A review on energy absorption performance of auxetic composites with fillings

Auxetic materials have garnered significant attention due to their lightweight and excellent energy absorption capabilities. Nonetheless, they often display relatively lower stiffness when compared with conventional materials. To address this limitation and enhance their mechanical properties, researchers have explored various avenues, including designing hybrid auxetic structures by combining two or more auxetic unit cells and developing auxetic composites using multiple materials. While previous reviews extensively covered hybrid auxetic structures, discussing their classification, design methodologies, fabrication techniques, applications and mechanical behaviours, there has been a noticeable gap in the literature concerning auxetic composites with fillings. Therefore, this paper concentrates on auxetic composites with fillings, delving into their classifications, mechanical responses, and underlying mechanisms. This review article also critically examines different design factors that influence the performance of auxetic composites and compares them with conventional counterparts in terms of mechanisms and mechanical properties. Overall, auxetic composites exhibit superior mechanical characteristics compared to equivalent conventional materials. However, several challenges and limitations persist regarding the design, fabrication, and applications of auxetic composites.