Abstract

Auxetic metamaterials possess enhanced impact resistance and hence are the ideal core of sandwich structures. Here we present the enhancement of the drop-weight impact resistance of composite sandwich beams with nanocomposite facesheets by taking advantage of auxetic 3D lattice cores with FG (functionally graded) configurations. 2D and 3D lattice metamaterials with negative Poisson’s ratios (NPRs) were modeled, analyzed, and compared. Furthermore, the 3D lattice cores were designed to possess four FG patterns along the thickness direction. The mechanical properties of graphene reinforced composites (GRCs) were determined by means of micromechanical modeling according to the extended Halpin-Tsai model. In view of shape changes of lattices due to the localized deformation, full-scale finite element modeling is necessary, followed by nonlinear analysis. Compared with a re-entrant honeycomb core having the same relative density, the auxetic 3D lattice core can lead to even better resistance. Moreover, FG configurations are proven to have different effects on the impactor displacement and local transient thickness decrease of sandwich beams subjected to low-velocity impacts. Our results demonstrated the advantages of FG auxetic 3D lattices, and are expected to be beneficial to further studies and instructive for practical applications.

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