My suspicion as to what caused the Titan disaster

[jmowreader]

Well...apart from the insanity of getting in such a thing and diving two miles below the surface of the ocean.

This vessel made something like 50 dives, many of them to the Titanic. The water pressure at Titanic depth is 5625 psi. By comparison, water will compress by one percent of its volume at the relatively low pressure of 3000 psi. Hence, this thing was at a depth high enough to compress something normally considered absolutely incompressible.

Titan's pressure hull was made of 660 layers of filament-wound carbon fiber. What that means is they got a big pipe or something that was the outside diameter of the inside of the pressure hull, coated it with something epoxy won't stick to, and put it in a machine that will rotate it at a certain number of revolutions per minute. This pipe would be called a mandrel. They then got a roll of carbon fiber, and wound the filament onto the mandrel through a machine that coated the filament in epoxy until the winding was as long as they needed it to be. Epoxy is used because it's the only thing that'll stick to carbon fiber. Once they get to the end of the winding they put a new roll of CF onto the machine and wind it back the other direction. Do this over and over until you have 660 layers of CF on the mandrel. After doing all this they stick the mandrel and its layer of CF into an autoclave to cure it. At the end of the curing cycle they pull out the mandrel and have a pressure hull.

This is a video of them making a Boeing 787 fuselage section the same way.

Filament-wound carbon fiber is used for many things like making bicycle forks. It is a proven and reliable technology.

Now for the problem: Epoxy is not flexible. At the depths this boat operated, it was going to compress at least slightly. US Navy submarines compress at their operating depth, which is far shallower than Titan worked at. Repeated compression and expansion is going to abuse the epoxy, and at some point the abuse is going to get severe enough that the epoxy in the CF matrix will fail. Unfortunately for five rich people, this failure happened at the worst possible time - when the boat was two miles below the surface.