4 ms·

Carbon Fiber just isn't suited for submarine type of loads. It really doesn't like being compressed, and it tends to give you no warning before snapping.

by 6SixTy 1y ago

potato3732842 1y ago
"Isn't suited" is a stretch. They still managed to make a few good dives with it despite comically bad decisions in just about every key area. Imagine what a well funded company with experience in CF, robust QC and non-laughable operating procedures could do. It's not ideal on a first pass analysis in the same way concrete can't to shit in tension yet with a bunch of carefully placed steel and number crunching magic it works great. I think they proved that CF has the same potential. A more serious attempt could likely work in some capacity.
- watwut 1y ago
  Around 23 plunges into the target depth with two different hulls both failing is not all that great result.
caffeinated_me 1y ago
This isn't the first carbon fiber submarine, although it is the first manned one. The US Navy tried out an unmanned model in the 80s, and got much better results- they were expecting at least 1000 successful dives before stress fatigue was an issue. Here's a detailed report on it. Pages 32-33 has their take on material analysis, probably the most relevant to this failure https://apps.dtic.mil/sti/pdfs/ADA270438.pdf https://apps.dtic.mil/sti/pdfs/ADA270438.pdf I'm personally more suspicious of oceangates manufacturing process than the material, but I'm far from an expert here.
- Retric 1y ago
  It’s the unpredictable nature of failure that’s at issue here. For unmanned subs it doesn’t matter if 10% of failures occur well below the expected lifespan but that’s a huge issue for manned subs.
- Aunche 1y ago
  Being manned is a major difference. Humans need a lot of space. Pressure grows with volume, which is cubic, but the hull grows with area. You can also submerge components in oil, which is much better at resisting pressure than air.
  - jjk166 1y ago
    Pressure doesn't grow with volume. The exterior design pressure is constant. The stress on the wall scales linearly with the diameter. Making submarines bigger actually makes it easier because the buoyancy scales cubically with the volume while the weight scales linearly with the perimeter, so the larger the submarine the thicker the walls can be.
    - Retric 1y ago
      There’s several kinds of scaling involved, once the radius increases enough thicker walls are less efficient than internal bracing. It’s impractical to build something like an Ohio class submarine that can reach the bottom of the Mariana Trench when you also want multiple internal compartments in case of damage.
      - jjk166 1y ago
        Internal bracing is to resist buckling. You need it as your cylinder gets longer (as military subs tend to be), but has nothing to do with the diameter. It's also good for torsional strength, which is not really a concern for a pressure vessel but is important for a ship that's going to be in the actual ocean. But for just resisting pressure, once your diameter exceeds 20 times the wall thickness, the relationship is linear. You can get better efficiency with multiple spherical pressure vessels joined together over a cylindrical vessel, as spherical pressure vessels better distribute the loads than cylinders. This is done in some particularly deep diving military subs, which are then surrounded by an unpressurized cylinder for hydrodynamics.
        Retric 1y ago
        Even with a spherical sub the diameter impacts a lot of things. For example a large sphere sees significantly lower pressure across the side facing the surface than the side facing the sea floor.
- jerlam 1y ago
  I'm not even sure it's the first manned carbon fiber submersible. Deepflight Challenger [...] is the first deep-diving sub to be constructed with a pressure hull (central tube portion) of carbon fibre composite, built by Spencer Composites for HOT. Its carbon fiber design would later influence the tube for the sub Titan,[12] which imploded... https://en.wikipedia.org/wiki/DeepFlight_Challenger https://en.wikipedia.org/wiki/DeepFlight_Challenger
  - esprehn 1y ago
    Notable from that page is this paragraph though: """ Based on testing at high pressure, the DeepFlight Challenger was determined to be suitable only for a single dive, not the repeated uses that had been planned as part of Virgin Oceanic service. As such, in 2014, Virgin Oceanic scrapped plans for the five dives project using the DeepFlight Challenger, as originally conceived, putting plans on hold until more suitable technologies are developed. """
jjk166 1y ago
Carbon fiber is actually a pretty good material for submarine type loads. Submarines have to balance their need for an extremely strong hull with the need for buoyancy. For a given size, to make your hull stronger, you must make your walls thicker, which makes you heavier. The only options are to make the sub bigger, increasing the internal volume, or making the hull out of something with a better strength to weight ratio, or more accurately a better strength to specific gravity ratio. In carbon fiber composite, it's actually the epoxy which provides the compressive strength, and while it has very good compressive strength, the real advantage is its very low density. It is only just barely denser than water, so you can make your hull extremely thick with essentially no loss in buoyancy. Carbon fiber does fail catastrophically, but they could have just made the hull so thick that they were never getting anywhere near the failure point. Further, since carbon fiber is built up in plied layers, you don't have the same sorts of processing limits as with thick metal plates. The basic concept of Titan was sound, it was just horribly horribly executed. With their flagrant violation of basic engineering and safety practices, they would have killed people no matter what they made their sub out of.

Carbon Fiber just isn't suited for submarine type of loads. It really doesn't like being compressed, and it tends to give you no warning before snapping.

by 6SixTy 1y ago

Carbon Fiber just isn't suited for submarine type of loads. It really doesn't like being compressed, and it tends to give you no warning before snapping.

potato3732842 1y ago

"Isn't suited" is a stretch. They still managed to make a few good dives with it despite comically bad decisions in just about every key area. Imagine what a well funded company with experience in CF, robust QC and non-laughable operating procedures could do. It's not ideal on a first pass analysis in the same way concrete can't to shit in tension yet with a bunch of carefully placed steel and number crunching magic it works great. I think they proved that CF has the same potential. A more serious attempt could likely work in some capacity.

watwut 1y ago
Around 23 plunges into the target depth with two different hulls both failing is not all that great result.

caffeinated_me 1y ago

This isn't the first carbon fiber submarine, although it is the first manned one. The US Navy tried out an unmanned model in the 80s, and got much better results- they were expecting at least 1000 successful dives before stress fatigue was an issue. Here's a detailed report on it. Pages 32-33 has their take on material analysis, probably the most relevant to this failure https://apps.dtic.mil/sti/pdfs/ADA270438.pdf https://apps.dtic.mil/sti/pdfs/ADA270438.pdf I'm personally more suspicious of oceangates manufacturing process than the material, but I'm far from an expert here.

Retric 1y ago
It’s the unpredictable nature of failure that’s at issue here. For unmanned subs it doesn’t matter if 10% of failures occur well below the expected lifespan but that’s a huge issue for manned subs.
Aunche 1y ago
Being manned is a major difference. Humans need a lot of space. Pressure grows with volume, which is cubic, but the hull grows with area. You can also submerge components in oil, which is much better at resisting pressure than air.
- jjk166 1y ago
  Pressure doesn't grow with volume. The exterior design pressure is constant. The stress on the wall scales linearly with the diameter. Making submarines bigger actually makes it easier because the buoyancy scales cubically with the volume while the weight scales linearly with the perimeter, so the larger the submarine the thicker the walls can be.
  - Retric 1y ago
    There’s several kinds of scaling involved, once the radius increases enough thicker walls are less efficient than internal bracing. It’s impractical to build something like an Ohio class submarine that can reach the bottom of the Mariana Trench when you also want multiple internal compartments in case of damage.
    - jjk166 1y ago
      Internal bracing is to resist buckling. You need it as your cylinder gets longer (as military subs tend to be), but has nothing to do with the diameter. It's also good for torsional strength, which is not really a concern for a pressure vessel but is important for a ship that's going to be in the actual ocean. But for just resisting pressure, once your diameter exceeds 20 times the wall thickness, the relationship is linear. You can get better efficiency with multiple spherical pressure vessels joined together over a cylindrical vessel, as spherical pressure vessels better distribute the loads than cylinders. This is done in some particularly deep diving military subs, which are then surrounded by an unpressurized cylinder for hydrodynamics.
      - Retric 1y ago
        Even with a spherical sub the diameter impacts a lot of things. For example a large sphere sees significantly lower pressure across the side facing the surface than the side facing the sea floor.
jerlam 1y ago
I'm not even sure it's the first manned carbon fiber submersible. Deepflight Challenger [...] is the first deep-diving sub to be constructed with a pressure hull (central tube portion) of carbon fibre composite, built by Spencer Composites for HOT. Its carbon fiber design would later influence the tube for the sub Titan,[12] which imploded... https://en.wikipedia.org/wiki/DeepFlight_Challenger https://en.wikipedia.org/wiki/DeepFlight_Challenger
- esprehn 1y ago
  Notable from that page is this paragraph though: """ Based on testing at high pressure, the DeepFlight Challenger was determined to be suitable only for a single dive, not the repeated uses that had been planned as part of Virgin Oceanic service. As such, in 2014, Virgin Oceanic scrapped plans for the five dives project using the DeepFlight Challenger, as originally conceived, putting plans on hold until more suitable technologies are developed. """

jjk166 1y ago

Carbon fiber is actually a pretty good material for submarine type loads. Submarines have to balance their need for an extremely strong hull with the need for buoyancy. For a given size, to make your hull stronger, you must make your walls thicker, which makes you heavier. The only options are to make the sub bigger, increasing the internal volume, or making the hull out of something with a better strength to weight ratio, or more accurately a better strength to specific gravity ratio. In carbon fiber composite, it's actually the epoxy which provides the compressive strength, and while it has very good compressive strength, the real advantage is its very low density. It is only just barely denser than water, so you can make your hull extremely thick with essentially no loss in buoyancy. Carbon fiber does fail catastrophically, but they could have just made the hull so thick that they were never getting anywhere near the failure point. Further, since carbon fiber is built up in plied layers, you don't have the same sorts of processing limits as with thick metal plates. The basic concept of Titan was sound, it was just horribly horribly executed. With their flagrant violation of basic engineering and safety practices, they would have killed people no matter what they made their sub out of.