OceanGate Expeditions Titan DSV loss

Divine said:
Currently at work so unable to fully dive through this thread but; so at the cost of repeating information;
it may be pertinent to note the winding pattern as used in the main pressure hull of Titan was wound using the "loop/hoop (fig B)" style of winding, which has drastically reduced strength & much easier delam in comparison to the "helical (fig A)" style.
Helical is almost exclusively used for such things as pressure vessels.
e.g paintball air tanks, as they are designed to withstand rather large pressures (Vary from 800, 1200, 1400, 2400, 4500 psi for über high end tanks), obviously not a 1:1 comparison because these tanks are in & designed specifically for tension loading, rather than the compression loads submersibles are subjected to.
Nonetheless I believe it highlights one of the core inadequacies of Titan.
Besides, you know, laughing in the face of experts for some extra pr

Unfortunately I cannot find a concise analysis through a quick Google but, it's fairly certain anyone with some sense can see why it's a bad idea to not only use carbon fibre (which notoriously relies on it's binder to provide compressive resistance) in this environment, but utilize it "improperly" to boot.

quick edit: it just occurred some of the more high-end gas cylinders (again, tension, but there's ressive loads tend to use steel vessels) use helical wound fibres as well, shedding more light on the... decisions made.
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The problem with the helical winding is, that it doens't work when you have metal end caps. Therefore I gues they were using mainly a radial winding. Maybe they added a longitudenal (might be partially helical) "loop winding aroung" it, meaning the fiber would go longitunenal on the outside and make a 180° turn on the endings and going back on the inside.

Just an idea, please don't blame it on me if youre sub implodes...
 
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Nicknick said:
The problem with the helical winding is, that it doens't work when you have metal end caps. Therefore I gues they were using mainly a radial winding. Maybe they added a longitudenal (might be partially helical) "loop winding aroung" it, meaning the fiber would go longitunenal on the outside and make a 180° turn on the endings and going back on the inside.

Just an idea, please don't blame it on me if youre sub implodes...
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Yep, pretty big caveat. Ideally the caps should've been wound-in but that may introduce challenges of its own, such as;
extracting the mandrel:D
 
Generally, composites' properties in compression are dominated by the matrix (resin) properties. This is a major reason why no one builds composite submarines.

A "rule breaking" design, like this one, needs extensive analysis and testing. Neither seems to have been done. One shouldn't speak ill of the dead, but Stockton Rush was an arrogant fool. Maybe that came with the Berkley MBA
 
1635yankee said:
Generally, composites' properties in compression are dominated by the matrix (resin) properties. This is a major reason why no one builds composite submarines.

A "rule breaking" design, like this one, needs extensive analysis and testing. Neither seems to have been done. One shouldn't speak ill of the dead, but Stockton Rush was an arrogant fool. Maybe that came with the Berkley MBA
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You nailed it...
 
Extracting the mandrel ist not the main proplem, inflatable mandrels could be used or it could just stay inside. Extracting the passengers is much more difficult, since the passenger pre implosion consitency is not well suited to squeeze them through a small opening....
 
Nicknick said:
Extracting the mandrel ist not the main proplem, inflatable mandrels could be used or it could just stay inside. Extracting the passengers is much more difficult, since the passenger pre implosion consitency is not well suited to squeeze them through a small opening....
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Most passengers will fit through a 24" diameter hatch.
 
But you cant use a 24" hatch in combination with a helical winding.
 
Nicknick said:
But you cant use a 24" hatch in combination with a helical winding.
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Sure you can. When they're making a paintball air cylinder, does the tank head thread directly onto CF or does it thread into the metal neck of the mandrel?

You put the 24" hatch opening, which is going to be more like 36" or so by the time you have enough bulk around the hatch for seating surfaces at full pressure, at the end of the mandrel that doesn't get covered by composites.
 
Please take a look on the upper pic of No. 310, with this type of winding, the fibers must pass close to the center of the sphere, otherwise they will shear of. Thats why you cant have a large opening with a helical winding.
 
Nicknick said:
Please take a look on the upper pic of No. 310, with this type of winding, the fibers must pass close to the center of the sphere, otherwise they will shear of. Thats why you cant have a large opening with a helical winding.
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And yet paintball gun air tanks have an exit opening that is roughly 1/3 of the diameter of the tank.
 
Scott Kenny said:
And yet paintball gun air tanks have an exit opening that is roughly 1/3 of the diameter of the tank.
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Paintball tanks are operating under internal, not external, pressure so the dominant stresses are tensile. A vessel under external pressure is under compressive loading, with failure modes like buckling, which don't occur in tension.
 
1635yankee said:
Paintball tanks are operating under internal, not external, pressure so the dominant stresses are tensile. A vessel under external pressure is under compressive loading, with failure modes like buckling, which don't occur in tension.
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Correct.

Which is why a deep submersible's pressure hull is the worst possible usage for a composite tank.

However, you could probably make a good case for a composite decompression chamber for dive medicine.
 
Scott Kenny said:
Correct.

Which is why a deep submersible's pressure hull is the worst possible usage for a composite tank.

However, you could probably make a good case for a composite decompression chamber for dive medicine.
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Or composite air tanks. Wound pressure vessels have a fairly long history,
 
Scott Kenny said:
Correct.

Which is why a deep submersible's pressure hull is the worst possible usage for a composite tank.
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Carbon fibre was used as a marketing gimmick, likewise their claims of the involvement of NASA and Boeing. Deception is all about convincing people just enough that they’ll give you some money.

Defrauding billionaires is a booming business these days as shown in a few others technology subjects discussed on Secret Projects;- “A fool and his money are easily parted”.

What’s somewhat sad is that genuinely good ideas are being squished because they’re uncompetitive against the nonsense hype fantasy being presented as “just within reach if some money is spent on it’..
 
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Zoo Tycoon said:
Carbon fibre was used a marketing gimmick, likewise just like their claims of the involvement of NASA and Boeing. Deception is all about convincing people just enough they’ll give you some money.

Defrauding billionaires is a booming business these days as shown in a few others technology subjects discussed on Secret Projects;- “A fool and his money are easily parted”. What’s somewhat sad is that genuinely good ideas are being squished because they’re uncompetitive against the nonsense hype fantasy being presented as just within reach.
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No, it's pretty well established that they really did use a CF cylinder with titanium endcaps, when they should have used a titanium cylinder with titanium endcaps, or better yet a titanium sphere... Though welding that would have been a nightmare.
 
Scott Kenny said:
No, it's pretty well established that they really did use a CF cylinder with titanium endcaps, when they should have used a titanium cylinder with titanium endcaps, or better yet a titanium sphere... Though welding that would have been a nightmare.
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Scott I’m not doubting they used CFRP, indeed they did;- I’m commenting on why they used such a ridiculous unsuitable material… what was in for them.

BTW - The Russian made Titanium submarines such as the deep diving Mike class, and I’m told successfully welded up to 280mm thickness…two sided EBW … not cheap.
 
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Zoo Tycoon said:
Scott I’m not doubting they used CFRP, indeed they did;- I’m commenting on why they used such a ridiculous unsuitable material… what was in for them.
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It was cheap and sounded high tech.

Then they had a bunch of engineering students who had never worked with CF in compression. I feel bad for those kids, they might as well get a job flipping burgers or something, because they're never going to get hired as engineers again.
 
Zoo Tycoon said:
BTW - The Russian made Titanium submarines such as the deep diving Mike class, and I’m told successfully welded up to 280mm thickness…two sided EBW … not cheap.
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DSV Alvin uses a titanium pressure sphere 75 mm thick, which was built in two halves welded together using EBW. This is rated for 6500 meters depth (with a 25% margin, it was tested to 8 km).
 
Welding might not be nessecary, the pressure will keep everything attached to another. The surfaces must be mashined for perfect sealing (without rubber sealings) and if this works you don"t need to weld anything.

I"m not an expert in carbon fiber and I know, that tension is, were they really shine, but working in conpression is nothing totally unusual for carbon fiber. Keep in mind, that every bending means conpressing in the shortenig half of the bended part. Every carbon fiber wing works with about 50 % of the fibers going into compression. The difference between a bending carbon fiber part and a part which works only in compression, is how to apply the load. In a bending wing, the compression load is applied by shear over the entire length of the wing. In the middle section of the sub, the load is applied on the endings of the cylinder, which is much more difficult to solve.
 
Nicknick said:
Welding might not be nessecary, the pressure will keep everything attached to another. The surfaces must be mashined for perfect sealing (without rubber sealings) and if this works you don"t need to weld anything.

I"m not an expert in carbon fiber and I know, that tension is, were they really shine, but working in conpression is nothing totally unusual for carbon fiber. Keep in mind, that every bending means conpressing in the shortenig half of the bended part. Every carbon fiber wing works with about 50 % of the fibers going into compression. The difference between a bending carbon fiber part and a part which works only in compression, is how to apply the load. In a bending wing, the compression load is applied by shear over the entire length of the wing. In the middle section of the sub, the load is applied on the endings of the cylinder, which is much more difficult to solve.
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The difference is the sheer force being applied in compression underwater.

1 bar per 15 10m, to use metric. (44psi per 100ft in SAE) 4000m is ~270 400 bar pressure.
 
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Zoo Tycoon said:
Scott I’m not doubting they used CFRP, indeed they did;- I’m commenting on why they used such a ridiculous unsuitable material… what was in for them.

BTW - The Russian made Titanium submarines such as the deep diving Mike class, and I’m told successfully welded up to 280mm thickness…two sided EBW … not cheap.
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I remember reading that the fUSSR's titanium submarines were welded in buildings were the air was replaced by argon.

I'm not sure I believe that; MIG and TIG welding are well-known technologies used to weld, among other materials, magnesium.
 
Scott Kenny said:
However, you could probably make a good case for a composite decompression chamber for dive medicine.
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And indeed such things exist for a number of applications where steel decompression chambers are undesirable.
1635yankee said:
I'm not sure I believe that; MIG and TIG welding are well-known technologies used to weld, among other materials, magnesium.
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AIUI, titanium welding requires that the weld is shielded with argon whilst it cools, whih requires that the work takes place completely surrounded by argon for an extended period. Flooding the entire building with inert gas, however, was a typically Soviet solution to limitations of their industry.
 
Scott Kenny said:
And yet paintball gun air tanks have an exit opening that is roughly 1/3 of the diameter of the tank.
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The internal diameter of the titan hull was just 1420 mm, one third of this would be very narrow. It would work e.g. with young people from Vietnam, but not with most rich older guys from the US... I'm pretty sure, that the air tanks have a metal inlay which also implies the thread, so the design is very different and not comparable.
 
Nicknick said:
I"m not an expert in carbon fiber and I know, that tension is, were they really shine, but working in conpression is nothing totally unusual for carbon fiber. Keep in mind, that every bending means conpressing in the shortenig half of the bended part. Every carbon fiber wing works with about 50 % of the fibers going into compression. The difference between a bending carbon fiber part and a part which works only in compression, is how to apply the load. In a bending wing, the compression load is applied by shear over the entire length of the wing. In the middle section of the sub, the load is applied on the endings of the cylinder, which is much more difficult to solve.
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Carbon fibre works exceptionally well in tension and is a little below that of aluminium in compression. While it’s true that bending structure experiences, in terms of top and bottom booms a 50:50 split tension to compression, the web experiences shear which can be largely taken in tension with careful fibre alignment (on the 45’s). In the case of a wing, the top and bottom covers ( aka Skins) react torsion, as do the ribs. Making the structure all temp/etc compatible the CFRP exceptional tension performance more than compensates for it’s mediocre compressive properties. Of course where CFRP excels is in internally pressurised structures, where with a bit of care, the fibres can be largely tension loaded.

Now 100 % external pressure loaded structure, CFRP at its best, is slightly worse than aluminium, so you just use more of it….. except this causes problem for very thick sections due to through ply thickness curing, whereby lots of things can go wrong such as;- curing gas bubbles, outer ply shrinkage causing the inner ply wrinkles/delamination to name a few.
 
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"Sightly lower than Aluminium" could, mean lower in regard to N/mm² but still slightly better in regard to weight/strength ratio. However, I wouldn't choose carbon fiber in compression as prefered material for such a critical application. As you mentioned, with very thick structures, new problems will arize. It will also become difficult to realize an about even tension level from inside to outside, especially when the endings are attached to metal structures with a different E-modul.

The plexi glas window of the Titan shouldn't be forgotten, this could have also caused the catastrophe...
 
The main advantage of the SI units is their logic, but destpite that, they fit much better to every day life. The athmospheric pressure is 100.000 Pa or one bar, the weight of 1 L water is one kg, 10 m of water collum is 1 bar, water freezes by 0° and boils at 100° C, gravitation is about 10 m/s², it all fits beautifully. Some things per definition (boiling/freezing point, density of water) and some by pure luck. I can't undestand why some people stick to the imperial system.
 
Nicknick said:
The main advantage of the SI units is their logic, but destpite that, they fit much better to every day life. The athmospheric pressure is 100.000 Pa or one bar, the weight of 1 L water is one kg, 10 m of water collum is 1 bar, water freezes by 0° and boils at 100° C, gravitation is about 10 m/s², it all fits beautifully. Some things per definition (boiling/freezing point, density of water) and some by pure luck. I can't undestand why some people stick to the imperial system.
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Maybe because they like imperialism?
 
Nicknick said:
I can't undestand why some people stick to the imperial system.
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It's what I grew up with, I was basically at the tail end of the time when the US was attempting to go metric and then got bored with it.

But honestly, Fahrenheit is a much more useful temperature scale to humans for weather. 100degF is a stupidly hot day. What's that in C? 38? Adding another digit at the "you have got to be kidding me" temperatures works better mentally.

Hobbes said:
That's 1 bar per 10 m.
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Ah, crap, Oops! that's what I get for going from memory and not looking it up. :facepalm:
 
Nicknick said:
The internal diameter of the titan hull was just 1420 mm, one third of this would be very narrow. It would work e.g. with young people from Vietnam, but not with most rich older guys from the US... I'm pretty sure, that the air tanks have a metal inlay which also implies the thread, so the design is very different and not comparable.
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Yeah, a 24"/650mm opening would end up closer to 1/2 the diameter of the pressure volume and probably wouldn't work well.

Does anyone know where they got those Titanium endcaps from? I'm assuming that they were not made specifically for OceanGate.
 
Scott Kenny said:
But honestly, Fahrenheit is a much more useful temperature scale to humans for weather
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It depends on what you're used to. I grew up with the metric system and the Celsius scale - any temperature below zero means imminent danger of iced up roads (danger! danger!) as well as a decent chance of skating (yay!). Win some, lose some. 37 degrees centigrade was hammered into my brain as normal body temperature - any weather hotter than that is, as you put it, 'stupidly hot'. 100 degrees centigrade is dead easy to remember as the boiling point of water at sea level.
The beauty of SI - (pedant warning!) which, by the way, uses the Kelvin scale - is the interconnectedness of its units, which spares any astronomer/physicist/biologist/chemist/engineer/mechanic the need to use endless arbitrary conversion constants to calculate what reality is likely to throw their way.
But, again, it's mostly whatever you're used to. Like those antique monetary units of twelve pence to the shilling, twenty shillings to the pound, guineas, crowns et cetera et cetera...

Remind me - how many Ningi go into a Triganic Pu?
 
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