4 ms·

> 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) th

> 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?

jackmott42 3y ago
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.
- Alupis 3y ago
  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...
  - zarzavat 3y ago
    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.
oofbey 3y ago
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.
- hn_throwaway_99 3y ago
  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.

jackmott42 3y ago

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.

Alupis 3y ago
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...
- zarzavat 3y ago
  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.

oofbey 3y ago

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.

hn_throwaway_99 3y ago
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.