Pages 69-80
The 6500m Deep Submergence Research Vehicle is now under construction in Japan. In order to obtain high maneuverability, the Vehicle should be compact in size and light in weight as possible. For this purpose, titanium alloy (Ti-6AI-4VELI) is adapted for the material of the pressure spherical hull. From the viewpoint of weight-strength ratio, titanium alloy is the best candidate for the pressure hull at the present stage, which was already adapted for the pressure vessels of subsidiary use in the 2000m Deep Submergence Research Vehicle "SHINKAI 2000". For a main pressure hull made of titanium alloy, the fabrication procedure was investigated by building a full scale model since there was no prior experience in electron beam welding fabrication so far. The material characteristics before and after fabrication were fully examined and it was confirmed that the fabrication procedure was satisfactory for the present purpose. Collapse behaviour has been examined by the collapsing test using three models of 500mm in diameter made of titanium alloy as described in the first report. Based on these investigation, titanium alloy has been proved to be applicable for the actual structure of the main pressure hull. The collapsing test was carried out with a 1/2.86 scaled model of 700mm in diameter, which was designed after the actual main hull and fabrication following the Procedure described above. The test consisted of two stages; (1) 1500 cyclic pressurization up to 680kgf/cm^2 corresponding to the cyclic submergence to 6500m deep sea within the Vessel's whole life, and (2) collapsing test following ordinary procedure. As a result, it is shown that such cyclic pressurization has no influence on the collapse behaviour, and that the shell fails after the occurence of considerable plastic deformation.
