Sustainable auxetic honeycomb sandwich cores: Effects of palm fiber reinforcement on compressive properties

Auxetic honeycomb structures (AHSs) are increasingly recognized in lightweight engineering applications for their negative Poisson's ratio (NPR) and excellent energy absorption capacity (EAC). However, limited research has examined sustainable, bio-based auxetic sandwich cores reinforced with natural fibers, particularly Chamaerops humilis fibers ( Ch Fs). This study experimentally investigates and optimizes bio-based auxetic honeycomb sandwich cores reinforced with Ch Fs, addressing a breach in the present literature. Mechanical and auxetic execution were systematically optimized using a combined Taguchi procedure and Response Surface Methodology (RSM). Re-entrant honeycomb cores were fabricated via three-dimensional printing utilizing polylactic acid and then infiltrated with bio-based epoxy compounds containing varying Ch F loadings (10–40 w t.%) and core thicknesses ( T , 2–5 mm). The effects of such design factors on compressive stress ( σ c ), compressive strain ( ε c ), EAC, and Poisson's ratio ( ν ) were evaluated during compression testing. Statistical optimization using the Taguchi method, analysis of variance, and RSM identified optimal design parameters and enabled the development of predictive models. The optimal configuration, comprising 30 w t.% Ch Fs and a 5 mm core thickness, achieved the highest σ c (119.29 MPa) and superior EAC. All fabricated structures exhibited NPRs, confirming stable auxetic behavior. Scanning electron microscopy revealed a comparatively regular fiber distribution at the optimal reinforcement level. It also identified matrix cracking, fiber pull-out, fiber fracture, and interfacial debonding as the primary failure mechanisms. Such results elucidate the possibility of Ch F-reinforced AHSs as potential, lightweight sandwich-core materials for aerospace, transportation, and civil engineering applications that require enhanced compressive strength, EAC, and auxetic performance.