Objectives Deep-sea pressure hulls are at risk of implosion when subjected to extreme hydrostatic pressures that exceed their ultimate bearing capacities. Therefore, it is essential to investigate the failure mechanisms and shock response characteristics of titanium alloy cylindrical shells under implosion conditions.

Methods First, an independent deep-sea implosion experimental platform was developed, and underwater experiments were conducted on the titanium alloy cylindrical shell in a deep-sea high-pressure environment. A compressible multiphase flow module was then developed to simulate the high-speed motion of the flow field during the underwater implosion. The explicit nonlinear finite element method was employed to analyze the dynamic response associated with the collapse and failure of the titanium alloy cylindrical shell. Finally, the characteristics of the titanium alloy cylindrical shell implosion were investigated, focusing on the fluid-structure interaction mechanism, the evolution of asymmetric shock waves in the multiphase medium, the nonlinear dynamic response of the structure, and the energy balance relationships.

Results The results showed that the titanium alloy cylindrical shell, with a length-to-diameter ratio of 2, collapsed in the first-order instability mode, and the implosion center formed twice successively. As hydrostatic pressure increased, a pronounced migration effect of the first implosion center was observed. Meanwhile, the failure mechanism of the shell transitioned progressively from inward extrusion to inward curling, and the rupture morphology evolved from an arcuate shape to an M-shaped configuration.

Conclusions This study reveals the failure mechanism and shock response characteristics of the titanium alloy cylindrical shell implosion, providing valuable insights for the implosion assessment and protection of deep-sea pressure hulls.