Poisson Coefficient Research Articles

Evaluation of particle models of corn kernels for discrete element method simulation of shelled corn mass flow

Bulk handling behavior of grains can be studied experimentally, but large-scale investigations of grain flow especially at the commercial scale are expensive, time consuming, and are therefore limited in the treatment factors that can be evaluated in any one study. Recent research has demonstrated the potential of discrete element method (DEM) in simulating grain flow in handling operations. However, application of DEM for simulating grain flow, requires development of appropriate particle models for each grain type. In this study, particle models comprised of one to four overlapping spheres were developed for shelled corn and tested. With these models, measurement of bulk properties, namely bulk density and angle of repose, both involving bulk flow were simulated using EDEM™ software with published data of material and interaction properties of shelled corn as inputs associated with each particle shape. Predicted time for the complete outflow from the bulk density test hopper (hopper emptying time), designated as simulation time in the study, was also recorded as another discriminant for model selection. Variable inputs into the simulation modeling were material properties particle shape, particle size distribution, Poisson's ratio, shear modulus, and density and interaction properties particle coefficients of restitution, static friction, and rolling friction. Computation time is critical in DEM modeling so single sphere particle models were emphasized over multi-sphere particles in the research even though multi-sphere particles represent the corn kernel shape more precisely because their simplicity can provide markedly reduced computation times to complete simulations. Predicted results for hopper emptying time, bulk density, and angle of repose were compared to experimental results or published data to select the most appropriate particle models for simulating bulk behavior of corn kernels in free-flowing grain applications using DEM. From the study, the most appropriate particle model (particle shape/physical properties combination) for corn kernels involved a single-sphere shape particle shape with a particle coefficient of restitution of 0.30, particle coefficients of static friction of 0.30 for corn-corn contact and 0.20 for corn-steel contact, particle coefficient of rolling friction of 0.05, normal particle size distribution with a standard deviation factor of 0.4, and particle shear modulus of 20 MPa.

Active fault detection and characterization by ultrashallow seismic imaging: A case study from the 2016 Mw 6.5 central Italy earthquake

We present the first high-resolution ultrashallow seismic image of a normal fault segment that ruptured the surface during the Mw 6.5 2016 Norcia earthquake (central Italy). This is the only fault, in the entire activated 25 km-long system, cutting a thick succession of Quaternary deposits, with an associated 3-m-high cumulative scarp. A 190-m-long profile crossing the fault was acquired and analyzed combining reflection seismic, non-linear multiscale refraction P-wave tomography and multi-channel analysis of surface waves. The joint interpretation of the seismic reflection, P- and S-wave velocity images unravels a 100-m-thick sequence of sandy-gravel alluvial fans, disrupted by a main normal fault zone, named as Valle delle Fonti fault (Vf1), which branches upward into three splays. The eastern splay of Vf1 matches with the 2016 coseismic surface rupture. Near-surface truncated reflections and growth strata in the hanging wall of the western and intermediate splays attest to their activity in Late Pleistocene-Holocene times. We also detect an additional normal fault in the footwall of Vf1, probably inactive since the Late Pleistocene.Comparing the seismic images with the Poisson's coefficient model and with the results of a previous electrical resistivity tomography, we constrain the lithology and the hydraulic behavior of the uppermost 50 m of the fault. A steep, W-dipping zone with high-Vp, very high Poisson's coefficient and low resistivity correlates with the eastern splay of Valle delle Fonti fault and unravels a water-saturated region. These results suggest that the fault zone may act as a partial barrier for horizontal fluid flow. Our findings indicate that the active fault zone detected by seismic imaging is much wider than what previously estimated from surface geological analyses. In terms of surface faulting hazard, this study confirms the effectiveness of high-resolution seismic surveys in defining the geometry and physical properties of active fault zones.

THEORETICAL MODELING OF THE NUCLEATION OF INTERNAL LATENT THERMAL DEFECTS IN A BITUMINOUS MEDIUM WITH RUBBER INCLUSIONS

The current state and progress of the technology and science associated with the reuse and recycling of the tyre rubber worldwide in the road industry compels to study more thoroughly high and low temperature performance of the road bitumen modified with rubber crumbs, permitting to understand influence of the temperature, rubber grain size and mixture bitumen-rubber modification on the composite strength and sustainability. Below, these issues are studied taking into account the peculiarities of the thermomechanical properties of rubber associated with its low rigidity when changing shape, practical incompressibility when changing volume, and low (zero or even negative) coefficient of linear thermal expansion. The purpose of the study is to determine the reasons leading to a violation of the strength of asphalt concrete materials with admixtures of rubber crumb. For this purpose, the influence of the incompatibility of thermomechanical characteristics (moduli of elasticity, Poisson's ratios and coefficients of thermal expansion) of bitumen and rubber on the concentration of additional internal thermal stresses in the system caused by seasonal and daily temperature changes is analyzed. Using the relations of the theory of thermoelasticity, a mathematical model of thermal deformation of crumb rubber in a bitumen medium has been constructed. With the possibility of complete and surface modification of rubber with bitumen, solutions for three-phase media are constructed, which make it possible to trace the influence of the parameters of each phase on the thermal stress fields in the system. It has been established that additional thermal stresses in bitumen, due to the thermomechanical incompatibility of the physical parameters of the phases, are concentrated in the zone of its contact with the surface of the rubber crumb and can cause defects and chippings in it. The influence of the effect of modifying rubber crumb with bitumen and of the depth of its penetration into crumb of different sizes on reducing thermal stresses in the system and increasing its sustainability is considered.

The influence of Poisson's ratio in the calculus of functionally graded plates

A current problem, of increased difficulty, which is still under continuous development, is the calculus of functionally graded plates (FGPs). Functionally graded materials (FGMs) represent a special category of composite materials, usually made on the basis of two materials, with very different properties, so they vary continuously between the extreme surfaces of the material, where the properties are those of the respective materials in their pure state. Today, the most used materials used in the construction of FGMs are ceramic materials and metals. Their volume fractions, in the thickness direction, varies continuously, according to a material law, valid for all material properties. A problem, generally poorly substantiated, is the one related to the assumption of a constant value of the Poisson's ratio over the entire plate thickness of the functionally graded plates. This hypothesis admits an analytical solution, by direct integration, of the stiffness of the plate, but it certainly does not reflect reality. There are some ways of approaching the calculation of functionally graded plates, such as the multilayer plate concept or the equivalent plate concept, which can take into account the variation of the Poisson's ratio on the plate thickness. The paper highlights this aspect and, in addition, evaluates the influence of the variation of Poisson's ratio on the calculation of displacements, stresses and natural vibrations of functionally graded plates. The work represents both an original way of approaching the calculation of functionally graded plates and a quantitative substantiation of the hypothesis of a Poisson coefficient with a constant value.

Determination of the stress-deformed state of a multilayer composite

An analytical determination algorithm was developed in the linear formulation, and a particular case of determining the stress-deformed state of a multilayer composite material was investigated. The algorithm is based on the use of the stress function (Ery) and the dependence of all indicators of the stress-deformed state of the material of each layer on its shape. Possible external factors affecting the composite structure are given. For the general case of building a composite structure, the sequence of adding the matrix of coefficients and the vector of free members of the system of linear algebraic equations is formed. The solution of the system of algebraic equations is proposed to be carried out by a method similar to the pre-race method, but for blocks of four equations supplemented by two equations of the influence of the previous layer in the calculation. As a result of actions similar to direct and reverse pre-race, we will obtain vectors of coefficient values of expressions of indicators of the stress-deformed state of the material of all layers as component sums.
 The acceptability of the algorithm for determining stresses and spatial deformations in a separate case of loading a composite sample with square layers is proven. The possibility of using the algorithm for the case of a significant (infinitely large) thickness the farthest from the loaded layer of the composite structure and single-layer (monolithic) material is shown. The following is established: characteristics of the distribution of normal stresses and displacements in the loaded layer of a two-layer composite material. They qualitatively coincide for different values of the Poisson coefficients of the layer materials. The amplitude of stress relief and displacements across the thickness of the loaded layer increases with a decrease in Poisson's ratio. The ratio of extreme values of normal stresses in the material of the loaded layer depends not only on the ratio of the shear moduli or the longitudinal elasticity moduli but also on the ratio of the values of the Poisson coefficients of the materials of the layers.

Numerical Study of Simultaneously Negative Thermal Expansion and Poisson's Ratio in a Class of Auxetic Structures

Cellular solids whose ligaments are made of two distinct materials are constructed for studying their auxeticity and negative thermal expansion via 2D models with the methodology of finite‐element numerical analysis. Three bimaterial cellular models with various radii of ligament curvature (Rc = 5, 8, 11 cm) are analyzed. It is found that when the ligaments comprise aluminum and titanium alloy with Rc = 5 cm, the cellular solid exhibits simultaneous negative effective Poisson's ratio (−0.418) and negative thermal expansion coefficient (−20.82 × 10−6 K−1). When the radius of ligament curvature increases, auxeticity is less pronounced. Positive and negative thermal expansion can be tuned solely by the coefficients of thermal expansion of ligaments’ constituents. Furthermore, smaller radii of curvature give rise to larger negative thermal expansion. In addition, modulus mismatch in the bimaterial ligament can be used to tune overall properties. Our findings herein may serve as foundations for the future quantitative design of such cellular materials. In addition, effective Poisson's ratio and coefficient of thermal expansion can be positively or negatively enhanced due to the interplay between the positive and negative phases. Interactions between negative stiffness and larger curvatures may make the system less unstable.

Упругие свойства кристаллов биосовместимых сплавов на основе TiNi с памятью формы

The authors present their own and literature data on the characteristics of elastic properties of crystals of biocompatible alloys based on titanium nickelide (nitinol) TiNi with shape memory, which have been widely used in science, technology and medicine. Elastic constants cij, malleability coefficients sij, Poisson coefficients μmin, μmax, <µ> and elastic anisotropy A, obtained experimentally and computationally, were evaluated.The numerical values of the studied parameters are analyzed in detail from the point of view of descriptive statistics. To visualize the differences in elastic characteristics, “box and whiskers” diagrams and a diagram with areas are used. Knowledge of the elastic constants of the TiNi crystal lattice and alloys based on it made it possible to calculate the values of macroscopic elastic modules E and G, the Poisson's ratio μ and their orientation dependence. Based on the data analysis, it is concluded that the low level of elastic properties of TiNi (nitinol) based alloys can be used, for example, in the development of bionic prostheses for medicine.

Bifunctional Metamaterials Incorporating Unusual Geminations of Poisson's Ratio and Coefficient of Thermal Expansion.

Natural materials overwhelmingly shrink laterally under stretching and expand upon heating. Through incorporating Poisson's ratio and coefficient of thermal expansion (PR and CTE) in unusual geminations, such as positive PR and negative CTE, negative PR and positive CTE, and even zero PR and zero CTE, bifunctional metamaterials would generate attractive shape control capacity. However, reported bifunctional metamaterials are only theoretically constructed by simple skeletal ribs, and the magnitudes of the bifunctions are still in quite narrow ranges. Here, we propose a methodology for generating novel bifunctional metamaterials consisting of engineering polymers. From concept to refinement, the topology and shape optimization are integrated for programmatically designing bifunctional metamaterials in various germinations of the PR and CTE. The underlying deformation mechanisms of the obtained bifunctions are distinctly revealed. All of the designs with complex architectures and material layouts are fabricated using the multimaterial additive manufacturing, and their effective properties are experimentally characterized. Good agreements of the design, simulation, and experiments are achieved. Especially, the accessible range of the bifunction, namely, PR and CTE, is remarkably enlarged nearly 4 times. These developed approaches open an avenue to explore the bifunctional metamaterials, which are the basis of myriad mechanical- and temperature-sensitive devices, e.g., morphing structures and high-precision components of the sensors/actuators in aerospace and electronical domains.

Critical Loads of Uniformly Compressed Orthotropic Rectangular Plate on an Elastic Base

Introduction. The problem of critical loads of a compressed orthotropic rectangular plate on an elastic base was considered. The following orthotropy parameters were set for the plate: Poisson coefficients, Young's modules for the main directions, and the shear modulus of the plate material. The components of the compressive load were uniformly distributed along two opposite edges of the plate and acted parallel to the coordinate axes. The edges of the plate were loosely pinched or pivotally supported. Cases were also considered when two parallel edges of the plate were free from loads, and the other two were freely pinched or pivotally supported.Materials and Methods. The problem was studied on the basis of a system of nonlinear Kármán-type equilibrium equations. The critical values of the load parameter were determined from a linearized problem based on a trivial solution. At the same time, the variational method in combination with the finite difference method was used to solve the boundary eigenvalue problem.Results. The problem was reduced to solving a parametric linear boundary eigenvalue problem. In case of boundary conditions of a movable hinge support, exact formulas of eigenvalues and eigenfunctions were given. While in case of free edge pinching, a variational method was used in combination with a finite-difference method, and a computer program for solving the problem was built. It was established that one or two eigenfunctions expressing the deflection of the plate could correspond to the critical value of the compressive load parameter at which the stability of the compressed plate was lost. The results of numerical calculations of the critical values of the compressive load at different values of the orthotropy parameters were presented, and graphs of the corresponding equilibrium forms were constructed. For the case of a long orthotropic plate on an elastic base, it was established that the main term of the asymptotic expansion of the solution to the linear eigenvalue problem was determined from the problem of critical loads of a compressed beam on an elastic base with an elastic modulus that coincides with the elastic modulus of the plate in the longitudinal direction.Discussion and Conclusions. The problem of critical loads of an orthotropic plate compressed in two directions lying on an elastic base was investigated. As the compressive load component increased along one direction, the critical value of the load compressing the plate along the other direction decreased. If an orthotropic plate was compressed by a load along a direction that corresponded to a greater bending stiffness, then the critical value of the loss of stability was greater than the critical value of the compressive load acting along the direction of a lesser bending stiffness. The presence of an elastic foundation increased the bearing capacity of the compressed plate.

Internal Friction and Mechanical Spectroscopy of SiO2/Si, Nanocomposites of Multiwalled Carbon Nanotubes and Polyamide, Polyethylene, Polyvinyl Chloride, Expanded Polystyrene

: In this work after X-ray irradiation outcomes of the evaluation of dynamic characteristics interstitial atoms Sij, vacancy V and O-complexes was applied for account of a condition of an annealing with the purpose of deriving specific structural defects in SiO2/Si wafer-plate. The nondestructive method, which is allow to determine from internal friction difference ΔQ-1/Q-1 0 of elastic vibrations structure defects density Nd and the depth of broken layer hb, is offered for SiO2/Si wafer-plates. 1. Introduction Defect annealing leads to a change in the shape of the internal friction (IF) temperature spectrum Q-1(T) [1]. IF method allows to set the spectrum of structural defects on the analysis of positions of maximums IF, on duration of relaxation time τ and on their deposit in attenuation of elastic vibrations [2]. A non-destructive method for the technological control of the structure defects by measuring internal friction (IF) and elastic modulus E after laser radiation was developed. 2. Experimental procedure Ultrasonic (US) pulse-phase method using USMV-LETI, modernized USMV-KNU and computerized “KERN-4” with frequencies f║ ≈ 1 MHz and f┴ ≈ 0,7 MHz, US invariant-polarization method for determining the effective acoustic μil and elastic constants Cijkl were used [3,4]. The measured velocity error was equal to ΔV/V = 0,5÷1,5%.The study of influence of structure defects on damping of vibrations in Si/SiO2 wafer-plates by the diameter of D = 100÷60 mm and by the thickness of hSiO2 ≈ 600 nm, hSi ≈ 470 000 nm, allows to estimate the degree of perfection of crystalline structureMetallography optical supervision of microstructure by means of the microscope ”LOMO MVT”, atomic-force microscopy (AFM) were used. 3. Results and discussion The quasi-longitudinal US velocity V║[001] = 5870 m/s, elastic modulus E001 = ρV║[001] 2 = 80,28 GPa for SiO2/Si from the oscillogram were determined. Temperature dependence of internal friction Q-1(T) in SiO2/Si wafer-plate p-type, doped with B, KDB-7.5(100) diameter D ≈ 76∙10-3 m, thickness hSi ≈ 460∙103 nm with SiO2 layer thickness hSiO2 ≈ 100 nm after X-ray irradiation with dose Dγ ≈ 102 Gy is showed. 4. Conclusions 1. The growth of internal friction maximum height QM -1 testifies the growth of the structural defects concentration n, and the broadening of internal friction maximum ΔQM -1 here represents the relaxation process of structural defects new types in SiO2/Si wafer-plate.2. It was found that as the result of the structural defect annealing IF background Q0 -1 significantly decreases during measuring of IF temperature dependence Q-1(T), which indicates the improvement of SiO2/Si crystal structure.3. The elastic modulus Е, the shear modulus G, Poisson coefficient μ, IF Q-1 are dependent from SiO2/Si wafer-plate anisotropy.4. The value of IF background Q-1 0 after temperature T, mechanical treatments describes the changes of the elastic stress σi fields in SiO2/Si wafer-plate.5. The study of vibrations of disk wafer-plate Si/SiO2 at different harmonic frequencies f0, f2 made it possible to develop the technique for determining the structural defects density nD for semiconductor wafers-substrates.6. The relationship between IF Q-1 value, the logarithmic decrement of ultrasound damping δ and the dislocations density nD was established for disk-shaped semiconductor wafers-substrates. Acknowledgements This work has been supported by Ministry of Education and Science of Ukraine: Grant of the Ministry of Education and Science of Ukraine for perspective development of a scientific direction "Mathematical sciences and natural sciences" at Taras Shevchenko National University of Kyiv.

Finite Element Analysis of the Reduction in Stress Concentration Factors in Shrink Fits by Using Contact Rings

As it is well known, shrink fits exhibit a stress concentration at the hub edges that can cause the failure of such mechanical components. A method for reducing such a stress concentration is placing a contact ring between the hub and the shaft. To achieve the desired effect, the Young Modulus of the material used for the contact ring must be lower than the one used in the hub and the shaft. Unfortunately, there are no design methods for estimating the optimal dimensions or materials of the contact ring. To fill this gap, in this study, diverse numerical simulations by the finite elements method (FEM) were carried out considering different geometries and materials in order to obtain recommendations that allow mechanical designers to significantly reduce the stress concentrations in these components. According to the obtained results, a contact ring of 25% of the hub thickness allows to significantly reduce up to 40% of the stress concentration. In addition, a linear influence of the stress reduction with the Young modulus was found thereby, and the most recommendable material for the contact ring is the one with the lowest Young modulus. On the other hand, according to the obtained results, the influence of the Poisson coefficient can be considered negligible.

Systematic study of optoelectronic and thermoelectric properties of new lead-free halide double perovskites A2KGaI6(A = Cs, Rb) for solar cell applications via ab-initio calculations

The variant perovskites are considered novel materials for studying solar cells and other electro-optic applications. Born’s stability criteria confirm the mechanical stability, while Poisson coefficient (ν > 0.26) and Pugh ratio (B0/G > 1.75) certify the ductile nature of the compounds by investigating elastic properties. For Cs2KGaI6 and Rb2KGaI6, the computed bandgap is direct 1.81 eV and 1.85 eV, respectively, in terms of exploring the band structures. Their band gaps may capture electromagnetic waves in the visible spectrum, excelling themfor solar cell devices. The optical properties have been studied against photon energy (eV) with maximum transition and absorption in the visible region. BoltzTrap code is employed for the thermoelectric properties executed by electrical conductivity, thermal conductivity, power factor, and figure of merit (ZT), which shows a slight variation in the temperature. Hence, the considered lead-free double perovskite compounds offer applications in solar cell devices and p-type semiconducting behavior predictive in transport investigations.

First-principles WC-GGA and mBJ calculations for structural, electronic, optical and elastic properties of MxGa1-xSb (M=Al, In, B) ternary alloys

GaSb based ternary alloys have indicated wide range variations in physical, electronic and optical properties. In the present study the structural, electronic, optical and elastic properties of MxGa1-xSb (M = Al, In, B) ternary alloys have been reported and discoursed based on the first-principles investigation. The current work attempts to provide an insight into the evolution of electronic, optical and elastic properties of ternary alloys of MxGa1-xSb (M = Al, In, B) with variation in their constituent compounds. Density functional theory (DFT) operation based on the augmented plane wave + local orbitals (APW + lo) method has been employed to estimate the structure, density of states (DOS), bandstructure, optical and the elastic properties of ternary alloys MxGa1-xSb (M = Al, In, B) for (x = 0, 0.25, 0.50, 0.75, 1) compositions. Computations were performed using the exchange-correlation energy functional from Wu-Cohen, a generalized-gradient approximation (WC-GGA) as well as the original modified Becke-Johnson exchange potential (mBJ) available with the WIEN2k code. As WC-GGA has been observed to underestimate the bandgap, the bandstructure of ternary alloys MxGa1-xSb (M = Al, In, B) for (x = 0, 0.25, 0.50, 0.75, 1) compositions has been reported using modified Becke-Johnson exchange potential (mBJ) method. In case of AlxGa1-xSb and BxGa1-xSb alloys, the bandgap values have been observed to deviate strongly from the Vegards law indicating the existence of a bowing parameter while the bandgap values of InxGa1-xSb alloys are in excellent agreement with the reported values and deviate marginally from the Vegards law. Further the optical properties, real and imaginary parts of ϵ(ω) and loss function of MxGa1-xSb (M = Al, In, B) for ternary alloys have been calculated using WC-GGA. The critical points, peaks and shoulders of imaginary part of dielectric function in these alloys have been reported. The elastic properties of these alloys, Bulk modulus (B), Shear modulus (G), Young modulus (E) and Poisson's coefficient (ν) have also been calculated using the Cubic-elastic and Tetra-elastic packages.

Mechanical Feasibility Study of Pressed and Burned Red Ceramic Blocks as Structural and Sealing Masonry.

In the search for better constructive efficiency and a reduction of the waste of construction materials, several researches have been performed in the last years around the world. Red ceramic blocks are artifacts widely used in civil construction around the world, and they result in a great consumption of raw materials and energy. The great innovation of this research was the development of ceramic blocks through an innovative method of pressing and dosing materials, replacing the traditional stage of extrusion in the manufacture of ceramics. In such a sense, a new manufacturing technology for ceramic blocks was proposed through the pressing process, adapting the soil-cement brick press machine, thus attaining more even pieces with greater compliance to the dimensions and preset geometry. In this work, the physical and mechanical features of the pressed and burned blocks (PBB) are produced in a partnership with Arte Cerâmica Sardinha, a traditional ceramic industry in the region of Campos dos Goytacazes, RJ, Brazil. It was sought to set the quality parameters for the blocks, to set their mechanical compressive strength, deformation modules and the Poisson coefficient. The blocks were tested in use by means of three layers of prism and small wall samples, and it was checked the fragile-type failure of the PBB. Results indicate that the blocks can be employed in small-sized construction works, as the characteristic compressive strength to block measured was 3.62 N/mm2 for average water absorption of 20.84%.

Numerical evaluation of macroscopic fatigue criterion of anisotropic materials using computational homogenization and conic programming

In this paper, an efficient computational approach, that combines the computational homogenization method with conic programming, is proposed to evaluate the macroscopic fatigue domain of anisotropic heterogeneous materials under variable repeated loads. The computational homogenization method is extended for use in the framework of kinematic shakedown analysis of micro-structures under macro-stress control, allowing the direct evaluation of the macroscopic fatigue domains. The discrete optimization problem is cast as conic programming and solved by using highly efficient solvers, demonstrating that the conic algorithm performs well for kinematic shakedown analysis involving a huge number of incompatible strain rate variables arising at each vertex of the convex load domain. The effects of hole shapes, porosity, plastic behaviors of metal matrices and hole distribution on the overall fatigue domains of micro-structures with regular and random patterns are studied. Numerical investigation shows that the Poisson coefficient does not effect on the macroscopic fatigue criterion in 2D analysis, at least for the problems investigated.

Effect on Compression Strength of Masonary Mortar by Replacing Fine Aggregates with Waste Glass

Abstract: Eco- friendly, low-carbon, and energy-intensive materials are required for a accountable approach to sustainable development. Glass debris can be used to substitute fine natural aggregate in a constructive way. The effects of adding glass cullet to the mechanical characteristics of mortar were investigated for this purpose. The glass aggregate was created from recycled post-consumer waste glass (mainly bottles) from the food, medical, and cosmetics industries. Four different contents of fine glass cullet were used in this experiment (5, 10, 15, and 20 wt. percent of fine aggregate). Compressive, flexural, and split tensile strengths were all assessed. The modulus of elasticity and the Poisson coefficient were also calculated. The inclusion of glass sand aggregate to mortar improves its mechanical qualities. The acquired improvement in split tensile strength was the least influenced when comparing the strengths. Rarely has the found effect for the increased examined attributes of the glass sandaggregate content been documented. Furthermore, it was discovered that increasing the recycled glass sand aggregate content in mortar reduced the density. The links between the properties of mortar containing glass sand aggregate were also investigated. Keywords: Portland Pozzolana Cement (ultra-Tech), Drinking Water, natural sand, and waste glass replacement were used in the current experiment.

Young's Modulus Calculus Using Split Hopkinson Bar Tests on Long and Thin Material Samples.

Young’s modulus is a key parameter of materials. The method of its calculation in the current paper is concerned with the mismatch of the mechanical impedance at the bar/specimen interface for a compression SHPB (split Hopkinson pressure bar) test. By using long and thin specimens, the signal recorded in the transmission bar presents itself as a multistep signal. The ratio between the heights of two successive steps represents the experimental data that are considered in the formula of the elastic modulus this article is devoted to. The oscillatory nature of the real signals on the horizontal or quasi-horizontal segments prevents a precise determination of the two successive step heights ratio. A fine tuning of this value is made based on the characteristic time necessary for the signal to rise from one level to the next one. The FEM (Finite Element Method) simulations are also used in calculation of the Poisson coefficient of the tested complex concentrated alloy.

Study of Structural, Elastic, Thermal and Transport Properties of Ternary X(X=Co, Rh and Ir)MnAs Obtained by DFT

The Density Functional Theory (DFT) with an approximation of generalised gradient is used for the study of elastic, thermodynamic and transport properties and for that of structural stability of ternary Half-Heuslers compounds X(X=Co, Rh and Ir)MnAs. This first predictive study of this compounds determines the mechanical properties such that the compression, shearing, Young modulla and Poisson coefficient without omitting the checking parameters of the nature of these compounds such that hardness, Zener anisotropic facto rand Cauchy pressure. The Pugh ratio and Poisson coefficient have allowed the identification of ductile nature of these compounds. The speed of sound and Debye temperature of these compounds has also been estimated from the elastic constants. The thermodynamic properties have been calculated as well for a pressure interval from zero to 25 GPa. The effect of chemical potential variation on Seebeck coefficient, electric, thermal and electronic conductivities, the power and merit factors have also been studied for different temperatures (300, 600, 900°K), so that these alloys can be better potential candidates for thermoelectric applications.

Analysis of cases associated with occurrence of elastic behavior of subsurface rocks while estimation of wellbore stability

Due to the generalization of the studies on the interaction of elastic behavior of subsurface rocks and carried out static analysis, the dependence of the speed of longitudinal waves on the subsurface rocks’ density has been obtained. The dependence of Poisson coefficient on the lithologic features of the rocks has been specified. The poor interaction by the well in a whole in the dependence of Poisson coefficient on the rock density is observed. Moreover, analogical dependences developed on the data of specific rocks are characterized with the closely connected correlation.

Structural, elastic, and optical properties of silicon carbide nanotubes using DFT

The structural parameters, elastic constants, electronic bandgap, and optical properties of zigzag silicon carbide nanotubes (SiCNTs) have been simulated utilizing the density functional theory (DFT) framework. The calculations suggest that, the zigzag SiCNTs (n, 0) (n = 4, 5) and SiCNTs (n, 0) (n = 6, 7) are metal and direct bandgap semiconductors, respectively. The cohesive energy shows that the tubes with larger diameters are more stable than the small tubes. Small-diameter SiCNTs also have smaller moduli due to the curvature effects and stronger π + σ hybridization. Compared to the armchair SiCNTs, the zigzag SiCNTs have an almost larger Poisson's coefficient in xz and yz directions. The negative Poisson's coefficients indicate that silicon carbide nanotubes behave like auxetic materials in some specific directions. For the z polarization, the first optical bandgap of ZSiCNTs (7, 0) (≈2.8 eV) is higher than that of SiCNTs (4, 0) (≈2.5 eV). Last but not least, the static refractive index of SiCNTs (4, 0) is smaller than that of the carbon nanotubes with the same chirality.