Negative Poisson's Ratio Effect Research Articles

Morning glory-inspired lattice structure with negative Poisson's ratio effect

Negative Poisson's ratio (NR) structures have compression-contraction properties. Many studies have focused on the NR effect of artificially designed microstructures, but very few studies have been conducted on biomimetic NR structures. In this study, inspired by the geometric features and living habits of a plant called morning glory, a biomimetic lattice structure is proposed. A finite element model of the morning glory-inspired lattice structure (MGS) was established and the sample was prepared by 3D printing. Axial compression experiments and simulations were performed, and the MGS exhibited the characteristics of light weight, efficient energy absorption, and the NR effect. The mechanisms of the NR and compression force characteristics were analyzed in detail. In addition, many MGS models have been proposed, based on various connection modes of cells. The effects of the cell distance and cell connection modes on the compression behavior of the MGS were further studied. It was found that the energy absorption efficiency and NR effect of the MGS deteriorated with an increase in vertical cell spacing, and the energy absorption efficiency and NR effect of the MGSs tended to contradict each other. Furthermore, the minimum NR (MNR) values obtained for W5MG and F6MG were –1.509 and –1.480, respectively. In summary, the MGSs have broad application prospects.

Dynamic crushing of uniform and functionally graded origami-inspired cellular structure fabricated by SLM

This paper investigated the dynamic crushing of a novel periodic origami-inspired cellular structure. The large-scale multi-layer metallic specimens considered geometry, anisotropy and gradient design were fabricated by an SLM system. Mechanical properties and energy absorption characteristics under dynamic load were investigated through drop hammer impact test. The results show that this novel structure has obvious negative Poisson's ratio (NPR) effect and relatively balanced mechanical properties in the three orientations under impact load. Among them, the z-axis orientation was the best bearing orientation. Three gradient modes of this structure were designed and tested for the first time. Results showed the gradient design effectively improved the energy absorption performance of this structure. Besides, high-speed tensile tests on the additively manufactured metallic coupons showed the strain rate effect and anisotropy of AM stainless steel 304L were significant. Corresponding Cowper-Symonds models were fitted. The numerical simulation reproduction based on LS-DYNA was validated to be well-matched with the test results. Parametric analysis showed that the initial folding angle was the crucial factor for the initial peak force, and the gradient growth rate can significantly affect the energy absorption of the structure.

Study on the mechanical properties of CFRP composite auxetic structures consist of corrugated sheets and tubes

In recent years, auxetic (negative Poisson's ratio) structures have attracted great attention because of their non-conventional behaviour. However, auxetic structures are usually characterized by low stiffness, which limits their application. Once, their stiffness can be improved, their application field will be significantly broadened. In addition, most auxetic structures are difficult to be produced due to their complex geometries. To solve these two problems, high-performance carbon fibre reinforced polymer (CFRP) composites are used to manufacture an auxetic structure consist of corrugated sheets and tubes. The mechanical properties of the composite auxetic structure consist of corrugated sheets and tubes (CorTube) are studied by experiments, finite element simulation and theory analysis. The results show that, the composite CorTube structures display obvious negative Poisson's ratio effect in large compression strain range, and the auxetic characteristics of the composite CorTube structures become more notable with the increase of the compression strain. The stiffness of the structure depends on the thickness of the corrugated sheets in small strain stage, while the material parameters of the tubes plays determining role in large strain stage. Finally, the deformation characteristics and failure modes of the CorTube during the compression process are discussed.

Dynamic crushing response of novel re-entrant circular auxetic honeycombs: Numerical simulation and theoretical analysis

Auxetic honeycombs have a variety of potential applications in aerospace engineering due to their excellent mechanical and multidisciplinary properties. A novel class of auxetic honeycombs have been invented recently named as Re-entrant circular (REC) honeycombs. The REC honeycombs can be obtained by replacing the sloped cell walls of the well-known re-entrant (RE) unit honeycombs with double circular arc walls to dissipate more energy. This study aims to investigate the in-plane dynamic crushing responses of the novel REC honeycombs through numerical simulations and theoretical analyses. LS-DYNA based numerical simulations revealed the “X” and “I” combined deformation mode of the REC honeycomb under low velocity crushing, and the “I” mode under high velocity loading. The geometric parameters of unit cell and the crushing velocity were both found to have great effects on the proximal end crushing stress of the REC honeycomb. It was also shown that the REC honeycomb presents obvious negative Poisson's ratio (NPR) effect, attributed to its re-entrant characteristic. Based on the meso-scale deformation mechanisms of the representative unit cell, theoretical models have been established to predict the plateau stress of the REC honeycomb under different crushing velocities. The theoretical predictions were in good agreement with the numerical simulation results. Moreover, the dynamic sensitivity index and the deformation mode map of the REC honeycomb were obtained to evaluate its dynamic response sensitivity to the loading velocity. Finally, the in-plane crushing characteristics of the REC and the RE honeycombs were compared. The REC honeycomb was found to show higher specific energy absorption (SEA) and penetration resistance than its RE counterpart, due to the more plastic hinges formed during the dynamic crushing process.

In-plane crushing behaviors of a new-shaped auxetic honeycomb with thickness gradient based on additive manufacturing

In this paper, the new honeycomb with the thickness gradient is proposed. The crushing behaviors of the new-shaped auxetic honeycomb is simulated by using finite element software ABAQUS/Explicit. A quasi-static experiment is conducted to compare the energy absorption effect of the uniform and the thickness gradient honeycombs. A significant negative Poisson's ratio effect is observed in the gradient honeycomb, and the energy absorption curves of different gradient rates are also analyzed. The results show that the platform stress and energy absorption are enhanced with the increase of the gradient rate and velocity. The effect of the positive gradient in reducing the peak crushing force is more obvious. It is proved that the thickness gradient design of the new-shaped auxetic honeycomb is an effective method to enhance the energy absorption capacity.

In-plane elasticity of the re-entrant auxetic hexagonal honeycomb with hollow-circle joint

This work proposed an improved modification on the common re-entrant hexagonal honeycomb (RHH) by replacing the solid junction of the cell walls with a small hollow circle, and thus achieving a novel kind of honeycomb. A simple energy-based approach was adopted to develop theoretical models for predicting the in-plane equivalent elastic moduli of the new honeycomb. Finite element analysis was employed to verify the theoretical models and then the effects of the micro geometrical parameters on the in-plane elastic behaviors were further discussed. The results showed that the new honeycomb possesses an obvious negative Poisson's ratio effect, meanwhile, can achieve higher specific Young's modulus and shear modulus than the RHH. Moreover, the new honeycomb was found to exhibit a more tailored anisotropy than the RHH from the off-axial properties analysis. As a result, the new honeycomb may be an effective substitute for the RHH in application and the new layout can be a good guide for the improved design of auxetic honeycombs.

Three-dimensional enhanced star-shaped honeycombs with negative thermal expansion

In this work, three kinds of three-dimensional enhanced star-shaped honeycombs (3D-ESSH) with enhanced effective Young’s modulus and negative Poisson’s ratio are proposed. Finite element simulations and uniaxial compression experiments are carried out to study the influence of the main parameters on the effective mechanical properties of the structures. The numerical results fit well with the experimental results. Compared with the three-dimensional star-shaped honeycomb (3D-SSH), the negative Poisson's ratio effect and effective Young’s modulus of the 3D-ESSH are significantly enhanced. Comparison among the proposed novel honeycombs indicate that the effective mechanical performance of the structure can be improved more obviously if the reinforcing rods are only added in the loading direction. In addition, the impact of reinforcing rods on the effective thermal expansion coefficient of the novel 3D-ESSH is investigated. It’s noticed that adding reinforcing rods can realize the negative thermal expansion in corresponding direction when combined with proper bi-materials.

Quasi-static compressive behaviour of 3D-printed origami-inspired cellular structure: experimental, numerical and theoretical studies

ABSTRACT This paper proposed a novel periodic cellular structure by introducing re-entrant hexagon-shaped honeycombs and Miura origami geometry. The large-scale multi-layer metallic specimens were manufactured by a selective laser melting (SLM) system and tested for the first time. The compression deformation and energy absorption characteristics under quasi-static load were investigated thoroughly, considering three loading directions and various geometric parameters. The results show that this novel structure has balanced mechanical properties in the three loading directions. Among them, the z-direction is the best bearing direction. Moreover, this structure exhibits an obvious three-dimensional negative Poisson's ratio effect during the compression process. Besides the experimental study, the numerical investigation base on ANSYS/LS-DYNA was carried out to provide an accurate and effective simulation method. Predictive formulas for the critical energy absorption indexes were derived by theoretical analysis based on the rigid folding assumption, validated to be well-matched with the experimental results.

Mechanical properties and damage characterizations of 3D double-arrowhead auxetic structure with high-relative-density realized via selective laser melting

It is an obstacle to constructing mechanics model for the deformation of the joint region in struts-made metamaterials with high relative densities. In this work, a generalized semi-empirical method is provided by the statistical fitting of numerical solutions for joint correction. The mechanical models of three-dimensional (3D) double-arrowhead honeycomb (DAH) auxetic structure are reconstructed with broad geometrical parameters applicability. Ti–6Al–4V specimens with varied relative densities are fabricated by selective laser melting and subjected to the uniaxial quasi-static compression. Results show that theoretical predictions of effective modulus, Poisson's ratio, critical strength and failure modes are consistent with experimental results. As the relative density increases, the negative Poisson's ratio effect gradually disappears, and the effective modulus and critical strength increase sharply. In most configurations, the structure's initial failure mode is the completely yielding at the root of short struts. Specimens with high relative densities display excellent energy dissipation, which have the maximal specific energy absorption of 17.33 J/g when the relative density is 11.1 %.

Hyperbolic‐Like Structure with Negative Poisson's Ratio: Deformation Mechanism and Structural Design

Mechanical metamaterials with negative Poisson's ratio (NPR) effect possess important practical applications in aerospace, nanotechnology, and other fields. The microstructure and its deformation mode directly determine the NPR ability and mechanical performance of auxetic metamaterials. Herein, inspired by the double‐negative‐index ceramic aerogels, a novel NPR structural model is proposed in which symmetric reentrant oblique ligaments and short transversal ligaments constitute the main framework inside a square, which is different from the traditional reentrant structure due to the hyperbolic‐like skeleton and deformation modes. The influence of structural parameters on the NPR effect is investigated using the Timoshenko beam model and finite element simulations. The structural model is then extended to design multiple reentrant structures and assembled structures, respectively. The multiple reentrant structures include multiple pairs of symmetrically hyperbolic‐like skeletons, and the distribution of horizontal ligaments can be regulated to achieve a better NPR effect. For assembled structures under compression, the local rotational deformation and buckling result in structural instability, demonstrated by inflection points in the NPR curves. Moreover, one special assembled structure is found for which there is a linear relationship between the compressive strain and NPR value. The insights should be significant for designing mechanical metamaterials with the NPR effect.

Laboratory tests on engineering properties of a new negative-Poisson′s-ratio geobelt

Reinforcement of elevated subgrades, embankments, or slopes is a focus of highway construction projects. In this study, a new negative-Poisson's-ratio geobelt (NPRG) is developed to facilitate such reinforcements. Herein, the NPRG design and manufacturing process are described in detail. Additionally, tensile tests, pull-out tests, and numerical simulations to test the negative-Poisson’s-ratio effect and mechanical behavior of the NPRG in soil are reported. The results show that the NPRG shell structures are lifted by the core structure under tension, thereby expanding the NPRG cross-section. Hence, a negative-Poisson's-ratio effect is generated. Further results show that the negative-Poisson's-ratio effect of the NPRG only appears when the axial strain exceeds 1.2% or 1.6% (from the test and numerical simulation, respectively). Moreover, with 300 kPa as the boundary, the NPRG peak pulling force first increases and then decreases with increasing upper pressure. Finally, the negative-Poisson's-ratio effect of the NPRG disturbs the surrounding soil. Simultaneously, the NPRG cross-sectional expansion makes it more closely integrated with the surrounding soil, thereby, improving the reinforcement effect.

Electro-induced shape memory effect of 4D printed auxetic composite using PLA/TPU/CNT filament embedded synergistically with continuous carbon fiber: A theoretical & experimental analysis

A novel strategy is proposed to fabricate continuous fiber-reinforced electro-induced shape memory auxetic composites (CFRSMCs) by combining conductive filaments and continuous carbon fiber through 3D printing technology. In the first step, the conductive filaments were manufactured based on Poly-lactic-acid/Thermoplastic-urethane/Carbon-nanotube (PLA/TPU/CNT) blend nanocomposite, and the CFRSMCs were then prepared, composing different carbonaceous fiber content with a variety of extrusion width. The main aim of the present work is to evaluate the mechanical, electrical, and thermal properties as well as the shape memory effect (SME). With regard to this, the negative Poisson's ratio effect of the printed CFRSMCs was precisely assessed through tensile measurement, and a well-adjusted theoretical model was employed for further predictions. Accordingly, as compared to free-fiber printed samples, the CFRSMCs exhibited superb mechanical properties and rapid electro-induced SME (a recovery ratio of 94% under 10 V within 25 s). Moreover, due to tailoring co-conductive networks by the CNTs and carbon fibers in the printed composites, a great deal of activation capability in the auxetic CFRSMCs could be revealed by various stimuli and for smart applications. This advanced strategy indicates a great potential to fabricate various auxetic electro-induced CFRSMCs used in small scale of deployable trusses or other lightweight smart components like adaptive energy absorption devices and human-scale orthopedic materials.

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.

Predicting an ideal 2D carbon nanostructure with negative Poisson's ratio from first principles: implications for nanomechanical devices

The intrinsic negative Poisson’s ratio effect at the level of molecule in two-dimensional nanomaterials, especially in the perfect planar nanostructures with a single atom thickness, is really rare and has attracted a lot of research interests because of its unique mechanical properties in the nanoscale and extensive applications in mechanical nanodevices. In this work, a novel ideal planar carbon nanostructure (PCNS) framework with a single atom thickness composed by carbon and hydrogen atoms is proposed and studied by means of first-principles density functional calculation. The results showed that the PCNS is, simultaneously, of excellent thermodynamic, molecular dynamic and mechanical stabilities. In addition, the electronic structure, mechanical characters, and optical-electronic characteristics of PCNS are also explored. Excitedly, it is found that the PCNS has a significant negative Poisson's ratio effect in plane, and the maximum value of Poisson's ratio is as high as − 2.094. Meanwhile, the material has a wide range of elastic mechanics. Moreover, the PCNS presents an ideal UV absorption performance. It is hoped that this work could be a useful structural design strategy for the development of the ideal 2D carbon-based nanomechanical devices with the intrinsic negative Poisson’s ratio effect and other electronic functions. An ideal 2D carbon nanostructure with negative Poisson's ratio was designed and its properties were investigated from first principles calculation.

MECHANICAL DESIGN, IMPACT ENERGY ABSORPTION AND APPLICATIONS OF AUXETIC STRUCTURES IN AUTOMOBILE LIGHTWEIGHT ENGINEERING

Lightweight and multi-function structures with negative Poisson's ratio have excellent auxetic mechanical properties, and have been demonstrated promising industrial application potentials as energy absorption structures and multifunctional devices in automobile industry due to their enhanced indentation resistance, shear modulus, fracture toughness, impact energy absorption, shock absorption, noise reduction performances and so on. This paper mainly summarizes the mechanical properties of structures with negative Poisson's ratio effect, and their typical structural design and applications in automotive engineering. The contents could be classified into six parts: (1) The concepts and mechanical characteristics of different materials and structures with negative Poisson's ratio are introduced firstly, and the rapid developments in recent decades are also discussed; (2) main design method of materials and structures with negative Poisson's ratio are performed, corresponding manufacturing technologies of foams with negative Poisson's ratio effect are summarized, the design developments of composite materials with negative Poisson's ratio and the frontier artificial intelligence design method for advanced structure with negative Poisson's ratio are also presented; (3) mechanical designs of typical cellular structures with negative Poisson's ratio are introduced in detail including: chiral structure, rigid node rotation structure, double-arrow structure with negative Poisson's ratio, re-entrant honeycomb structure, structure with tensile-torsion effects and so on; (4) many experimental, theoretical and finite element simulation results about the energy absorption characteristics of materials and structures with negative Poisson's ratio are presented; (5) typical industrial applications of advanced materials and structures negative Poisson's ratio as high performance energy application structures in the field of lightweight vehicle design are demonstrated, mainly including: automobile energy absorption box, B-pillar, engine hoods, seat belts, suspension structures, and non-pneumatic tires and so on; (6) industrial application prospects of advanced materials and structures with negative Poisson's ratio (NPR) in automotive engineering, and the technical challenges and promising industrial application potentials are also pointed out.

Study on Negative Poisson Ratio and Energy Absorption Characteristics of Embedded Arrow Honeycomb Structure

Impact collision exists widely in people's daily life and threatens people's life safety. Negative Poisson's ratio structure has good mechanical properties. Therefore, it is of great significance to design and study the energy absorption structure with negative Poisson's ratio effect. Based on the traditional symmetrical concave honeycomb structure (SCHS) with negative Poisson's ratio, two modified negative Poisson's ratio honeycomb structures are proposed by adding embedded straight rib arrow structure and embedded curved rib arrow structure, which are respectively called embedded straight rib arrow honeycomb structure (SRAH) and embedded curved rib arrow honeycomb structure (CRAH). Through finite element simulation experiment, the negative Poisson's ratio characteristics of two cellular cells were studied and the influence of structural parameters of the cells on the Poisson's ratio was discussed. ANSYS/LS-DYNA was used to analyze the energy absorption of the proposed three cellular structures at different impact velocities. Numerical simulation results show that the SRHS and CRAH have greater stress platform value, specific energy absorption and impact force efficiency than SCHS, indicating that the SRAH and CRAH exhibited better energy absorption efficiency and impact resistance performance.

A Novel Strategy for Constructing 3D Dislocated Chiral Metamaterial with Negative Poisson's Ratio

Metamaterials with negative Poisson's ratio (NPR) have a broad range of application background, such as aerospace engineering, automotive engineering, medical instrument engineering, and wearable engineering. Herein, a novel strategy for constructing 3D dislocated chiral metamaterial is proposed that can achieve NPR effect in three directions. According to this strategy, a new dislocated chiral metamaterial composed of dislocated tetrachiral honeycombs and inclined rods is designed and selected as an example to investigate the effectiveness of the strategy. Experiments and numerical simulations are carried out to study the mechanical properties of the new metamaterial, confirming that this metamaterial exhibits NPR effect. The influence of geometric parameters on the elastic constants of the metamaterial is discussed based on experimental and numerical results. Meanwhile, the local loading performances of this dislocated chiral metamaterial and the previous aligned chiral metamaterial are studied and compared. Results show that this dislocated metamaterial possesses a stronger damage resistance capacity than the aligned one. By adjusting the rotational direction of ligaments in honeycombs and the arrangement of inclined rods, more special 3D dislocated chiral metamaterials with advanced properties are available, such as metamaterial with both positive and NPRs, metamaterial with compression–torsion effect.

A novel 3-D structure with tunable Poisson's ratio and adjustable thermal expansion

Abstract： A novel 3-D structure is proposed by adding the reinforcing rods into the original 2-D star-shaped structure to obtain more obvious negative Poisson's ratio effect. The influence of length parameter, thickness parameter, angle parameters and material combination on the effective Poisson's ratio, effective Young's modulus and effective shear modulus of the novel 3-D structure is systematically investigated using cell-based finite element modeling. Additionally, the change rule of material combination sequence and length parameter of the structure's thermal expansion is also studied. The results show that the novel 3-D structure can achieve positive, zero and negative Poisson's ratio, as well as positive, zero and negative thermal expansion when appropriate material combination is adopted. Moreover, the negative Poisson's ratio effect of the novel 3-D structure is distinctly enhanced, and the effective Young's modulus is slightly increased through comparing with other two 3-D star-shaped structures. By selecting material combinations and structural geometry parameters, metamaterials with special properties can be designed for different application fields.

Enhancing indentation and impact resistance in auxetic composite materials

Auxetic materials exhibiting a negative Poisson's ratio are of great research interest due to their unusual mechanical responses and a wide range of potential deployment. However, due to the cellular structure and the bending or rotation deformation nature of the elements in auxetic materials, they usually have relative low stiffness, limiting their applications where high stiffness, strength, hardness, and energy absorption are simultaneously desired. To overcome this limitation, we apply the auxetic lattice structures as the reinforcements combining with the nearly incompressible soft materials as the matrix to create a class of high-performance composites. This coupled geometry and material design concept is enabled by the state-of-the-art additive manufacturing technique. Guided by static and dynamic experimental testing, we systematically study the indentation behavior of the 3D printed auxetics reinforced composites and achieve a significant enhancement of their indentation stiffness and impact resistance compared with the non-auxetic reinforced composites. By digital image correlation processing of experimental tests and numerical simulation, this improved mechanical performance is found due to two deformation mechanisms. The first mechanism is the negative Poisson's ratio effect of the auxetic reinforcements, which makes the matrix in a state of biaxial compression during indentation and impact and hence provides additional support. The second mechanism is the negative Poisson's ratio effect of the overall composites, which makes the auxetic reinforced composites denser at the site of the indentation and therefore are more resistant to indentation. The results show that auxetic structures can lead to design stiffer, harder and tougher composite materials. The material design strategy provides insights into the development of classes of novel auxetic composites with a wide range of mechanical and structural applications.

Deformation behavior of auxetic woven fabric made of foldable geometry in different tensile directions

Auxetic woven fabrics made with special geometrical structures have gained the interest of textile scientists in recent years. This paper reports a study on auxetic woven fabric based on a double-directional parallel in-phase zig-zag foldable geometrical structure. Such a fabric has been already produced and investigated for its negative Poisson's ratio effect in two principal directions (weft and warp directions). However, its negative Poisson's ratio effect in biased tensile directions as well as under repeated tensile loading conditions has not been studied yet. Therefore, in this paper, these two limitations are addressed. The auxetic woven fabric was firstly fabricated, and then subjected not only to tensile tests in different tensile directions, including two principle directions and three biased directions, but also to repeated tensile loading. It was found that both the negative Poisson's ratio effect and the resistance to tensile deformation are dependent upon the tensile direction, and the highest negative Poisson's ratio effect and higher resistance to tensile deformation are obtained in two principal directions.