Two simple models of two-dimensional auxetic (i.e. negative Poisson’s ratio) foams are studied by computer simulations. In the first one, further referred to as a Y-model, the ribs forming the cells of the foam are connected at points corresponding to sites of a disordered honeycomb lattice. In the second one, coined a Δ-model, the connections of the ribs are not point-like but spatial. For simplicity, they are represented by triangles centered at the honeycomb lattice points. Three kinds of joints are considered for each model, soft, normal and hard, respectively corresponding to materials with Young’s modulus ten times smaller than, equal to and ten times larger than that of the ribs. The initial lattices are uniformly compressed, which decreases their linear dimensions by about 15%. The resulting structures are then used as reference structures with no internal stress. The Poisson’s ratios of these reference structures are determined by stretching them, in either the x or the y direction. The results obtained for finite meshes and finite samples are extrapolated to infinitely fine mesh and to the thermodynamic limit, respectively. The extrapolations indicate that meshes with as few as 13 nodes across a rib and samples as small as containing 16 × 16 cells approximate the Poisson’s ratios of systems of infinite size and infinite mesh resolution within the statistical accuracy of the experiments, i.e. a few per cent. The simulations show that by applying harder joints one can reach lower Poisson’s ratios, i.e. foams with more auxetic properties. It also follows from the simulations performed that the Δ-model gives lower Poisson’s ratios than the Y-model. Finally, the simulations using fine meshes for the samples are compared with the ones in which the ribs are approximated by Timoshenko beams. Taking into account simplifications in the latter model, the agreement is surprisingly good.

Preliminary results on the influence of periodically distributed cylindrical nanoinclusions introduced into the f.c.c. hard sphere crystal on its elastic properties and the Poisson's ratio are presented. The nanoinclusions are oriented along the [001]-direction and filled with hard spheres of diameter different from the spheres forming the matrix crystal. The Monte Carlo simulations show that symmetry of the crystal changes from the cubic to tetragonal one. In the case when spheres inside the inclusion are smaller than spheres forming the crystal, the changes of Poisson's ratio are qualitatively similar to the changes observed earlier in the Yukawa sphere crystal, that is, the introduction of nanochannels causes simultaneous decrease of the Poisson's ratio in the [110][1 10]-direction, and its increase in [110][001]-direction. Filling the nanochannel with spheres having diameters greater than that of the spheres in the crystalline matrix, causes a decrease of the Poisson's ratio value from 0.065 down to À0.365 in [111][11 2]-direction. The dependence of the minimal Poisson's ratio on the direction of the applied load is shown in a form of surfaces in spherical coordinates, for selected values of nanochannel particle diameters. The most negative value of the Poisson's ratio found amongst all systems studied was as low as À0.873.

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This study reports the moment resistance, stiffness, and numerical analysis of various sizes of round-end mortise and tenon joints. L-shaped and T-shaped specimens were constructed. Joints were manufactured using three tenon widths and three tenon lengths with 10 replications for each combination. Specimens were constructed of Turkish beech, and the joints were assembled with polyvinylacetate (PVAc) adhesive. Bending tests were carried out in compliance with accepted test methods. Numerical analyses were performed with finite element method (FEM) software. At the end of the study, the joints became stronger and stiffer as either tenon width or length increased. Tenon length had a more significant effect on moment resistance, while tenon width had a more significant effect on stiffness. Ultimate moment resistances were obtained with Lshaped joint construction of 50 × 50 mm tenons and T-shaped joint construction of 40 × 50 mm tenons. Strength of a chair could be increased by considering these results in engineering design process. Results showed that the numerical analyses gave reasonable estimates of mechanical behavior of joints. Analytical calculations and numerical simulations confirmed that the maximum stress in the glue line was concentrated at the edge and corners, and that the modeled joints had a shape-adhesive nature.

Light cellular wood panels have been gaining increasing interest among furniture manufacturers, but only a few articles can be found dealing with modeling of mechanical properties of cellular wood panels with a paper honeycomb core inside. The present paper intends to fi ll this gap, and thus, the elastic properties of cellular wood panels with paper honeycomb of hexagonal and auxetic cells were evaluated. Analytical models have been employed by comparison of experimental data with those obtained by numerical calculations. The cores of the examined cellular wood panels exhibited strong orthotropic properties. Results of numerical calculations of sandwich beam defl ections corroborated their satisfactory conformity. The results of laboratory measurements proved the correctness of the determined elastic constants.

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The objective of this study was to determine normal impedance on the surface as well as sound absorption coefficients for several wood species from Europe and from the tropical zone. The mathematical models of Miki, Attenborough, and Allard – dealing with acoustic properties of porous materials – have also been compared. The air flow resistivity exhibits a distinct link between fiber dimensions and wood porosity. The highest sound absorption coefficient was found for oak, ash, sapeli, and pine woods at 2 kHz frequency. The Attenborough model provides results closest to laboratory measurements, although it still requires significant improvements. The Miki and Allard models have some drawbacks and should be applied with reservation for the determination of wood acoustic properties.