Layup angle effects on the damage and fracture behaviour of fibre composite foldcore sandwich structures under impacts

The S-shaped foldcore structure, an evolution of the V-shaped foldcore, offers enhanced energy absorption and impact resistance. Due to the complexity of the foldcore and the strong anisotropy of the fiber material, the fiber laying angle significantly influences the foldcore's performance. This study investigates the effect of the fiber lay-up angle on the S-shaped foldcore's anisotropy by fabricating foldcore sandwich composite panels using hot compression molding. Panels were laid along the in-face folding direction, the out-face folding direction, and cross-laid in both directions. A low-speed impact method was used to observe and analyze the damage to the foldcore structure. The impact process was also simulated using the finite element method combined with the Hashin's criterion as a means of identification of material failure initiation to analyze the damage and fracture process. Results showed that the composite foldcore sandwich panel laid along the in-face folding direction exhibited the strongest impact resistance. Panels laid in the in-face folding direction were more prone to fracture due to higher damage levels, while those with fibers in the out-face folding direction were more susceptible to fiber tensile damage, causing more fracture in rear panel. © 2025 The Author(s)