this post was submitted on 26 Jun 2023
301 points (100.0% liked)
Technology
37603 readers
572 users here now
A nice place to discuss rumors, happenings, innovations, and challenges in the technology sphere. We also welcome discussions on the intersections of technology and society. If it’s technological news or discussion of technology, it probably belongs here.
Remember the overriding ethos on Beehaw: Be(e) Nice. Each user you encounter here is a person, and should be treated with kindness (even if they’re wrong, or use a Linux distro you don’t like). Personal attacks will not be tolerated.
Subcommunities on Beehaw:
This community's icon was made by Aaron Schneider, under the CC-BY-NC-SA 4.0 license.
founded 2 years ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
That guy was a backyard inventor and charlatan, like those 19th century backyard aircraft inventors. It's one thing to take yourself out of the gene pool through your own recklessness, it's another to take others with you.
Rush bypassed over a hundred years of engineering lessons learned the hard way with the rationale it stifles innovation. He even fired and sued one of his own employees for calling him out on it. The sub had zero certifications and then he lied to customers about it saying his designs were approved by NASA and Boeing who never even heard of the guy.
Aside from the lack of safety engineering and lack of proper fail-safes in his design, there's a reason engineers don't use carbon fiber composites in subs. They have a tendency to delaminate. When used in aircraft, composites have to be examined and certified at a regular service interval with special inspection equipment.
I think that sub was an accident waiting to happen from day one. The hull probably failed due to inspection negligence and a failure to detect delamination. That's even if the hull could have been rated properly for 4km. If it wasn't the hull, it would been one of the other jury-rigged systems.
I can't believe people smart enough to acquire the wealth for that excursion weren't smart enough to check out the qualifications of the company hosting it. I think it was plainly obvious just looking at the sub yourself. A navigation system that consists of a consumer laptop PC and Logitech gaming controller should have been a dead giveaway.
I don't get why carbon fiber was used in the first place. The composite material is known for its great tensile strength: tensile as in tension, not compression. Carbon fiber is actually also known for being lousy at handling crushing (compressive) loads. If you crush carbon fiber, it'll fail shortly after.
Going under water would place the vessel under compressive loads, which at a quick glance would be the wrong type of loads for carbon fiber. That's my initial take on it, however I haven't spent any real time trying to engineer one.
First, he was an aerospace guy and several things he's said make me think he was sort of chauvinistic about deep sea exploration in general, stuff like "It’s perfectly fine. Having all these certifications for airplanes is one thing, but the carbon fiber was perfectly sound."
Second, his business model, taking four people down with him in something other than Cameronesque claustrophia, and doing so without the cost of owning a proper launch vessel, instead renting any ship that could hold and then monitor his launch sled, meant it was critical he make something big and light, by deep sea submersible standards, that was at least nominally expected to handle the load. Shit, I guess in some sense, he did, since it went down and back two or three times or whatever. At the absolute best, though, he'd invented a disposable sub, and he clearly didn't worry about that limitation any more than the rest.
— How l'any atmospheres can the ship withstand!?
— Well, it's a spaceship, so I'd say anywhere between zero and one...
Fiber composites are complex. Carbon fibers can be made to withstand compressive loads in that you make composites with the CF and other materials. Even so carbon fibers are about half as strong in compression as tension. Even so, carbon fiber might have a specific strength of around 3000 kN-m/kg, steels might be around 63 kN-m/kg. So it's not as simple as "carbon fiber isn't as good in compression as tension, never use it in compression." A lot of current research in aerospace is to produce better manufacturing methods and resins for carbon fibers to phase out aluminum and steel parts. Mostly in tension yes, but compression too, all parts without preloading generally are some degree in compression during their stress lives.
Should he have bought expired carbon fiber for a submarine? No. Is carbon fiber completely absurd in submarine usage? I don't imagine so. Though steel is plenty fine for a submarine, normally the hard part is the sinking by design, not the floating, so weight savings aren't super important.
I have absolutely zero knowledge on deep sea submersibles but every bit of reporting I've read or listened to over the past week has said that carbon fiber is a very poor choice for a deep sea vehicle. Given its propensity to eventually delaminate, it is much more likely to fail over repeated uses than titanium or the other materials the industry uses (I've primarily heard comparisons to titanium).
Delamination is just carbon fiber composites main mode of failure. As long as the material you use is rated for its stress life it's fine. Buying expired material means the resin was decomposing, making the carbon fiber composite more prone to failure.
All materials eventually fail, some have endurance limits with infinite stress lives, like most steels. Some don't, like aluminum. Without knowing the details of their design there's not an easy way to say whether carbon fiber was even a bad choice at all. But buying expired carbon fiber absolutely is a bad idea for anything critical.
The stress life curves for carbon fibers vary a lot, they certainly won't be as nice or long lasting as most metal alternatives, but that just means more replacement or maintenance, something a luxury submarine doesn't necessarily care about as much.