Negative Poisson Research Articles

Cushioning performance of origami negative poisson's ratio honeycomb steel structure

The honeycomb structure with a negative Poisson's ratio, inspired by the Miura origami unit, exhibits three-dimensional negative Poisson's ratio characteristics and effective energy dissipation performance. This unique property provides significant potential in the field of protection applications. This study aims to comprehensively understand the impact of auxetic and origami structures on the cushioning performance of honeycomb structures. For this purpose, 316 L stainless steel specimens were fabricated using 3D printing technology and subjected to drop hammer impact tests, and the results were verified by finite element simulation. This paper focuses on assessing the deformation mode and energy dissipation performance of origami auxetic honeycomb structures with varying width-to-thickness ratios and folding angles under different impact energy levels. The results indicate that the negative Poisson's ratio origami specimens exhibit higher plateau stress and specific energy absorption compared to their positive and zero Poisson's ratio origami counterparts with the same geometry. In addition, a smaller width-to-thickness ratio and higher input impact energy enhance the cushioning performance of honeycomb structures.

Word high gauge factor flexible capacitive strain sensor based on auxetic structure

Capacitive flexible stretch sensors, compared to resistive ones, offer better linearity and are thus more promising for human motion detection applications. Current capacitive sensors, however, face challenges in effectively enhancing their Gauge Factor (GF), limiting their sensitivity. This paper presents a capacitive stretch sensor utilizing a negative Poissons ratio structure made of high Shore hardness silicone as the framework and low Shore hardness silicone as the dielectric layer. Liquid metal composite material is used for the electrodes. Finite element simulation validated the sensors stretching effect. The sensor achieved a sensitivity of 2 pf/mm and a GF value of 2.19. Its efficacy is demonstrated through the measurement of finger joint movements, indicating broad application potential in human motion detection.

Impact resistance of a double re-entrant negative poisson’s ratio honeycomb structure

Auxetic metamaterials, usually consisting of cellular solids or honeycombs, exhibit the advantages of high designability and tunability. In particular, the negative Poisson’s ratio (NPR) property endows them with innovative mechanical properties and makes them promising for a wide range of applications. This paper proposes a modified double re-entrant honeycomb (MDRH) structure and explores its Young’s modulus and Poisson’s ratio through theoretical derivation and finite element analysis. Additionally, it discusses the relationship between these parameters and the concave angle. Furthermore, the deformation mode, nominal stress–strain curve, and specific energy absorption of this MDRH are investigated for different impact velocities and compared with traditional re-entrant honeycomb (TRH) materials. The results show that the MDRH honeycomb structure greatly widens the range of effective modulus and NPR values. At different impact velocities, the MDRH exhibits high plateau stress and specific energy absorption, indicating good impact resistance. These results provide a theoretical foundation for the design and implementation of new energy-absorbing structures.

Research and defence application progress of negative poisson's ratio materials

In contrast to traditional materials, materials and structures with negative Poisson's ratio (NPR) transverse shrinkage (expansion) occurs under uniaxial pressure (tension). This characteristic makes NPR materials have many excellent advantages. Shear capacity and indentation resistance of NPR materials are introduced in this paper. According to these two characteristics, the paper also introduces the defence application of NPR materials.

Analysis and optimization of impact energy absorption performance of mine refuge chamber filled with concave triangular negative poisson's ratio material

Analysis and optimization of impact energy absorption performance of mine refuge chamber filled with concave triangular negative poisson's ratio material

Impact energy absorption composites with shear stiffening gel-filled negative poisson's ratio skeleton by Kirigami method

A new type of Negative Poisson's ratio skeleton composites (NPRSC) filled with shear stiffening gels (SSG) is presented in this work. The skeleton is manufactured by Kirigami method for a simplest folding process. Combined with the shear stiffening property of SSG and auxetic effect of Negative Poisson's ratio (NPR) skeleton, the flexible composites show excellent impact energy absorption performance. Static compression experiment displays that compared with Positive Poisson's ratio (PPR) skeleton, the NPR structure composed of re-entrant elements is more flexible with a lower initial compression modulus for its special curvature effect. Dynamic impact experiments and numerical simulation reveals that the auxetic effect of NPR skeleton further facilitates the dynamic shear stiffening property of SSG and helps to dissipate the stress transversely. Specifically, the NPR skeleton contributes to a lower peak load, higher energy absorption ratio (EAR) and specific energy absorption (SEA) cooperated with SSG. The NPRSC exhibits improved energy absorption with the increase of impact velocity due to the strain rate sensitivity of SSG. This method provides an innovative idea for the structural design of shear stiffening materials and may be widely applied in the field of intelligent protection.

Soft Actuation of Auxetic Cylinder Structure Based on Liquid Metal and Pneumatic Cntrol

Soft robots employing soft polymer materials such as gels and elastomers have various advantages such as compact, lightweight, and silent motion. Recently, biomimetic structures driven by pneumatic control have been attracting attention though various driving sources have been proposed. In this study, we have fabricated auxetic channel structure in elastomer using 3D printer and aimed to develop a novel wearable device with liquid metal inflow, and cylinder-shaped soft robot with an armored (exoskeleton-like) auxetic structure with a negative poisson's ratio that placed around bellows-typed tube. We have investigated the structural variability and walking performance of the armored cylinder structure.

Unique Deformation of Soft Cylinder Integrated with Auxetic Structure and Bellows-typed Tube

Soft robots employing soft polymer materials such as gels and elastomers have various advantages such as compact, lightweight, and silent motion. Recently, biomimetic structures driven by pneumatic control have been attracting attention though various driving sources have been proposed. In this study, we have fabricated cylinder-shaped soft robot with an armored (exoskeleton-like) auxetic structure with a negative poisson's ratio that placed around bellows-typed tube. We have investigated the structural variability and walking performance of the armored cylinder structure.

Locomotion Performance of Soft Actuator with Auxetic-typed Armored Structure

Soft robots employing soft polymer materials such as gels and elastomers have various advantages such as compact, lightweight, and silent motion. Recently, biomimetic structures driven by pneumatic control have been attracting attention though various driving sources have been proposed. In this study, we have fabricated cylinder-shaped soft robot with an armored (exoskeleton-like) auxetic structure with a negative poisson's ratio that placed around bellows-typed tube. We have investigated the structural variability and walking performance of the armored cylinder structure.

Impact Analysis of Auxetic Structures for Military Applications

Abstract: Auxetic structures are special structures which tend to become wider when subjected to longitudinal tension instead of getting compressed, which implies structures having a negative poisson’s ratio. These structures are used in impact pads due to this unique property. In this comparative study were done on different types of materials and structures which are recognized for 3D printing the auxetic structures. The three stages of explicit dynamic analysis involves firstly selecting the most appropriate structures from chiral truss, re-entrant hexagon, arrow head and one non- auxetic structure which is hexagon structure. From this the structure having the least deformation at the impact point is selected which is re-entrant hexagon. Following this, keeping re-entrant hexagon as the structure, the next set of analysis is performed by varying the structure materials. Polycarbonate, polystyrene, polyvinyl chloride and high density polyethylene were studied and the analysis results showed, polyvinyl chloride as the suitable material. Lastly the limiting velocity for the impact is calculated by varying the impact velocity from 800m/s, 1000m/s and 1200m/s beyond which the structure experienced fracture. This study proposes the selection of suitable auxetic structure and material for manufacturing impact pads. Keywords: Auxetic structures, impact pads, indentation resistance, explicit dynamics, 3D printing, FDM, Poisson’s ratio

Dynamic Analysis of Eccentrically Stiffened Sandwich Thick Plates with Auxetic Honeycomb Core and GPL-RC Face Layers under Blast Loading

The object of this study is eccentrically stiffened sandwich thick plates with the core layer made of negative poisson material. The analytical method base on the first order shear deformation theory (FSDT) is applied to analyse dynamic response and vibration of the plates. The numerical results of the study have been compared with other studies to evaluate the reliability of the calculation. The analysis results of the nonlinear dynamic response and the vibration show that the elastic foundation and the graphene volume ratio positively impact the behavior of the plates. On the other hand, imperfection and thermal environment have a negative effect on the behavior of sandwich plates. Research has also been performed to evaluate the effect of blast load, axial load and shape on the dynamic response of the plate.

Assessment of negative poisson's ratio effect on thermal post-buckling of FG-GRMMC laminated cylindrical panels

This paper examines the thermal post-buckling behaviors of graphene-reinforced metal matrix composite (GRMMC) laminated cylindrical panels which possess in-plane negative Poisson's ratio (NPR) and rest on an elastic foundation. A panel consists of GRMMC layers of piece-wise varying graphene volume fractions to obtain functionally graded (FG) patterns. Based on the MD simulation results, the GRMMCs exhibit in-plane NPR as well as temperature-dependent material properties. The governing equations for the thermal post-buckling of panels are based on the Reddy's third order shear deformation shell theory. The von Karman nonlinear strain-displacement relationship and the elastic foundation are also included. The nonlinear partial differential equations for GRMMC laminated cylindrical panels are solved by means of a singular perturbation technique in associate with a two-step perturbation approach and in the solution process the boundary layer effect is considered. The results of numerical investigations reveal that the thermal post-buckling strength for (0/90)5T GRMMC laminated cylindrical panels can be enhanced with an FG-X pattern. The thermal post-buckling load-deflection curve of 6-layer (0/90/0)S and (0/90)3T panels of FG-X pattern are higher than those of 10-layer (0/90/0/90/0)S and (0/90)5T panels of FG-X pattern.

Application of mixture distributions for identifying thresholds of frequent and high inpatient mental health service use in longitudinal data

Background There is a need for greater understanding about frequent and high use of inpatient mental health services, and those with ongoing increased needs. Most studies employ a threshold of frequent use (e.g. numbers of admissions) and high use (e.g. lengthy stays) without justification. Aims To identify model-driven thresholds for frequent/high inpatient mental health service use and contrast characteristics of patients identified using various models and thresholds. Method Retrospective population-based study using 12 years of longitudinal data for 5631 patients admitted with a mental health diagnosis. Two-component negative binomial and poisson mixture (truncated/untruncated) models identified thresholds for frequent/high use in a 12-month period. Results The two-component negative binomial mixture model resulted in the best model fit. Using negative binomial-derived thresholds, 5.3% of patients had a period of frequent use (admitted six or more times), 15.8% of high use (hospitalised for 45 or more days) and 3.5% of heavy use (both frequent and high use). The prevalence of specific mental health disorders (e.g. mood disorder and schizophrenia) among frequent and high use cohorts varied across thresholds. Conclusions This model-driven approach can be applied to identify thresholds in other cohorts. Threshold choice may depend on the magnitude and focus of potential interventions.

Energy absorption characteristics of honeycomb materials with negative poisson’s ratio*

Using a combination of finite element numerical simulation and experimental verification, the honeycomb structure with different parameters of negative Poisson’s ratio is compressed at a uniform speed. The influence of angle parameter θ, size parameter h and thickness parameter t on Poisson’s ratio and energy absorption of the whole structure is studied, and the main factors influencing Poisson’s ratio and energy absorption are discussed. The results show that the larger concave angle, the smaller size and the larger thickness of the honeycomb cell, the better energy absorption of the overall structure, and the angle is the parameter that has the greatest influence on the Poisson’s ratio and energy absorption. Meanwhile, it is demonstrated that the honeycomb hybrid auxetic material has better energy absorption.

Why European biodiversity reporting is not reliable.

The Convention on Biological Diversity (CBD) aims to end the loss of biodiversity, which is one of the greatest ecological challenges of our time. The lack of success in biodiversity policy implementation is partly related to gaps in biodiversity monitoring. Our overall objective is to contribute to the preparation of the upcoming post 2020 period by a review of biodiversity indicator choices in European CBD reports and hence in national monitoring systems. Negative binary generalized models and poisson generalized linear models prove that through free indicator choice in CBD reporting, countries do not choose biodiversity indicators according to their national geographic and socioeconomic characteristics. Moreover, species and ecosystem diversity indicators were chosen with a disproportionate frequency compared to that of genetic diversity indicators. Consequently, trends derived from national CBD reports and monitoring systems in Europe are not reliable, which should be an alarming signal concerning biodiversity policy implementation. Finally, a flow chart to revise national biodiversity monitoring systems is proposed.

Effect of negative poisson's ratio on the axially compressed postbuckling behavior of FG-GRMMC laminated cylindrical panels on elastic foundations

Auxetic materials are one of the metamaterials that have potential applications in many scientific and engineering fields. In this paper, an investigation is presented on the postbuckling responses of axially loaded graphenereinforced metal matrix composite (GRMMC) laminated cylindrical panels with in-plane negative Poisson's ratio (NPR). The panels are made of GRMMC laminates and rest on an elastic foundation in thermal environments. The graphene volume fraction in GRMMC layer may vary across the panel thickness in order to achieve a piece-wise functionally graded (FG) pattern. The GRMMC layers have in-plane NPR and temperature dependent material properties. The governing differential equations for the GRMMC laminated cylindrical panels are formulated based on the Reddy's third order shear deformation shell theory and are solved by using a singular perturbation technique along with a two-step perturbation approach. Numerical investigation is carried out to study the influence of the in-plane NPR, the FG patterns, the thermal environmental conditions and the foundation stiffness on the postbuckling responses of the GRMMC laminated cylindrical panels under axial compressive load. The results reveal that the in-plane NPR can lead to a substantial change of the postbuckling behaviors of the GRMMC laminated cylindrical panels.

Development of helical auxetic yarn with negative Poisson’s ratio by combinations of different materials and wrapping angle

Auxetic materials have negative Poisson ratio which has a multiple ranges of functional applications. The helical auxetic yarn was successfully developed through direct twist system by using core and wrap yarn or filament, which shows Auxeticity when the HAY is stretched in longitudinal direction in response it expand in transverse direction, Helical Auxetic Yarns were developed using various parameters of the core and warp filament, these parameters are wrapping angle (Twist per meter), diameter ratio, and modulus ratio. The strength of Helical yarn was characterized using single yarn strength and Image J software was used for the calculation of poisson’s ratio. According to test results, it is concluded that the core filament of helical auxetic yarn increased its thickness in transverse direction under stress, and a considerable negative poisson’s ratio was calculated. The values of negative poisson’s ratio described that the auxeticity had a direct relation with core filament thickness or diameter and inversely proportional to the linear density of wrap filament, in case of the wrap angle the auxeticity of HAY yarn had an inverse effect with wrap angle. Kevlar/polypropylene combination sample showed maximum auxeticity at a 15-degree angle while Kevlar/nylon combination sample showed minimum auxeticity at a 25-degree wrap angle.

The use of auxetic materials in tissue engineering.

A number of biological tissues have been reported as behaving in an auxetic manner, defined by a negative Poisson's ratio. This describes the deformation of tissue which expands in the axial and the transverse directions simultaneously while under uniaxial tension; and contracts axially and transversely upon uniaxial compression. The discovery of auxetic behaviour within biological tissues has implications for the recreation of the auxetic loading environment within tissue engineering. Tissue engineers strive to recreate the natural properties of biological tissue and in order to recreate the unique loading environment of cells from auxetic tissue, an auxetic scaffold is required. A number of studies have used a variety of auxetic scaffolds within tissue engineering. Investigation into the effect of auxetic micro-environments created by auxetic scaffolds on cellular behaviour has demonstrated an increased cellular proliferation and enhanced differentiation. Here, we discuss studies which have identified auxetic behaviour within biological tissues, and where cells have been cultured within auxetic scaffolds, bringing together current knowledge of the potential use of auxetic materials in tissue engineering applications and biomedical devices.

Magnetic borophenes from an evolutionary search

A computation methodology based on ab initio evolutionary algorithms and the spin-polarized density functional theory was developed to predict two-dimensional (2D) magnetic materials. Its application to a model system borophene reveals an unexpected rich magnetism and polymorphism. A stable borophene with nonzero thickness was an antiferromagnetic (AFM) semiconductor from first-principles calculations, which can be further turned into a half metal by finite electron doping. In this borophene, the buckling and coupling among three atomic layers are not only responsible for the magnetism, but also result in an out-of-plane negative Poissons ratios under uniaxial tension, making it the first elemental material possessing auxetic and magnetic properties simultaneously.

Extreme values of Young’s modulus and Poisson’s ratio of hexagonal crystals

The variability of Young’s modulus and Poisson’s ratio for hexagonal crystals was studied. Expressions for three stationary values of Young’s modulus and eight stationary values of Poisson’s ratio were obtained. Numerical analysis of the extrema of the elastic characteristics for crystals was given based on experimental data from the Landolt-Börnstein reference book. Classification schemes for extreme values of Young’s modulus and Poisson’s ratio are proposed. Data on hexagonal materials with negative Poissons ratio are obtained. It was shown that global extremes of Poisson’s ratio can exceed the value 0.5, which is the upper limit for isotropic materials. On the other hand, hexagonal crystals were not found for which the global minimum value was less than −1 (lower limit for isotropic materials).