Titanic Sub missing

[rgmwa]

About the only positive thing that can be said about this submersible is that it imploded so they didn't slowly suffocate. Hopefully they were properly briefed on the risks before they got on board, but at US$250k per ticket I'm sure the company wouldn't want to have frightened the passengers off by being overly pessimistic.  Nevertheless, all of these people were there by choice, not necessity. Hopefully, any other tourist ventures will learn the lesson and use properly designed and tested subs.

 

[red750]

The 17yo didn't want to go but accompanied his father.

[facthunter]

Composite titanium and Carbon fibre. How is that a stable structure taking immense pressure. Meanwhile Hundreds of poor people die in the Mediterranean.  Nev

[Old Koreelah]

51 minutes ago, willedoo said:

It sounds like the sub was a disaster waiting to happen. A bit of a rough show; the ballast was building site waste material balanced on outer pylons. To release the ballast, the crew all move to one side so the weight falls off...

Crikey! A weight-shift craft.

Sounds like this composite capsule was very experimental, so it should have been more rigorously tested than conventional ones.

Makes this Australian- built device all the more impressive, because it took James Cameron to the bottom of the ocean and back up again safely:

https://www.smh.com.au/national/sydney-designer-of-james-cameron-s-submersible-describes-what-can-go-wrong-20230622-p5dilo.html

[onetrack]

I think a lot of the problem with this Titan submersible, is that the builder failed to study the Comet design disaster. I see major similarities to the Comet problem here - the submersible was used on a number of previous dives to the Titanic - and it seems fairly obvious now, that no-one considered the possible damage to the submersible hull from the repeated pressure cycles.

 

https://en.as.com/latest_news/how-many-expeditions-has-the-oceangate-submarine-made-to-the-titanic-when-were-they-n/

 

Here we had a submersible hull that was subject to regular pressure cycles that varied from 1 atmosphere at the surface, to 380 atmospheres at 3800 metres, where the Titanic lies.

 

The repeated massive pressurising and then the pressure release upon return to the surface, MUST have degraded the hull structure.

The experts are saying that microscopic weepage into the carbon fibre would cause delamination - and result in substantially weakened carbon fibre. This would have all been aided by the repeated pressure cycles.

 

Carbon fibre is not designed to resist massive water pressure, this is a whole new field of experimentation, and obviously there's still a lot to learn about how carbon fibre handles repeated pressure cycling under water.

 

Then there's the fact that building a cylinder to resist pressure from the outside, is a vastly different exercise to designing a cylinder to hold pressure on the inside.

 

The hoop shape under pressure internally is stable, but the hoop shape under external pressure is unstable, and dependent on the shape remaining perfectly spherical.

Any slight distortion in the spherical structure, and the hoop shape weakens enormously, and implosion is guaranteed at high external pressures.

 

A very revealing discussion here - https://news.ycombinator.com/item?id=36392416

 

This is a railroad tank car implosion caused by blocking valves to create a near-perfect vacuum - at 1 atmosphere!!  Imagine 380 atmospheres operating on it!!

 

 

[onetrack]

The company that built this submersible is building, or has built, several more of them. I reckon they won't be able to get anyone within a bulls roar of their products now, and it will be "back to the drawing board".

 

Here is a 2017 article where the manufacturer is essentially bragging about how great his product is.

 

https://www.compositesworld.com/articles/composite-submersibles-under-pressure-in-deep-deep-waters

[facthunter]

Carbon fibre doesn't perform well in compression. That's been well known for ages. It's also hard to assess for internal damage which could progressively accumulate.. Nev

[Jerry_Atrick]

Here is an interesting vid on the subject:

 

[Bruce Tuncks]

What mechanism is there for fatigue with a carbon-fiber structure? I understand the mechanism for metal structures but carbon-fiber is quite a different material.

 

[Old Koreelah]

1 hour ago, Bruce Tuncks said:

What mechanism is there for fatigue with a carbon-fiber structure? I understand the mechanism for metal structures but carbon-fiber is quite a different material.

 

My understanding of composites is that carbon fibres have immense tensile strength, much greater than fibreglass and others. One of the main advantages of carbon fibre is that under load it stretches much less than other fibres.

Why use it underwater, where these advantages are not needed? Composites have little resistance to compression- that’s taken by the resin, so that sub was a plastic tube with metal end caps.

[facthunter]

Totally WRONG application for carbon fibre. Progressive DAMAGE is not what we normally regard as Fatigue though the result is similar..   Nev

[onetrack]

This is an excellent video and it should be used as a training video on NOT what to do with deep submersible design. Stockton Rush was a huge risk taker, arrogant, not prepared to take professional engineering advice (because he knew better, and a "bit of risk" is good, isn't it?), and was supremely confident in his own design abilities. As they say, "it's not what you know that kills you, it's what you don't know" (and are not interested in learning, in this case).

 

I don't think this bloke had any real idea of the pressure at 12,500 feet - it's not like he was only to going to dive into a shallow river.

 

 

[rgmwa]

It looks like the carbon fibre tube was just butt jointed to the titanium ring and relied entirely on the glue to hold the two parts together. With no sleeve or some other form of mechanical interlock, the shear stresses in the glue and on ends of the carbon fibre layers due to the different material properties (carbon fibre, glue and titianium) under pressure must have been huge. No wonder the ends of the tube delaminated.

[facthunter]

Carbon Fibre is crap in  compression. Like trying to make tomato stakes out of sisal rope and resin. 4' thick steel would be more appropriate for the hull.  Nev

Edited June 30, 2023 by facthunter
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[spacesailor]

STEEL !.

Like the Titanic was made from .

It Was supposed to be Malable,  but the cold made it brittle .

Instead of ' Buckling & Bending ' it split .

BUT

Those 'rivets ' held , All the years since it was built .

spacesailor

[facthunter]

COLD ? Around 0 Celcius? That's not cold. It's minus 50 0r more at height ( Tropopause) and at the Poles and steel stuff doesn't become brittle to any significant extent. It's used for containing liquid nitrogen.. Nev

[pmccarthy]

In Arctic conditions they have all sorts of problems with steel becoming brittle and breaking. 

[red750]

I was flipping channels during a commercial break, and happened on the Discovery Channel, and a show called The Explorers Club. This episode related to a 1960 dive in a submersible to the depth of 7 miles in the Challenger Deep, the deepest point of the Mariana Trench in Micronesia. Two divers took the submersible to the bottom, risking death like the crew of Titan. They heard a bang on the way down, but continued the dive. An expert said that if you hear a bang, that's good, because if you don't hear it, you are already dead.