Poisson's Ratio Values Research Articles

First-principle investigation of thermoelectric and optoelectronic properties of Rb2KScI6 and Cs2KScI6 double perovskite for solar cell devices

Double perovskite (DP) halides are a reliable source of renewable energy that plays a vital role to fulfill the requirements of energy crunch. Therefore, the analysis of these perovskite halides have promising uses for thermoelectric and optoelectronics purposes. We investigated the thermoelectric and optoelectronics properties of Rb2KScI6 and Cs2KScI6 halides for use in renewable energy devices by using FP-LAPW + lo approach based on DFT. The calculated Goldsmith's tolerance factor and enthalpy of the formation of studied halides reveal that these are structurally and thermodynamically stable in cubic phase. Moreover, the analyzed value of Poisson and Pugh ratio reveals ductile nature of these materials. Further, we computed the bandgaps by analyzing electronic characteristics. For bandgap calculations of Rb2KScI6 (Eg = 2.75 eV) and Cs2KScI6 (Eg = 2.65 eV), we employed mBJ potentials to obtain precise values as comparison to experimental values. The complex dielectric function used to reveal the optical properties of the analyzed materials. The calculated optical results clearly show the maximum absorption of light in infrared (IR) region revealed that the analyzed materials are appropriate for optoelectronic purposes. The thermoelectric behavior was examined as to figure of merit (ZT), electrical-conductivity (EC), the Seebeck-coefficient (S) as well as thermal-conductivity. Animatedly in future, the analyzed consequences would be supportive to experimental investigation of Rb2KScI6 and Cs2KScI6 for renewable energy device applications.

Towards biomimetic, lattice-based, tendon and ligament metamaterial designs

The engineering of tendon and ligament tissue biocompatible restoration materials constitutes a long-standing engineering challenge, from the chemical, biological and mechanical compatibility analysis and design perspective. Their mechanics are inherently anisotropic, exceeding the potential limits of common, non-architected engineering materials. In the current contribution, the design of advanced material or “metamaterial” architectures that can emulate the mechanical properties observed in native tendon and ligament tissues is analytically, experimentally, and numerically investigated. To that scope, anisotropic metamaterial designs that are based on rectangular cuboid architectures with and without inner body-centered strengthening cores are considered. Thereupon, the metamaterial design specifications required for the approximation of the highly anisotropic tissue performance, namely of the characteristic normal, shear and Poisson's ratio attributes are studied. It is shown that certain strengthened, anisotropic body-centered cuboid lattice architectures allow for substantial effective metamaterial stiffness along the primal tissue loading direction, upon a rather low shear loading resistance. The previous mechanical attributes come along with Poisson's ratio values well above unity and moderate relative density values, furnishing a combination of material characteristics that is highly desirable in restoration praxis. The analytically and numerically guided anisotropic metamaterial performance is experimentally reproduced both for the case of uniaxial and shear loads, using a microfabrication stereolithography additive manufacturing technique. The obtained scanning electron microscopy images highlight the fabrication feasibility of the identified metamaterial architectures, in scales that are directly comparable with the ones reported for the natural tissues, having feature sizes in the range of some 10ths of micrometers and elastic attributes within the range of clinical observation.

Effects of geometry and boundary constraint on the stiffness and negative Poisson's ratio behaviour of auxetic metamaterials under quasi-static and impact loading

Auxetic metamaterials exhibit a negative Poisson's ratio and superior energy dissipation characteristics under dynamic (impact) loading. This makes them attractive candidates for components that provide crash or impact protection (such as crumple zones) in automotive and aerospace applications. However, little prior work on the effect of boundary constraint on the behaviour of these structures exists. Therefore, the primary goal of this investigation is to assess the effect of boundary constraint on the energy-absorbing properties of auxetic metamaterials. Specifically, auxetic metamaterials (lattice structures) were fabricated from stainless steel powders via 3-D laser printing (selective laser melting). Additional structures were printed with constraining walls attached in order to evaluate the effects of boundary constraint on the auxetic behaviour. A comprehensive investigation of the mechanical performance of the structures was then carried out under both quasi-static and dynamic (impact) loading conditions. Poisson's ratio and elastic modulus values were determined from the experimental results and compared with theoretical calculations. Dissipation of vertical forces into the lateral boundaries was confirmed by about 20% less negative Poisson's ratios, for otherwise identical auxetic structures. In addition, dynamic loading simulations have shown that with optimized geometric parameters, auxetic metamaterials are capable absorbing over 90% of the energy of an impact. However, critical overestimation of the energy absorbing abilities of auxetic crash protectors could occur if the effects of lateral constraint are not carefully considered.

Effective stiffness, wave propagation, and yield surface attributes of Menger sponge-like pre-fractal topologies

In the current work, the effective stiffness, long-wavelength attributes, and yield limits of Menger sponge-like pre-fractal topologies are investigated for the first time. Three types of Menger sponge-like structures with circular (MC), rhombic (MR), and square (MS) cavities are considered up to their third-level fractal topology. For each level, the elastic, shear, and bulk moduli, as well as the Poisson's ratio values are computed. Moreover, third-level Menger sponge-like fractal structures are additively manufactured and experimentally tested. A clear difference between the elastic stiffness and yield strength of the different Menger sponge-like structures is numerically and experimentally identified. It is observed that the cavity type considerably affects the scaling of elastic stiffness attributes upon increasing fractal level. The MS and MC topologies relate to lower relative density structures compared to the MR topology for all fractal levels investigated. The percentage relative density reductions induced by the fractal topology are a multiple of the corresponding decrease in the magnitude of the propagating shear and longitudinal phase velocities. Furthermore, all Menger sponge levels and inner cavity types yield analogous wave propagation directional dependencies, though with different phase velocity magnitudes. It is also found that increasing fractal topologies diminish the yield strength limits of the Menger fractal structures, with the factor associating the normal and shear loading yield strength of two successive Menger topology levels to be lower, but comparable in magnitude with the fractal dimension number. The fractal level evolution of the yield surface is well-captured by the extended Hill's criterion both for bi-axial and axisymmetric loads. The corresponding coefficients are identified for first, second, and third-level MS structures.

Insights into the Prediction Structural, Electronic, Optic, Elastic, and Phonon Properties of Half-Heusler Compound LiAgSe via Density Functional Theory

The structural, electronic, optic, elastic and dynamic features of LiAgSe half-Heusler structure are studied by using first principle calculations. LiAgSe half-Heusler compound is examined with the Generalized Gradient Approximation using the Density Functional Theory. The Quantum Espresso simulation program is preferred to investigate its structural, electronic and dynamic features. The ABINIT simulation program is preferred to investigate its elastic and optic properties. The electronic band structure graph of the LiAgSe crystal formed as a result of the calculation shows that this crystal has a semi-metallic structure. Optic properties such as, complex dielectric constant, extinction coefficient, reflectivity, for the volume of LiAgSe are calculated and plotted. In this study, elastic constants, Poisson's ratio and Debye Temperature values of LiAgSe half-Heusler crystal are determined. Apart from these, phonon dispersion curve graph is obtained. It has been calculated that the LiAgSe half-Heusler crystal is not dynamically stable in the ground state. However, when applied a pressure under nearly 16.396 GPa the crystal becomes stable.

Seismic characterization of source rocks: Why should it be assessed on a site-by-site basis?

Seismic characterization of source rocks (SRs) became widely used in exploration risk assessment, partly driven by the evaluation of petroleum systems conditioned by the presence of organic-rich SRs. Generally, rock physics combined with seismic amplitude variation with offset (AVO) analysis and inversion of seismic data are used to detect SR presence and to assess SR lateral and vertical variations measured in total organic carbon (TOC) content (in weight percent [wt%]). Despite its great potential, this method suffers from a range of pitfalls and uncertainties. In this study, based on several data sets, we highlight the variability of seismic responses of SRs. From well data, rock property studies of SRs show that the relation between acoustic impedance, which is the product of density and P-wave velocity, and TOC turns out not to be representative in SRs with TOC contents less than approximately 4–5 wt%. In the screening phase of rock-physics data, SR also reveals a large range of Poisson's ratio values, which relates to P-wave and S-wave velocities and has a direct impact on AVO. Moreover, from real seismic data, AVO analysis gave support for this complex behavior, highlighting AVO class I, III, and IV anomalies. Therefore, the expectation that the top of SR intervals would feature a “clear dimming with offset” (AVO class IV) should not be generalized for SR identification, especially in frontier areas lacking nearby well calibration, as suggested by the results of this study.

Technical Assessment of Green lightweight concrete containing manufactured plastic aggregates

The disposal of plastic waste is a global problem and many solutions have already been proposed to lower the environmental impact. The utilization of manufactured plastic-based coarse aggregate in concrete is one of the possible alternatives. The current study focuses on evaluating the fresh and hardened properties of concrete incorporating the plastic based manufactured aggregates. The concrete mixes were prepared at a constant water to cement ratio of 0.5 and four replacement levels (25%, 50%, 75% and 100%) of manufactured plastic-based aggregates along with two references mixes (Normal aggregate concrete and Lightweight aggregate concrete). The slump increased, while the fresh density, compressive strength and splitting tensile strength of manufactured aggregate concrete decreased with increased in the replacement ratio of manufactured aggregates. The percentage decrease for dry density, compressive strength and splitting tensile strength at 100% replacement of coarse aggregate in comparison to normal weight aggregate concrete was found to be 18.6%, 28% and 37% respectively. The Poisson ratio and abrasion values increased with increase in the replacement percentage. In addition, to predict the splitting tensile strength of concrete containing plastic-based aggregate, an equation was also proposed. Overall, the manufactured aggregates have displayed their ability to be used for construction purposes specifically where lightweight structural concrete is required as majority of properties satisfied the ASTMC330/C330M − 14 criteria.

The effect of radiolytic oxidation on the elastic properties of nuclear graphite measured by electronic speckle pattern interferometry

• Three-point bend measurement data characterised by ESPI and inverse modelling. • Static Young's modulus , Poisson's ratio and strength determined. • Measurements performed on 218 irradiated graphite beams taken from UK AGR stations. • Graphite samples (6 × 6 × 19 mm) cover dose range to 21.1 DPA and weight loss to 46%. • Modulus and strength correlate well with radiolytic weight loss. The Young's modulus, Poisson's ratio and flexural strength of 218 beams of radiolytically oxidised nuclear graphite have been determined by combining electronic speckle pattern interferometry, ESPI, and inverse finite element modelling techniques. The graphite was extracted from three operational advanced gas cooled reactor stations where it had been subjected to fast neutron irradiation and radiolytic oxidation resulting in mass loss. The 6 × 6 × 19 mm beam samples had densities ranging from 1063 – 1840 kg.m −3 , equivalent to weight losses up to 46%, with cumulative neutron doses of up to 161 × 10 20 n.cm −2 equivalent Dido nickel dose, or 21.1 displacements per atom, significantly extending the datasets available in the open literature to higher levels of both dose and oxidation. In situ ESPI measurements were collected during three-point bend tests, creating full field displacement maps of the evolving deformation to which simulations were matched by chi-squared minimisation of the elastic properties. Potential loading abnormalities were accounted for in the fitting process to ensure the simulations were representative, with total uncertainties in the determined Young's modulus and Poisson's ratio values of ± 4.5% and ± 0.08, respectively. Consistent trends were observed in the behaviour of the material from the different stations, with strong positive dependences on density for both the flexural strength and Young's modulus. The strength and Young's modulus remained well correlated even to high levels of oxidation mass loss. Conversely, the Poisson's ratio was practically invariant with oxidation with mean values of 0.21 ± 0.03, 0.24 ± 0.05 and 0.25 ± 0.05 for the three stations. The combined ESPI-finite element measurement approach is demonstrated as robust for irradiated small specimens, making it suitable for monitoring graphite in future reactors. The collected data support the safety assessments of the current reactors, enabling predictions of the responses to progressively higher mean core mass loss.

Simultaneous measurement of elastic constants from dynamic mechanical analysis with digital image correlation

Dynamic mechanical analysis (DMA) method is used for measuring viscoelastic properties of materials. The governing equations used for calculating modulus neglect shear deflection component and use an assumption of constant Poisson's ratio in absence of methods that can conduct full field deformation measurement. The present work is focused on using an in-situ imaging method to obtain the full field displacement during the specimen deformation. Digital image correlation is used to calculate the values of Poisson's ratio over temperature and strain to implement a correction factor in the complex moduli calculations. The method developed in this work will provide accurate measurements of viscoelastic properties of polymers, especially for materials whose properties are very sensitive to Poisson's ratio values and temperature variations.

First-principle study of mechanical, optical and thermophysical properties of NiTiSn

In present work we have studied half-Heusler compound NiTiSn in perspective of optical, mechanical and thermophysical properties at high temperature and high pressure using density functional theory. We have calculated various dielectric properties viz absorption coefficients, optical conductivity, optical reflectivity and electron energy loss. We have also found high refractive index n(0) ≈ 5 of NiTiSn indicating highly denser medium for low energy waves. The calculated absorption coefficient and optical conductivity are in agreement with the experimental ones for optical device. The optical investigation of the compound shows high reflectivity in the UV region of the photon energy. The elastic properties are investigated in most stable structure of NiTiSn in order to ensure its mechanical applications. Our estimated values of Poisson ratio (n = 0.2735) and pughratio (B/G = 1.87) confirm the metallic nature of NiTiSn. Various thermophysical properties viz. Debye temperature, isothermal coefficients, heat capacity, entropy and volume have been studied at high temperature and high pressures which will upgrade its thermoelectric properties study. The thermophysical properties ensures the Debye T3 law and Dulong Petit limit of NiTiSn at high temperatures and high pressures.

Structural and Elastic Properties of Pd2CrPb Heusler Compound

Electronic, structural and elastic properties of Pd2CrPb compound were examined with Density Functional Theory (DFT). The lattice constant in state of balance and the total magnetic moment value were calculated and 6.454 A0 and 3.678 µB f.u. values were obtained respectively. The lattice constant and total magnetic moment value obtained for Pd2CrPb compound were compared to existing values in the literature, and the results obtained were found to be consistent with the literature results. The calculation of bulk modulus in this study is non-existent in the literature. The bulk modulus of this molecule is presented in the literature in this sense. The aim of the study is to publish the results of studies on non-existent electronic, structural and elastic properties for Pd2CrPb compound conducted using density functional theory. The electronic band structure, total and partial density graphs for Pd2CrPb compound were drawn. Bulk modulus (B), Shear modulus (G), B/G ratio, Young modulus (E), Poisson ratio, C11, C12 and C44 values were also calculated for this compound. Pd2CrPb compound meets Born stability principles and calculated elastic stabilities show that this compound is mechanically stable.

Finite elements analysis of stresses formed in core and spongious bone tissue by restored implanted fixed prostheses with Polyetheretherketone (PEEK) and fiber-reinforced composite

Aim: This study uses the finite element analysis method to compare the effects of different abutments and prosthetic materials on stress distribution in the rehabilitation of maxillary anterior tooth deficiencies with fixed implanted prostheses. Methodology: In our study, two titanium implant models with a diameter of 4.1 mm and a length of 10 mm were designed for the maxillary central and canine teeth regions. 3D models of the prosthetic restorations were created with PEEK and fiber-reinforced composite and two different abutment materials (titanium and zirconia). After meshing the materials used with cortical and cancellous bone, Poisson ratio and young module values were loaded into the program. Maxillary central and canine to the palatal surface of the tooth, 2 mm below the incisal edge; a 178 N force was applied in both the vertical and 45° oblique directions, and analysis was performed. The distributions of the highest compression and tensile stress values in peri-implant cortical and cancellous bone were examined, and the results were compared. Results: Material with low elastic modulus caused higher stress accumulation in the cortical and cancellous bone tissue around the implant during oblique force application. In all study groups, the maximum stress values ​​observed in the cancellous and cortical bone during oblique force application were significantly higher than those observed during vertical force application. Thus, different prosthetic materials had different effects on stress distribution in peri-implant cortical and cancellous bone tissue, and the highest stress accumulations were in the peri-implant cortical bone. Conclusion: Different prosthetic materials had different effects on stress distribution in peri-implant cortical and cancellous bone tissue. How to cite this article: Zengingul AI, Goncu Basaran E, Celik H. Finite elements analysis of stresses formed in core and spongious bone tissue by restored implanted fixed prostheses with Polyetheretherketone (PEEK) and fiber-reinforced composite. Int Dent Res 2021;11(Suppl.1):250-8. https://doi.org/10.5577/intdentres.2021.vol11.suppl1.37 Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.

Geomechanical properties will constrain CO2 injection into the lower Ordovician Rose Run sandstone deep saline reservoir, Appalachian Basin, Kentucky, USA

The Kentucky Geological Survey (KGS) 1 Hanson Aggregates stratigraphic research well, Carter County, Kentucky, USA, was drilled to a total depth of 1474 m as a field-scale test of potential CO 2 storage reservoir properties in the Central Appalachian Basin. Geomechanical properties of the Rose Run sandstone (upper Ordovician Knox group) were tested for its suitability as a storage reservoir. A 9.8-m thick section of the Rose Run was penetrated at 1000 m drilled depth and a whole-diameter core and rotary sidewall cores were taken. Average porosity and permeability measured in core plugs were 9.1% and 44.6 mD, respectively. Maximum vertical stress gradient calculated in the wellbore was 26 MPa/km. Wellbore fractures in dolomites underlying and overlying the Rose Run follow the contemporary N53°E Appalachian Basin stress field. The Rose Run elastic geomechanical properties were calibrated to values measured in core plugs to evaluate its fracturing risk as a CO 2 storage reservoir. Mean Young's modulus and Poisson's ratio values of the Rose Run were 45 GPa and 0.23, respectively, whereas Young's modulus and Poisson's ratio values were 77.1 GPa and 0.28, respectively, in the overlying Beekmantown dolomite, suggesting the Rose Run may fracture if overpressured during CO 2 injection but be confined by the Beekmantown. Triaxial compressive strength measured in core plugs found the Rose Run and Beekmantown fractured at mean axial stresses of 156.5 MPa and 282.2 MPa, respectively, confirming the Beekmantown as suitable for confining CO 2 injected into the Rose Run. A step-rate test was conducted in a mechanically-isolated 18.6-m interval bracketing the Rose Run. Static Rose Run reservoir pressure was 9.3 MPa, and fracture gradient under injection was 13.6 MPa/km, suggesting step-rate testing before CO 2 injection, and subsequent pressure monitoring to ensure confinement. As the region around the KGS 1 Hanson Aggregates well is underpressured and adjacent to faulted Precambrian basement, further research is needed to evaluate its induced seismicity risk during CO 2 injection.

Mechanical properties estimation of additively manufactured metal components using femtosecond laser ultrasonics and laser polishing

Directed energy deposition (DED), also known as laser cladding, is one type of additive manufacturing where a high-power laser combined with a coaxial powder delivery system is used to produce metal components layer-by-layer. Despite many advancements in DED, little work has been accomplished in online estimation of mechanical properties, such as Young's modulus and Poisson's ratio, during the DED process. In this study, an online mechanical properties estimation technique was developed for the DED process using femtosecond laser ultrasonics and laser polishing. The unique contributions of this study are the following: (1) the development of a fully noncontact and nondestructive technique for the estimation of Young's modulus and Poisson's ratio using a femtosecond laser, (2) layer-by-layer estimation of mechanical properties accomplished by achieving micrometer-level spatial resolution, (3) laser ultrasonic measurement from a deposited metal layer using laser polishing instead of mechanical polishing, and (4) potential for online operation during the DED process. The performance of the proposed technique was examined using specimens fabricated under various DED operation conditions. The Young's modulus and Poisson's ratio values estimated by the proposed technique were consistent with those obtained from independent tensile tests performed after the completion of the DED process.

Locking-Proof Tetrahedra

The simulation of incompressible materials suffers from locking when using the standard finite element method (FEM) and coarse linear tetrahedral meshes. Locking increases as the Poisson ratio ν gets close to 0.5 and often lower Poisson ratio values are used to reduce locking, affecting volume preservation. We propose a novel mixed FEM approach to simulating incompressible solids that alleviates the locking problem for tetrahedra. Our method uses linear shape functions for both displacements and pressure, and adds one scalar per node. It can accommodate nonlinear isotropic materials described by a Young’s modulus and any Poisson ratio value by enforcing a volumetric constitutive law. The most realistic such material is Neo-Hookean, and we focus on adapting it to our method. For ν = 0.5, we can obtain full volume preservation up to any desired numerical accuracy. We show that standard Neo-Hookean simulations using tetrahedra are often locking, which, in turn, affects accuracy. We show that our method gives better results and that our Newton solver is more robust. As an alternative, we propose a dual ascent solver that is simple and has a good convergence rate. We validate these results using numerical experiments and quantitative analysis.

3D gradient auxetic soft mechanical metamaterials fabricated by additive manufacturing

Materials with a negative Poisson's ratio, also known as auxetics, have attracted a lot attention as they have shown innovation potential in applications for energy damping, modern fasteners, biomedical implants, piezoelectric sensors, and soft actuators. In this study, we introduce different patterns of graded distribution of unit cells with positive and negative Poisson's ratio in tubular configurations. Seven types of patterns are programmed into the fabric of the metamaterial to create desired shape changes upon applying far-field external loads. Two of the patterns demonstrate near-zero Poisson's ratio even at axial strains as high as 44%. Other pattern distributions convert the initially cylindrical shape of the tubes to vase, barrel, hourglass, nonsymmetrical vase, and nonsymmetrical hourglass geometries. The experimental Poisson's ratio values for the linear negative-to-positive-to-negative gradient (resulting in hourglass shape) and linear positive-to-negative-to-positive gradient (resulting in barrel shape) cases are +0.53 and −0.47, respectively. The measured Poisson's ratio values at tube level are in good accordance with the analytical values of +0.5 and −0.5. Benefits of the proposed designs in applications such as action-at-a-distance actuators and wrinkle-free jointless hinges in both 3D and 2D configurations are demonstrated.

Mechanical properties of neutron-irradiated single crystal tungsten W(100) studied by indentation and FEM modelling

The aim of this work is to investigate the effect of high-temperature neutron irradiation on the mechanical properties of single-crystal tungsten W(100) studied by mechanical testing and modelling. Neutron irradiation up to 0.12 displacements per atom was performed at 600, 800, 900 and 1200 °C in the Belgium material test reactor BR2 at SCK•CEN in Mol. The mechanical properties of the irradiated tungsten were assessed by impulse excitation and depth-sensing indentation measurements. The values of Young's modulus, shear modulus and Poisson ratio are not affected by the irradiation. The mean hardness of the irradiated tungsten increases by 48, 45, 46, and 34% after irradiation at 600, 800, 900 and 1200 °C, respectively. The results obtained by the instrumented hardness tests were used as input for the finite element method model, applied to deduce the contributions coming from the neutron irradiation defects to the plastic deformation upon the indentation process, which include the impediment of gliding dislocations by sessile defects and modification of surface morphology due to the inhibited strain hardening ability through the dislocation-defect interaction. The validation of the fitted constitutive laws was realized by the crystal plasticity finite element method (CP-FEM) model which was applied to simulate the indentation load-depth curves, with certain assumptions on the irradiation-induced microstructure, and to calculate the distribution of stress under the indenter to investigate the extension of the plastic zone in the process of the indentation.

Характеристики упругой анизотропии кристаллов Ti-Ni с памятью формы и их связь с экстремальными значениями коэффициента Пуассона

Характеристики упругой анизотропии кристаллов Ti-Ni с памятью формы и их связь с экстремальными значениями коэффициента Пуассона

Comparison of Static and Dynamic Elastic Moduli in Concrete: Effects of Compressive Strength, Curing Conditions and Reinforcement

The elastic moduli are important parameters in engineering applications. In particular, the elasticity modulus and Poisson ratio are the main parameters for evaluating the bending and shear rigidity of concrete. Elastic modulus’s calculations are made by taking a fixed value of concrete’s Poisson ratio in the worldwide standards. The aim of this study is to show whether the Poisson ratio of concrete with different compressive strengths and different pores, saturation is a fixed value, and harmony with each other of the relationship between static and dynamic elastic moduli. Therefore, totally 540 samples were prepared. These samples consist of reinforced cubic, unreinforced cubic and unreinforced cylindrical concrete samples of the 9 concrete designs with different compressive strengths. In certain days, the ultrasonic P- and S-wave measurements and the uniaxial compressive strength test were performed on these samples exposed to water and air curing. In addition, the static and dynamic elastic moduli, the velocity ratio and the Poisson ratio of these samples were calculated using the obtained data. At the same time, the static and dynamic elastic parameters of the concrete were compared with each other depending on curing conditions because the elastic parameters could be effected from the water or air saturation of the concrete depending on location of existing structures. Consequently, new multi-parameters relationships with low RMSE were generated to determine the relationships among static and dynamic elastic parameters, and to demonstrate the effect of different curing and compressive strength conditions on static and dynamic elastic parameters. In addition, the Poisson ratio values were obtained between 0.22 and 0.34 for different curing conditions and compressive strength (2–70 MPa). This indicates that the Poisson ratio value is not a constant value.

Novel Method for Preparing a High-Performance Auxetic Foam Directly from Polymer Resin by a One-Pot CO2 Foaming Process.

So far, negative Poisson's ratio foam (auxetic foam) is usually prepared by the transformation of conventional polymer foam, and it is a challenge to prepare auxetic foam directly from polymer resin. In this work, a novel method based on the synergism between the phase transition of water and the permeability rate difference of the CO2 blowing agent from air in the foaming process is put forward to prepare auxetic foam directly from the polymer resin. Using this method, herein, nylon elastomer (NE) foam with auxetic behavior is successfully prepared from NE resin by a one-pot CO2 foaming method inside an autoclave aided by water; the obtained auxetic foam has a Poisson's ratio value of -1.29 and has excellent tensile cycle stability and energy absorption performance. This method breaks through the bottleneck for preparing auxetic foams from the polymer resin directly, which is also green and environment-friendly. It is believed that the abovementioned method also applies to other thermoplastic polymers, which paves a way for designing and preparing multifunctional auxetic foam materials in the future via a one-pot CO2 foaming process. Furthermore, this work first demonstrates that the transformation between auxetic foam and positive Poisson's ratio foam is reversible due to the closed cell structure, which provides an opportunity to reversibly adjust the performance and the shape of polymer foam materials.