Poisson Coefficient Research Articles

Mechanical and dynamic stability of ZnX chalcogenide (X=O, S, Se, Te) monolayers and their electronic, optical, and thermoelectric properties

Graphene-like ZnX (X=O, S, Se, Te) structures are studied using the DFT+U method to address in detail the questions regarding the dynamical stability and also their utility in optoelectronic devices. The layer modulus, the Young's modulus, the shear modulus, and the Poisson coefficient demonstrate the stability of all ZnX in the presence of the Hubbard parameter U. Cohesion energy calculations show ZnO to be the most stable one and ZnSe to be the least stable one among the four systems. The presence of a direct bandgap in all the systems makes them suitable for use in optoelectronic devices. The gap values range between 2.13 eV in ZnTe and 3.50 eV in ZnO. U values tend to increase the bandgap in all the systems. This increase is seen to be as high as 100% in ZnO. A detailed study of the band structure and partial density of states is carried out. The electronic, optical, and thermoelectric properties of the ZnX monolayers are exhibited. The superior limit of the figure of merit increases with temperature and the highest value is found to be of the order of 0.6 in ZnO at 900 °C. Overall, the inclusion of the Hubbard parameter demonstrates better stability and also its importance in technological applications.

Analysis of randomly damaged triangular beam lattice: elastic field and effective properties

The decay of elastic moduli of the triangular beam lattice with randomly missed links is studied. Random low-intensity damage is considered with no more than 10% of the links removed. Unidirectional and isotropic damage models are considered. Approximate analytical formulas for elastic moduli of damaged lattice are suggested and numerically verified. Models of isotropic and scalar damage are discussed; the variation of the Poisson coefficients as a result of damage is studied. Beams of different thicknesses are examined; the dependence of moduli on thickness is investigated. Random damage is simulated using a method based on the discrete Fourier transform; the mean value and standard deviation are calculated.

Theoretical Investigation of CsBX3 (B = Pb, Sn; X = I, Br, Cl) Using Tran–Blaha Modified Becke–Johnson Approximation for Flexible Photoresponsive Memristors

AbstractThe structural, elastic, charge conduction and photoresponsive properties of halide perovskites, i.e., CsBX3 (B = Pb, Sn; X = I, Br, Cl) are investigated using the full potential‐linearized augmented plane wave (FP‐LAPW) method in the frame work of density functional theory (DFT). Perdew Burke Ernzerhof (PBE) functional belonging to the generalized‐gradient approximation (GGA) is implemented. For the better estimation of electronic parameters, the Tran–Blaha modified Becke–Johnson (TB‐mBJ) potential is employed. The elastic parameters such as bulk modulus, shear modulus, Young's modulus, the Pugh's ratio, anisotropy factor, Poisson's coefficient, and melting temperature (Tm) are estimated within Voigt‐Ruess‐Hill approximations. The energy band structure results, total density of states (TDOS), partial density of states (PDOS) outcomes, and isosurface charge density contour plots disclose that Sn2+and I1− are more appropriate divalent cation and anion respectively, among all studied composites especially for the application of photoresponsive resistive random access memory (RRAM) devices. Moreover, partial density of states (PDOS) outcomes depict that conduction band formation is consequence of hybridization of electrons from p‐orbitals of divalent cations, i.e., Pb, Sn and I/Br/Cl halogen anions. Besides, regarding charge conduction Sn‐based composites offer minimal energy bandgap as compared to Pb‐based composites. The energy bandgap order for Sn‐based compounds is found as CsSnI3> CsSnBr3> CsSnCl3. The optical analysis renders that CsSnI3 have the capability to absorb a wide range of ultraviolet (UV), visible and infrared (IR) electromagnetic incident radiations thus, make it much suitable material for optoelectronic memristors and associated applications.

Numerical modelling of porphyroclast rotation in the brittle-viscous transition zone

Porphyroclasts have been widely used to determine the shear sense, vorticity and other kinematic parameters of shear zones. Previous studies have revealed that several factors affect the rotation angle of porphyroclasts. These studies mostly regard porphyroclasts as rigid objects or viscous deformable objects to simulate porphyroclast rotation in the upper or lower crust. However, research on how these porphyroclasts behave in the brittle-viscous transition zone is still limited.In this study, a two-dimensional viscoelastic finite element model is presented to simulate the rotation and deformation of an elastic porphyroclast embedded in a viscoelastic matrix with various mechanical parameters (Young's modulus, Poisson's ratio and viscosity coefficient) and different boundary conditions (load magnitude and load time). The modelling results demonstrate that the rotation angle of the porphyroclast is strongly influenced by the Young's modulus, Poisson's ratio and viscosity coefficient of the matrix and boundary conditions. The modelling results have a level of consistency with the natural examples of porphyroclast-matrix systems of the Taili and Tianhuang ductile shear zones of the North China Craton. These results are helpful to further explain the rotation and deformation mechanism of porphyroclasts in the brittle-viscous transition zone.

BCC lattice cell structural characterization

In this work, a numerical characterization of BCC lattice cells is performed through the use of an homogenization approach. The main goal is to establish a relationship among those properties and the relative density of the cubic unit cell. The BCC cell struts diameter are the inputs parameters of the homogenization analysis campaing in order to vary the relative density of the unit cell. A linear periodic condition has been applied to the model in order to simulate a clear probing situation. Traction load tests are used in order to evaluate the Young modulus and the Poisson coefficient, differently a pure shear load case is employed for the evaluation of the shear modulus. Hence the final results will be presented in a graphic visualization.

The normal stiffness of the edentulous alveolar process

The normal stiffness of the jawbone is seldom considered, as opposed to the mechanical properties of its individual cortical and trabecular components. Our standpoint is essentially structural, rather than purely material-oriented, as the jawbone is considered as a natural load-bearing structure. Throughout the work, 3 representative sections in the mandible and the maxilla are modelled and compared. Specifically, we evaluate the sections' elastic structural stiffness numerically, according to the recent geometrical classification proposed by Shemtov Yona (2021). Each case is modelled using two extreme configurations for the cortical-trabecular interaction, namely bonded and unbonded. Those two configurations reflect extreme interfacial conditions, though the bonded one is more physical. For the unbonded cases, the structural stiffness is the sum of the individual stiffnesses of the components. By sharp contrast, the bonded case results in a much larger stiffness than that obtained by the simple sum of the individual stiffnesses, indicating a strong synergistic stiffening effect between the components through their interface. We also investigate the role of the elastic moduli, whose reported values vary widely in the literature, emphasizing the role of the trabecular Poisson's coefficient, whose stiffening effect is evidenced when it exceeds about 0.3. The bone's structural stiffness shown here complements the geometrical classification of the jawbone types with a fundamental mechanical/structural property delineating the coupling between the mechanical properties and the geometry. The adopted approach is not limited to the jawbone and applies in principle to other bone types. From a clinical standpoint, the results presented here complement not only the basic mechanical aspects of the geometrical characterization, but also provide a starting point for future studies on dental implant placement and stability, the latter being directly related to the structural stiffness.

NUMERICAL STUDIES OF THE INFLUENCE OF THE PARAMETERS OF THIN-SHELL DOME STRUCTURE ON THEIR OPTIMIZATION FROM THE POSITION OF SPATIAL STABILITY

Statement of the problem. The task was to evaluate the influence of the parameters of thin-walled dome coatings using the capabilities of modern software complexes. The method of optimization of dome covering structures with selection of criteria and parameters of the task has been improved. Results. The article presents the results of refinement and testing of the methodology for addressing the problem of optimizing dome structures with the choice of criteria and parameters of the optimization problem using the capabilities of the Topological Optimization module of the finite-element computational complex MidasCivil. The objective function was considered dependent on the thickness of the dome, the modulus of elasticity of the Poisson coefficient of the material. The study employs the positions of the theory of elasticity, solid body deformation mechanics, construction mechanics, as well as mathematical modeling methods based on the use of the finite element method employing modern licensed finite-element computing complexes Midas Civil and the Ing + architectural and construction design system of the calculation module MicroFe. Conclusions. Using the methods of optimal (in particular, geometric) design, the most affecting parameters of thin-walled dome coatings and their combinations were identified. This will allow us to design the most rational, economical and architectural-expressive dome structures as well as to make sound design decisions.

Mechanical and Material Properties of Mortar Reinforced with Glass Fiber: An Experimental Study.

The progressive increase in the amount of glass waste produced each year in the world made it necessary to start the search for new recycling methods. This work summarizes the experimental results of the study on mortar samples containing dispersed reinforcement in the form of glass fibers, fully made from melted glass waste (bottles). Mortar mixes were prepared according to a new, laboratory-calculated recipe containing glass fibers, granite as aggregate, polycarboxylate-based deflocculant and Portland cement (52.5 MPa). This experimental work involved three different contents (600, 1200, and 1800 g/m3) of recycled glass fibers. After 28 days, the mechanical properties such as compressive, flexural, and split tensile strength were characterized. Furthermore, the modulus of elasticity and Poisson coefficient were determined. The initial and final setting times, porosity, and pH of the blends were measured. Images of optical microscopy (OM) were taken. The addition of glass fibers improves the properties of mortar. The highest values of mechanical properties were obtained for concrete with the addition of 1800 g/m3 of glass fibers (31.5% increase in compressive strength, 29.9% increase in flexural strength, and 97.6% increase in split tensile strength compared to base sample).

A theoretical model for elastic-perfectly plastic flat cylindrical punch indentation

Instrumented indentation is widely used to evaluate the hardness and other mechanical properties of materials. This requires a theoretical model for the indentation curve (load vs. penetration) based on the Young's modulus, Poisson's coefficient, yield stress, hardening exponent, friction, and shape of the indenter. Several papers have been devoted to modeling spherical, conical, or pyramidal indentation in cases of both elastic and plastic deformation; in contrast, there are relatively few theoretical studies on flat cylindrical punch in the elastic–plastic regime. Indeed the singularity in the stress field at the edge of the contact is difficult to solve even if the aim is only to obtain an approximate solution. In this paper, after reviewing the theoretical basis of flat cylindrical indentation for elastic and rigid-plastic materials three different steps have been used to describe the entire progress of penetration: pseudo-elastic, elastic–plastic and full plastic. This final condition begins when the entire contact area undergoes plastic deformation. Using this classification as the starting point, a new simplified equation represents the stiffness of the specimen under flat cylindrical indentation, taking into account the elastic–perfectly plastic behavior. Integrating this equation gives the curve of indentation for an elastic–perfectly plastic material. As the characteristic parameters of this equation are unknown, in this paper the results of an extended numerical investigation using finite-element models of many different materials facilitates their calculation and validates the model. Using this new model, the direct and the inverse problems of flat indentation can be solved with good accuracy as shown through several FEM analyses. Finally, considering that the new model does not take the hardening effect into account, experimental data from the literature facilitate the verification of the relevance of this approximation. This final check successfully assesses the accuracy and the usefulness of the new method.

Optoelectronic and thermoelectrical and mechanical properties of CdLu2X4 (X = S, Se) using first-principles calculations for energy harvesting applications

First-principles study of spinel compounds CdLu2X4 (X = S, Se) has been carried out using density functional theory based Wien2k code. Lattice parameters are consistent with the experimental data. Born's stability criteria confirm the mechanical stability, while the Poisson coefficient (ν > 0.26) and the Pugh ratio (B0/G > 1.75) certifies the ductile nature of the compounds. Tran and Blah modified Becke-Johnson exchange potential was employed, which gives accurate values of direct bandgap 2.08/1.44 eV for CdLu2S4/Se4. The maximum absorption of photon energy in the visible to the ultraviolet region is found. The high absorption in ultraviolet and visible regions makes them good candidates for solar cells and energy storage devices. Thermoelectric properties are studied using BoltzTrap code in terms of electrical and thermal conductivity, Seebeck coefficient, power factor, and figure of merit.

Structural, elastic, electronic and optical properties of the half-Heusler ScPtSb and YPtSb compounds under pressure

First-principles calculations using the plane-wave pseudopotential method within the generalized gradient approximation method were performed to study the pressure dependence of the structural, elastic, electronic and optical properties for the half-Heusler compounds ScPtSb and YPtSb in a cubic MgAgAs-type structure. The calculations were performed with the inclusion of spin-orbit coupling. The calculated equilibrium lattice parameters are in good agreement with the available experimental and theoretical values. The crystal rigidity and mechanical stability were discussed using the elastic constants and related parameters, namely bulk modulus, shear modulus, Debye temperature, Poisson's coefficient, Young's modulus and isotropic sound velocities. The calculated electronic band structures show that ScPtSb has an indirect gap of Γ-X type, whereas YPtSb has a direct band gap of Γ-Γ type. Furthermore, the effect of pressure on the optical properties, namely the dielectric function, absorption spectrum, refractive index, extinction coefficient, reflectivity and energy-loss spectrum is investigated for both compounds ScPtSb and YPtSb.

Коэффициент Пуассона TiNi

A review of the literature data and methods for calculating the Poisson coefficient of the TiNi intermetallic compound in the poly- and single-crystal state is performed. The results of our own research are also presented. Significant variability of the presented data is noted, due to differences in the thermomechanical processing of the alloys and the measurement and calculation methods used. By averaging the matrices of elastic constants and compliance coefficients using the Voigt, Reuss, and Hill approximations, we obtained the values of the parameters of the effective elastic properties of TiNi polycrystals and calculated the Poisson’s ratio. Using analytical expressions to calculate the values of the extreme values, the extrema of the Poisson’s ratio of cubic TiNi crystals are determined for standard orientations. Based on a number of data, TiNi crystals are auxetics (materials having negative Poisson’s ratio values), on the basis of others they are not. We found that TiNi crystals belong to the so-called partial auxetics, in this case the signs of the inequalities (s12 < 0, s = s11 + s12 − s44/2 > 0 or s12 > 0, s = s11 + s12 − s44/2 < 0) are opposite. The values of the Poisson’s ratio TiNi averaged over the transverse directions of deformation are analyzed. Isosurfaces of the Poisson’s ratio and their sections are presented using the ELATE computational graphic package and the MATHCAD computer algebra program. Aspects of TiNi elastic anisotropy, its parameters, and their relationship with martensitic transformations in TiNi and alloys based on it are discussed.

Effect of surface treatment of fibers on the accelerated aging of biocomposites

The effect the surface treatment of fibers on the accelerated aging of biocomposites was evaluated. For the surface modification of the fibers, cold plasma and ozone treatments were applied. The moisture content, the surface water absorption, the basic specific gravity, the effective absorption, and the percentage of swelling were determined. Static bending and compression tests were performed. The effect of the degradation process on the dynamic modulus of elasticity, the Poisson coefficient, the shear modulus, and the apparent modulus of elasticity was evaluated by means of ultrasound techniques. The results were compared with the results obtained for panels that did not undergo the degradation process.

Structural and Physical Properties of DyCu, NdAg, LaCd, YIn, ErCu, ErAg, and ErAu Rare-Earth Intermetallic Compounds: Ab initio Investigations Analyzed by Data Mining Technique

In this work, the structural, elastic, mechanical, thermodynamic, and electronic properties of ErCu, ErAg, ErAu, DyCu, NdAg, LaCd, and YIn compounds have been investigated systematically using full-potential linearized augmented plane wave (FP-LAPW) within the density functional theory (DFT). In this approach, the exchange–correlation energy was calculated with generalized gradient approximation (GGA), by Perdew–Burke–Ernzerhof (PBE). We have firstly calculated lattice constants, bulk modulus, elastic constants, and mechanical properties such as Young’s and shear moduli, Pugh factor (B/G), anisotropy constant, and Cauchy pressure, as well as Poisson coefficient. The elastic constants and their related properties verify the criteria of mechanical stability, signifying that these compounds are stable in B2 structure. The ductility of the intermetallics investigated here is evaluated. The obtained values show that ErCu is the most rigid while NdAg the most ductile. The total and partial electron density of states (DOS) were evaluated to offer a detailed explanation of the contribution of atomic orbitals in the energy bands. The thermodynamic properties of ErCu, ErAg, ErAu, NdAg, LaCd, YIn, and DyCu are calculated via the quasi-harmonic Debye model, in which the lattice vibrations are considered. So temperature-dependent parameters such as lattice constant, thermal expansion, and specific heat at constant volume are analyzed. Furthermore, the relationship between several thermo-physical and mechanical properties was discussed and analyzed with data mining techniques. The obtained results confirm that this B2-type of rare-earth intermetallics has very interesting mechanical and thermal properties for structural applications.

Method of Determining the Elastic Characteristics of Graphene and Other 2D Nanoallotropes

To calculate and design nanoelectronic and nanophotonic devices, in which graphenes and graphene-like 2D nanoallotropes of carbon, silicon, and binary III–V compounds are used, knowledge of the elastic characteristics and piezoelectric, photoelastic, and other properties of 2D materials, which depend on them, is of great significance. In this work, a simple method suitable for engineering calculations of determining the isothermal values of the force constants, elastic rigidities, Young’s modulus, and Poisson coefficient for 2D nanoallotropes of elements of Group IV of the periodic table and binary III–V compounds is proposed. The method is based on the Harrison method of bonding orbitals modified by S.Yu. Davydov and the R. Keating model for describing the elastic properties of such materials. It is shown that the method makes it possible to perform evaluative calculations of the elastic properties for known synthesized 2D crystal structures as well as for structures “constructed” theoretically. It is established that single-layer hexagonal boron nitride and other binary III–V compounds in the form of 2D nanoallotropes of various types of symmetry, which are piezoelectrics in addition, can be promising materials for nanoelectronics along with graphene. This extends the spectrum of the possible practical applications of the studied 2D materials (C, Si, BN, AlN, GaN, AlP, and GaP) both with a graphene-like and more complex structure. The results of this work can be used when developing the acoustic delay lines of the terahertz-frequency range, piezoelectric transducers for exciting and receiving elastic waves in nanoscale 2D acoustic lines, as well as piezoelectric sensors.

Discovering the mechanisms that form the auxetic properties of single crystals in a monoclinic crystal system

This paper reports the analysis of patterns and mechanisms that form the characteristic surfaces of the Young modulus, the angular distributions of Poisson coefficients, and the pointing surfaces of auxeticity of single crystals in cubic, hexagonal, tetragonal, and rhombic crystal system. The crystals have been detected that can reach the limit negative values predicted by the classical elasticity theory for isotropic environments. It was found that near the points of phase transition or melting temperatures, the pointing surfaces of auxeticity rapidly increase, thereby turning the crystals into auxetics. It is shown that an array of negative Poisson coefficient values forms an image of the pointing surfaces of auxeticity. It is established that a reduction in the symmetry of crystals increases the number of crystallographic directions along which crystals gradually turn from partial to mixed or even absolute auxetics. An analysis of the anisotropy of elastic properties, characteristic surfaces of the Young modulus, and the pointing surfaces of auxeticity has revealed that most single crystals of the highest and middle category barely reach the minimum limit values of Poisson coefficients. Therefore, in order to obtain more reliable auxetic materials with high impact-energy and seismic-resistant characteristics, it is necessary to investigate the anisotropy of elastic properties of low-category single crystals. The characteristic surfaces of the Young modulus have been constructed. The volumetric images of the angular distributions of Poisson coefficients of the examined single crystals have been built, which make it possible to determine the values and crystallographic orientation of the maximum and minimum values of Poisson coefficients. The pointing surfaces of the auxeticity of the studied single crystals have been constructed

Multitemporal analysis of ambient noise polarization to characterize site response in the town of Amatrice, shattered by the 2016 central Italy earthquake

SUMMARYThe Mw 6.0 earthquake that hit central Italy on 2016 August 24 caused an abnormally high level of destruction in the town of Amatrice. In order to clarify the role of site response in causing such a disaster, a series of ambient noise recordings acquired in the aftermath of the event are analysed here to identify site resonance properties from the ratios H/V between horizontal and vertical amplitudes of ground motion. Although the noise data acquisition was limited by the emergency management activities, the use of a new analysis technique, which isolates the contribution of Rayleigh waves to the noise wavefield and averages instantaneous estimates of H/V ratios, provided more stable results compared to the standard Nakamura's technique based on mean spectral ratios. The results demonstrated the occurrence of significant resonance phenomena, but without an obvious correlation with the spatial distribution of damage severity. It is apparent that the damage severity was also influenced by some additional local factors related to building vulnerability. Moreover, the time-series analysis revealed seasonal variations in the Rayleigh wave ellipticity curves likely related to the water content changes in the surface deposits and their influence on the Poisson coefficient. Finally, the new method proved capable of recognizing time-varying directions of Rayleigh wave propagation. This capability could be exploited to support other passive seismic methods (e.g. ReMi), whose results’ reliability is limited by the lack of control on wave direction origin.

Thermal vibration and buckling analysis of functionally graded carbon nanotube reinforced composite quadrilateral plate

This paper investigates the thermal vibration and buckling of the functionally graded carbon nanotube reinforced composite (FG-CNTRC) quadrilateral plate using the meshless method. Four distributions of the reinforcements along the thickness direction are considered, which are the uniform distributions (UD), FG-V, FG-O and FG-X. The corresponding effective material properties including Young's modulus, mass density, Poisson's ratio and thermal expansion coefficients are estimated by the rule of mixture with the CNT efficiency parameters accounting for the size-dependence. The first-order shear deformation theory (FSDT) with the consideration of thermal effects is employed. Based on Hamilton's principle and the moving least square (MLS) approximation, the discrete governing equations for the vibration of the FG-CNTRC plate are derived. The free vibration of the regular and irregular plates with and without the temperature effect are considered respectively, and the corresponding natural frequencies and mode shapes are obtained by the eigenvalue problem. The stability analysis of the uniaxial and biaxial mechanical and thermal buckling are also conducted subsequently. The effects of the volume fraction, distribution pattern, geometrical characteristics and temperature on the buckling behaviors of the CNTRC quadrilateral plate are discussed in detail.

Effect of fine recycled concrete aggregate on the mechanical behavior of self-compacting concrete

The high flowability of Self-Compacting Concrete (SCC) is achieved by adding large amounts of fine aggregate. Therefore, the addition of fine Recycled Concrete Aggregate (RCA) in this type of concrete can very noticeably change its behavior. SCCs with different percentages of fine RCA (0%, 25%, 50%, 75%, and 100%) and 100% coarse RCA were manufactured in this study, to evaluate their performance, and to analyze the effect of fine RCA in an SCC when a high amount of coarse RCA is also added. Both the fresh properties (flowability, density, and air content) and their mechanical behavior (strengths, non-destructive tests, stress–strain curves, and Poisson coefficient) at different curing ages were studied. These mechanical properties were compared with the values calculated using the formulas from two of the most common structural design standards. High values of strength and modulus of elasticity were obtained up to a fine RCA content of 50%. Additionally, any increase in fine RCA increased flowability and elastic and plastic deformability of the SCC. The theoretical values overestimated the experimental ones by around 25%. From the mechanical point of view, SCC with up to 50% fine RCA could be used for structural applications, although service requirements regarding deformability recommend that its content should be limited to 25%.

Study interrelation between deformational characteristics of rocks with longitudinal and cross-sectional wave speed based on experimental data (in the order of discussion)

The paper is dedicated to the study of the interrelation between deformational characteristics of rocks (dynamic frame module, module of incompressibility, Poisson coefficient, compression ratio) with cross-sectional and longitudinal wave rates based on the systematic analysis of experimental data and carried out analysis enabled to obtain corresponding theoretical-practical outcomes. As a result of conducted analysis, it was defined that in studied exploration areas there are rocks with such lithology that to some extent may have reservoir properties marked in initial geophysical surveys as absorbing zone. Obtained analysis results are recommended to be used for efficiency increasing of carried out studies.