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Comment by adql | Hacker News Reader

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

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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...

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.

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

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.

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