[83]

This is misleading. Only raw CF is like a rope, once made into a composite with resin it becomes a stiff member with entirely different properties. It's more analogous to a wood beam - very stiff and resistant to bending but once you get past it's limit it cracks.

I suspect the failure mode in a submersible like this isn't so much the carbon fibers themselves but either the carbon > metal interface at the ends or gradual delamination between layers of fibers due to the cyclical pressure loads.

[hef19898]

Under outside pressure, the fibers in the matrix take close to no load, while under tension they take a lot. That alone is the reason why carbon fibre composites are the least suited materials for submarines and submersibles.