Effective Poisson's Ratio Research Articles

Reliable comparison of multi-directional mechanical properties for biomimetic circle arc honeycombs

Abstract Compared to straight honeycombs, curved honeycombs derived from biomimetic strategies typically exhibit superior mechanical properties and a broader tunable range. Consequently, there has been a surge in research focusing on curved honeycombs. However, few studies have concurrently designed multiple honeycombs for reliable comparisons, and little attention has been given to isotropy. In this study, circle arc walls were introduced to replace the straight walls of five classical honeycombs, thereby creating representative curved honeycombs for analysis. The numerical modeling method in ANSYS software was validated by experimentally testing 3D printed specimens of circle arc honeycombs. At the same mass and under loading conditions in different directions, it was found that the Young's modulus, yield strength, Poisson's ratio, and energy absorption of circle arc hexagon (CAH), circle arc square (CAS), circle arc triangle (CAT), circle arc re-entrant (CAR), and circle arc double-V (CAD) were assessed. Both experimental and numerical results revealed that CAH demonstrates superior energy absorption while maintaining a high degree of isotropy, characterized by all isotropic factors below 0.1 in mechanical properties. Notably, CAD exhibits a Negative Poisson's ratio (NPR) effect across all loading directions. These results provide benchmarks for future studies on curved honeycombs and guide further research in this field.

Quasi-static and dynamic responses of gradient hexachiral auxetics: Experimental and numerical analysis

In the current paper, the mechanical responses of polymer gradient hexachiral auxetic metamaterials were experimentally and numerically investigated under quasi-static and intermediate strain rate loadings. Five gradient design strategies were explored, including uniform, positive, negative, center positive, and center negative gradients. The deformation/failure mechanism, Poisson's ratio, and energy absorption capability were experimentally analyzed, together with the effects of impact velocity and gradient distribution. Experimental results revealed that the gradient design can mitigate the shear deformation of hexachiral auxetics, which efficiently remain its negative Poisson's ratio effect under dynamic loading. Compare with the quasi-static loading, earlier failure of auxetics was observed under dynamic loads due to the strain rate and inertial effect, which diluted their negative Poisson's ratio effect and energy absorption capability. Among the designs, auxetics with negative gradient configurations showed the best energy absorption under dynamic loading. Numerical analysis further supported the experimental findings and provided insights into the influence of geometric parameters. It shows that thicker configurations and non-uniform node gradient series with coefficients of 1.15 (positive, center positive) and 0.87 (negative, center negative) provided optimal energy absorption under the dynamic loading. This work offers profound insights into enhanced performance mechanisms and provides avenues for optimizing structural design of auxetic metamaterials.

Predicting the properties of metamaterials consisting of curved-wall triangles using ensemble neural networks with interpretability

Machine learning has emerged as a promising tool for predicting the properties of metamaterials, owing to its substantially faster prediction speed compared to conventional methods. However, the lack of interpretability of black-box machine learning models has impeded their adoption in this field. In this work, we develop an ensemble of neural networks (NNE) for predicting the mechanical properties of metamaterials consisting of curved-wall triangles. Our method achieves high prediction accuracy for the effective Young's modulus and Poisson's ratio for most samples. The average relative errors of the NNE are less than 5% for predicting the dimensionless Young's modulus and less than 10% for predicting Poisson's ratios. Additionally, our method is orders of magnitude faster than finite element simulations. More importantly, by explaining the predictions of NNE using SHapley Additive exPlanations (SHAP), we are able to quantify the relationships between geometric features and metamaterial properties. This reveals insights into parameter couplings and nonlinear effects. New physical insights can thus be obtained and new design rules discovered through this machine learning interpretability approach. Overall, our interpretable machine learning model can accelerate the design and discovery of metamaterials while providing physical insights into the inner workings of the models.

Effect of alloying element segregation on theoretical strength and structural low-energy transition of Ni grain boundaries: A first-principles computational tensile test study

Enhancing the stability and strength of nanocrystalline metals through the manipulation of grain boundary (GB) chemistry and structure is crucial for their engineering applications. In this study, first-principle computational tensile tests on Ni Σ5 [001] (210) GBs were conducted with considering Poisson's ratio and strengthening effect of alloying elements B, W, Zr, Ta, B-W and Zr-Ta segregation. The results indicate that the Zr-Ta co-segregated GB shows a remarkable increase in theoretical tensile strength by 195 % compared to the clean GB under small strain conditions. As tensile strain increases, both clean and segregated GBs undergo a low-energy structural transition from the Σ5 [001] (210) to the more stable Σ11 [110] (113). This work presents a promising approach for enhancing the stability of Ni nanograined materials through tensile deformation and GB segregation.

Evaluating predictive scheme for thermomechanical properties of Si-diamond composites.

A novel, parameter-independent multiscale correlational constitutive model has been devised to predict thermomechanical properties of Si-diamond-SiC and Si-diamond composites, including the effective elastic modulus, effective bulk modulus, effective shear modulus, effective Poisson's ratio, average coefficients of thermal expansion as well as thermal conductivity. Based on this model, the effective thermomechanical response of two kinds of composites was simulated, and the underlying mechanisms of thermomechanical coupling between constituents were also critically evaluated. The findings were shown that the effective elastic properties of composites, including effective elastic modulus, effective bulk modulus, effective shear modulus, increased with diamond and SiC, and that the introduction of dispersed diamond with highly thermal conductivity and lowly thermal expansion significantly enhanced thermophysical properties of Si-diamond-SiC composites. The thermomechanical coupling of these composites was influenced by the effective elastic properties of composites and the disparity in the intrinsic properties of constituents.

In‐Plane Energy Absorption Properties of Novel Curved‐Ligaments Auxetic Cellular Structures with Dual‐Platform Performance

To improve the energy absorption capacity of honeycomb, four novel curved‐ligaments auxetic cellular structures (CLACS‐i [i = 1, 2, 3, 4]) based on the Diabolo‐shaped honeycomb (DSH) are introduced in this article. In the simulation results, it is demonstrated that the energy absorption performance of CLACS‐i (i = 1, 2, 3, 4) surpasses that of DSH under low‐, medium‐, and high‐velocity impacts. However, the negative Poisson's ratio effect of novel structures is inferior to that of DSH. With the increase in impact velocity, the inertial effect of the structure is enhanced, and the deformation mode of the structure changes from global deformation to local deformation. Furthermore, different impact velocities and geometric parameters also affect the energy absorption capacity of the structures. Platform stress and specific energy absorption (SEA) of CLACS‐i (i = 1, 2, 3, 4) increase with the increase of velocity. Under medium‐velocity impact loading, the platform stress and SEA of CLACS‐i (i = 1, 2, 3, 4) increase as the geometric parameter θ decreases and the wall thickness t increases. In this study, a reference is provided for the optimal design and application of honeycomb energy‐absorbing components.

Dynamic damage behavior of auxetic textile reinforced concrete under impact loading

To investigate the dynamic compression behavior of Textile-reinforced concrete (TRC) under impact load, low speed and high speed impact tests were performed using a ball drop test and a split Hopkinson pressure bar (SHPB) with ϕ50mm, respectively. In view of the advantages of auxetic materials in impact resistance and energy absorption, the auxetic fiber preforms with negative Poisson's ratio effect were woven into meshes and added to the cement-based materials to obtain the auxetic textile-reinforced concrete. Thus, the auxetic textile reinforced cement-based material is obtained. In this paper, TRC with different textile types, laying layers and surface treatments were prepared, and impact tests with different impact speeds were carried out to evaluate the impact resistance of TRC. The impact damage behavior of TRC was analyzed through the method of digital scattering analysis, and then the impact damage mechanism of TRC was investigated. The results show that the auxetic effect of auxetic textiles can still be stabilized under impact loads of different velocities, which provides better control of deformation and energy consumption in the matrix material. Under different impact heights of falling balls, the impact fracture energy of cementitious materials reinforced with auxetic textiles was increased by up to 22.5 and 20 times, respectively, compared with that of blank samples.

Experimental behavior and fracture prediction of a novel high-strength and high-toughness steel subjected to tension and shear loading tests

In this study, laboratory testing and numerical simulation methods are used to investigate the mechanical behavior and perform fracture prediction of a novel high-strength and high-toughness steel with a negative Poisson's ratio (NPR) effect under combined tensile-shear loading conditions. A test device capable of meeting different tensile-shear combination test angles is designed and manufactured, wherein the mechanical experiments on the NPR (Negative Poisson's Ratio) steel specimens are carried out at various testing angles. Q235 steel and MG400 steel are used as experimental control groups. The results show that the mechanical deformation of NPR steel is significantly better than that of Q235 steel and MG400 steel. Its tensile-shear test curve has no yield plateau and it has quasi-ideal elastic-plastic mechanical properties. The loading direction gradually changes from tension-dominated to shear-dominated as the tension-shear angle increases, and the strength and deformation of the specimens show a decreasing trend. Based on the laboratory test results, a finite element numerical model of NPR steel is established. A series of numerical simulations are carried out under the conditions of different tension and shear angles and the average stress triaxiality and fracture strain data are obtained. The fracture data of NPR steel are fitted using the Johnson-Cook fracture criterion, and the Johnson-Cook fracture parameters under the tensile-shear test conditions of NPR steel are thus obtained. The numerical simulation verifies that the fracture model can accurately predict the tensile-shear fracture behavior of NPR steel.

Compensation mechanics application of NPR anchor cable to large deformation tunnel in soft rock

NPR anchor cable is a new type of support material with negative Poisson's ratio effect, which is widely used in mine support because of its superb compensating mechanical effect. In order to study more deeply the support effect of NPR anchor cable in soft rock large deformation tunnel, indoor test, numerical simulation and field monitoring were used to study the strong weathering carbonaceous slate tunnel in Min County. The study shows that NPR anchor cable has extraordinary compensating mechanical behavior for soft rock large deformation tunnel, which can control the deformation of tunnel surrounding rock below 300 mm and keep the constant resistance value around 350 kN, which has obvious effect on the control of broken rock. To provide a basis for other research on support for large deformation tunnels in soft rock.

A metamaterial with enhanced effective stiffness and negative Poisson's ratio for frictional energy dissipation

Unlike traditional energy dissipation structures that dissipate energy through irreversible plastic deformation or collapse, metamaterials based on friction energy dissipation have attracted attention due to their reusability. This article proposed a novel energy dissipation metamaterial by integrating friction energy dissipation mechanism into negative Poisson's ratio (NPR) structures. The integration of friction energy dissipation mechanism can simultaneously enhance the effective stiffness and NPR effect. The mechanical properties of the proposed structure were investigated using theoretical analysis, experiments, and finite element (FE) simulations. The influence of variables such as internal concave angle, friction coefficient, and number of reinforcing ribs was discussed. The results indicate that both unit cell and honeycomb structure can repeatedly dissipate energy within the elastic range. Compared with the traditional concave hexagonal structure, the effective stiffness and NPR effect were enhanced. This work provides a novel idea for the design of NPR energy dissipation structures.

Origami-Enhanced Mechanical Properties for Worm-Like Robot.

In recent years, the exploration of worm-like robots has garnered much attention for their adaptability in confined environments. However, current designs face challenges in fully utilizing the mechanical properties of structures/materials to replicate the superior performance of real worms. In this article, we propose an approach to address this limitation based on the stacked Miura origami structure, achieving the seamless integration of structural design, mechanical properties, and robotic functionalities, that is, the mechanical properties originate from the geometric design of the origami structure and at the same time serve the locomotion capability of the robot. Three major advantages of our design are: the implementation of origami technology facilitates a more accessible and convenient fabrication process for segmented robotic skin with periodicity and flexibility, as well as robotic bristles with anchoring effect; the utilization of the Poisson's ratio effect for deformation amplification; and the incorporation of localized folding motion for continuous peristaltic locomotion. Utilizing the high geometric designability inherent in origami, our robot demonstrates customizable morphing and quantifiable mechanical properties. Based on the origami worm-like robot prototype, we experimentally verified the effectiveness of the proposed design in realizing the deformation amplification effect and localized folding motion. By comparing this to a conventional worm-like robot with discontinuous deformation, we highlight the merits of these mechanical properties in enhancing the robot's mobility. To sum up, this article showcases a bottom-up approach to robot development, including geometric design, mechanical characterization, and functionality realization, presenting a unique perspective for advancing the development of bioinspired soft robots.

Auxetic Two‐Phase Chevron Mechanical Metamaterial

This investigation explores novel two‐phase chevron mechanical metamaterials that exhibit auxetic properties. Unlike traditional foam‐like cellular or porous auxetic materials, these designs are composed of chevron patterned layers embedded in anisotropic matrix. This innovation design allows for auxeticity in two orthogonal in‐plane directions (bi‐auxeticity) or in all in‐plane directions (complete auxeticity), providing not only a general strategy but also detailed guidelines for designing non‐porous auxetic mechanical metamaterials with tunable auxetic behaviors. One goal of this work is to explore the mechanical behavior, specifically effective stiffness and Poisson's ratio, of these new designs and to identify the design space for auxetic behavior using numerical and experimental methods. Systematic finite element (FE) simulations are conducted using ABAQUS and Python scripts to quantify effective stiffness and Poisson's ratio within a small strain range. To validate the numerical predictions, three representative designs are selected and fabricated via multi‐material polymer jetting. Uniaxial tension experiments are conducted on these specimens. Design spaces for non‐auxeticity, partial‐auxeticity, and complete auxeticity are identified through an integrated numerical approach. Theoretical criteria for determining the completeness of auxeticity are proposed and verified via FE simulations.

Experimental and numerical investigations of an auxetic support structure used for local repair of buried pipelines

Due to the ongoing disasters caused by local damage to underground pipelines in urban areas, a new method has been proposed for local trenchless rehabilitation of pipelines.This method utilizes the auxetic effect of an auxetic pipe structure to create support brackets inside the pipeline for repairing damaged sections, with the aim of reducing overall repair costs and improving efficiency. The main objectives of this study are to demonstrate the feasibility of using auxetic pipes for pipeline repairs and to enhance key parameters of auxetic support pipes. This paper presents a tube with auxetic support - the Surrounding Auxetic Tubular Structure (SATS). Using 3D printing technology, the preparation of SATS specimens was carried out, and the compressive properties of SATS were studied through finite element analysis and quasi-static compression test. The results show that the proposed SATS has a significant negative Poisson's ratio effect during the compression process and exhibits a high structural rebound rate after the load is removed. The size of the structure's boundary is the most influential factor on the auxetic effect. Additionally, the compression displacement of SATS increases with the increase of the elliptical short axis, and decreases with the increase of the elliptical long axis. The compressive load decreases with the increase of the short axis, and increases with the increase of the long axis. This demonstrates the excellent mechanical performance of the proposed auxetic support structure and lays the foundation for the feasibility of local repair work for trenchless rehabilitation.

Finite element analysis of a generalized rotating FGM vessel subjected to thermo-mechanical loadings: Effect of Poisson ratio and inhomogeneity parameters

Cylinders and thick walled cylindrical shells are commonly utilized in several industries to transport and store fluids under certain pressure and temperature conditions. In the present paper, a numerical solution is developed in order to investigate displacement, temperature and stress fields in a rotating pressure vessel made of generalized functionally graded material (FGM) subjected to different thermo-mechanical boundary conditions. The aim is to investigate the effect of Poisson ratio, internal pressure and temperature and inhomogeneity parameters on the stress and deformation distributions of the rotating pressure vessel. The material is considered isotropic nonhomogeneous and linearly elastic with its properties varying along the radial direction. Additionally, certain conditions, such as exterior or interior problems where r → ∞ or r → 0, respectively, are impossible to resolve using the variation of attributes as a power-law distribution. An approach to the spatial Young modulus distribution that is more broad has been suggested in the literature which can be applied to such physical challenges. The rotation of the pressure vessel is considered in the analysis, and the temperature distribution is assumed to be non-uniform. Since an analytical solution to the differential equation is not accessible, the conventional Galerkin discretization approach of the Finite Element Method (FEM) is applied, nowadays is considered one of the main numerical tools for solving Boundary Value Problems (BVP). It is addressed how stress, strain, and displacement are affected by the inhomogeneity parameter, rotation speed, pressure, temperature, and Poisson ratio. The examination of the various findings indicates that changes in the temperature profile, rotation, and inhomogeneity parameter on the thermoelastic field have a substantial impact on the stress and strain in the FGM cylinder. The findings indicate that the Poisson ratio and inhomogeneity parameters have a significant impact on the stress and deformation distributions. According to the results, the above-mentioned parameters can be adapted to control the thermoelastic filed in a FGM cylinder. The present research offers significant perspectives on the development and enhancement of rotating FGM pressure vessels intended for high-temperature applications.

Investigation of additively manufactured lattice structures for refractive optical systems based on auxetic properties

This paper reports on a novel concept of thermally stable lattice structures for next-generation refractive optical systems. The aim is to develop a metallic mount for optical lenses based on auxetic structures fabricated by additive manufacturing. Auxetic structures exhibit an effective negative Poisson ratio at the macroscopic level. This property is used to develop a mounting structure that compensates for thermal defocus between refractive optical elements. Numerical and experimental studies of the mechanical behavior of additively manufactured body-centered cubic cells provide the basis for the development of this application-specific mounting structure. Several static load cases are analyzed and deviations between numerical and experimental data are examined to quantify differences in dependence of element type, element size, and manufacturing-related geometrical inaccuracies. These results are used to compare the numerical analysis of the Poisson ratio of an auxetic unit cell with the analytical descriptions. This comparison is then applied to two-dimensional auxetic unit cell compounds. These studies provide the basis for the further development process of an auxetic mounting structure.

Dynamic bandgap responsiveness of modified re-entrant metamaterials in thermal-mechanical field

This paper introduces a nested sinusoidal re-entrant (NSR) metamaterial characterized by tunable complete bandgaps (CBGs) and dynamic responsiveness in thermal-mechanical dual fields. NSR comprises shape memory polymer and features a sinusoidal modification with nested re-entrant hexagonal and star-shape re-entrant structure. Dynamic response of NSR is studied using the representative volume element method, specifically focusing on the effective modulus and Poisson's ratio and CBGs under varying average strains. The findings indicate that both the mechanical properties and CBGs exhibit dynamic responses to mechanical field, demonstrating interrelation between mechanical adjustments and functional performance. Moreover, the study examines how temperature fluctuations influence the NSR's elastic modulus, thereby altering its CBGs. Hence, manipulating both compression and temperature variations presents a viable approach to control and adjust the CBGs of NSR effectively. These results are validated by computations of the frequency response function under various average strains. Overall, this design presents a promising approach for developing mechanical metamaterials with tunable functionality.

A novel cylindrical mechanical metamaterial: Design, fabrication, and compressive properties

Mechanical metamaterials exhibit fascinating deformation characteristics and exceptional mechanical properties due to their distinctive unit cell structure and the repetitive development of these units. This research presents the design of a novel cylindrical metamaterial featuring a concave hexagonal structure. This design incorporates an auxetic structure within the outer circular tube in order to enhance radial shrinkage and improve bearing capacity and stability by leveraging the negative Poisson's ratio effect. The specimens were fabricated using 3D printing technology, and their mechanical properties and uniaxial compression deformation characteristics were subsequently investigated through experiments. Additionally, the accuracy of the finite element model was verified by comparing the simulated predictions with the experimental results. The specimens differ in terms of their internal and external structures. The external structures vary based on the combination of single cells and interlayers, resulting in three distinct types. The internal structures differ based on the angle of inward depression. The mechanical properties and deformation characteristics of specimens composed of different internal and external structures were analyzed, revealing that the cylindrical structure can possess adjustable stiffness, high stability, and compressive capacity.

In-Plane Elastic Properties of 3D-Printed Graded Hierarchical Hexagonal Honeycombs.

In this study, the graded hierarchical hexagonal honeycomb (GHHH) integrating gradient design and hierarchical design was fabricated using the 3D-printing technique, and its in-plane elastic properties were investigated theoretically, experimentally, and numerically. Theoretical solutions were developed based on the Euler beam theory to predict the effective elastic modulus and Poisson's ratio of GHHH, and theoretical values were in good agreement with the experimental and numerical results. The effect of gradient design and hierarchical design on the in-plane elastic properties of GHHH was also analyzed and compared. Results showed that the hierarchical design has a more significant effect on Poisson's ratio and adjusting the internal forces of GHHH compared with the gradient design. In addition, it was found that GHHH exhibited higher stiffness compared with regular hexagonal honeycomb (RHH), graded hexagonal honeycomb (GHH), and vertex-based hierarchical hexagonal honeycomb (VHHH) under the constraint of the same relative density, respectively. Specifically, the effective elastic modulus of GHHH can be enhanced by 119.82% compared to that of RHH. This research will help to reveal the effect of integrating hierarchical design and gradient design on the in-plane elastic properties of honeycombs.

Dynamic behaviors of sandwich panels with 3D-printed gradient auxetic cores subjected to blast load

This study experimentally and numerically investigated the blast resistance of sandwich panels composed of steel face sheets and 3D-printed gradient auxetic chiral core. Five gradient strategies were utilized in the design of auxetic core, including uniform gradient, positive gradient, negative gradient, center positive gradient and center negative gradient. Varying blast loadings were applied by adjusting the masses of explosive charges. The deformation/failure modes of sandwich panels were obtained in the experiments, in terms of the face sheets and gradient auxetic core. The effects of impulse and gradient type of auxetic core on dynamic responses of specimens were examined. In addition, the numerical simulation was employed to clarify the deformation process of sandwich panel, and to analyze the deformation mode of auxetic cores under sufficient compression. It was shown that higher impulse was associated with increased plastic deformation in the face sheet and more serious shear and tensile tearing within the auxetic core. The auxetic cores of varying gradient types displayed distinct compress deformation behaviors. Among them, the negative gradient variant exhibited the least permanent deflection, and the superior negative Poisson's ratio effect, indicating enhanced blast resistance. This work not only contributes to a strategy for designing gradient auxetic cores with enhanced blast resistance, but also provides valuable insights into experimentally understanding the response of complex auxetic configurations under blast loads.

Mechanical properties of bionic lattice and its hybrid structures based on the microstructural design of pomelo peel

Bionic design has been widely used in real life, while providing ideas for innovative design of structures. In this work, a bionic lattice structure (Y-structure) with negative Poisson's ratio effect is obtained based on the principle of bionic design by taking design inspiration from the microstructure of pomelo peel. Meanwhile, in order to reduce the fabrication difficulty, the Y structure is combined with the BCC structure to obtain four overall lattice structures containing the Y structure. The required samples are prepared by additive manufacturing technique using PA2200 as the matrix material. Quasi-static compression tests are performed on the specimens at room temperature, and the mechanical properties and energy absorption capacity of the bionic lattice structure are examined under different compression directions, considering the anisotropy of the structure. Through the experimental results, it can be found that, compared with the traditional BCC structure, the four lattice structures containing the bionic lattice show obvious anisotropy, and exhibit good mechanical properties in different directions, while the energy absorption capacity is also generally improved. However, the change in the occupancy ratio of the BCC structure has a significant effect on the mechanical properties of the mixed lattice structure. The results obtained in this study can provide valuable references for further creative new developments of lattice structures based on bionic principles.