Effective properties and dynamic response of a sandwich panel made of two face sheets and auxetic core are analyzed in this study by computer simulations. The inner composite layer is made of a cellular auxetic structure immersed in a filler material of a given Poisson's ratio (filler material fills the voids in structure). Each cell is composed of an auxetic structure (re‐entrant honeycomb or rotating square), i.e., exhibiting negative Poisson's ratio without any filler. Influence of filler material on the effective properties of the sandwich panel is investigated. The proposed structure shows interesting structural characteristics and dynamic properties. Our results clearly show that it is possible to create auxetic sandwich panels made of two solid materials with positive Poisson's ratio. This is even possible if the filler material is nearly incompressible, but can move in out‐of‐plane direction. Moreover, effective Young's modulus of such sandwich panels becomes very large if the Poisson's ratio of the filler material tends to −1.

A sandwich-structured composite is a special class of composite materials that is fabricated by attaching two thin but stiff layers to a lightweight but thick core. Composites analyzed in this paper consist of two different materials: auxetic and structural steel. The optimization criterion is minimum compliance for the load case where the frame's top boundary is downward loaded. Outer layers are made of steel while the middle layer is twophase solid material composite. Only the middle layer is optimized by means of minimization of the objective function defined as the internal strain energy. In the first part of this paper we study the application of the solid isotropic material with penalization (SIMP) model to find the optimal distribution of a given amount of materials in sandwich-structured composite. In the second part we propose a multilayered composite structure in which internal layers surfaces are wavy. In both cases the total energy strain is analyzed.

Negative Poisson's ratio has already been discovered for many geometrical structures. In most cases, however, the metamaterials built upon such geometries are foams or cellular solids. In this paper, a unidirectional fibrous composite built of two constituent materials of different thermomechanical properties has been studied. The resultant composite is a solid material in its volume. In order to obtain a material of the required properties, both the geometry of fibers and the influence of temperature on both materials have been investigated.

Optimization of structures with complex shapes is a big challenge for computational physics. Results of numerical calculations show that composite or sandwich panel structures have a great influence on their effective properties. This article presents numerical results of optimization of sandwich panel properties. Calculations were provided for a three-layer sandwich two-phase composite. Optimization techniques were used for minimization of the effective Poisson's ratio of the core. The resultant composite structure exhibits a negative Poisson's ratio (NPR), although all its constituents are characterized by positive values of the Poisson's ratio. The structure of the composite is completely filled with solid materials, hence no voids appear within its whole volume. To find a solution, the finite-element method combined with an optimization algorithm MMA (method of moving asymptotes) was used. For the purpose of analysis, the material parameters were written by means of the shape interpolation SIMP (solid isotropic material with penalization) scheme.

Studies of mechanical properties of materials, both theoretical and experimental, usually deal with linear characteristics assuming a small range of deformations. In particular, not much research has been published devoted to large deformations of auxetic structuresi.e. structures exhibiting negative Poisson's ratio. This paper is focused on mechanical properties of selected structures that are subject to large deformations. Four examples of structure built of sinusoidal ligaments are studied and for each geometry the impact of deformation size and geometrical parameters on the effective mechanical properties of these structures are investigated. It is shown that some of them are auxetic when compressed and non-auxetic when stretched. Geometrical parameters describing sinusoidal shape of ligaments strongly affect effective mechanical properties of the structure. In some cases of deformation, the increase of the value of amplitude of the sinusoidal shape decreases the effective Poisson's ratio by 0.7. Therefore the influence of geometry, as well as the arrangement of ligaments allows for smart control of mechanical properties of the sinusoidal ligament structure being considered. Given the large deformation of the structure, both a linear elastic material model, and a hyperelastic Neo-Hookean material model are used.