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Bending Performance and Failure Behavior of Wooden Sandwich Panels with Corrugated Cores
Wooden sandwich panels with a corrugated core have not been the subject of scientific research so far. The anisotropic properties of the wood make it challenging to form corrugated shapes. Therefore, it is decided to determine the effect of geometric imperfections of the corrugated core made of wood veneers on the stiffness and strength of sandwich panels and the core elasticity modulus. The beams are manufactured in industrial conditions and subjected to three‐point bending. The research is carried out in the form of tests and numerical calculations. It is demonstrated that geometric imperfections of the core affect the stiffness and strength of sandwich panels. The modulus of elasticity can reach values lower by up to 37% and the strength by up to 24% compared with reference panels with an ideal, symmetrical core geometry. However, their average linear elasticity modulus (1449 MPa) indicates excellent construction properties. Under the tests, four stages of beam bending are revealed. The last stage means that panels can increase stiffness even after the core is destroyed. The corrugated core's modulus of elasticity is also determined.
Modelowanie właściwości nowych lekkich drewnopochodnych płyt komórkowych z auksetycznymi rdzeniami
Auxeticity Tuning by Nanolayer Inclusion Ordering in Hard Sphere Crystals
Designing a particular change in a system structure to achieve the desired elastic properties of materials for a given task is challenging. Recent studies of purely geometrical atomic models have shown that structural modifications on a molecular level can lead to interesting and desirable elastic properties. Still, the result of such changes is usually difficult to predict. The present work concerns the impact of nanolayer inclusion ordering in hard sphere crystals on their elastic properties, with special attention devoted to their auxetic properties. Two sets of representative models, based on cubic crystals consisting of 6×6×6 unit cells of hard spheres and containing either neighboring or separated layers of spheres of another diameter, oriented orthogonally to the [001] direction, have been studied by Monte Carlo simulations in the isothermal–isobaric (NpT) ensemble. Their elastic constants have been evaluated using the Parinello–Rahman approach. The Monte Carlo simulations showed that introducing the layer inclusions into a pure face-centered cubic (FCC) structure leads to the system’s symmetry changes from cubic symmetry to tetragonal in both cases. Essential changes in the elastic properties of the systems due to layer ordering were found both for neighboring and separated inclusions. It has been found that the choice of a set of layer inclusions allows one to tune the auxetic properties in two crystallographic directions ([110][11¯0] and [101][1¯01]). In particular, this study revealed that the change in layer ordering (from six separated layers to six neighboring ones) allows for, respectively: (i) enhancing auxeticity of the system in the [101][1¯01] direction with almost loss of auxetic properties in the [110][11¯0] direction in the case of six separated layers, while (ii) in the case of six neighboring layers, keeping the auxetic properties in both auxetic directions independently of the size of spheres constituting inclusions.
Comparative study on the properties of cellulose nanofiber (CNF) and cellulose nanocrystals (CNC) reinforced 1C-PUR adhesive bonded wooden joints
Effect of Poisson's ratio on the mechanical properties and behaviour of auxetic bolts withdrawal from holes in beech wood
Analyses of L-Type Corner Joints Connected with Auxetic Dowels for Case Furniture
Tests were carried out to develop and manufacture various types of auxetic dowels using 3D printing technology. These dowels were then used to connect L-type corner joint specimens for case furniture, and their strength and stiffness were analyzed through experimental, theoretical, and numerical means. In the scope of the study, eight different types of auxetic dowels including two inclusion types, two inclusion sizes, and two dowel hole diameters, as well as a reference non-auxetic dowel, were designed. Accordingly, a total of 180 specimens that included 10 replications for each group were tested; 90 were tested under tension and the remaining 90 were tested under compression. The results demonstrated that the assembly force required for the corner joints connected with auxetic dowels was significantly lower compared to non-auxetic dowels. Furthermore, the numerical and theoretical analyses yielded similar outcomes in this study. Both analyses revealed that the dowels used to connect the corner joints experienced substantial stresses during mounting and bending, ultimately leading to their failure. Upon concluding the test results, it was observed that the corner joints connected with dowels featuring rectangular inclusions exhibited superior performance when compared to those with triangular inclusions. In light of these findings, it can be concluded that further enhancements are necessary for auxetic dowels with rectangular inclusions before they can be utilized as alternative fasteners for traditional dowels.
Akustyczna płyta komórkowa z rdzeniem listewkowym oraz sposób wytwarzania akustycznej płyty komórkowej z rdzeniem listewkowym
Drewniane płyty komórkowe z rdzeniem pryzmatycznym i sposób wytwarzania drewnianych płyt komórkowych z rdzeniem pryzmatycznym
Fine‐Tuning of Elastic Properties by Modifying Ordering of Parallel Nanolayer Inclusions in Hard Sphere Crystals
It is known that changes on the microscopic, structural level of materials exert changes on their macroscopic properties, in particular elastic ones. This approach can be used to alter the elastic properties of materials. However, it is not easy to predict the impact of a particular change in the structure of crystals. The recent studies show that depending on the size, shape, and orientation of inclusions used, the resulting elastic properties may differ. Inclusions may enhance, weaken, or eliminate the auxetic properties in a hard sphere model. This study is focused on the influence of the spatial distribution of planar inclusions within the hard sphere crystal and its impact on its elastic properties. Periodic systems containing two nanolayer inclusions in the representative volume element, oriented orthogonally to ‐direction and in various spatial ordering, are considered. It has been shown that introducing layer inclusions causes the deterioration of auxetic properties in the ‐direction. However, the latter weakly depends on the spatial ordering of the inclusion layers. Moreover, changes in the size of the inclusion particles, combined with different ordering of the inclusion layers, can be used to coarsely and finely tune the elastic properties of the model crystal.
