[g1313]

just out of curiosity, are there any engineers here with knowledge of the advantages and disadvantages of constructing deep-sea submersibles with carbon composite materials?

Just an educated layperson, but have been following this pretty closely out of morbid curiosity.

From what I gather, the main advantage in this use case is carbon fiber is lightweight compared to steel or titanium. That's great when you are shooting something into the air or space, but typically not as necessary for sinking to the bottom of the ocean. The real benefit here is having a lighter weight vessel fits on a smaller boat because you don't need a giant crane to launch it. 

Traditionally carbon fiber seems more known for tensile strength (it won't break when you pull it apart) and is not considered optimal for strength under compression. From what I have read it is possible to be used for compression with the correct design, but it is relatively novel and perhaps not well studied.

The big drawback seems to be that it is hard to inspect carbon fiber for fatigue in a non-destructive way, and that difficulty increases with the thickness (in this case five inches).  Also, the design of the Titan is a carbon fiber cylinder with titanium end caps, so the interface between the two materials is a potential failure point.

Finally, to the original point on the cost to society of a rescue effort, this seems like a relative drop in the bucket, I'm sure it is dwarfed by the aggregate cost of other fun, less risky but more common activities (skiing, playing sports, etc). There is already a big disincentive (risking your own life) so I don't think there is some big moral hazard.

[g1313]

just out of curiosity, are there any engineers here with knowledge of the advantages and disadvantages of constructing deep-sea submersibles with carbon composite materials?

Just an educated layperson, but have been following this pretty closely out of morbid curiosity.

From what I gather, the main advantage in this use case is carbon fiber is lightweight compared to steel or titanium. That's great when you are shooting something into the air or space, but typically not as necessary for sinking to the bottom of the ocean. The real benefit here is having a lighter weight vessel fits on a smaller boat because you don't need a giant crane to launch it. 

Traditionally carbon fiber seems more known for tensile strength (it won't break when you pull it apart) and is not considered optimal for strength under compression. From what I have read it is possible to be used for compression with the correct design, but it is relatively novel and perhaps not well studied.

The big drawback seems to be that it is hard to inspect carbon fiber for fatigue in a non-destructive way, and that difficulty increases with the thickness (in this case five inches).  Also, the design of the Titan is a carbon fiber cylinder with titanium end caps, so the interface between the two materials is a potential failure point.

Finally, to the original point on the cost to society of a rescue effort, this seems like a relative drop in the bucket, I'm sure it is dwarfed by the aggregate cost of other fun, less risky but more common activities (skiing, playing sports, etc). There is already a big disincentive (risking your own life) so I don't think there is some big moral hazard.