US Navy heavy-section titanium submarine program

Ti-100 is the Navy alloy for titanium submersibles; same ratio-analysis story as steel, with one-inch critical flaw size at the strength of interest. "They've never had the money to build" — program never executed.

Titanium. The Navy was interested in titanium for submarines, so they did the same thing. Now we're up at about sixty percent of the strength of steel in terms of both toughness and strength, and you still have the one-inch critical flaw size. Ti-100 is the Navy alloy for titanium submersibles, which they've never had the money to build. You have this same analysis in terms of critical flaw size if you want to go to 180 ksi strength. Titanium sheets, if you go back, have a much higher toughness. The thin titanium sheets we put on fancy aircraft now have a much higher toughness than the plane strain fracture toughness. All these ratio-analysis diagrams are for the plane strain fracture toughness — thick stuff for building submarines, basically.