A flexible concentric coupled re-entrant-star composite structure with an enhanced negative Poisson's ratio and mechanical strength

Abstract

The flexible concentric coupled re-entrant-star (CCRS) composite structure is proposed to address premature instability of re-entrant honeycomb (RH) and the limited load-bearing capacity of star-shaped honeycomb (SH) with a flexible structure. To elucidate deformation mechanisms, mechanical performance, and Poisson’s ratio response, systematic comparative studies between CCRS and conventional RH and SH were conducted, including uniaxial tension and cyclic loading. CCRS simultaneously exhibits a pronounced negative Poisson’s ratio of -0.7 and markedly enhanced mechanical performance, outperforming RH by approximately 1.5 times and SH by about 3 times, while maintaining high deformability with fracture elongation exceeding 1060% and stable cyclic recovery of about 96% even at a strain of 180%. These performance enhancements arise from an inner star-shaped unit that drives lateral expansion at low strain and an outer re-entrant hexagonal unit that provides load-bearing constraint at high strain, thereby producing more uniform stress distribution and suppressing local buckling. Consequently, CCRS offers an effective design strategy for architected soft matter systems requiring large deformation and enhanced load-bearing capacity.