Despite its numerous potential applications, two-dimensional monolayer graphyne, a novel form of carbon allotropes with sp and sp2 carbon atoms, has received little attention so far, perhaps as a result of its unknown properties. Especially, determination of the exact values of its elastic properties can pave the way for future studies on this nanostructure. Hence, this article describes a density functional theory (DFT) investigation into elastic properties of graphyne including surface Young’s modulus and POISSON’S RATIO. The DFT analyses are performed within the framework of generalized gradient approximation (GGA), and the Perdew–Burke–Ernzerhof (PBE) exchange correlation is adopted. This study indicates that the elastic modulus of graphyne is approximately half of that of graphene due to its lower number of bonds.

In this study, to determine POISSON’S RATIO and modulus of elasticity of white seedless grapes during matuRATIOn, the fresh fruit samples were harvested from a vineyard at seven sequential weeks from 6th September to 18th October. In each run, six grape berries were randomly selected and the static loading test and digital photography were done together. Considering true shape of the fruit and an allowable deformation value, and also using Hertz’s theory with a true POISSON’S RATIO (experimental), modulus of elasticity was calculated. Apparent POISSON’S RATIO was determined by the image processing, too, and then obtained values of POISSON’S RATIO were modified using finite element software (ABACUS). Results showed that measured modulus elasticity by the Hertz’s theory depends on the magnitude of axial strain and increases with increasing that. Regarding the results, the calculated poissoon’s RATIOs are less than that true one, depending on the axial strain value. It was found that both modulus of elasticity and POISSON’S RATIO decreased during matuRATIOn.

The main aim of this study is to present a new theory which shows the relationship between the warp knitted structures and some parameters of the fabric stiffness matrix. One of the important factors in this matrix is Poisson's RATIO that influence on the mechanical behavior of knitted fabric. The theoretical loop model based on geometry is used to investigate the tensile behavior of the fabric. The proposed loop model is basically based on the previously published assumption of fabric structure. This geometrically loop model is assumed to be two dimensional, but this model is applicable to analysis of the three dimensional structures as well. The specimen fabrics are produced with various two bar warp knitted fabric structures with changing the underlap length of the front or back guide bar (Tricot, Locknit, Reverse Locknit, Satin and Sharkskin) from polyester yarn. A uni-axial tensile tester is used for measuring the experimental work and geometrical parameters such as wale and course spacing of the fabrics are obtained during the extension. The model predicts the variation of Poisson's RATIO with longitudinal strain in all structures on the jamming point. Comparison between experimental and theoretical results for variety of fabric structures shows reasonable agreement between predicted and measured extension behavior of warp knitted fabric.

Auxetic metamaterials are a class of material with tunable Poisson's RATIO. Nonetheless, most auxetics have weak mechanical properties, thus, implementing graphene origami (GOri) as a strong reinforcement can overcome this deficiency. This review explores the burgeoning field of auxetic metamaterials enhanced through the integRATIOn of graphene origami. This study also presents an in-depth investigation of the background of NEGATIVE Poisson's RATIO auxetic metamaterials, most importantly, graphene origami. Furthermore, it focuses on the notable mechanical characteristics such as increased flexibility, strength, and dynamic response of GOri-reinforced composites. Leveraging Hamilton's principle and other theoretical frameworks, this paper collates and examines the equation of motion derivations and the impact of various parameters on GOri behaviour.

In this paper, the interface crack of two non-homogenous functionally graded materials is studied. Subsequently, with employing the displacement method for fracture of mixed-mode stress intensity factors, the continuous variation of material properties are calculated. In this investigation, the displacements are derived with employing of the functional graded material programming and analysis of isoparametric finite element; then, with using of displacement fields near crack tip, the mixed-mode stress intensity factors are defined. In this present study, the problems are divided into homogenous and non-homogenous materials categories; and in order to verify the accuracy of results, the analytical and numerical methods are employed. Moreover, the effect of Poisson's RATIO variation on mixed-mode stress intensity factors for interface crack be examined and is shown in this study. Unlike the homogenous material, the effect of POISSON’S RATIO variations on mixed-mode stress intensity factors at interface crack between two nonhomogenous is considerable.

In this paper, the effect of NEGATIVE Poisson's RATIO on the mechanical response and improving the damage behavior of carbon/epoxy composite laminates under low-velocity impact is studied. For this purpose, a MATLAB code is developed to determine the range of sequence angles to achieve both NEGATIVE Poisson's RATIO in-plane and through-thickness based on CLT. Also, the progressive damage model is written and implemented using the user-material subroutine-VUMAT consisting of Hashin and Puck failure criteria and the damage evolution model based on the equivalent-strain method to predict the initiation and evolution of damage for matrix and fiber. In the research process, the impact resistance performance of auxetic laminates is evaluated in comparison with composite laminates with positive Poisson's RATIO with cross-ply and angle-ply sequences. The results showed that in some damage modes, auxetic behavior can lead to the improvement of composite laminate damage. Based on the analysis of the results, the highest damage amount of delamination, matrix tension, matrix compression, and fiber tension damage is observed in angle-ply, through-thickness auxetic, cross-ply, and through-thickness auxetic laminates, respectively. Meanwhile, cross-ply, angle-ply, and through-thickness auxetic laminates with characteristics such as high impact force, low impact time, low maximum displacement, and less dissipated energy than in-plane auxetic laminate are suitable for use in structures with hardwall design approach. Also, the in-plane auxetic laminate with features such as low impact force, high impact time, high displacement, and more dissipated energy than other composite laminates, is practical and opeRATIOnal for use in sacrificial structures.

In this paper, the effect of NEGATIVE Poisson's RATIO on the mechanical response and improving the damage behavior of carbon/epoxy composite laminates under low-velocity impact is studied. For this purpose, a MATLAB code is developed to determine the range of sequence angles to achieve both NEGATIVE Poisson's RATIO in-plane and through-thickness based on CLT. Also, the progressive damage model is written and implemented using the user-material subroutine-VUMAT consisting of Hashin and Puck failure criteria and the damage evolution model based on the equivalent-strain method to predict the initiation and evolution of damage for matrix and fiber. In the research process, the impact resistance performance of auxetic laminates is evaluated in comparison with composite laminates with positive Poisson's RATIO with cross-ply and angle-ply sequences. The results showed that in some damage modes, auxetic behavior can lead to the improvement of composite laminate damage. Based on the analysis of the results, the highest damage amount of delamination, matrix tension, matrix compression, and fiber tension damage is observed in angle-ply, through-thickness auxetic, cross-ply, and through-thickness auxetic laminates, respectively. Meanwhile, cross-ply, angle-ply, and through-thickness auxetic laminates with characteristics such as high impact force, low impact time, low maximum displacement, and less dissipated energy than in-plane auxetic laminate are suitable for use in structures with hardwall design approach. Also, the in-plane auxetic laminate with features such as low impact force, high impact time, high displacement, and more dissipated energy than other composite laminates, is practical and opeRATIOnal for use in sacrificial structures.

Auxetic cellular solids in the forms of honeycombs and foams have great potential in a diverse range of applications, including as core material in curved sandwich panel composite components, radome applications, directional pass band filters, adaptive and deployable structures, filters and sieves, seat cushion material, energy absorption components, viscoelastic damping materials and fastening devices etc. In this paper, the characteristic of wave propagation in sandwich panel with auxetic core is analyzed. A three-layer sandwich panel is considered which is discretized in the thickness direction by using semi-analytical finite element method. Wave propagation equations are obtained through some algebraic manipulation and applying standard finite element assembling procedures. The mechanical properties of auxetic core can be described by the geometric parameters of the unit cell and mechanical properties of the virgin core material. The characteristics of wave propagation in sandwich panel with conventional hexagonal honeycomb core and re-entrant auxetic core are discussed, and effects of panel thickness, geometric properties of unit cell on dispersive curves are also discussed. Variations of POISSON’S RATIO and core density with inclined angle are presented.

In this paper, the behavior of a new type of auxetic composite (composite with NEGATIVE POISSON’S RATIO) consisting of polyester fibers and ABS tubes as reinforcement as well as polyurethane foam as matrix was investigated by finite element method. Furthermore, the effect of NEGATIVE POISSON’S RATIO and mechanical properties of auxetic composite under quasi-static pressure were analyzed and the results were compared with the published experimental works. Good agreements were found between the results. Considering stress-strain diagram, it is concluded that this type of composite can operate as a damping material due to the specific properties such as high shear strength, indentation strength toughness. So, the foresaid properties make them a great choice with high potential application in various industries.Also, the ways to get the effective parameters to achieve more NEGATIVE POISSON’S RATIO were investigated. The parameters include the foam density as well as material, diameter and distances between ABS tubes. The results show that with decreasing foam density and decreasing distances between ABS tubes, the NEGATIVE POISSON’S RATIO first increases to reach the critical value and then decreases.