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The importance of cellular materials continues to increase in lightweight structural applications as more industries realize these materials are becoming more reliable, repeatable and allowing for lower production costs. Among all the common structural applications of cellular architected materials, cores for sandwich panels may perhaps be the most important one, and therefore, were the focus of this work. On the other hand, the fast-paced growth of computational power, in combination with the development of software and numerical methods such as Meshless Methods provide the necessary conditions to study intricate topologies which may offer improved mechanical properties for each different application. In this work, two periodic cellular topologies which are typically used in the cores of sandwich structures were designed, namely conventional honeycombs and re-entrant honeycombs, for 7 different values of relative density, and tested in two different in-plane directions in the linear-elastic domain. The Radial Point Interpolation Method (RPIM) is used in this study, for the first time in the literature, to simulate the elasto-static behaviour of honeycomb structures and provides advantages over the Finite Element Method (FEM) in this field. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a study of the mechanical response of hexachiral honeycombs with transversally curved ligaments under planar uniaxial tensile, compressive and shear loads. The impact of the chiral cell design parameters on the resulting macroscopic behaviour is assessed utilising finite elements calculations. It is shown that the presence of ligament curvature permits to attain mechanical responses which are not achievable through conventional chiral honeycomb designs. In addition, the resulting responses exhibit, for all considered load cases, significant tunability through the investigated geometrical design parameters. Two chiral lattices with identical geometries, only differing in their ligament curvature, were manufactured and experimentally tested to validate the finite elements predictions. A connection and assembly strategy is presented and utilised, offering a fast and robust approach to build larger finite lattice structures through 3D printed single basic cells. The hexachiral lattices were tested in tension, compression and in-plane shear, showing good agreement with the numerical predictions. [ABSTRACT FROM AUTHOR]

The advent of additive manufacturing has enabled the precise manufacturing of lattice materials at different length scales. While honeycombs are usually constructed from a tessellated array of identical unit cells, most structures in nature tend towards stochastic or disordered tessellation. In this work, we explore the effect of disorder properties of honeycombs, in particular, stiffness, strength, fracture toughness, and crack propagation paths using finite element models. The honeycombs are created using Voronoi tessellations with different levels of disorder measured by a regularity parameter δ , where δ = 1 corresponds to a regular hexagonal honeycomb and decreasing values of δ correspond to increasing levels of disorder. We consider three constituent materials: very brittle, quasi-brittle, and very ductile (0.0007–0.25 in failure strain). The results show that pseudo-order realizations with 0.5 ≤ δ ≤ 0.8 show the best strength-toughness trade-off. With increased plasticity, the improvement in fracture toughness compared to regular honeycombs can be as high as 50% at the expense of a 20% decrease in strength. This increase in fracture toughness is achieved both at crack initiation with crack blunting intrinsically and extrinsically during crack growth by a combination of crack deflection and crack bridging. Also, a single mathematical variable δ usually referred to as a "regularity parameter" to control cell stochasticity cannot account for the variability in tensile strength and fracture toughness parameters for brittle or quasi-brittle constituent materials and significantly more for a ductile constituent material. Thus, a local parameter for disorder is required to explain the large statistical variance seen in the mechanical properties of disordered honeycomb structures across the same irregularity value. [ABSTRACT FROM AUTHOR]

Abstract: Wave propagation and its frequency bandgaps in a parametrically modulated composite laminate are reported in this paper. The modulated properties under considerations are due to periodic microstructure, for example honeycomb core sandwich composite, which can be parameterized and homogenized in a suitable scale. Wave equations are derived by assuming a third-order shear deformation theory. Homogenization of the wave equations is carried out in the scale of wavelength. In-plane wave and flexural–shear wave dispersions are obtained for a range of values of a stiffness modulation coefficient . A clear pattern of stop-bands is observed for . To validate the band-gap phenomena, we take recourse to time domain response obtained from finite element simulation. As predicted by the proposed analytical technique, a distinct correlation between the chosen frequency band and the simulated wave arrival time and amplitude reduction is found. This promises practical applications of the proposed analytical technique to designing parametrically modulated composite laminate for wave suppression. [Copyright &y& Elsevier]