Fiber-reinforced composites are basically analogous to spaghetti dispersed in glue. Really strong in tension, when the (in this case, carbon) fibers are taking nearly all of the load. In compression, the fibers have nearly zero resistance to flexure, and the load is mainly being taken up by the glue (the matrix, in composite-speak). When the fiber/matrix interface fails due to fiber flex-induced shear force, you're done.
I just can't imagine why a submersible structural designer would select composites for this application. IMHO, this project was doomed from the moment of that design decision, even setting aside all the other idiocy.
Well the "glue" in this case is actually a very good material for the application. Epoxy has compressive strength comparable to structural steel, and more importantly its density is almost the same as water. This means you can make incredibly thick walls for a small internal volume while remaining buoyant. It also resists biofouling and corrosion, which is why it's popular in other marine applications.
Submarines of this size should be using composites, once sufficient data is gathered on their behavior to develop proper factors of safety. The issue was all the idiocy that came after. This team was going to kill people no matter no matter what they made the sub out of.
> I just can't imagine why a submersible structural designer would select composites for this application
Maybe it's easier to imagine if you consider the designer in question not as a submersible structural designer per se, but rather a nepo baby cosplaying as one.
I just can't imagine why a submersible structural designer would select composites for this application. IMHO, this project was doomed from the moment of that design decision, even setting aside all the other idiocy.