The problem is the use of CF and titanium. Traditionally you’d machine a big block of titanium into a hollow sphere for sub’s pressure chamber to withstand that much pressure. The Titan is different in that it’s a cylinder with hemisphere plugs. While many submarines have used this shape these other submarines also a) doesn’t dive anywhere nearly as deep and b) aren’t using 2 different materials (titanium caps and CF cylindrical body).
Other deep dive subs use a spherical pressure vessel because it is the most efficient use of material to withstand the pressure at the sea floor. The trade off is that you have a lot less internal volume. While you can probably design something by with a tube and cap shape to withstand that load, the joint between the cap and the tube needs to be carefully design and built, and will likely need to be reinforced to withstand the same pressure. Doing this all out of titanium is probably prohibitively expensive for a startup company, you can probably machine a shape like that without a joint as well but that’s likely to be even more prohibitively expensive than trying to join them.
The titan tried to cut that cost by using CF composites for the tube section instead but I have serious reservations about how it’s used here. This is because the primary load from water pressure on a sub is compression, carbon fiber’s primary strength is in tension. So you need to build the structure in a way that translate the huge compression load into tension to best take advantage of the CF. If you don’t then it’s a waste of material and you probably could build the sub more efficiently (mechanics of material wise) with a different material. As expensive as CF is, it’s probably whole heck of a lot cheaper to build the cylindrical section out of CF than Titanium. Of course they pay that price with a dubious ability to meet their requirements of surviving multiple trips to a depth of 4km.
From what I've heard, even pristine unexpired carbon fiber would have been a bad choice for a sub.
Yeah I can't find the interview, but James Cameron recently said that it's because carbon fiber isn't a single "material" or something, and that it can't withstand nearly as many repeated dives as steel can.
I was used to sub meaning submissive, then I had to learn it's also subreddit, I wish the submarine stuff would go away already
The main one is the resin that is bring used, that will have a shelf life like paint or glue as the solvent will evaporate. The second one is fibre primers that are used to help the resin integrate with the Carbon Fibers can degrade and cause improper bonding between the fibres and layers. For fabrics this is normally over a year but for prepregs (where the resin already in the fibres but not set) is generally a year and will need testing for a longer shelf life.
Another issue is the storage you want a cool dry environment and covered to avoid contamination from other rolls/prepregs. Additionally the other thing that worries me is although salt water is not an issue to the fibres and resins themselves when you add metal to them the salt acts as an electrolyte and will cause galvanic corrosion "rusting" away the fasteners and causing damage to the fibres in that area.
Not to mention Carbon Fiber is best for coaxial (along the length of the tube) tension not hoop (around the tube) compressive forces. And differences in the layup and curing process can impact the viability of the final part which is why lots of places will weigh the resin and have a procedure to soak the fibres and lay them up as well as sensors to keep the pressure and temperature with a margin for curing, to keep the variability between the parts minimal.
Trust me I'm an Engineer
The more information that comes out the dumber they all sound for going, I guess they thought with the owner going out would be safe. Oops.
