Study on the Crushing Modes and Energy Absorption of Foam‐Filled Regular Hexagonal <scp>GFRP</scp> Tubes

ABSTRACT To clarify the effect of polyurethane (PU) foam filler on the failure mechanisms and energy absorption of glass fiber‐reinforced polymer (GFRP) tubes, this study involved the fabrication of regular hexagonal (RH) GFRP tubes filled with PU foams of various densities (ranging from 27 to 80 kg/m 3 ) using compression molding. Quasi‐static out‐of‐plane and in‐plane compression tests were then performed on the tubes using a universal testing machine to analyze their load‐bearing and energy absorption behaviors. The results show that RH‐GFRP tubes exhibit interface debonding and local wall buckling under out‐of‐plane compression, leading to sudden instability and loss of load‐bearing capacity. This is most significant when the compression stroke reaches 70%–80%. For in‐plane compression, the process can be divided into four stages: elastoplastic climb, plastic failure, stress plateau and densification. Here, the higher the density of the filled PU foam, the more it facilitates a smoother transition of the plastic failure stage and accelerates the transition from plateau to densification. Notably, RH‐GFRP tubes filled with 50 kg/m 3 PU foam achieve the best average crushing force, total energy absorption and specific energy absorption in both the in‐plane and out‐of‐plane loading directions. This work provides experimental references for the application of lightweight composite materials in energy‐absorbing components.