Stiffness of Synclastic Wood‐Based Auxetic Sandwich Panels

Abstract

The research in materials with auxetic properties [1] (i.e., exhibiting negative Poisson's ratio [2] at least in some directions) has been growing for about 30 years. The manufacturing of the first man-made auxetic foam by Lakes [3] as well as the formulation and solution of the first mechanical [4,5] and thermodynamic models [6,7] explaining their unusual mechanical properties sparked an ongoing interest and intense studies of these interesting novel materials. Over these past 30 years, the studies on auxetics diverge into different aspects. Among others, the search for auxetic properties in new materials, [8,9] the theoretical studies of various models exhibiting auxetic properties, [10-46] or the creation of auxetic composites [47,48] to enhance mechanical properties of materials. The latter is of particular importance if one considers practical applications of negative Poisson's ratio materials. [49-55] In this respect, auxetic structures [24,54,56-66] are interesting (among others) in terms of improving stiffness and durability of materials. They tend to form synclastic, sphere-like shapes instead of anticlastic curvature which is characteristic for common materials with positive Poisson's ratio, subjected to bending. [67-69] Nowadays in wood industry, furniture which were designed with the use of synclastic shapes, are typically made from bent steel frame (usually upholstered), plastics, or bent plywood. Technology of bent plywood is strictly connected with thermophysical treatment, mold casting, and temperature-pressure bending process. The process is both time-and resourceconsuming. Furthermore, with the development of each new shape, expensive procedure of a new mold preparation and implementation into technological process is required. This situation could be significantly improved by implementation of auxetic structures into the industry. Auxetic structures improve several of mechanical properties, especially shear, impact, and bending resistance. They also improve ability to absorb impact energy as well as improve overall stiffness of structure. [65,66] Despite promising results of mechanical characteristics in the work by Smardzewski, [70] concerning examination of multilayered sandwich panels, particularly honeycomb panels with auxetic core manufactured from wood-based materials, to the date, the literature lacks research on the use of auxetic structures in wood-based composites. International research is focused on innovative, light composites, that could reduce the cost of product manufacturing by reducing material usage and overall product weight. Thus, in effect reducing also costs related to logistics. [70,71] Such composites could replace typically used wood-based materials such as particleboard, low, medium, and high-density fiberboard (LDF, MDF, and HDF) or plywood. Many studies [67,72-78] deal with honeycomb sandwich panels and their usage in wood industry for the purpose of door filling, vertical, and horizontal elements of furniture body, package filling, etc. Sandwich panels should have ...

Computational Study of Non-Porous Auxetic Plates with Diamond Shape Inclusions

“…One of the first mechanical structures with auxetic behavior was proposed by Almgren [25] and the first 2D molecular models (spontaneously forming auxetic phases) were studied by Wojciechowski [19]. Auxetic structures can provide a variety of improved properties such as high shear and overall stiffness [26][27][28], fracture toughness [29], and indentation resistance [9]. In addition, the damping capacity of auxetic structures [10], their sound absorption [30,31], and crashworthiness [32] were also found to be enhanced 2 of 13 compared to conventional materials.…”

Towards Self-shaping Metamaterial Shells:

“…Auxetics are a class of metamaterials that show unusual behavior when stretched or compressed due to their engineered geometry that causes negative Poisson's ratio [15]. Unlike most other bending-active plate materials that create single curvature when bent [16], these materials can create double curvature [17]. By carefully designing these MMPs, the resulting bent geometry can be pre-programmed to exhibit anticlastic, single curved, and synclastic areas [18].…”

Design and Characterization of Asymmetric Cell Structure of Auxetic Material for Predictable Directional Mechanical Response

“…In addition, current research provides evidence and potential applications for the wood industry, specifically in furniture manufacturing, because plywood and bending processes consume significant time and resources, which could be considerably improved by implementing auxetic structures. For example, the potential application of sandwich panel manufacturing with auxiliary cores, enabling the reuse of materials [ 50 , 51 , 52 ]. The development of these structures allows the application of these auxiliary panels in a wide range of everyday products, such as doors and furniture [ 53 ], with improved impact energy absorption capacity and overall stiffness.…”