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Comment by bilekas | Hacker News Reader

I'm really curious about the carbon fibre design, I'm not a material expert but I do dive and for tanks they work because of the internal pressure of tank.

The 'weaving' is supposed to be link connecting your two hands together interlocking fingers, in one direction you will meet a full resistance, but in the opposite direction your fingers will unlock.

I have no idea but seems to me if there is external pressure the weaving would have 'imploded' depending on the design I guess. Really want to know more about this.

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Your intuition is spot on, carbon fiber is much better at tensile loads than compressive loads.

Tensile load capacity is pretty much the resin that keeps the fibers from moving.

The most I could find about the design

> The entire pressure vessel is comprised of two titanium hemispheres, two matching titanium interface rings, and the 142 cm (56") internal diameter, 2.4-m (100") long carbon fiber wound cylinder – the largest such device ever built for use in a manned submersible.

suggest that yeah, they relied entirely on its compressive strength of it

It's wild how carbon fibre is a insanely powerful in it's application yet it's misused.

I'd like to say it's caveat being as you mentioned but honestly, given then community in this field, even the technical diving alone. Someone must have said it to them.

Thanks for some numbers, maybe tomorrow will play with the simulations to determine the AP's that could collapse the craft. The titanium hemispheres are probably the best option but the sealing would need to be almost clinical.

I'm anxious just thinking about the construction of this sub.

There is a video going around of the lead guy saying (obviously before this incident) something to the effect of “I will be remembered for innovation and the rules I broke, I was told not to build using such and such materials and I’ve proven people wrong”.

“I’ve broken some rules to make this, I think I’ve broken them with good logic and good engineering behind me. The carbon fiber and titanium, there’s a rule you don’t do that – well I did,” said the CEO in an interview in 2021. [1]

[1] https://www.youtube.com/watch?v=uD5SUDFE6CA&t=1446s&pp=2AGmC...

I have a feeling his well intentioned motivational interviews will not age well in the next few weeks.

James Cameron was quite interesting on the similarities between the original Titanic disaster where the captain was warned about icebergs but said nah and went ahead and crashed, and this time where the guy was similarly warned.

(in the vid https://abcnews.go.com/US/james-cameron-compares-submersible... about 3 mins in)

I guess it's in the spirit of the Titanic to kill your passengers doing dumb stuff.

Aren't most/all materials much stronger in tensile load than compressive loads, because of buckling anomalies?

No, brittle materials like concrete are famously weak in tension and strong in compression. Ductile materials are generally equally strong in both. I can't think of any material offhand that's stronger in tension and weaker in compression.

Buckling is not a material failure, it's a structural failure. In pure buckling [0], the strength of the material is not actually a factor in whether something buckles or not. In most cases, material failure does occur as a side effect of the buckling, but not always. (The material's stiffness does matter, though. All else equal, something that's more flexible will buckle sooner than something stiff.)

[0] https://en.wikipedia.org/wiki/Euler%27s_critical_load

I believe wood is stronger in tension than it is in compression?

No way.

> I can't think of any material offhand that's stronger in tension and weaker in compression.

Rope.

No, concrete and bricks are much stronger in compressive loads.

The looking glass was only rated for 4,000 feet. Implosion happened around 9,000 feet, which would suggest the glass handled over twice its rated depth.

and survived several dives before that to 13000ft, no?

Flip a coin enough times, it's bound to be tails

I'm wondering this myself, they don't have any history logged of a trip before.

I think this might have been the first one. In minimal fairness, at least the owner put his money where is mouth was.

Sidebar : The owner/ceo did a 10 hour overall at max ~3kMeteres

A lot of measure of units thrown around in this thread too.

David Pogue observed them visiting the Titanic.

https://www.nbcnews.com/tech/internet/david-pogue-misinforma...

They did many many trips

There’s also a documentary on bbc about one of those trips

Many? The picture in the news early on showing signatures of the passengers on a poster titled Mission V.

I took that to mean this was their 5th trip with this submersible

So that’s added stress at pressures that it wasn’t rated for.

Pressure cookers that are rated for 15 PSI typically come apart at 75 PSI.

But that’s the thing about ratings. The manufacturer guarantees safe usage at 15 PSI and anything above that all bets are off and you’re on your own. Same with milk and expiration dates. Many times the milk is fine after the date, but the dairy won’t guarantee freshness and food safety.

Same for this looking glass. It says what the CEO thought about safety. He was willing to take chances and roll the dice. And every once in a while you get snake eyes. The consequences of rolling • • at 9,000ft of depth in the ocean is sadly instant soup. The water entering the vessel would likely be 5,000F degrees or so. While some people say it would be an instant death and not consciously detectable, I disagree. I think they were given just enough time for the brain to go oh shit, but only got to the oh part, and lights out.

Sorry but for metric units, 9k feet is around <3k~

Looking glass rated 4k 'feet' around 1200 meters..

Not sure as there is a video of the ceo going to 3k meters solo in the titan on a 10~ hour trip..

That said, not much of this craft was 'rated' for anything..

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