Collapse Strength of Spherical Pressure Hull for Deep Submergence Research Vehicle Made of Titanium Alloy

Abstract

Titanium alloy is one of the best candidate for the pressure sphere of a Deep Submergence Research Vehicle. The authors applied the material (Ti-6AI-4V ELI) for the medium scale pressure vessels of "SHINKAI 2000". In the case of a large scale pressure sphere of about 2m in diameter, and of about 70mm in thickness, a technical limit prevented the material from application, such as the manufacturing process of heavy thickness plate and hot forming. With the response to the requirement of a large scale material today, the pressure sphere made of titanium alloy has come to a real structure in Japan. The authors have already established the manufacturing process of the titanium sphere by building a full scale model in the field of hemisphere fabrication, precise machining, electron beam welding, and of nondestructive testing. In this report, the authors have investigated the collapse behaviour of titanium alloy spheres using 3 machined models, and also confirmed the current design procedure to be reasonable. In addition the authors have investigated the influence or room temperature creep on the collapse behaviour by the model test of 160 hours continuous loading under 105% of design pressure, and by the simulation analysis using the elastic plastic large deformation analysis with the finite element method. As a result, the current design procedure is also reasonable for titanium alloy and as long as the procedure is applied, the room temperature creep is not necessary to be considered in design. This result, combined with the former established of fabrication procedure, confirmed the titanium alloy (6AI-4V ELI) to be effective for the pressure sphere of the Deep Submergence Research Vehicle in Japan.