A novel star-shaped re-entrant circular auxetic honeycomb to enhance in-plane crushing mechanical properties

Auxetic structures exhibited excellent impact resistance, indentation resistance and lightweight properties, while their weakened compression stiffness limited application in vehicle collision protection. This study introduced a novel star-shaped re-entrant circular (SRC) honeycomb, which was achieved by embedding a circular structure into a star-shaped structure and shortening the length of vertical ligaments. A quasi-static crushing test investigated the in-plane compression behavior of the SRC honeycomb. The simultaneous plastic buckling of all cell walls caused the SRC honeycomb to exhibit an “I”-shaped deformation mode , and the compression stiffness was significantly enhanced while maintaining the negative Poisson’s ratio (NPR) effect. A reliable finite element model was established to systematically reveal the deformation mechanism of the SRC honeycomb. Subsequently, theoretical models were established to predict the compression stiffness of the SRC honeycomb, and theoretical equations matched well with numerical simulation results. Under dynamic impact loading , the SRC honeycomb still exhibited an “I”-shaped deformation mode, and SEA was enhanced with an increase in impact velocity while CSE was decreased. The thickness ratio ( δ ) of different types of cell walls significantly regulated the crushing stress efficiency (CSE), compression stiffness ( E ) and specific energy absorption (SEA) of the SRC honeycomb. Compared with those of the elliptical annular re-entrant (EARE) honeycomb with the same relative density, the E and SEA of the SRC- δ honeycomb were enhanced by about 513.04% and 47.4 %, respectively. This design concept of embedded circular structure significantly enhanced compression stiffness and energy absorption capacity , providing a novel design idea for auxetic honeycombs. • A novel star-shaped re-entrant circular (SCR) honeycomb was designed by embedding a circular structure into a star-shaped structure. • Theoretical models were established to predict the compression stiffness of SRC honeycombs with different deformation modes. • Embedded circular structures significantly enhanced the compression stiffness and strength of the SRC honeycombs while maintaining the NPR effect.