Impact Response and Efficiency Based Ranking of Auxetic - Conic Hybrid Sandwich Composites Under Normal Impact Loads

Abstract

Composite materials continue to reshape modern engineering by enabling deliberate manipulation of impact response through their geometric and material tailoring. Sandwich composites particularly allows variations in core geometries for different deformation modes under dynamic loading. Presented here is the High Velocity Impact behaviour of a class of hybrid auxetic - conic sandwich cores. Re-entrant hexagonal topology is combined with parametric conic profiles for building cores in sandwich composites. Auxetics are known for their negative Poisson’s ratio. They offer valuable deformation kinematics in impact processing. Combining auxetic core configuration with conic wall profiles, defined by a conic parameter ρ, induces graded stiffness and progressive damage patterns. These hybrid mechanisms, which are by virtue of core geometries, are useful for efficient conversion of impact energy to composite internal energy. This enables processing of the impact by the composites through absorption of the energy rather than transmission of it.

Four layered hexagonal re-entrant auxetic cores further modified to conic profiles ρ = 0.5 and ρ = 0.7 (HEX_0.5CON, HEX_0.7CON), are evaluated along with a bare hexagonal re-entrant auxetic core (HEX), a chiral featured hexagonal re-entrant auxetic core (HEX_CHIRAL) and a primitive vertical walled core (PRIMITIVE). All cores were subjected to normal impacts of 11.7 J, 26.47 J and 46.8 J.  Impact responses are quantified through kinetic energy decay and internal energy build-up. A performance indicator by the term of Energy Absorption Efficiency at Stabilization is adopted to compare the ability of each core topology to convert incident kinetic energy into internal deformation energy. The HEX_0.7CON core achieves unity-level efficiency at all energy levels indicating complete conversion of impact energy through its multistage collapse sequence. The HEX_0.5CON core provides efficiencies between 0.957 and 0.978. These two results confirm that the conic architecture in cores along with hexagonal re-entrant overall core configuration offers better energy dissipation across varied impact energies. HEX_CHIRAL, which utilizes chiral element in the hexagonal re-entrant core configuration offers higher efficiency than HEX, which is a classic hexagonal re-entrant core.  This proves the influence of its rotational mechanisms in core architecture for impact processing. However, conic profiles stands out with higher energy absorption efficiencies   than chiral featured cores. Classical re-entrant auxetic, HEX, cores show moderate efficiencies at 0.82 to 0.94 , suggesting that re-entrant action alone is not sufficient for impact mitigation. Clearly auxetic geometries have to be supplemented with higher order geometric curves like conics. Primitive core configuration returns the lowest efficiencies (0.57 to 0.67), reinforcing its inherent limitation in processing impact energy. In essence, the study confirms that conic parameterization significantly advances the impact resilience of auxetic core systems.