Load-bearing capacity improvement and failure mechanisms of integrated multi-cell sandwich hybrid tube under lateral deformation

In this study, an integrated multi-cell sandwich hybrid (MCSH) tube with foam filling and localized thickness enhancement is proposed and fabricated using an internal thermal expansion forming process. Systematic three-point bending and lateral compression tests reveal that increasing the number of internal cells significantly enhances the load-bearing capacity and failure stability, achieving a desirable balance between stiffness and toughness. Under three-point bending, the triple-cell sandwich hybrid (TCSH) tube exhibits a structural stiffness of 4.2 kN/mm and crush force efficiency (CFE) of 96.22 %, surpassing most previously reported structures. Finite element simulations further indicate that the multi-rib design activates the responses of both the top and bottom flanges, forming symmetric shear paths and establishing a multi-path load transfer mechanism. The MCSH tube demonstrates a combination of high stiffness, superior energy absorption (EA), and structural lightweighting. The rib structure effectively alleviates stress concentration, delays interfacial debonding and shell buckling, and promotes a transition from localized failure to multi-stage progressive damage mode. The MCSH tube exhibits outstanding performance in terms of load-bearing, specific energy absorption, damage delay, and lightweight design, offering theoretical foundations and design insights for high-performance composite structures in protection, transportation, and aerospace applications.