Flame-retardant sustainable sandwich beams with 3D-Printed peanut-shaped cellular cores and natural composite face sheets: Structural analysis

This study investigates the structural behavior of a novel type of eco-friendly sandwich beam, combining 3D-printed peanut-shaped cellular cores and natural composite face sheets, taking flammability considerations into account. The core was fabricated from polylactic acid (PLA), while the face sheets consisted of flax fabric (FF)/vinyl ester (VE) composites enhanced with flame-retardant additives. The research was guided by two specific aims. The first aim was to explore how the geometric parameters of the peanut-shaped cells influence the bending performance of the sandwich beams. To this end, 25 beam configurations were produced and tested under three-point bending, based on a Taguchi design. A deep neural network (DNN) was subsequently trained on the experimental data to capture the complex load–deflection interactions. The second aim was to evaluate the influence of flame-retardant systems—ammonium polyphosphate (APP) with halloysite nanotubes (HNTs), and APP with magnesium hydroxide (MH)—on the fire resistance and stiffness of the FF/VE composites used as face sheets, and, consequently, on the global structural response in buckling, vibration, and bending, from a theoretical perspective. Cone calorimetry tests and theoretical analyses revealed that FF/VE face sheets with 3 % APP +6 % HNT achieved superior flame resistance, while those with 3 % MH + 3 % HNT provided an optimal balance between fire safety and mechanical performance, making them the preferred choice for multifunctional applications.