RESEARCH ON FABRICATION PROCEDURE OF SPHERICAL PRESSURE HULL MADE FROM TITANIUM ALLOY FOR DEEP SUBMERGENCE RESEARCH VEHICLE

As a new project for a deep submergence research vehicle following the SHINKAI 2000, a concept for a 6,000 m vehicle is now under consideration in Japan. One of the main design problems for such a vehicle is the reduction of the weight to achieve the desired manoeuvrability and operational efficiency. A pressure hull material with a high strength to density ratio is indispensable for this application. Titanium alloy (6 A1 -4 V ELI) has been utilised with success in construction of the small pressure vessels of SHINKAI 2000. In the present work, a full-scale model of a titanium alloy pressure hull was built to establish a fabrication procedure. Subsequently, by disassembling the model, the authors have investigated the material characteristics as to their suitability for a deep submergence vehicle. The research covered the fields of mechanical properties, fracture toughness, fatigue strength, stress corrosion cracking, etc. The results confirm titanium alloy 6 A1-4 ELI to be one of the most effective materials for the pressure hull of a deep submergence research vehicle.