Compressive creep behavior of spherical pressure hull scale model for full-ocean-depth manned submersible

The phenomenon of room temperature creep in titanium alloys has drawn great attention for decades. With the increasing application of titanium alloys to the manned submersible pressure hull, the traditional calculation and analysis based on strength and stability cannot meet the requirement of structure design and safety evaluation for the spherical pressure hull completely. In this paper, a series of compressive creep tests were performed to reveal the change rule and distribution characteristics for creep behavior of the spherical pressure hull model. Results show that there is no measurable creep strain for pressure hull under maximum operating pressure and steadystate creep appeared in high stress areas of the pressure hull under 1.25 times maximum operating pressure, with the characteristics of internal creep strain and strain rate being greater than the external counterparts. The stress threshold value of the pressure hull model for steady-state creep is 853.7 MPa (equivalent to 0.88Rp0.2), and a creep constitutive equation is proposed based on improved Norton power law model. The results of this paper can provide support for the safety assessment and optimization design of manned submersibles for long-term service.