Low velocity impact behavior of natural fiber-reinforced sandwich composites with date palm fiber cores

Worldwide consumption of synthetic polymer foams in sandwich structures poses a threat to environment. As a sustainable alternative, this study addresses this challenge by reinforcing the polyurethane (PU) foam core natural-fiber reinforced sandwich composites (NFRSCs) with date palm fiber. This approach reduced PU foam consumption by about 33–35% and improved energy absorption by ∼20%. Five sandwich configurations with reinforced (FD, PD, ED) and unreinforced (FF, PF) cores were fabricated and tested under 4 J and 10 J impact energies. A high-speed camera-based image processing method was developed to track impactor displacement and estimate peak force and energy absorption, showing excellent precision with a mean error of 0.69% (range −0.49% to +2.50%) relative to accelerometer-based measurements; the method was further validated using root-mean-square-error and area-under-curve comparisons of the force–time histories. At 10 J, only date palm fiber-reinforced cores sustained the impact, with FD exhibiting the highest normalized peak force and absorbed energy, along with minimal scatter, attributed to its integrated core–skin structure. At 4 J, FD again showed superior energy absorption. Scanning electron microscopy (SEM) of the damaged regions beneath the impactor showed that FD samples exhibited core-dominated shear plasticity with intact skin–core interfaces, whereas PD, ED, and PF samples exhibited pronounced skin–core debonding and localized fracture, providing microstructural evidence for the superior performance of the integrated fabrication route. The results demonstrate that combining natural fiber reinforcement, optimized fabrication, and image-based, SEM-corroborated damage characterization can enhance impact performance while promoting material efficiency and structural reliability.