Ratio Of Bulk Modulus Research Articles

Effect of order-disorder transition and lattice distortion on the mechanical properties of W-X (X = V, Nb, Ta) solid solutions

With the prosperity of high entropy alloys, short-range ordering is getting more and more attentions and regarded as the deciding role in the hardening or softening of solid solutions. In this work, the phase stability and mechanical properties of short-range ordered and disordered body-centered cubic (BCC) structures of W-X solid solutions (X = V, Nb, and Ta) are systematically investigated through a combination of first-principles calculation, cluster expansion and quasi-harmonic Debye formula. Based on the calculated heat of formation (ΔHf), W-X solid solutions show a strong short-range ordering tendency, as those ordered structures have a lower ΔHf than the disordered ones. Generally, short-range ordering results in the decrease of the shear modulus to bulk modulus ratio (G/B) and hardness for W-V and W-Ta systems, while an increase for W-Nb system, manifesting solid-solution softening and hardening effect, respectively. The short-ranged ordered C11b W2X phase exhibits a singularity in mechanical properties characterized by a higher G/B than solid solution phases compared to other ordered phases. The lattice distortion breaks the symmetric W-W bonds and leads to partial covalency in the W2X phases. Besides the increased brittleness, this distortion also causes the increase of ideal strength and the reduction of maximum tensile elongation of W2X. The effect of short-range ordering and lattice distortion on the hardening or softening of the W-X systems disappears after the order-disorder transition. The W-V and W-Ta phases have higher order-disorder transition temperature than W-Nb phase. Nevertheless, the transition temperature is relatively low in comparison to their melting points, signifying the important role in controlling the solute concentration at lower temperature.

Machine-learning assistant DFT study of half-metallic full-Heusler alloy N2CaNa: Structural, electronic, mechanical, and thermodynamics properties

We studied the structural, electronic, mechanical, and thermodynamic properties of N2CaNa full Heusler alloys using density functional theory (DFT). Results for the structural analysis establish structural stability with a minimum formation energy of 29.9 eV. The compound is brittle and mechanically stable, having checked out with the Pugh criteria. The B/G ratio of bulk modulus B to shear modulus G for N2CaNa is 4.766, hence the material is ductile. N2CaNa alloy is ductile in nature. The Debye model correctly predicts the low-temperature dependence of heat capacity, which is proportional to Debye’s T3 law. Just like the Einstein model, it also recovers the Dulong–Petit law at high temperatures, suggesting the thermodynamic stability of the compounds at moderate temperatures. The results demonstrate potential N2CaNa for applications in spintronics, structural engineering, and other fields requiring materials with tailored properties.

Theoretical investigation of structural, mechanical, electronic, optical, and thermal properties of ternary compounds of heusler alloy ANiSn (A= TI, TH, U) using first principles calculations

In this study, we investigated the ANiSn (A = Ti, Th, U) half-Heusler materials for various properties, including structural, electronic, mechanical, elastic anisotropic, optical, and thermal properties, using Density Functional Theory (DFT) with the Cambridge Serial Total Energy Package (CASTEP) code. The elastic constants satisfied Born's criteria, confirming the thermodynamic and mechanical stability of the ANiSn compounds. Mechanical stability was further assessed through bulk modulus, shear modulus, and Poisson's ratio. Our analysis revealed that TiNiSn and ThNiSn exhibit ductile behaviour, whereas UNiSn is brittle. The calculated elastic modulus indicated that the compounds we studied are elastically anisotropic. The electronic and optical properties confirmed the semiconducting nature of these materials, with significant absorption and conductivity observed in the ultraviolet region. ANiSn is suitable for manufacturing various optoelectronic devices, such as laser diodes (LDs), photodetectors, LEDs, and UV sensors, due to its high absorption coefficient in the IR to UV regions. Additionally, measured Debye and melting temperatures confirmed that TiNiSn is more thermally conductive and can be used in high-temperature structural substances. The low minimum thermal conductivity suggests that UNiSn may be a more efficient material for thermal barrier coatings (TBC) compared to TiNiSn and ThNiSn.

First-principles calculations to investigate phase stability, elastic and thermodynamic properties of TiMoNbX (X=Cr, Ta, Cr and Ta) refractory high entropy alloys

This work uses first-principles calculations to investigate the phase stability, thermophysical and mechanical properties of refractory high entropy alloys (RHEAs) at finite temperatures. On the basis of plane wave quasi-potential and density functional theory, construct the structure model of a solid solution. The TiMoNbX (X = Cr, Ta, Cr and Ta) RHEAs have been determined to preserve a single body-centered cubic solid solution structure by calculations and the equilibrium lattice parameters and elastic modulus are consistent with experimental data obtained by laser cladding, which is combined with TC4 (Ti-6Al-4V) substrate. Using the quasi-harmonic Debye-Grüneisen model, the thermophysical characteristics of three RHEAs are investigated. The Voigt-Reuss-Hill scheme is used for calculating the Young's modulus (E), bulk modulus (B), shear modulus (G), and Poisson's ratio (ν), which indicates that all three RHEAs are ductile materials. Additionally, the modulus and hardness of materials decrease as temperature rises, whereas the properties of TiMoNbX RHEAs are predicted, as the nanoindentation hardness values at room temperature are comparable to, and slightly higher than the calculated values.

Ab-Initio calculations on physical properties of Dirac semimetal AMgBi (A=K, Rb, Cs)

This study presents a comprehensive first-principles investigation of the structural, mechanical, vibrational, thermodynamic and electronic properties of AMgBi (A = K, Rb, Cs) compounds using Density Functional Theory. Also, the effect of substituting alkali atoms on the physical properties has been discussed. The tetragonal PbClF-type structure has been confirmed by the analysis and the results revealed good agreement between calculated and experimental lattice parameters for KMgBi. The mechanical properties have been investigated for the first time for RbMgBi and CsMgBi. The mechanical stability of the materials in the ground state has been confirmed through the use of obtained elastic constants. Furthermore, derived parameters from elastic constants such as bulk modulus, shear modulus, and Poisson's ratio indicated that the materials are brittle and exhibited anisotropic mechanical behavior due to their layered structure. This study conducts a detailed analysis of phonon modes, explores their connections to thermal and elastic properties, visualizes the movements of phonon modes at the gamma point, determines Born effective charges, and discusses LO/TO splitting, which is for the first time for RbMgBi and CsMgBi. Phonon dispersion calculations confirmed the dynamical stability of the compounds and revealed the presence of phonon band gaps, supporting their quasi-two-dimensional nature. Investigation of thermodynamic properties using the quasi-harmonic approximation has shown the temperature dependence of internal energy, Helmholtz free energy, specific heat, and entropy for the first time for all compounds. The materials exhibited relatively low thermal conductivity, following the order KMgBi > RbMgBi > CsMgBi. The calculated Grüneisen parameter values were found to be 1.42, 1.44, and 1.53 for KMgBi, RbMgBi, and CsMgBi, respectively, suggesting relatively weak anharmonicity within the materials.

Exploring the hydrogen storage in novel perovskite hydrides: A DFT study

This work employs density functional theory calculations to investigate the structural, hydrogen storage, mechanical, electronic, optical, and bonding characteristics of perovskite hydrides KNaX2H6 (X = Mg, Ca) for potential hydrogen storage applications. Negative formation energies, positive phonon dispersions, and appropriate tolerance factor values confirm the thermodynamic, dynamic, and cubic structural stability of these compounds. KNaMg2H6 exhibits a promising gravimetric hydrogen storage capacity of 5.19%, while KNaCa2H6 shows 4.09%. Both compounds display semiconducting behavior with indirect energy band gaps of 3.31 eV and 3.17 eV, respectively. Key mechanical properties, including bulk modulus, shear modulus, and Poisson's ratio, were evaluated using computed elastic constants. The desorption temperature for KNaMg2H6, determined to be 470.4 K, renders it suitable for practical applications. Partial Bader charge analysis reveals both ionic and slightly covalent bonding interactions. Optical analysis demonstrates strong ultraviolet absorption capabilities with a redshift in the absorption spectrum. The computed properties indicate these materials hold promise for hydrogen storage applications.

Pressure-dependent band gap engineering with structural, electronic, mechanical, optical, and thermal properties of CsPbBr3: first-principles calculations.

In the renewable industry, pressure-dependent CsPbBr3 perovskite has a lot of potential due to its exceptional properties. Present work revealed the mechanical stability of CsPbBr3 between 0 to 50GPa. The bandgap of unstressed CsPbBr3 is 2.90eV, indicating a direct bandgap. Band gap values decrease by increasing external pressure. CsPbBr3 structure showed a direct band gap from 0 to 35GPa and in-direct from 40 to 50GPa. The unit cell volume and lattice constants are substantially decreased. Mechanical parameters, i.e., Young's modulus, bulk modulus, anisotropy factor, shear modulus, and poison's ratio are obtained. Under ambient conditions, the mechanical properties of CsPbBr3 showed ductile behavior and with induced pressure, their ductility has significantly improved. By applying stresses ranging from 0 to 50GPa, the considerable fluctuation in values of dielectric function (imaginary and real), absorption, reflectivity, loss function, refractive index (imaginary and real), and conductivity (imaginary and real), was also identified. When pressure rises, the optical parameters increase and drag in the direction of high energies. Response functions are used to predict the density of states and the phonon lattice dispersion to study the phonon properties. By using the quasi-harmonic Debye model, the thermal effect on the free energy, entropy, enthalpy, and heat capacity were predicted and compared. These results would be useful for theoretical research and indicate how external pressure significantly affects the physical characteristics of CsPbBr3 perovskites, which may open up new possibilities for use in optoelectronic, photonic, and solar cell applications. The structural, electrical, mechanical, optical, and thermal properties of cesium lead bromide (CsPbBr3) are investigated by applying external pressure from 0 to 50GPa, using generalized gradient approximations (GGA) and Perdew-Burke-Ernzerhof (PBE) with CASTEP code built-in material studio by density functional theory (DFT).

First-principles calculations of the mechanical properties of Mg2Si intermetallic via ternary elements doping

Abstract Site preference, structural stability and mechanical properties of Mg2Si doped by ternary elements were studied by first-principles calculation. Formation enthalpies show that light element impurity Al and rare earth elements Sc and Y tend to occupy the Mg site, while transition element Cu has a preference for the Si site. Shear modulus to bulk modulus ratio (G/B), Poisson’s ratio ν and Cauchy pressure show that the ductility of Mg2Si is improved for ternary element addition. The introduced parameter of ductility factor D indicates that the enhanced dislocation emission but suppressed micro-crack propagation is the key to enhancing ductility. Electronic structure indicates the brittleness is due to the strong covalent interaction between Mg-2p and Si-3p (Mg-3s and Si-3p/3s). While, with the incorporation of alloying elements, abundant electrons are injected into the matrix Mg2Si. Thereby, the covalent interaction is effectively suppressed and the ductility is improved.

Analytical calculation model for elastic modulus and strength of foamed concrete

Foamed concrete has gained increasing attention for its excellent engineering performance. Endeavors have been made to experimentally and numerically elucidate the mechanism of foamed concrete, while few theoretical methods are used to analytically calculate mechanical properties. This paper proposes a theoretical framework to describe the elastic behavior of foamed concrete by combining Eshelby’s equivalent inclusion theory with the Mori–Tanaka method. In the analytical model, foamed concrete is regarded as a two-phase composite comprising a homogeneous cement matrix and randomly oriented ellipsoidal air void. During derivation, the elastic modulus, strength, bulk modulus, shear modulus, and Poisson ratio are measured. A good agreement is established between the proposed method and experimental data.

Analysis of high-energy radiation shielding features of SeTeSn glass after incorporation of bismuth

The main goal of this study is to evaluate how well several quaternary Chalcogenide Glasses (ChGs) shield against extremely intense radiation, such as X-rays and gamma rays. The ChGs under investigation are part of the quaternary glass system SeTeSnBi. By using the Phy-X/PSD program, it was possible to determine some important safety factors. We were specifically able to compute the linear/mass attenuation coefficients thanks to this software. Interestingly, we discover that these values are higher than those of several traditional and commercially available glasses, suggesting better-shielding characteristics. In addition, we investigated numerous important shielding characteristics, such as the removal cross-section, mean free path, transmission factor, half-value layer, and radiation protection efficacy. Furthermore, estimates have been made for the mechanical properties, such as the bulk modulus, shear modulus, longitudinal modulus, and Poisson's ratio. Examining the effects of substituting Bismuth atoms for Selenium atoms on the shielding capabilities of the original SeTeSn glass was a crucial component of our study. These thorough examinations offer insightful information on the possible uses of these quaternary ChGs as cutting-edge radiation shielding materials.

Molecular dynamics simulation of mechanical properties of decagonal quasicrystal approximate phase Al2Fe

By using the molecular dynamics method, the tensile and elastic mechanical properties of Al2Fe (tI6 and oF24) alloys for decagonal quasicrystals approximation are simulated. Structural models for tI6 and oF24 are first established and then the appropriate embedded atom method (EAM) potential function is selected to analyze the effects of temperature and strain rate on the stress-strain relation, atomic structure and deformation mechanism. Furthermore, all the elastic constants Cij of tI6 and oF24 are calculated by the molecular dynamics explicit deformation method, and the crystal structure and stability of tI6 and oF24 are also judged. Besides, the elastic mechanical properties of tI6 and oF24 including bulk modulus, shear modulus, elastic modulus, and Poisson's ratio, are derived by means of both the general formula and the independent crystal system formula. The results show that the elastic modulus and tensile strength of tI6 and oF24 almost decrease linearly with increasing temperature. An increase of strain rate has little effect on the elastic modulus of tI6 and oF24, but it can result in an obvious increase of the tensile strength and ultimate strain. By calculating, tI6 possesses a stable tetragonal crystal structure and oF24 has a stable orthorhombic crystal structure, which are consistent with the previous results derived by the first-principle. The Young's modulus, shear modulus and Poisson's ratio display high anisotropy except for the bulk modulus. The anisotropic of oF24 is higher than that of tI6, while the stiffness and hardness of tI6 are greater than those of oF24. The present work can provide a theoretical reference for analyzing the mechanical properties of the approximate phase of decagonal quasicrystal as well as a novel numerical calculation method for determining the mechanical properties of related materials.

ElasTool v3.0: Efficient computational and visualization toolkit for elastic and mechanical properties of materials

Efficient computation and visualization of elastic and mechanical properties are crucial in the selection of materials and the design of new materials. The ElasTool v3.0 toolkit marks a significant advancement in the computational analysis and visualization of elastic and mechanical properties of materials, essential in material selection and design. This enhanced version extends beyond standard calculations like elastic tensor, Young's modulus, bulk modulus, and Poisson's ratio. It introduces capabilities for computing minimum thermal conductivity, linear compressibility, rendering the Christoffel equation, and elastic energy density. Notably, it integrates advanced visualization tools, including compatibility with Plotly and Elate web platforms for interactive web-based property exploration. A key feature of ElasTool v3.0 is the implementation of second-order elastic constants (SOECs) for tubular 2D-based nanostructures and nanotubes. Leveraging high-efficiency strain-matrix sets (OHESS), the toolkit now facilitates efficient computation of elastic constants and mechanical properties at both zero and finite temperatures for 1D, 2D, and 3D dimensions. ElasTool is openly accessible on GitHub: https://github.com/elastool. Program summaryProgram Title: ElasTool v3.0CPC Library link to program files:https://doi.org/10.17632/9hpgmspfmk.1Licensing provisions: GNU General Public License, version 3Programming language: Python 3Nature of problem: A computational toolkit that can efficiently compute the elastic and mechanical properties of materials using ab initio methods and provide advanced visualization capabilities is crucial to accurate material analysis.Solution method:ElasTool addresses this need by incorporating high-efficiency strain-matrix sets that require only small strain sets with ab initio methods such as density functional theory and molecular dynamics. This package is versatile and adept at calculating elastic constants for both 2D and 3D structures, including tubular 2D-based nanostructures and nanotubes and 1D nanoribbons at zero and finite temperatures. Beyond basic elastic moduli, ElasTool now boasts advanced visualization capabilities and computes additional critical properties such as minimum thermal conductivity, elastic energy density, and linear compressibility. This enhancement transforms ElasTool into a comprehensive tool for accelerated material design and modeling, and advanced visualization, offering both efficiency and depth in material property analysis.Additional comments including restrictions and unusual features:ElasTool is currently integrated with the Vienna Ab initio Simulation Package (VASP). Adapting to other electronic structures is straightforward.ElasTool offers serial and parallel execution. Depending on the system size, the number of strains, the nature of the calculations (zero or finite temperature), and the computing architecture, the computing time can vary from a minute to as long as 15 hours.

A novel large-cell boron nitride polymorph

Through density functional theory simulations, the structural properties, stability, mechanical properties, elastic anisotropy as well as electronic properties for boron nitride allotropes with cubic structure, Pn-3n BN, are investigated in this work. Studying the phonon spectra, molecular dynamics as well as elastic constants of Pn-3n BN, it is found that porous Pn-3n BN is stable in dynamics, thermodynamics and mechanics. The B (bulk modulus), G (shear modulus) and E (Young's modulus) of Pn-3n BN are 64 GPa, 26 GPa and 69 GPa, respectively. The B/G (the ratio of bulk modulus to shear modulus) and v (Poisson's ratio) of Pn-3n BN are 2.43 and 0.319, respectively, which exhibit ductility. The three-dimensional surface construction for Young's modulus, the maximum and minimum of shear modulus, the maximum and minimum of Poisson's ratio of Pn-3n BN are all irregular spheres, indicating that Pn-3n BN has elastic anisotropy. The Emax/Emin of Pn-3n BN displays isotropy with 1.00 in (111) plane, and is not equal to 1.00 in other principal planes, showing anisotropy. The conduction band minimum (CBM) and the valence band maximum (VBM) of Pn-3n BN are both located at point G, and the band gap width of Pn-3n BN is 5.197 eV, from which Pn-3n BN is a wide band gap and direct band gap semiconductor material.

Molecular dynamics simulation and experimental verification of the effects of vinyl silicone oil viscosity on the mechanical properties of silicone rubber foam.

The molecular motion trajectories of silicone rubber foam (SRF) at various vinyl silicone oil viscosities were studied via molecular dynamics (MD) simulation from the perspective of all atomic molecules. The influence of different viscosities of vinyl silicone oil on interaction, compatibility, and aggregation degree of molecules was determined based on the mean square displacement, diffusion coefficient, binding energy, solubility parameter, radial distribution function, and radius of gyration. The mechanical properties of the SRF were also experimentally verified. Results revealed that as the viscosity of vinyl silicone oil increased, the mean square displacement, fractional free volume, diffusion coefficient, and solubility parameter of the system decreased, whereas its larger radius of gyration increased. Moreover, the radial distribution function showed a weaker relative interaction between molecular chains. The calculated binding energy demonstrated that the system had better compatibility at a viscosity of 0.45 Pa s. This study provided a deeper insight into the relation between the viscosity of vinyl silicone oil and mechanical properties of the SRF. As the viscosity of vinyl silicone oil increased, the changing trend in MD simulation results of elastic modulus, shear modulus, bulk modulus, and Poisson's ratio was consistent with the experimental results. The MD simulations can promote theoretical predictions and scientific basis for the design of the SRF with desired performances.

Mechanical properties of Mo-Re alloy based on first-principles and machine learning potential function

This study utilizes first principles calculations of density functional theory and Spectral Neighbor Analysis Potential (SNAP) machine learning potential to investigate the influence of rhenium concentration and temperature on the fundamental mechanical properties of Molybdenum-Rhenium alloy. The Mo1−xRex alloys (x = 0.0625–0.5) are constructed using a special quasi-random structure BCC model. The optimized geometries and lattices are used to calculate elastic constants and derivate mechanical parameters, including Bulk modulus, Young's modulus, Shear modulus, etc. The results show that with the increase of rhenium content, the mechanical properties of Mo1−xRex alloy are significantly improved, and higher than pure molybdenum, the best properties are reached at x(Re) = 0.3125. On the other hand, by analyzing the ratio of bulk modulus to shear modulus (B/G) and Poisson's ratio, the alloying of rhenium can also improve the ductility of molybdenum rhenium alloy. To address the challenge of calculating the high-temperature mechanical properties of Molybdenum-Rhenium alloy, a machine learning potential was developed within a training set called Spectral Neighbor Analysis Potential (SNAP). We accurately predicted the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio of Molybdenum-Rhenium alloy over the temperature range of 300–1300 K. Additionally, we provided an accurate description of how temperature affects the mechanical properties and solubility of Molybdenum-Rhenium alloy. This approach aims to overcome the limitations associated with traditional methods and provide accurate predictions of the alloy's mechanical behavior at elevated temperatures.

First-Principle Investigation of La0.7Ba0.3Mn(1-x)FexO3 Structural Properties Using CASTEP

<p>We conducted first-principles Density Functional Theory (DFT) calculations using the CASTEP software package to investigate the crystal structure and mechanical properties of Fe<sup>3+</sup>-doped La<sub>0.7</sub>Ba<sub>0.3</sub>MnO<sub>3</sub> material at the Mn<sup>3+</sup> site, with doping concentrations ranging up to 50%. Through geometry optimization, we simulated the X-ray diffraction (XRD) pattern. We observed that the doping of Fe did not result in a shift in the peak positions of the diffraction pattern. However, it led to an increase in intensity at the [012] peak and the splitting of peaks [104] and [110]. Regarding the mechanical properties, we examined the elastic constants and observed a reduction in the Bulk, Shear, and Young's modulus values. The Shear and Bulk modulus and Poisson's ratio indicated that La<sub>0.7</sub>Ba<sub>0.3</sub>Mn<sub>(1-x)</sub>Fe<sub>x</sub>O<sub>3</sub> becomes less ductile with increased Fe<sup>3+</sup> doping content. Furthermore, we performed calculations for the Debye temperature, which revealed a decrease in the thermal conductivity of the La<sub>0.7</sub>Ba<sub>0.3</sub>Mn<sub>(1-x)</sub>Fe<sub>x</sub>O<sub>3</sub> material.</p><p class="Abstract"> </p>

Effective mechanical properties of frozen hydrogel with ice inclusions

Hydrogel exhibits attractive mechanical properties that can be regulated to be extremely tough, strong and resilient, adhesive and fatigue-resistant, thus enabling diverse applications ranging from tissue engineering scaffolds, flexible devices, to soft machines. As a liquid-filled porous material composed of polymer networks and water, the hydrogel freezes at subzero temperatures into a new material composed of polymer matrix and ice inclusions: the frozen hydrogel displays dramatically altered mechanical properties, which can significantly affect its safety and reliability in practical applications. In this study, based upon the theory of homogenization, we predicted the effective mechanical properties (e.g., Young's modulus, shear modulus, bulk modulus and Poisson ratio) of a frozen hydrogel with periodically distributed longitudinal ice inclusions. We firstly estimated its longitudinal Young's modulus, longitudinal Poisson ratio and plane strain bulk modulus using the self-consistent method, and then its longitudinal and transverse shear modulus using the generalized self-consistent method; further, the results were employed to calculate its transverse Young's modulus and transverse Poisson ratio. We validated the theoretical predictions against both finite element (FE) simulation and experimental measurement results, with good agreement achieved. We found that the estimated transverse Poisson ratio ranges from 0.3 to 0.53 and, at low volume fraction of ice inclusions, exhibits a value larger than 0.5 that exceeds the Poisson ratios of both the polymer matrix and the ice inclusion (typically 0.33–0.35). Compared with other homogenization methods (e.g., the rule of mixtures, the Halpin-Tsai equations, and the Mori-Tanaka method), the present approach is more accurate in predicting the effective mechanical properties (in particular, the transverse Poisson ratio) of frozen hydrogel. Our study provides theoretical support for the practical applications of frozen liquid-saturated porous materials such as hydrogel.

Molecular dynamics simulation and experiment on analyzing mechanical properties of PMMA/SiO2 composites based on interfacial interaction

In this paper, we investigate the impact of modified SiO2 nanoparticles on the mechanical properties of Polymethyl methacrylate (PMMA) composites through a combination of molecular dynamics simulation and experimentation. Our investigation focuses on analyzing the elastic modulus, bulk modulus, shear modulus, and Cauchy ratio of pure PMMA, PMMA/SiO2 composites, and PMMA/modified SiO2 composites over a temperature range of 200–400 K. Our results indicate that, as the temperature increases, the elastic modulus, bulk modulus, and Cauchy ratio of all materials decrease, while the shear modulus initially increases and then decreases. Notably, at room temperature, the elastic modulus, bulk modulus, and shear modulus of the composites increase with an increase in the degree of nanoparticle modification, while the Cauchy ratio exhibits the opposite trend. Our findings suggest that modified SiO2 nanoparticles have the potential to enhance the mechanical properties of composite materials. To validate our simulation results, we also conducted experiments that demonstrated the rationality of our approach.

An investigation on microscopic and mechanical properties of polyethylene/boron nitride graphene nanocomposites by DFT calculations

In this paper, the molecular dynamics (MD) simulation is used to explore the mechanical properties of polyethylene (PE) /boron nitride (BN) graphene nanocomposite in the pressure range of 0–20 GPa and temperature range of 100–600 K. Parameters of the adsorption energy, Young's modulus, glass transition temperature and radius of gyration are analyzed. For the interaction between PE and BN-graphene, the constant adsorption energy is reached with the eight degree of polymerization. Meanwhile, the Young's modulus, bulk modulus, shear modulus and Poisson's ratio of PE/BN-graphene nanocomposite are all improved, where the PE/BN-graphene nanocomposite performs well in resisting the changes in volume and shape to reflect the enhanced mechanical effect of BN-graphene on polyethylene. The mechanical properties of the PE/BN-graphene nanocomposite during the pressurization process are strong enough without fracture, and the best performance is achieved at 18 GPa. BN-graphene heightens the glass transition temperature of the nanocomposite with the enhanced structural and thermal stability. Besides, friction and wear properties of the PE/BN-graphene are guaranteed according to the gyration radius diagram.

DFT prediction of the stability and physical properties of M2GaB (M = Sc, V, Nb, Ta)

This study explored the physical properties of MAX phase borides, M2GaB (M = Sc, V, Nb, Ta), aided by the density functional theory (DFT) for the first time. The optimized lattice constants were obtained by minimizing the total energy. We checked the thermodynamic stability by computing the formation energies. We calculated the electronic band structure, density of states (DOS), and charge density mapping to reveal the electronic ground state and bonding nature. The computed stiffness constants (Cij) confirmed the mechanical stability of the investigated compounds. Young's modulus, shear modulus, bulk modulus, and Poison's ratio have been computed using Cij. We calculated the Pugh's ratio, Poisson's ratio, and Cauchy pressure to judge the ductility/brittleness. The Vickers hardness values were calculated. The anisotropic properties of M2GaB compounds were studied by the elastic moduli's directional projections and the anisotropy indices' calculations. We have discussed the acoustic behavior of the M2GaB phases. We have also investigated the Grüneisen parameter, the Debye temperature ϴD, the thermal expansion coefficient, the specific heat, the Helmholtz free energy, the entropy, the internal energy, and the lattice thermal conductivity (Kph) of these borides. To determine the suitability as thermal barrier coating (TBC) materials or whether the compounds are appropriate for high-temperature applications, the minimum thermal conductivity (Kmin) and melting temperature (Tm) have also been calculated. The compounds' dynamical stability was examined using the phonon dispersion curves. The optical parameters have been studied, and it has been found that these compounds are compatible as coating materials to reduce solar heating.