Bending performance of GFRP pultruded profile core sandwich structure reinforced by CFRP sheets

To address the limitations of traditional lightweight core sandwich structures, such as core brittleness and interfacial debonding, this study proposes a novel multi-axial fiber-reinforced pultruded pipe multi cavity cross-section composite beam and examines its mechanical properties under four-point bending loads. The composite beam, consisting of pultruded pipes encased in glass fiber-reinforced composites (GFRP), was prepared by vacuum infusion moulding process and was tested under four-point bending to compare damage modes, load-deflection behaviors, and load-strain relationships. The study further investigated the effects of core arrangement methods and carbon fiber-reinforced composite (CFRP) reinforcement types on the bending performance of the beams. The findings demonstrate that the arrangement of core materials significantly influences the flexural performance of the beam. When four cores are arranged vertically in a cross-shaped configuration, the beam exhibits the highest bending performance. The addition of outer CFRP layers enhances the beam's bending performance, with the semi-wrapped CFRP specimens showing a 7.17 % increase in ultimate load-carrying capacity and a 7.80 % increase in flexural stiffness compared to specimens without CFRP. Fully wrapped CFRP specimens demonstrated improvements of 21.19 % in ultimate load-carrying capacity and 22.08 % in flexural stiffness. Finally, flexural stiffness and load-carrying capacity analytical formulation for sandwich pipe composite beams were derived based on classical beam theory, with an error margin of less than 15 % between theoretical and experimental results.