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Carbon fiber is a great material for certain things like skis and bike frames. A submersible vehicle just isn't one application where carbon fiber is useful. The reason is the material micro fractures under stress. Sure, it's extremely strong. It's also very brittle. Every time it's put under extreme pressure, it flexes and creates new micro fractures. For skis and bike frames, this only becomes a problem after many years of use. Then the integrity starts to fail gradually.

In the case of the submersible, the failure will suddenly occur with no warning.

Carbon fiber is a great material for certain things like skis and bike frames. A submersible vehicle just isn't one application where carbon fiber is useful. The reason is the material micro fractures under stress. Sure, it's extremely strong. It's also very brittle. Every time it's put under extreme pressure, it flexes and creates new micro fractures. For skis and bike frames, this only becomes a problem after many years of use. Then the integrity starts to fail gradually. In the case of the submersible, the failure will suddenly occur with no warning.

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[–] • 2 pts (edited )

Yep. CF is guaranteed to catastrophically fail for this use case. It is not an appropriate material based on material science and the repeated forces it would resist. It would continuously develop fatigue fractures until it reaches the point of material failure. Material failure means death in the span of milliseconds, if at depth.

[–] • 1 pt

Another problem with it is that the development of fatigue fractures is stochastic, so the progression to failure is virtually unpredictable, as opposed to something more traditional like steel, where the failure modes under stress (from elastic deformation through plastic deformation to failure are well know and predictable). Although, in these extreme environments, any plastic deformation of a steel pressure vessel would also likely end in catastrophic failure.