Ultimate strength of sandwich elliptical pressure hulls: experimental, numerical and analytical investigations

This study investigates the buckling resistance of sandwich elliptical pressure hulls using experimental, numerical, and analytical methods. The hull, composed of two thin stainless steel faces bonded to a resin core, was fabricated through shell hydroforming. Geometric and thickness measurements confirmed manufacturing accuracy, and hydrostatic testing was performed to evaluate its structural performance. Nonlinear finite-element analysis (FEA) was used to examine the buckling mechanisms and ultimate strength of the hull. The results reveal that the sandwich structure significantly enhances ultimate strength and stability compared to single-layer elliptical pressure hulls. Specifically, the resin core functions as a barrier and stabilizes the structure by redistributing stresses between the external steel faces, which act as the primary load-bearing components. A semi-analytical equation was also developed and validated to predict the ultimate strength of the sandwich hull under hydrostatic conditions, providing a useful tool for structural design.