5 ms·
Carbon fiber is used because it is rigid. The failure mode for a member in compression is buckling, which is resisted by stiffness, not strength. It's also a
by CarVac 3y ago
Carbon fiber is used because it is rigid.
The failure mode for a member in compression is buckling, which is resisted by stiffness, not strength.
It's also a lot easier to make a huge thick tube out of composites than out of titanium. That's why only the spherical ends are titanium, and the middle tube part is CF.
- marksmithhfx 3y agoPoor design choice. Too many materials expanding and contracting at different rates leads to friction stress and ultimate material failure. Maybe not at first, but over repeated compression and expansion cycles.
- floxy 3y ago>The failure mode for a member in compression is buckling, which is resisted by stiffness Hmm, this is probably the right answer. When things start to buckle, you'd be putting part of the surface in tension, which would be resisted by the fiber. I would definitely be very interested to see the plots of strain gauges embedded throughout the thickness of the wall as it goes to depth (in all three axes, hoop, radial, and axial). My intuition completely fails here. Good thing I'm not making submersible vehicles.
- CarVac 3y agoOnce buckling occurs, it hardly matters what's in compression and what's in tension: the applied force has a tremendous mechanical advantage over the material strength resisting it once the stiffness fails to prevent it from crossing a threshold. Secondly, CF does substantially improve compressive strength over neat resin, which would fail in shear. The fibers individually may not withstand compression, but embedding them in the epoxy resin prevents them from buckling and the composite material exhibits substantially improved performance over either base material. The exception is tensile stress that causes delamination, for which there is no benefit over the neat resin.
- jacquesm 3y agoIt would be a good thing if the people who did make this contraption also didn't make submersible vessels based on the bits and pieces that have made it into the news so far. This sounded like an accident waiting to happen. At those pressures if something goes wrong it will crumple like a tin can and having the hatch sealed from the outside means that even if they didn't die at depth they may not have a way out if their comms have failed. The whole thing strikes me as beyond irresponsible. I wonder if the people that built the sub would take it to depth.
- Yeroc 3y agoWell it seems like the President and CEO of the company was onboard the craft so I suppose the answer is "yes".
- jacquesm 3y agoI highly doubt he built the sub.
- wnkrshm 3y agoThey copied the glass fiber + titanium rings idea from the Deepflight Challenger that Virgin wanted to dive with. [0] Virgin deemed the design not safe enough for more than a single dive and quietly scrapped the diving events: "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." [1] [0] https://www.compositesworld.com/articles/composite-submersibles-under-pressure-in-deep-deep-waters https://www.compositesworld.com/articles/composite-submersib... [1] https://en.wikipedia.org/wiki/DeepFlight_Challenger https://en.wikipedia.org/wiki/DeepFlight_Challenger
- jacquesm 3y agoThat makes very good sense. Pity they didn't copy the conclusion too.
- 3y ago