Three-plateau smooth crushing responses of a bio-inspired double re-entrant combined honeycomb

Inspired by the butterfly profile, a novel hybrid double re-entrant combined structure (DRCS) has been designed to exhibit high energy absorption characteristics across the three plateaus. The two convex angles of the hexagonal lattice overlap with the two re-entrant angles, allowing for a smooth transition between plateaus. Two types of DRCSs are constructed by considering right (DRCS-I) and obtuse (DRCS-II) angles, respectively. Numerical simulations indicate that, under low-velocity crushing conditions, the introduction of a smooth re-entrant structure enables DRCS-I to undergo a three-step deformation mode, corresponding to three distinct plateau stresses. The stress–strain curves exhibit a smooth rise during the transition between plateaus, with no abrupt pulse-shaped peak stress variations, as anticipated. Moreover, the right-angle effect introduced by DRCS-I induces a staircase-shaped rise in the stress–strain curve, and the average plateau stress is 1.95 times that of DRCS-II in the second stage. As for medium-velocity crushing, DRCS-I exhibits a two-step deformation mode, with the average plateau stress in the second stage being 1.38 times that of DRCS-II, while the right-angle effect still plays a stable role. For high-velocity crushing, the right-angle effect causes the stress–strain curve to oscillate gently due to the presence of the vertical strut. Furthermore, based on energy conservation theory, it is revealed that the higher average plateau stress and specific energy absorption (SEA) characteristics of DRCS-I depend on its novel right-angle structural design, unique three-step deformation mode, and plastic hinge dissipation.