Implosion collapse of externally pressurized steel/CFRP/titanium cylindrical shells with a hybrid sandwich thin-walled structure

A steel/CFRP/titanium cylindrical shell with a hybrid sandwich structure was proposed, designed, fabricated and hydrostatically experimented. Subsequently, to evaluate the collapse load of such hybrid sandwich structure under external pressure without excessive computational cost, an analytical formula was derived in this study. The rationality of the derived formula was verified by the comparison with experimental and numerical investigations. The hybrid sandwich structure comprised an inner steel metallic layer, a CFRP core layer, and an outer titanium foil metallic skin layer. To determine the contribution of the sandwich structure to the loading capacity, this study compared the loading capacity of the hybrid sandwich shells with that of single-layer steel cylindrical shells. Three nominally identical multilayer cylindrical shells with a sandwich structure and three nominally identical single-layer cylindrical shells were fabricated. The dimensions of these shells were measured, and the shells were subjected to hydrostatic testing. Moreover, theoretical and numerical analyses were performed to evaluate the collapse properties of the fabricated shells. The experimental, theoretical, and numerical data of this study agreed with each other and suggested that the loading capacity of the multilayer shell samples was considerably higher than that of the single-layer shell samples. Additionally, the structural efficiency of the hybrid sandwich shell samples was approximately 141.9 % higher than that of the single-layer samples.