How do submarines commonly fail? Is the assumption of a violent implosion warranted?
I would think another failure mode could be water rushing in without the overall structure catastrophically failing, which would actually relieve pressure on the structure as it happened and be much less energetic.
It's hard enough to make a small hole that doesn't turn into a big hole under such pressure when you're trying to. Even harder for a small hole you're not expecting.
Just note that the body was experimental: while the hull indeed have a thick titanium body, it was mixed with (don't know exactly how and where though) carbon fibers, which are known to catastrophically break under pressure if there's even a microscopic impurity or damage. At least that's what the experts say. Carbon fibers is great for lightweight things that need to bend, terrible for things to be relied under pressure.
It was just the end caps that were titanium - the entire tube was just a 5inch thick carbon fiber wrap. In one of the videos with the CEO I saw him saying that he was a rule breaker because common consensus was that you shouldn't build a submarine out of carbon fiber and titanium.
I'd really like more detail on that tube's layup schedule.
Solid 5inch thick carbon composite OR a sandwich design with thick outer facesheets of carbon fiber? I suppose under that pressure not much would take the hydrostatic loads other than carbon, but that seems thick compared to everything I've seen made out of composites.
There are videos of them building it. From what I remember, they rolled carbon fiber around a cylinder, making the flat part of the cylinder. Then they mated two titanium half spheres to the end of the carbon fibre cylinder. This was done using some kind of "glue". Meaning that the middle part had no titanium.
I saw a bit of video where they showed the construction- it’s a few inch wide band of carbon fibre wrapped around an inner tube like a spool of thread until it reaches 5” thickness.
"The Spencer-built composite cylindrical hull either was repaired or replaced by Electroimpact and Janicki Industries in 2020 or 2021, prior to the first trips to Titanic."
And composite materials are basically threads embedded in glue. Threads can be extremely strong in tension. In compression, you have only the strength of the glue and the fiber/glue interface strength, which isn't a whole lot. Composite materials are in general poor in compression.
Crewed submersible hulls are always in compressive stress from the ocean outside. I can't fathom why somebody would choose a composite for a deep submersible hull. It's just asking for a buckling failure. Bad design choice, IMO.
It’s been a while since physics for me, but I was under the impression that this only really applies when pressure is greater inside the solid shape. In this case, it seems roughly equivalent to pulling a vacuum inside a soda can at sea level, which fairs quite poorly for the soda can, and I cannot imagine an unfortified sphere-ish shape performing better.
>Carbon fibers is great for lightweight things that need to bend, terrible for things to be relied under pressure.
Composite Overwrapped Pressure Vessels (COPVs) are fairly common in cases where a pressurized system needs to be relatively lightweight (e.g., spacecraft). To your point though, the failure mechanisms can be hard to model.
Take this with a grain of salt because I worked on the data acquisition side of COPV testing and not the engineering side, but my understanding is that while carbon fiber is strong in tension but weak in compression, epoxy is strong in compression but weak in tension. So the combination is thought to make a vessel strong in both.
I would think another failure mode could be water rushing in without the overall structure catastrophically failing, which would actually relieve pressure on the structure as it happened and be much less energetic.