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Comment by hn_throwaway_99 | Hacker News Reader

> The craft survived several launches - that proved it can do it.

Exactly, that's my point. I didn't realize that (this present catastrophe notwithstanding) that carbon fiber could even begin to have such compressive strength. How is the fiber formed in such a way to maintain that strength?

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align layers of fibers in different directions and you can get strength in different directions. But it is tricky! The glue holding the metal end caps to the carbon tube is also a possible failure point. Imagine a metal ring slid over a carbon tube held on with glue. If pressure deforms the metal differently than the carbon, you get a gap at the interface and BOOM

or if sea water degrades the glue, or if the carbon fiber degrades after each trip and eventually isn't strong enough any more, etc.

A point raised by James Cameron (and others) was the titanium bands mated to the carbon fiber hull. Apparently in the material science community, that's a huge no-no, and a well known one to boot. Galvanic corrosion or something like that...

It’s a dumb idea for numerous reasons. The titanium and carbon fibre will expand and contract in relation to temperature and pressure at different rates, they are two different materials with totally different material properties. So you’ve added a second force on the vehicle which is the pulling and pushing of the carbon fiber and titanium from one another. And all you have to hold that together is fancy glue, the glue is taking all that force. A 5 year old could do better.

It’s counter-intuitive, but the so-called hoop stress on a cylinder being compressed from the outside actually results in tensile stress not compressive. This is because the material as it resists shrinking to a smaller radius is being pulled apart.

Is this accurate? All of the examples I found online about hoop stress had diagrams where the pressure inside the cylinder was higher (as in a water pipe for example).

Tensile strength would make sense in that scenario, but I don't see how it would apply when the cylinder is empty and being crushed by outside forces.

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