Structural design and experimental validation of a titanium alloy hemispherical shell for ultra-deep-sea applications

Abstract

This paper presents a comprehensive investigation into the design, numerical simulation, and experimental validation of an ultra-high-strength titanium alloy hemispherical shell intended for pressure-resistant applications at depth of 11,000 meters. Employing the strength and stability theories of spherical shells, the geometric parameters of the hemispherical structure, flat sealing head, and sealing grooves were determined based on available billet dimensions and experimentally characterized material properties. A finite element model incorporating assembly contact effects and material nonlinear constitutive relationships was developed to simulate the static strength and ultimate load-bearing capacity. To address the critical challenge of sealing the hemispherical shell using a flat head configuration—necessitated by limited billet availability—an innovative flat head geometry incorporating a projecting boss was proposed to resolve deformation mismatch induced by stiffness discrepancies between components. A physical model was fabricated and subjected to hydrostatic external pressure testing up to catastrophic failure. The results demonstrate excellent concordance among theoretical calculations, numerical simulations, and experimental measurements regarding characteristic stresses and failure pressures. The hemispherical shell exhibited a failure pressure of 193.5 MPa, and the fracture morphology revealed both ductile and intergranular characteristics. The research methodology and findings provide validated guidance for analogous engineering challenges in deep-sea pressure hull design.