Search

This paper dealt with the vibration characteristics of an auxetic rectangular plate under in-plane compression. Firstly, the equivalent bending stiffness matrix of a star-shaped auxetic plate was obtained using Castigliano's theorem and the homogenization technique. Then, employing the classical plate theory (CPT) in conjunction with the Rayleigh–Ritz method, the natural frequencies of auxetic plate were extracted. The chebyshev polynomial series has been selected to define the assumed displacement fields of the plate. Convergence study for the Rayleigh–Ritz method was conducted. The accuracy of the proposed mathematical model for the star-shaped auxetic plate was validated using the results from a finite element analysis (FEA). Effects of unit cell geometric parameters on the natural frequencies of the plate were examined. The auxeticity angle of star-shaped pattern had a significant effect on the natural frequencies. The present approach can be extended into other auxetic patterns, such as re-entrant bowtie auxetics. [ABSTRACT FROM AUTHOR]

This paper introduces a novel metasurface based on Auxetic metamaterials for attenuating and isolating low-frequency Rayleigh waves. Distributed scatterers are embedded in the Auxetic substrate to form the unit cell, and the meticulously designed layout is intended to induce more multipolar resonance modes. Firstly, the propagation characteristics of Rayleigh waves in the elastic half-space containing metamaterial domain are investigated under the dynamic effective framework of elastic media, and the effective parameter combinations for shielding Rayleigh waves are summarized, which provide a guide for customized design. Then, a new ultra-low frequency band gap is revealed via eigenstate analysis and effective parameter calculation. More noteworthy is the discovery of bridging effects in hybrid bands. Finally, multiple bandgaps, including ultra-low frequency bandgap, are integrated through hybrid bands, achieving an ultra-wide attenuation from 3.2 Hz to 20 Hz, almost perfectly covering the main frequency range of real seismic Rayleigh waves. At the same time, a reduction of up to 96.3% in the response peak is also validated in time-domain testing. More promisingly, there is still room to improve the low-frequency performance of the metasurface by optimizing the effective modulus of the Auxetic metamaterial. Undoubtedly, it further explores the physical boundary of extremely compact metamaterials in modulating even larger wavelength, which will inspire more potential Auxetic metamaterials for applications in emerging fields. [ABSTRACT FROM AUTHOR]

In this paper, the free vibration characteristics of stiffened sandwich plates with auxetic core and functionally graded piezoelectric face sheet are investigated. The sandwich plate configuration comprises three distinct layers: a top layer consisting of functionally graded piezoelectric material (FGPie), a core layer composed of auxetic material exhibiting a negative Poisson's ratio, and a bottom layer made of functionally graded material (FGM). The sandwich plate is reinforced by isotropic stiffeners along the x and y directions. A novel model is established based on the four-variable shear deformation refined plate theory and the pb2-Ritz method. This model offers the flexibility to analyze plates with diverse mechanical boundary conditions and supports two types of electrical boundary conditions: closed circuit and open circuit. The accuracy and convergence of the proposed model are validated through comparative analyses against published results, thereby confirming the reliability when analyzing the vibration characteristics of this complex sandwich structure. Furthermore, some new investigations are carried out to explore the influence of various parameters on the vibrational characteristics of the stiffened piezoelectric auxetic sandwich (SA-FGPie) plates. The results suggest that the properties of the reinforcing stiffeners, such as quantity or dimensions, alter the free vibration characteristics of the SA-FGPie plates significantly. In addition, parameters such as the volume fraction indexes of the FGPie and FGM layers, electrical boundary conditions or FGPie layer thickness, as well as geometric parameters of the auxetic unit cell also have a significant influence on the vibration response of SA-FGPie plates. However, the influence of these parameters depends on the specific boundary conditions. [ABSTRACT FROM AUTHOR]

This paper presents a novel rhombic star-shaped honeycomb (RSSH) configuration with tunable Poisson's ratio and elastic modulus, and an RSSH with the U-shaped ligaments (URSSH) configuration is generated to analyze the effect of the curved ligaments on the elastic properties of RSSH. Cellular structure of RSSH combines with a rhombic and an improved star-shaped geometry, which can also be subdivided into flexible segments and rigid segments. In-plane elastic properties of the RSSH cell, including Poisson's ratio and elastic modulus, are both derived by analytical model based on flexibility modeling method and Castigliano's second theorem. Based on the guidance of theoretical model, quasi-static tensile experiments and finite element simulation of RSSH and URSSH specimens are carried out with different Poisson's ratio. The experimental results are in good agreement with the theoretical predictions and finite element analysis results. Length of cellular ligaments Lt1, dt have linear relationship with mechanical properties of the RSSH cell under constant angle θ1 and make the cellular configurations with different Poisson's ratio more obtainable. The effect of the symmetry of the flexible segments on the cellular mechanical properties is also analyzed through theoretical prediction. The introduction of asymmetry can bring wider design space of RSSH mechanical properties, especially Poisson's ratio. This work demonstrates the promising potential for applying RSSH configurations in 2D morphing structures with tunable auxetic behaviors. [ABSTRACT FROM AUTHOR]

As a measuring device, an auxetic piezo-resistant sensor must have the characteristics of the measuring equipment. One of these features is to have the correct and same answer in different strains and directions (same answer in different conditions). This issue should be considered in the case of auxetic piezo-resistant sensors because of having different Poisson's ratios at different strains and also being generally anisotropic. In this paper, the problem of instability of Poisson's ratio during the strain for auxetic structures was investigated and showed that the sensing performance of re-entrant auxetic piezo-resistant sensors is nonlinear due to the nonlinearity of Poisson's ratio over a broad range of stain values. To investigate this issue, highly sensitive, stretchable, piezoresistive sensors based on graphite powders sandwiched between silicon rubber layers were prepared using a re-entrant auxetic structure. The sensing performance of the auxetic sensors was identified and compared with previous sensors. The presented sensor showed piezoresistive enhancement under tension loading, with improvement up to 176 and 380% (in terms of gauge factor) in comparison with previous mix auxetic and conventional composite sandwich sensors, respectively. Furthermore, we proposed an auxetic structure that has a constant Poisson's ratio over a broad range of strains. Using this auxetic structure made it possible to design an auxetic sensor with linear sensitivity over a broad spectrum of strain values. The auxetic sensor with a constant value of Poisson's ratio has stable sensitivity changes at different strains. It means that the sensor sensitivity has a fixed slope. In the next works, we intend to use isotropic auxetic structures to make piezo-resistant auxetic sensors. [ABSTRACT FROM AUTHOR]

Each year 65% of young athletes and 25% of physically active adults suffer from at least one musculoskeletal injury that prevents them from continuing with physical activity, negatively influencing their physical and mental well-being. The treatment of musculoskeletal injuries with the adhesive elastic kinesiology tape (KT) decreases the recovery time. Patients can thus recommence physical exercise earlier. Here, a novel KT based on auxetic structures is proposed to simplify the application procedure and allow personalization. This novel KT exploits the form-fitting property of auxetics as well as their ability to simultaneously expand in two perpendicular directions when stretched. The auxetic contribution is tuned by optimizing the structure design using analytical equations and experimental measurements. A reentrant honeycomb topology is selected to demonstrate the validity of the proposed approach. Prototypes of auxetic KT to treat general elbow pains and muscle tenseness in the forearm are developed. [ABSTRACT FROM AUTHOR]

Each year 65% of young athletes and 25% of physically active adults suffer from at least one musculoskeletal injury that prevents them from continuing with physical activity, negatively influencing their physical and mental well-being. The treatment of musculoskeletal injuries with the adhesive elastic kinesiology tape (KT) decreases the recovery time. Patients can thus recommence physical exercise earlier. Here, a novel KT based on auxetic structures is proposed to simplify the application procedure and allow personalization. This novel KT exploits the form-fitting property of auxetics as well as their ability to simultaneously expand in two perpendicular directions when stretched. The auxetic contribution is tuned by optimizing the structure design using analytical equations and experimental measurements. A reentrant honeycomb topology is selected to demonstrate the validity of the proposed approach. Prototypes of auxetic KT to treat general elbow pains and muscle tenseness in the forearm are developed. [ABSTRACT FROM AUTHOR]

Materials whose Poisson's ratio is negative (e.g., so-called auxetic materials) have a number of unusual mechanical and functional properties. This paper solves an orthotropic and elastic layer under a rigid cylinder indenter. The intensity factor of the stress field is adopted to characterize the concentration of the stresses at the edge of the indenter. Closed form solutions can be obtained if the diameter of the indenter is considerably small than the thickness of the elastic layer. Otherwise, the field intensity factors can be found numerically based on the dual integral equation technique. The effects of the layer thickness and Poisson's ratio of the material on stress concentration at the indenter tip are discussed. The results show that materials with negative Poisson's ratio can substantially reduce the stress concentration at the edge of the indenter and increase the energy absorbing. This research is helpful for understanding the possible failure behavior and to optimize the mechanical properties of the materials (i.e., Poisson's ratio and elastic modulus) in order to achieve a maximum indentation resistance for auxetic materials. [ABSTRACT FROM AUTHOR]

The vibration and damping performances of carbon fiber-reinforced polymer (CFRP) three-dimensional double-arrow-head (3D DAH) auxetic metamaterials are investigated in this paper. The negative Poisson's ratio effects of the CFRP 3D DAH auxetic metamaterials are analytically studied by the energy method. 3D finite element models based on Modal Strain Energy approach are developed to analyze their vibration and damping characteristics. To validate the numerical models in the present study, the CFRP 3D DAH auxetic metamaterials are designed and manufactured. The sine-sweep response tests are conducted to investigate their vibration performances. The influence of different inclined corrugated angles, and fiber orientations on the natural frequencies, loss factors and the nominal Young's modulus are plotted and discussed using validated numerical models. Meanwhile, the effect of Poisson's ratio on the nominal Young's modulus, natural frequencies and loss factors is also revealed explicitly. Furthermore, the comprehensive evaluation parameter that simultaneously characterizes the structural bearing capacity and vibration damping performance is further improved through parameter optimization. [ABSTRACT FROM AUTHOR]

A band gap region, or simply a band gap, is a range of frequencies where vibrations of certain frequency ranges are isolated. In the present paper, such ranges are sought through the study of different cases for the shape of the unit cells of a lattice, i.e., of an assembly of classical structural elements, such as beams and plates. A lattice with a specific, special designed microstructure is considered in the present investigation. Each particular cell of the examined lattice is studied as a classical composite material consisting of a matrix and the reinforcing core (e.g., matrix-fiber composite), and it is discretized by using two-dimensional plane stress finite elements. The form of the core of the unit cells can be of several shapes, e.g., quadratic, circular, and star. Some of these shapes provide the whole lattice with auxetic behavior, with negative Poisson's ratio at the homogenized properties. The shape and the microstructure of the lattice is optimized in order to achieve isolation of the desired frequencies. A first attempt on the optimization of star-shaped microstructures is also presented. The optimization is carried out using powerful global optimization methods, such as the genetic algorithms. Results indicate that band gaps may appear in both conventional and auxetic microstructures. Moreover, the appearance and the size of the band gaps depend on the selected microstructure. [ABSTRACT FROM AUTHOR]

The annulus fibrosus exhibits complex osmotic and inelastic effects responsible for unusual transversal behavior with a Poisson's ratio higher than 0.5 in fibers plane and negative (i.e., auxetic) in lamellae plane. In this paper, we present a new chemo-mechanical approach for the intrinsic osmo-inelastic response of the annulus fibrosus in relation to the microstructure of the layered reinforced soft tissue, the biochemical environment and the mechanical loading conditions. The constitutive model introduces the coupling between the deformation-induced inelastic stress in the tangled extracellular matrix and the stress-free swelling due to internal fluid content variation by osmosis. The proposed formulation is implemented into a finite element code, and numerical simulations on annulus specimens, including explicitly lamellae and interlamellar zones, are presented. To illustrate the capability of the approach to capture experimental observations quantitatively, the simulated results are compared to experimental results obtained by monitoring the full-field strain in annulus specimens using digital image correlation method. Some material constants are found by matching the free swelling in a water bath with different salt concentrations, and others are found by matching tensile results in terms of loading–unloading stress–stretch curve and transversal behavior. The constitutive model is found to successfully capture the variations in osmolarity and strain-rate conditions (both statistically significant, p < 0.05) on the intrinsic response and the auxeticity. The stress/strain patterns in the model simulation provide valuable insights into the role of the interlamellar zone in the osmo-inelastic mechanisms. [ABSTRACT FROM AUTHOR]

This paper evaluates the longitudinal wave speed through a plate in which its two opposing sides are elastically restrained in the width direction, taking into consideration the material auxeticity and strain as well as changes to the density and cross-sectional area. Apart from the known role of Young's modulus and density, the present results reveal that the wave speed can be enhanced by increasing the width elastic restraint. In the case of high elastic restraint, the speed of both tensile and compressive waves can be minimized by selecting plate materials with Poisson's ratio of low magnitude. In the case of low elastic restraint, the speed of tensile and compressive waves can be greatly reduced by selecting plate materials with large positive and large negative Poisson's ratio, respectively. For the special case of negligible strain, the longitudinal wave speed reduces to the elementary wave speed in prismatic rods and in plates of infinite width when the width elastic restraint stiffness approaches zero and infinity, respectively. The obtained results not only avail more parameters for adjusting the longitudinal waves in plates, but also identify the differing methods of effectively controlling the wave speed between tensile and compressive waves when the strain magnitude is non-negligible. [ABSTRACT FROM AUTHOR]

Jounce bumpers are indispensable components in vehicle suspension systems. It can attenuate impact energy and improve the ride comfort performances during transient pulse impacts from roads. However, the traditional jounce bumpers cannot achieve ideal mechanical performance and are difficult for parametric optimization due to its various shapes which are hard for parameterization. In this paper, a cylinder auxetic structure was introduced and applied as the suspension jounce bumper. Auxetic jounce bumper can be primarily defined by several variables. With tunable structure parameters, a large region of mechanical performances can be realized. In order to evaluate and optimize the performance of auxetic jounce bumpers, they were assembled into vehicle models to conduct virtual ride comfort tests under bump road. The maximum vertical acceleration of vehicle was defined as the objective function of the optimization problem of auxetic jounce bumper. On the purpose of improving optimization efficiency, Gaussian process regression method was employed to establish the metamodel of auxetic jounce bumper based on the sample set created by orthogonal design of experiments method. A series hybrid GA-SQP (Genetic algorithm-Sequential quadratic programming) algorithm, provided with both global and fast local searching abilities, was used for the optimization of auxetic jounce bumper. For comparison, GA algorithm was also applied for auxetic jounce bumper optimization alone. It is proved that the proposed optimization process is accurate and can improve optimization efficiency. Then the optimized design through hybrid algorithm was compared with original design. The maximum vertical acceleration of vehicle when travelling through bump was reduced with optimized design, and the vehicle ride comfort performance was improved. [ABSTRACT FROM AUTHOR]

3D auxetic textile composite is a special type of auxetic materials which has attracted more attention in recent years. Its deformation behaviour and mechanical properties under quasi-static compression have been investigated in the previous studies. In this paper, a further study on its mechanical properties under low-velocity impact is presented. Both single and repeating impact tests were conducted at different impact energy levels ranging from 12.7 to 25.5 J. Results show that the 3D auxetic textile composite has better impact protective performance than the 3D non-auxetic textile composite due to better transmitted force reduction and higher energy absorption capacity under single-time impact and higher structural stability under repeating impacts. The results also show that the difference in protective performance between the auxetic and non-auxetic textile composites get increased with the increase in impact energy. [ABSTRACT FROM AUTHOR]

This paper is concerned with the deformation of a chiral elastic bar subjected to a thermal field. The bar is composed of two different materials welded together along the surface of separation. The behavior of chiral materials is of interest for the investigation of bones and auxetic materials. We study the deformation of isotropic chiral materials by using the equilibrium theory of Cosserat thermoelasticity. The temperature variation is assumed to be a polynomial in the axial coordinate. It is shown that a plane thermal field, in contrast with the result predicted by the theory of achiral materials, produces torsional effects. The solution of the problem could be used to investigate the behavior of bone implants and other compound cylinders. The method is applied to the case of a circular bar reinforced by a longitudinal circular rod. [ABSTRACT FROM AUTHOR]

The design of mechanical microstructures having auxetic behaviour is proposed in this paper using techniques of topology optimization for compliant mechanisms. A robust hybrid algorithm based on evolutionary algorithms and local search steps is used. The result may need verification in order to accommodate needs not taken into account in the topology optimization. Therefore, a numerical homogenization scheme is used in order to show that the final design still has the wished negative Poisson's property. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

In this paper we explore the effect of the orientation of the main crystallographic axes in relaxor-ferroelectric single crystals (SCs) on the piezoelectric anisotropy and squared figures of merit of 2-2 parallel-connected SC/auxetic polymer composites. The single-crystal component for the composite is chosen from the perovskite-type solid solutions with compositions near the morphotropic phase boundary and poled along the perovskite unit-cell [011] direction ( mm symmetry of domain-engineered SCs). The orientation of the main crystallographic axes in the single-crystal component is observed to strongly influence the piezoelectric coefficients $$d_{3j}^{*}$$ , squared figures of merit $$d_{3j}^{*}$$ $$g_{3j}^{*}$$ , electromechanical coupling factors $$k_{3j}^{*}$$ , and hydrostatic analogs of these parameters of the 2-2 composite. Inequalities $$| {d_{33}^{*} /d_{3f}^{*} } | > 5$$ and $$| {k_{33}^{*} /k_{3f}^{*} } | > 5$$ ( f = 1 and 2) are achieved at specific orientations of the main crystallographic axes due to the significant anisotropy of the elastic and piezoelectric properties of the single-crystal component. The use of an auxetic polyethylene (a polymer component with a negative Poisson's ratio) leads to a significant increase in the hydrostatic parameters. Particular advantages of such composites over conventional ceramic/polymer composites are taken into account for transducer, hydroacoustic, energy harvesting, and other applications. [ABSTRACT FROM AUTHOR]

This paper is dedicated to Prof. Jacques Friedel, an inspirational scientist and a great man. His excellence and clear vision led to significant advances in theoretical physics, which spilled into material science and technological applications. His fundamental theoretical work on commonplace materials has become classic. We can think of no better tribute to Friedel than to apply a fundamental analysis in his spirit to a peculiar class of materials-auxetic materials. Auxetic materials, or negative-Poisson'-ratio materials, are important technologically and fascinating theoretically. When loaded by external stresses, their internal strains are governed by correlated motion of internal structural degrees of freedom. The modelling of such materials is mainly based on ordered structures, despite the existence of auxetic behaviour in disordered structures and the advantage in manufacturing disordered structures for most applications. We describe here a first-principles expression for strains in disordered such materials, based on insight from a family of 'iso-auxetic' structures. These are structures, consisting of internal structural elements, which we name 'auxetons', whose inter-element forces can be computed from statics alone. Iso-auxetic structures make it possible not only to identify the mechanisms that give rise to auxeticity, but also to write down the explicit dependence of the strain rate on the local structure, which is valid to all auxetic materials. It is argued that stresses give rise to strains via two mechanisms: auxeton rotations and auxeton expansion/contraction. The former depends on the stress via a local fabric tensor, which we define explicitly for 2D systems. The latter depends on the stress via an expansion tensor. Whether a material exhibits auxetic behaviour or not depends on the interplay between these two fields. This description has two major advantages: it applies to any auxeton-based system, however disordered, and it goes beyond conventional elasticity theory, providing an explicit expression for general auxetic strains and outlining the relevant equations. [ABSTRACT FROM AUTHOR]

Additive Manufacturing (AM) has brought new opportunities to the mechanics of materials research community because of new capabilities to access and control the material meso- and microstructure, which previously was possible only by computational means. The Special Issue begins with three papers on AM stainless steel focusing on tensile failure and thermal strain development. In I Analysis of the Material Behavior of 3D Printed Laminates via FFF i by Czekanski, et al., the authors investigated the mesoscale influence on mechanical properties of AM composites using a laminate modeling approach. [Extracted from the article]