There must be interior bulkheads(walls), your idea of shear could very well happen where the bulkheads prevent tension of the inside surface.

Like ribs in an airplane wing, which provides the bulk of compression strength and transfers loads to spars.

Re: Titanic tourist submersible goes missing with search under way

#645

Post by interner_reader »

ohazi wrote: post #237
saltcured wrote: post #144

Earlier quoted context omitted.

Wouldn't this be a bit like reinforced concrete? In practice there are not just pure compressive loads, but flexing and shearing that put some areas under tension, so the embedded reinforcements fight that and help keep the bulk material in the right places. Also, think of the bill of a toucan or fiberglass surf board. A lot of rigidity comes from the tensile strength of the skin wrapped around an enclosed volume of…

Here "in practice" actually means "in sheets." If you have a flat sheet of concrete / carbon fiber composite supported at both ends, and then you apply a downward force in the middle, the top of the sheet will be in compression while the bottom of the sheet will be under tension. In a negative pressure vessel that's a cylindrical shell, all of the force is being applied uniformly inward from the outside surface of th…

>Also, think of the bill of a toucan or fiberglass surf board. A lot of rigidity comes from the tensile strength of the skin wrapped around an enclosed volume of relatively weak stuff that mostly keeps the skin in the right configuration.

So in other words carbon fibers are a bit elongated (or straindd) in CFRP? What increases shear strength of the composite but could weaken its compressive strength?

Re: Titanic tourist submersible goes missing with search under way

#646

Post by materials2023 »

floxy wrote: post #55
scarnz wrote: post #30

This appears to be the vessel in question: https://oceangate.com/our-subs/titan-submersible.html Pressure hull made from titanium and carbon fiber, capable of diving to 4000m (13,000 ft). I recall that one reason SpaceX switched from carbon fiber to stainless steel pressure vessels (fuel tanks) was the difficulty of detecting structural flaws. Can any engineers comment on whether that task is easier for a vessel expo…

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 th…

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.

Re: Titanic tourist submersible goes missing with search under way

#647

Post by materials2023 »

floxy wrote: post #55
scarnz wrote: post #30

This appears to be the vessel in question: https://oceangate.com/our-subs/titan-submersible.html Pressure hull made from titanium and carbon fiber, capable of diving to 4000m (13,000 ft). I recall that one reason SpaceX switched from carbon fiber to stainless steel pressure vessels (fuel tanks) was the difficulty of detecting structural flaws. Can any engineers comment on whether that task is easier for a vessel expo…

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 th…

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.

Re: Titanic tourist submersible goes missing with search under way

#648

Post by bubblehead8780 »

scarnz wrote: post #30

This appears to be the vessel in question: https://oceangate.com/our-subs/titan-submersible.html Pressure hull made from titanium and carbon fiber, capable of diving to 4000m (13,000 ft). I recall that one reason SpaceX switched from carbon fiber to stainless steel pressure vessels (fuel tanks) was the difficulty of detecting structural flaws. Can any engineers comment on whether that task is easier for a vessel expo…

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.

Re: Titanic tourist submersible goes missing with search under way

#649

Post by hef19898 »

jonathankoren wrote: post #471
wombatpm wrote: post #456

Earlier quoted context omitted.

I still have problems with Voyager and Enterprise landing at all. Besides the maxim that everything is airdroppable at least once.

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.

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!
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