Enhancing mechanical performance of sandwich structures via uniform and gradient auxetic cores

Auxetic metamaterials have attracted substantial attention as core materials for sandwich structures for advanced lightweight applications due to their unconventional deformation behavior. This investigation studies the nonlinear dynamic response of re-entrant auxetic sandwich panels with various core designs subjected to three-point bending. The examined core designs include pure auxetic and gradient variations of the unit cell wall thickness -vertically and horizontally- across the core. Acrylonitrile Butadiene Styrene (ABS) polymer is chosen as the overall material, due to its high toughness, impact resistance, good processability and suitability for additive manufacturing processes. Finite element simulations were conducted in Abaqus/CAE to evaluate the influence of auxetic core geometry on load distribution, failure behavior, and energy absorption capacity. The numerical models were validated using previously published experimental data from the literature. The results showed that the graded designs improved the distribution of loads and postponed localized failure, thus improving maximum load bearing capacity and energy absorption resulting in enhanced bending performance. The horizontal internal graded configuration exhibited the best mechanical response, achieving a 23.2% increase in maximum load capacity and a 32.8% increase in energy absorption relative to the uniform auxetic core. Furthermore, the gradient effect introduced a progressive deformation mechanism, which induced smoother force-displacement responses alongside decreased stress concentrations. These findings demonstrate that graded auxetic core architectures provide an effective approach for enhancing the mechanical performance of sandwich structures in lightweight engineering applications.