This paper proposed a two-dimensional lattice structure with a nested core. The bandgap distribution and the anisotropy of phase velocity and group velocity were studied based on Bloch’s theorem and finite element method. The effects of eccentric ratio (e) and rotation angle (θ) of dual-phase structure on the bandgap distribution were investigated, and the anisotropy was studied via phase velocity and group velocity. The structure of (e) = 0.3 displayed the maximum total bandgap width. With (θ) increasing, the total bandgap widths of structures of different (e) all increased apparently and the low-frequency bandgap properties were improved. The phase velocity and group velocity of (e) = 0 displayed strong anisotropy, and the anisotropy was tuned by tuning (θ). Furthermore, the group velocity of the eighth mode displayed high directional wave propagation. For practical application, a single-phase structure was proposed and analyzed. Through additive manufacturing technology, the single-phase structure was prepared and tested by a low amplitude test setup. The experimental results displayed a good agreement with numerical results which demonstrated high directional propagation. This finding may pave the way for the practical application of the proposed lattice metamaterial in terms of wave filtering.

Based on a modified Voronoi tessellation technique, a series of isotropic negative Poisson's ratio (NPR) Voronoi foam models were proposed via finite element method (FEM). And the proposed models were prepared by reverse modeling method. Poisson's ratio and stress-strain relationship of the proposed models were studied via FEM and experimental method. Results showed that the structure exhibited negative Poisson's ratio and isotropic behavior. With the increased of the relative density of the model, the absolute value of Poisson's ratio decreased gradually. The results of FEM and experiment showed good consistency. Then, a foam-filled structure was built by filling the proposed NPR Voronoi foam into a square tube. And its energy absorption ability was studied and compared with an isotropic chiral lattice foam-filled tube. Results showed that the energy absorp-tion ability of the proposed NPR Voronoi foam-filled structure was 11% higher than that of the isotropic NPR chiral lattice foam-filled tube with the same relative density. The research was ex-pected to be meaningful for the further research and application of the isotropic NPR foam.

This paper proposed a one-dimensional (1-D) meta-beam through embedding re-entrant hexagons on a 1-D single beam. Then a two-dimensional (2-D) square resonator lattice with re-entrant hexagons was designed via replacing the ribs with the 1-D meta-beams. Based on Bloch’s theorem and finite element method (FEM), the dispersions and bandgap properties of 1-D meta-beam and 2-D lattice with re-entrant hexagon were analyzed. The numerical results indicated that the bandgap property of both structures was improved via embedding re-entrant hexagons. For the 2-D square resonator lattice with re-entrant hexagon, the total bandgap width was 34.3% higher than the 2-D lattice without re-entrant hexagon. Then a parametric study was implemented, and the results showed the re-entrant ratio, rib thickness and the number of re-entrant hexagons had strong effects on bandgap distribution, especially the re-entrant hexagons, which enhanced the bandgap property in the low-frequency region significantly. Through calculating the contours of group velocity, the anisotropy of the 2-D square resonator lattice with re-entrant hexagons was investigated, and the results indicated that there was pronounced caustic at specific parameter sets which reflects energy focus. To verify the bandgap property in the realistic application, the specimen of 2-D square resonator lattice with re-entrant hexagons was prepared through additive manufacturing technology, and a low amplitude harmonic test was performed. The experimental result demonstrated the bandgap property of the 2-D square resonator lattice with re-entrant hexagons. This paper may introduce a method to enhance the bandgap property of lattice metamaterial.

Based on the refined first-order shear theory (simplified zig-zag model), using quasi-conforming finite element method with path-following and switching approach, the postbuckling behaviors and postbuckling bearing capacity (PBC) of composite sandwich panels (CSPs) axially loaded were studied and discussed in detail. To utilize the carrying potential of CSPs in postbuckling, the effects of the key parameters on postbuckling behaviors of the CSPs were analyzed by finite element method. The numerical results show that the PBC of CSPs increases with the increase of face sheets thickness, core thickness and core shear modulus, but it is insensitive to the change of the side length ratio. The enhancement of core shear strength can increase the PBC of CSPs and change the failure mode, but it is found there is a threshold value, beyond which, the PBC will no longer or slightly increases with the increase of core shear strength. The failure of CSPs is mainly determined by the tensile strength in the direction perpendicular to the fiber. Finally, a parameter selection optimization approach is proposed to effectively improve the PBC of CSPs under axial compression.

This paper proposed a two-dimensional composite square lattice structure containing two kinds of inclusions (polymethylmethacrylate and T2 copper). To maximize the relative widths of the gaps between the adjacent energy bands of the phononic crystals (PnCs), an improved multi-parameter genetic algorithm was adopted in this paper. The material distribution and ligament sizes were considered simultaneously by ternary encoding and binary encoding. The propagation wave behaviors of the composite lattice structures were studied by the finite element method. The effects of different lattice shapes and other relevant influencing parameters on the bandgaps were discussed. The results showed that the lattice shape, ligament width, and material density affect the width and the location of the bandgaps, and the effectiveness of the proposed method was demonstrated by a transmission spectrum experiment.