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Carbon fiber is wonderful stuff, I machine it all the time. What I’m understanding about it from the engineers I work with is that it’s great stuff for elongation pressures, but the epoxy would want to start failing in a compressive state. The fibers are meant to hold up under expansion just fine, they are tough as hell and won’t stretch at all, it’s why they are so good for high pressure tanks from the inside. These forces are exactly opposite of that, the pressure wants to push the fibers shorter and then the epoxy comes in to hold the shell rigid. I would love to see the FEA analysis of the sub, especially around the Plexiglas portal area. Wouldn’t it be interesting if Ansys or Nastran showed it failing at only 8% or so safety factor instead of something much higher like what OSHA would demand.

If the reports are true, the vessel was almost completely hoop wound carbon fiber tows, which means the vessel had virtually zero strength in the longitudinal direction because there were no carbon fibers in that direction to hold it together. only weak epoxy type resin.

It worked for a few dives because the loads were mostly all in compression but eventually matrix cracking caught up and caused a failure. Had the vessel been subjected to positive internal pressure it would have exploded at a very low pressure

Back in the days when boring 50 year old white engineers were still 20 year old innovators, carbon fiber filament wound pressure vessels were the state of the art for solid fuel rocket motor cases.

They had to be pressure tested before filling with the solid fuel so they were filled with water and pressurized to a thousand or so psi. They had so many leaks due to voids and air pockets from the winding process that some looked like sprinkler heads.

No big deal because they used a rubber liner to seal the leaks which was adequate because the vessels only saw positive internal pressure and they only had to live for a couple of minutes.

Thank you... I am one of those engineers that have designed around the stuff for years. Tensile strength of good CF is up to 150kpi. Compression 0 kpsi. I give this example. Try pushing one end of a rope from the other end. If they had hired an uninspiring 50 year old white dude like me, I would have told them hell no. I would LOVE to get my hands on their 3d model and run it through my FEA software.