Approximate analytical buckling model for capsule-shaped honeycomb-sandwich subsea shells under external pressure

Capsule-shaped pressure shells are widely employed in subsea energy development, and honeycomb-sandwich composite shells have significant advantages in enhancing buckling resistance for ultra-deepwater applications. In the published papers, the buckling behavior of cylindrical and spherical shells has been widely investigated, while the case of capsule-shaped honeycomb-sandwich composite shells has received less attention. The present paper presented a new approximate analytical model for buckling analysis of capsule-shaped honeycomb-sandwich composite shells subjected to uniform external pressure. The effect of the hemispherical shell on the cylindrical shell was equivalent to elastic restraint at the sphere–cylinder connection joint, so the problem was transformed into solving the buckling of a honeycomb-sandwich composite cylindrical shell with equivalent elastic boundary restraint subjected to uniform external pressure. Analytical solutions for the critical buckling pressure were obtained using the generalized Galerkin method, considering transverse shear and edge-curvature. The accuracy of the new model was well verified by finite element results. Parametric results showed that increasing the radius from 400 to 600 mm reduced the critical pressure by 75.2%, whereas increasing the wall thickness from 46 to 54 mm raised it by 86.1%. The formulas provided an efficient tool for buckling evaluation and preliminary design of capsule-shaped subsea composite shells.