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[Display omitted] • The elastic, electronic and thermoelectric properties of Bi 2 Se 3 are deduced using the first-principles PW-PP method. The PBE-D3 type dispersion corrections are included. • The bandgap 0.21 eV obtained using dispersion corrections is very close to the experimental data 0.22 eV. • The thermoelectric figure of merit zT = 0.02 found at 300 K using PBE-D3 is in very good agreement with the experimental values 0.01 and 0.09. It is found to decrease with increasing in temperature. • The power factor at 300 K is 93.4 × 10−5 W.m−1.K−2 is in excellent agreement with the experimental values 100 × 10−5, and 95 × 10−5 W.m−1.K−2.It is found to increase linearly with temperature. • Improvement in agreement of all calculated properties using PBE-D3 type dispersion correction with the experimental data corroborates that the PBE-D3 captures interlayer vdW interaction adequately in Bi 2 Se 3. The dispersion corrected elastic, electronic and thermoelectric properties of Bi 2 Se 3 are studied using the density functional theory deploying the Quantum ESPERSSO package. The ground state is achieved using the PBE exchange and correlation functional. PBE-D3 type dispersion correction is applied to capture the van der Waal interaction between the quintuple layers in Bi 2 Se 3. The computed lattice constants considering the dispersion correction are in excellent agreement with the experimental data. The elastic constants namely the bulk modulus, shear modulus, Young's modulus and Poisson ratio are evaluated. Effect of dispersion correction is observed in the elastic constants. The compression and shear anisotropy studies indicate that Bi 2 Se 3 is more anisotropic against shearing stress than against compression. The direct bandgap of 0.47 eV is obtained using the PBE functional which reduces to 0.21 eV when PBE-D3 dispersion correction is applied. The dispersion corrected direct bandgap is very close to the experimental value 0.22 eV. The total and projected density of states are computed and analyzed in terms of state contributions. The Bader charge analysis shows that Bi-Se2 bond is more ionic than the Bi-Se1 bond. Among the thermoelectric properties, the computed power factor and figure of merit zT , are in excellent agreement with the experimental data. The temperature dependent study shows that the figure of merit decreases while the power factor increases linearly. [ABSTRACT FROM AUTHOR]

MgAlSi alloy materials have the main properties of light weight and high strength, good electrical and thermal conductivity and corrosion resistance, and have various applications in the industrial field, making an important contribution to the realization of lightweight and high performance needs. In order to be able to predict the material properties of MgAlSi alloys with a high degree of accuracy, this paper develops for the first time an interatomic potential function for MgAlSi alloys based on a neural network machine learning approach. The effectiveness of the developed machine learning potentials is verified by analyzing the problems encountered during the training process and the errors of the finally obtained potential functions, and comparing some of the radial distribution functions, coordination numbers, and predictions of properties such as the equation of state, lattice constants, shear modulus and bulk modulus with those of AIMD. It is found that the performance error of the deep potential model is basically kept in the same order of magnitude as that of DFT calculations, the computational speed can be up to nearly a thousand times that of DFT, and the computational cost is linearly related to the atomic number, which is well suited for large-scale molecular dynamics simulations, and it will provide a promising solution for accurate large-scale molecular dynamics simulations. [Display omitted] • Interatomic potential functions for MgAlSi alloys are developed based on MLP. • Analyzing problems in training and errors in potential functions. • Calculation of mechanical properties from the developed potential function. • Calculated results and efficiencies were compared with and AIMD. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) was employed to perform an ab-initio study of new hydrogen storage materials NaXH 3 (X = Ti, Cu) using the Generalized Gradient Approximation (GGA) and CASTEP package. The structural, electronic, elastic, optical, and hydrogen storage properties of NaTiH 3 and NaCuH 3 were calculated within the Pm 3 ̄ m cubic-perovskite phase. The thermodynamic stability of both structures was ensured by their negative formation energy. The dynamic stability has been investigated through phonon dispersion, and it has been proven that these compounds are stable. The calculations of elastic constants confirm the mechanical stability of these materials. Furthermore, bulk modulus, shear modulus, and Poisson's ratio have been derived by employing the obtained elastic constants. NaXH 3 hydrides were found to be elastically anisotropic and brittle. The electronic band structures turn out metallic behavior in NaXH 3 perovskites. The optical characteristics demonstrate that both compounds exhibit their highest absorption and conductivity levels within the ultraviolet wavelength range. The calculation of gravimetric hydrogen storage capacities for NaTiH 3 and NaCuH 3 was performed and found to be ≈ 3.932 and 3.266 wt%, respectively. The hydrogen desorption temperature was identified as 637 and 563 K for NaTiH 3 and NaCuH 3 , respectively. The current DFT results highlight that NaXH 3 (X = Ti, Cu) hydrides have considerable potential as candidates for H 2 storage purposes. [Display omitted] • The physical properties of two new NaXH 3 (X = Ti, Cu) perovskite materials are explored via ab-initio calculations. • The NaXH 3 compounds displays thermodynamic, mechanical and dynamic stability. • NaXH 3 perovskite materials are metallic, brittle and elastically anisotropic. • The gravimetric H 2 storage of NaTiH 3 and NaCuH 3 is found to be 3.932 and 3.266 wt%. [ABSTRACT FROM AUTHOR]

A stochastic 3D microstructure model for polycrystals is introduced which incorporates two types of twin grains, namely neighboring and inclusion twins. They mimic the presence of crystal twins in γ -TiAl polycrystalline microstructures as observed by 3D imaging techniques. The polycrystal grain morphology is modeled by means of Voronoi and –more generally– Laguerre tessellations. The crystallographic orientation of each grain is either sampled uniformly on the space of orientations or chosen to be in a twinning relation with another grain. The model is used to quantitatively study relationships between morphology and mechanical properties of polycrystalline materials. For this purpose, full-field Fourier-based computations are performed to investigate the combined effect of grain morphology and twinning on the overall elastic response. For γ -TiAl polycrystallines, the presence of twins is associated with a softer response compared to polycrystalline aggregates without twins. However, when comparing the influence on the elastic response, a statistically different polycrystalline morphology has a much smaller effect than the presence of twin grains. Notably, the bulk modulus is almost insensitive to the grain morphology and exhibits much less sensitivity to the presence of twins compared to the shear modulus. The numerical results are consistent with a two-scale homogenization estimate that utilizes laminate materials to model the interactions of twins. • Introduction of a stochastic 3D microstructure model for twinned polycrystals. • Modeling two types of morphologically different crystallographic twins. • Investigation of combined effect of grain morphology and twinning on overall elastic response. • A statistically different polycrystalline morphology has a much smaller effect than the presence of twin grains. [ABSTRACT FROM AUTHOR]

[Display omitted] 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 -3 n BN, are investigated in this work. Studying the phonon spectra, molecular dynamics as well as elastic constants of Pn -3 n BN, it is found that porous Pn -3 n BN is stable in dynamics, thermodynamics and mechanics. The B (bulk modulus), G (shear modulus) and E (Young's modulus) of Pn -3 n 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 -3 n 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 -3 n BN are all irregular spheres, indicating that Pn -3 n BN has elastic anisotropy. The E max / E min of Pn -3 n BN displays isotropy with 1.00 in (1 1 1) 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 -3 n BN are both located at point G, and the band gap width of Pn -3 n BN is 5.197 eV, from which Pn -3 n BN is a wide band gap and direct band gap semiconductor material. [ABSTRACT FROM AUTHOR]

[Display omitted] Orowan strengthening is a key strengthening method for metallic materials. However, a debate still exists on the effect of temperature on the Orowan strengthening mechanism. Herein, the effect of temperature on the Orowan strengthening mechanism is systematically investigated, an Orowan strengthening mechanism with thermal activation is developed, and the corresponding Orowan stress is deduced. The results indicate that the precipitate scales substantially affect the thermal activation–based dislocation that bypasses the precipitate processes. In small precipitate scales, the thermal activation contribution to Orowan stress cannot be ignored; while in big precipitate scales, the thermal activation contribution can be ignored even at high temperatures. In addition to temperature, the effects of shear modulus, strain rate, and dislocation density on Orowan stress are investigated. This study not only provides new insight into the Orowan strengthening mechanism but also aids in designing new high-temperature structural materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Analyzing the refractory element on Ni 2 TiAl by first-principles calculation. • Nb provides the maximum toughness and maintains hardness simultaneously. • Hf provides the largest hardness and maximum toughness loss. • V and Cr significantly enhance the bonding strength and stability. Refractory high entropy alloys (RHEAs) are attracting wide attention due to their excellent high-temperature strength. L2 1 -Ni 2 TiAl was found as a strengthening phase in high entropy alloys (HEAs) which significantly improves room and elevated-temperature mechanical properties. To explore the potential application in RHEAs, we address the calculations of 7 refractory elements (i.e., V, Cr, Zr, Nb, Mo, Hf, and Ta) doping from first principles on the site preference, elastic properties and bonding effect of Ni 2 TiAl. The results show that the antisite defects is more stable than the vacancy defects. Elements Cr and Mo prefer the Ni-sites, while V, Zr, Nb, Hf, and Ta prefer the Ti-sites. Moreover, all the doping elements lead to a lattice shrinkage, among which V cause the largest distortion. For the normalized shear modulus (G/G 0), all the elements increase except Nb, of which Hf rank the top. While for the normalized bulk modulus (B/B 0), all the elements slightly increase except Hf. Furthermore, Nb is the only one to improve the toughness but has little impact on hardness (Hv), then Hf improves hardness the most. Additionally, all the doping elements decrease the anisotropy of Young's modulus for Ni 2 TiAl, of which Nb has the largest anisotropy, leading to a weak resistance to deformation. Notably, the density of states (DOS) shows that V and Cr can effectively improve the bonding stability and strength of Ni 2 TiAl. Overall, the alloying of Nb, V, and Cr may synergistically improve the stability and toughness of Ni 2 TiAl, which is expected to develop novel RHEAs. [ABSTRACT FROM AUTHOR]

In recent years, there has been an explosive rise in the combination of density-functional theory (DFT) computation and machine learning in materials science research. In this paper, a cuckoo algorithm-optimized random forest (CS-RF) based alloy elastic modulus prediction model is proposed using density-functional theory. 320 alloy samples are used as test materials to calculate elastic modulus using the density-functional theory method, and the calculated raw data are normalized to establish a cuckoo algorithm-optimized random-forest model to predict alloy elastic modulus. The experiments show that for predicting the elastic modulus of alloys, CS-RF also has obvious advantages in computational efficiency with improved prediction accuracy. In conclusion, CS-RF is an advanced machine learning (ML) method for predicting the elastic modulus of alloys, which can provide a scientific reference for metal elastic modulus prediction. [Display omitted] • Calculated bulk and shear modulus of metal materials based on DFT. • Realized the LSSVM, Bi-LSTM and RF model to predict the elastic modulus. • Employed CS algorithm to optimize the random forest model parameters. • Proved the accuracy and effectiveness of RF model in predicting elastic. • Proved the efficiency of the optimization algorithm compared other models. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel ML based inverse framework for predicting elastic properties of carbon fiber. • Predicts transverse and shear modulus that are challenging to obtain experimentally. • Homogenized RVE with random fiber distribution used to generate input data. • Multiscale framework to evaluate elastic properties of woven fabric laminates. Evaluating the transverse and shear modulus of carbon fibers experimentally is challenging and are usually obtained by an inverse approach using a micromechanical model. This paper presents an inverse approach for predicting the fiber properties from experimentally evaluated properties of the unidirectional (UD) lamina, using a machine learning (ML) based surrogate model. The ML framework is based on Gaussian process regression (GPR), which also provides a measure of uncertainty in the predictions. The ML model is trained using synthetic data generated using Finite Element (FE) homogenization considering different fiber and matrix properties, volume fractions, and fiber distribution. The proposed inverse framework is demonstrated to predict the elastic properties of polyacrylonitrile (PAN)-based fibers used in carbon-epoxy composites that have significant variations (low to high modulus) in its properties (T300-M60J). The fiber properties predicted using the GPR surrogate shows good agreement with the values reported in the literature, with a difference of less than 1.5%. The computational framework is further extended to predict the elastic properties of the woven fabric laminate using multi-scale homogenization. In summary, the results show that the GPR-based surrogate model offers an accurate and computationally efficient alternative to FE-based forward model for predicting the properties of the fiber. [ABSTRACT FROM AUTHOR]

• A hierarchical model is built using ExtraTrees and DNN. • Feeding features show the insights of elastic properties. • Composition and temperature are key factors for bulk modulus. • Ordering effect, composition and temperature are important in shear modulus. We apply extremely randomized trees and deep neural network to cluster expansion generated data to construct the hierarchical model that predicts the ternary properties using machine learning model trained by binary data. We focus on the elastic properties bulk modulus and shear modulus. By feeding composition and temperature as features and elastic property as target property into extremely randomized trees, the predictions of ternary alloys achieve the mean absolute errors of 0.56 GPa and 1.49 GPa in bulk modulus and shear modulus, respectively. The performance in shear modulus predictions can be improved by adding point probability that characters the ordering effect into feeding features. We find that the compositions and temperature are key features in bulk modulus, while compositions, temperature, and the ordering effect are important in shear modulus. [ABSTRACT FROM AUTHOR]

• Cubic-B 6 N 6 , a new boron nitride polymorph, is theoretically proposed. • Cubic-B 6 N 6 is an insulator with a 5.97 eV wide band gap. • Cubic-B 6 N 6 may possess potential super-hard application. The current work introduces a new type of cubic boron nitride with a special sodalite cage structure, named Cubic-B 6 N 6 , based on the first principle of density functional theory (DFT). After determining the lattice parameters at the lowest energy state, the phonon spectra and elastic constants were calculated to demonstrate the dynamical and mechanical stability of the structure, respectively. Cubic-B 6 N 6 possesses its bulk modulus of 274.0 GPa, shear modulus of 258.5 GPa, Young's modulus of 675.8 GPa and Poisson's ratio of 0.09, indicating its large hardness. The electronic band structure indicates that Cubic-B 6 N 6 is an insulator with a wide indirect band gap of 5.97 eV (HSE06). Moreover, XRD and Raman spectra are calculated to predict the experimental characteristics of Cubic-B 6 N 6. Due to the large bulk modulus and large band gap, Cubic-B 6 N 6 may provide potential super-hard and electronic resistance applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The mechanical properties of RDX, PETN, and δ -HMX are examined. • Calculated second-order elastic constants reveal strong anisotropy of crystal. • Third-order elastic constants could describe the nonlinear mechanical response. Abstract Accurate calculations of second-order elastic constants (SOECs) and third-order elastic constants (TOECs) are important for energetic materials to describe the linear and nonlinear mechanical responses quantitatively. Homogeneous deformation method combined with first-principles total energy calculations are performed to calculate a complete set of SOECs and TOECs for cyclotrimethylene trinitramine (RDX), pentaerythritol tetranitrate (PETN) and cyclotetramethylene tetranitramine (δ- HMX). The computed SOECs for RDX, PETN and δ- HMX agree well with previous experiments and theoretical calculations. Bulk modulus, shear modulus, Young's modulus and Poisson's ratio deduced from SOECs reveal quantitatively the anisotropic mechanical properties along different crystal orientations. TOECs of these three energetic materials, which can be used to construct constitutive equations and provide input parameters for mesomechanics model and macroscopic simulations, are predicted. In particular, the TOEC results provide guidance for future experimental measurements and lay the foundation for more accurate calculations. [ABSTRACT FROM AUTHOR]

[Display omitted] Applying the advanced CALYPSO structure searching method and first principles calculations, we predict a novel superhard structure for Ti 2 B 5 , which belongs to the monoclinic C 2/ m space group. The previously known Hf 2 B 5 , W 2 B 5 , and δ -V 2 O 5 -type structures are also selected as the potential structures for Ti 2 B 5. It is shown that the predicted C 2/ m structure is the most stable phase among these considered structures within the range of 0-100GPa. The calculations of the phonon dispersion and elastic constants affirm that the predicted C 2/ m phase is dynamically and mechanically stable. The predicted high shear modulus (249 GPa) and large hardness (46.9 GPa) show that it should be an underlying superhard material. In addition, the elastic anisotropy of Ti 2 B 5 is also explored by investigating the directional dependence of the Young's modulus, shear modulus, and Poisson's ratio as well as some well anisotropy indices. The particular analyses of the density of states and electron charge density distribution verify that the strong B-B and Ti-B covalent bonds in the predicted C 2/ m- Ti 2 B 5 phase play an important part in its hardness and structural stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • A CG model is employed to scale up the time range of atomistic simulations. • Basic mechanical and thermal properties are well reproduced by the new CG model. • Plasticity of single crystal in the CG model agrees well with that of all-atom MD simulation. • Submicron-order CG simulation of crystal growth was performed on the supercomputer. It is not yet straightforward to expand the time scale of molecular dynamics simulations in spite of recent progress in high-performance computing since time series of atomic motion cannot be parallelized easily. In this study, a novel coarse-grained molecular dynamic model is employed to scale up the time range of atomistic simulations for metallic materials. Basic mechanical and thermal properties of nickel including elastic constants, bulk modulus, shear modulus, Young modulus and melting point are well reproduced with the definition of the coarse-grained model. Moreover, it was found that single crystal plasticity occurring in the coarse-grained model compares very well with all-atom molecular dynamics simulations. This can be explained by the equality of the ratio in the generalized stacking fault energy curve between coarse-grained and all-atom models. Furthermore, a large-scale coarse-grained molecular dynamics simulation of the crystal growth was performed on the supercomputer as a practical example of the acceleration of simulation, in which a submicron-order crystal appears from the seed crystal in the undercooled melt. It is expected that the coarse-grained molecular dynamics method has a variety of applications in the future since it can handle calculations on such a large scale with relative ease. [ABSTRACT FROM AUTHOR]

The structural stability and mechanical properties of Co 3 (Al, M) (M = Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W) compounds with cubic L 12 -type and hexagonal D0 19 -type structures have been investigated by first-principles calculations. Calculated temperature-dependent formation energies indicate that all the L 12 -type Co 3 (Al, M) can be generated at high temperature and show better stability than their D0 19 -type according to the quasi-harmonic Debye model. Furthermore, we reveal that the element Al plays a major role in promoting L 12 structure more stable than D0 19 structure for the Co 3 (Al, W), and the element W reduces metastability as well as improves the strength of L 12 . We also find that most of the L 12 -Co 3 (Al, M) compounds possess good mechanical stability and ductility, which are verified by the elastic constants and Poisson’s ratio. More importantly, the element Cr can be used to replace the W of L 12 -Co 3 (Al, W) to increase the strength to weight ratio as the L 12 -Co 3 (Al, Cr) possesses comparable elastic properties to the L 12 -Co 3 (Al, W), including the Young’s and shear moduli. It is also observed that all the L 12 -Co 3 (Al, M) compounds show a high degree of elastic anisotropy. The electron localized function and suggests that the rise of the Young’s moduli in Co 3 (Al, M), with the alloying element M changing from group IVB to VIB, is mainly attributed by the increasing bonding strength of the nearby transition-metal atoms. Our results will be useful for the study of thermodynamic and mechanical properties as well as the design of Co-based high-temperature alloys. [ABSTRACT FROM AUTHOR]

To reveal the origin of modulus anomaly over a wide temperature range (about 240 K) observed in Mn 0.70 Fe 0.25 Cu 0.05 alloy, a phase-field model considering antiferromagnetic (AF) transition with doping Fe was established, in which the average modulus is considered as a functional of order parameter. Simulation reveals that the pining effect by doping Fe leads to the increase of low spin non-collinear AF domain walls (LS), meanwhile, the LS domain walls gradually evolve to high spin collinear AF domains (HS) with lowering temperature, accompanying the growth of HS domains and the decrease of modulus, and vice versa. Such a dynamic antiferromagnetic domain size (DAFDZ) effect gives rise to modulus anomaly, while the proper volume ratio of LS and HS is a crucial factor for the wide temperature range of modulus anomaly. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations were carried out to study the glass transition temperature and mechanical properties of glycidyl azide polymer (GAP) most widely used in propellants and explosives as an energetic binder. Other three polymers derived from GAP with different side groups were designed and simulated under the COMPASS force field, with the ensembles of constant particle number, volume, temperature (NVT) and constant particle number, pressure, temperature (NPT). It was found that the densities and free volumes of polymers changed regularly along with the decrease of temperature and the transition occurred at the turning point. Thus the glass transition temperatures ( T g ) were predicted in two methods based on density and free volume theory. The simulation results showed that the introduction of –NO 2 made important contribution on reducing the T g of polymers, and the probable mechanism was discussed. Moreover, several mechanical properties of four pure polymer systems such as Young’s modulus, Shear modulus, Bulk modulus and Poisson’s ratio, etc, were calculated. The calculated results revealed that the single introduction of –NO 2 increased the mechanical properties parameters more obviously than other two polymers. Overall, a new method was used for GAP modification in order to improve its mechanical properties at low temperatures, and provides some guidance to the GAP modification via changing substituent groups of side chain. [ABSTRACT FROM AUTHOR]

The structural, thermodynamic and elastic properties of zirconium hydrides have been systematically investigated from first principles. ZrH 2 is the only stable structure in Zr–H system and other zirconium hydrides are thermodynamically metastable. The enthalpy of formation of P 4 2 / mmc -ZrH, P 4 2 / nnm -Zr 2 H 3 (a > c) and P 4 ̄ 2 m -Zr 4 H 7 (a > c) is just a few meV/atom above the convex-hull. To determine the overall stability of the material, the dynamical and mechanical stabilities of the zirconium hydrides, including the thermodynamically stable and metastable phases, are evaluated by calculating their phonon dispersion and elastic constants, respectively. Except for P 4 2 / mcm -Zr 2 H, P 4 ̄ 3 m -Zr 4 H 3 and P 4 ̄ 3 m -ZrH, the other investigated ZrH x phases are all dynamically stable. The mechanical instability of cubic and tetragonal zirconium hydrides is induced by their negative tetragonal shear moduli. The mechanical properties (bulk modulus, shear modulus, Young's modulus, Poisson's ratio and hardness) of zirconium hydrides and their dependence on the hydrogen concentration are calculated and discussed. The bulk modulus almost monotonically increases with H concentration. Compared with hydrogen-rich zirconium, the calculated values of mechanical properties, including elastic modulus, Poisson's ratio and hardness of subhydrides (Zr 4 H, Zr 2 H and Zr 4 H 3) are closer to those of the pure zirconium. Among these hydrides, newly discovered metastable P 4 ̄ 2 m -Zr 4 H 5 is the hardest and has a Vickers hardness of 4.3 GPa. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] The equiatomic face-centered cubic NiCoCrFeMn high entropy alloy has exhibited a rare but desired combination of the strength and ductility at cryogenic temperatures, and a similar phenomenon has been observed in equiatomic subsets of the alloy. To obtain a fundamental understanding of the underlying deformation processes, here we investigate the compositional effects on dislocation properties in the model NiCo and NiFe alloys using atomistic simulations. First, the fidelity of the employed interatomic potential is examined by comparing calculated material properties with available experimental data and first principles calculations. Then, we systematically examine the dislocation energy, core radius, core width, Peierls stress, and separation distance between the Shockley partial dislocations for edge and screw dislocations, as a function of the composition. The core energy of a screw dislocation is found to be lower than that of an edge dislocation, suggesting screw dislocations are more energetically stable in both alloys. It is found the compositional dependence of the core width is not relevant to that of the Peierls stress in the alloys, in contradiction with the classical Peierls–Nabarro model. The results suggest local atomistic environment plays a significant role in the Peierls stress. The separation distance increases with decreasing Ni concentration, except for a screw dislocation in the NiFe, which is attributed to the compositional dependence of the stacking fault energy and shear modulus. This study provides fundamental insights into the dislocation properties of these alloys, which can serve as a basis for understanding many dislocation features and underlying deformation mechanisms in compositionally complex alloys. [ABSTRACT FROM AUTHOR]

[Display omitted] • The cluster structure with two doped atoms was constructed to investigate the site preference and elastic properties. • The site preferences for cube corner and face center and the short-range ordering were considered comprehensively. • The charge redistribution and orbital hybridization between the doped atoms and Ni atoms contributed to the stability of cluster structure. • The anisotropy of modulus caused by the linear cluster structure was due to the change in differential charge density along different directions. The cluster structure with two doped atoms (M: W, Mo, Cr, Ti, Ta, Nb, Ru, Re, Al, Co) in γ-Ni was constructed and investigated by first-principles calculations. The doped systems had the most stable cluster structure along 〈1 0 0〉 directions except for the 〈1 1 1〉 direction of Ru. The W, Mo, Cr, Ti, Re, Al, Co and Ru tended to form the "-M-M-" linear cluster structure, while the Ta and Nb formed the "-M-Ni-M-" linear cluster structure. The doped systems were ductile and enhanced with the addition of M atoms except for Ru atom, while only Ru atom improved the Young's modulus and shear modulus. Cr and Co atoms increased the anisotropy factor, while Ti, Ta, Nb and Ru atoms decreased the anisotropy factor. From the electronic basis, the charge redistribution and the orbital hybridization between the M atoms and Ni atoms contributed to the stability of cluster structure. The modulus anisotropy caused by the linear cluster structure was due to the change in differential charge density along different directions. [ABSTRACT FROM AUTHOR]

The study attempts to investigate the mechanical properties of single-walled black phosphorene nanotubes (SW-BPNTs) at atmospheric pressure through molecular dynamics (MD) calculation incorporating with the Nosé-Hoover Langevin (NHL) thermostat. Their dependences on size, chirality and temperature are also addressed. Two typical cross-sectional area definitions, i.e., hollow tube and equivalent solid cylinder, are used in the estimate of the mechanical properties. The predicted results are compared with each other and also with the literature data. The calculation results reveal that the Young’s modulus, shear modulus, specific heat and CTE of both armchair and zigzag SW-BPNTs would increase with the tube length and diameter, and additionally, the Young’s modulus and shear modulus appear to change significantly with chiral angle. It is also found that the Young’s modulus calculated using the hollow tube assumption would increase with the tube diameter while there is an opposite trend for the equivalent solid cylinder assumption. According to the equivalent solid cylinder assumption, the nanoscale SW-BPNTs are not a very stiff material. Moreover, the specific heat and linear coefficient of thermal expansion (CTE) of SW-BPNTs, irrespective of chirality and size, increase with temperature at low temperature and tend to converge to a certain value when temperature is larger than 600 K. Besides, the calculated specific heat of SW-BPNTs closely follows the Debye T 3 law. [ABSTRACT FROM AUTHOR]

The elastic properties and thermodynamic properties of insensitive high explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) are investigated by using molecular dynamics simulation. We first analyse the elastic anisotropy of TATB, which makes up for the shortage of research on the anisotropic mechanical properties of explosives. The three-dimensional contours and their planar projections of Young’s modulus and shear modulus are plotted to illustrate the anisotropy in elasticity. TATB shows high elastic anisotropy and strong dependence on direction. With pressure increasing from 0 to 50 GPa, the anisotropy of Young’s modulus shows a decreasing trend, while the anisotropy of shear modulus exhibits an increasing trend. Based on Debye theory and phonon dispersion model, we use a method derived by our group to calculate the thermal conductivity of TATB in the temperature range 0–700 K and pressure range 0–30 GPa. The calculated thermal conductivity at 300 K and 0 GPa is 0.53 W/m K, which is in agreement with the available experimental results. Using Cahill’s model, the minimum anisotropic thermal conductivity of TATB is discussed. The results indicate that the thermal conductivity of TATB has strong dependence on direction. [ABSTRACT FROM AUTHOR]

Exchange-correlation functionals with corrections for van der Waals interactions (PBE-D2, PBE-D3, PBE-D3(BJ), PBE-TS, optPBE-vdW and vdW-DF2) are tested for graphene and hexagonal boron nitride, both in the form of bulk and bilayer. The characteristics of the potential energy surface, such as the barrier to relative sliding of the layers and magnitude of corrugation, and physically measurable properties associated with relative in-plane and out-of-plane motion of the layers including the shear modulus and modulus for axial compression, shear mode frequency and frequency of out-of-plane vibrations are considered. The PBE-D3(BJ) functional gives the best results for the stackings of hexagonal boron nitride and graphite that are known to be ground-state from the experimental studies. However, it fails to describe the order of metastable states of boron nitride in energy. The PBE-D3 and vdW-DF2 functionals, which reproduce this order correctly, are identified as the optimal choice for general studies. The vdW-DF2 functional is preferred for evaluation of the modulus for axial compression and frequency of out-of-plane vibrations, while the PBE-D3 functional is somewhat more accurate in calculations of the shear modulus and shear mode frequency. The best description of the latter properties, however, is achieved also using the vdW-DF2 functional combined with consideration of the experimental interlayer distance. In the specific case of graphene, the PBE-D2 functional works very well and can be further improved by adjustment of the parameters. [ABSTRACT FROM AUTHOR]

A quantitative understanding and prediction of the viscoelastic relaxation behavior of polymer melts is required to build up predictive multiscale models, which can be utilized for the practical design of viscoelastic materials. We report the application of the Green–Kubo method to compute the common shear relaxation modulus and the rarely reported bulk relaxation modulus for a realistic united atom model of poly(tetramethylene oxide) (PTMO), which is one key components of the segmented polyurethane (PU) elastomers. The temperature and molecular weight dependent viscoelastic behavior is investigated in detail by computing the bulk relaxation modulus K (t) along with shear relaxation modulus G (t). Our results provide new rheological data for PTMO melt based on the united atom model, which incorporates the chemical details of the polymer backbone. The predicted stress relaxation are mapped onto master curves using the time–temperature superposition principle with horizontal and vertical shift factors. The computed shift factors agree with the Williams–Landel–Ferry equation and appear to be similar for the shear and bulk relaxation modulus. The underlying dynamics for the shear and bulk relaxation modulus appear to stem from the same mechanistic origin as both processes seem to sample similar kinetic signature of the reference time scale of the underlying thermally activated processes in the liquid. Our results demonstrate furthermore, that MD simulations with the chemical details beyond coarse-grained models can sample the Rouse dynamics and the transitions towards entanglement, which is evident by the emergence of a plateau in shear relaxation modulus and scaling relations in the diffusion behavior of the monomer at larger molecular weights. [Display omitted] [ABSTRACT FROM AUTHOR]

A second nearest neighbour (2NN) modified embedded atom method (MEAM) potential was recently derived by Joost et al. (2015) for Ti–O. Transferability of the potential was demonstrated by those authors through zero temperature molecular statics modelling of various phases of Ti–O not included in the original set of fitting parameters. In the study presented here, the Ti–O potential is tested over a temperature range from 300 K to 700 K by comparing elastic properties against experimental data, in order to assess its transferability to high temperature behaviour. It is found that the Ti–O MEAM accurately predicts the hcp titanium Youngʼs modulus as a function of oxygen content at room temperature. At higher temperatures, however, the simulated Youngʼs modulus over predicts the experimentally determined response. It is further shown that the inaccuracies in Ti–O MEAM potential predictions are directly related to the inability of the Ti MEAM potential to predict the temperature dependence of the shear modulus of hcp titanium above 300 K. [ABSTRACT FROM AUTHOR]

In the present work the influence of nc-TiN nanocrystals on the elastic properties of nc-TiN/a-Si 3 N 4 nanocomposite is discussed. The elastic moduli (shear modulus, compression modulus, Young’s modulus) for both amorphous matrix a-Si 3 N 4 and nc-TiN nanocrystals of different size were calculated by first-principles method and molecular static method correspondingly. The Volkov-Stavrov approach was applied for modeling elastic properties of nanocomposite taking into account size and volume fraction of the TiN inclusions. The results of modeling showed the increase the effective elastic moduli of the nc-TiN/a-Si 3 N 4 nanocomposite with nc-TiN inclusions size and volume fraction growth. The obtained results are compared to the experimental data. [ABSTRACT FROM AUTHOR]

[Display omitted] • The first-principles modelling based on the density functional theory was used to study the site dependent mechanical properties, such as elastic constants and related modulus for 3d transition metal doped MnV intermetallic. • The calculated properties show a dopant-site dependency. • Ni, Cu and Zn doping into MnV is a promising way to further improve ductility while maintaining appreciable hardness. • Data mining revealed that ductile materials show higher formation energies, suggesting that these systems are less stable. In this paper, the first-principles modeling based on the density functional theory (DFT) was used to explore the structural, mechanical, and thermodynamical properties of 3d transition metal-doped MnV intermetallic. The site-dependent mechanical properties such as elastic constants C ij , bulk modulus B , shear modulus G , Young's modulus E , Vickers hardness H V , Poisson's ratio ν , Cauchy pressure C 12 - C 44 , Pugh ratio B / G , and Debye temperature Θ D were systematically presented. Our study suggests that doping 3d metal elements into MnV is a promising way to tune the mechanical properties of the MnV intermetallic and further improve its intrinsic ductility while maintaining appreciable hardness. Data mining is also employed alongside DFT calculations to classify the hard/ductile systems and to study the interrelationships among the systems studied here and their physical properties in order to generate unexpected knowledge. [ABSTRACT FROM AUTHOR]

Pugh’s criterion in terms of the bulk/shear modulus ratio ( B / G ) is widely used to distinguish the ductility and brittleness of metals, with the recommended B / G ratio of 1.75 for the boundary ratio between ductility and brittleness. The present first-principles calculations yield a B / G = 3.69 for the C15 Laves phase NbCr 2 , suggesting the ductility of NbCr 2 according to Pugh’s criterion. However, experiments indicate that NbCr 2 is a brittle phase at room temperature with the fracture toughness of 1.0–1.4 MPa m 1/2 . NbCr 2 is hence a compound with its ductile and brittle behavior beyond Pugh’s criterion, and this finding also validates for other Laves phases and compounds. New insight into Pugh’s B / G criterion is also discussed. [ABSTRACT FROM AUTHOR]

We apply the exact-muffin-tin-orbitals (EMTO) method to investigate structural properties, formation enthalpies, mechanical stability and polycrystalline moduli in Ni–Re, Ni–Cr and Cr–Re disordered fcc, bcc and hcp phases. Substitutional disorder is treated by using the coherent potential approximation (CPA). We predict the alloy lattice parameters in good agreement with the experiment. We find a continuous softening, as a function of Cr composition, of the tetragonal shear modulus C ′ in fcc Ni–Cr phase indicating mechanical instability in Cr-rich Ni–Cr alloys. On the other hand, we show that the mechanical stability of fcc Ni–Re alloys persists through the whole composition range. We observe an intriguing behaviour of the Young’s modulus vs. the intrinsic ductility curve in Ni-rich Ni–Re fcc phase. [ABSTRACT FROM AUTHOR]

The modified Nosé–Hoover (NH) thermostat incorporated with molecular dynamics calculation is applied to evaluate the mechanical properties of multi-layered graphene structures at atmospheric pressure, including Young’s modulus, shear modulus, Poisson’s ratio, specific heats, linear coefficient of thermal expansion (CTE) and thermal conductivity. The thermostat method takes into account the contribution of phonons by virtue of the vibrational energy of the lattice and the zero-point energy, thereby providing a better prediction of the low temperature thermodynamic properties. The focuses of this study are placed on exploring their temperature, size, chirality and layer number dependences. The validity of the calculations is further demonstrated by comparing the calculated results with those derived from the existing thermostats, namely, the standard NH, Nosé–Hoover chain (NHC), “massive” NHC and velocity-rescaling thermostats, and also with the literature experimental and theoretical data. It was found that the calculated mechanical properties of the graphene sheets agree well with the published experimental and theoretical results. The results also show that their Young’s modulus, shear modulus, linear CTE and Poisson’s ratio tend to decrease with the increase of temperature, size and layer number, where the linear CTE would eventually converge to that of the bulk graphite. Besides, the heat capacity and thermal conductivity at low temperatures show the high temperature dependences, i.e., the third and λ ( λ = 2–3) power of temperature, which are more consistent with that obtained from Debye model. [ABSTRACT FROM AUTHOR]

Empirical Gupta-type potentials based on the second-moment approximation of tight-binding model have been developed for five hexagonal-closed-packed (hcp) rare earth metals: Er, Dy, Gd, Tb, Lu. The potentials can reproduce experimental cohesive energies, lattice constants and elastic constants of Er, Dy, Gd, Tb and Lu. The calculated bulk moduli, shear moduli, sound velocities and Debye temperatures are in reasonable agreement with the measured values. Vacancy formation energies and surface energies of these metals are also calculated and compared with previous theoretical results. Our potentials are able to simulate the phonon dispersions of Tb, Er, Dy, Gd, and Lu solids and reproduce Tb’s experimental data in detail. The present Gupta potentials would be useful for future simulations of elementary metals of Er, Dy, Gd, Tb, Lu and their alloys. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pure alias ideal shear strength first-principles calculations of 26 binary Ni alloys. • Relative importance of atomic properties revealed through feature ranking techniques. • Top features promising for machine learning descriptor of mechanical properties. • Combining Ni and Mg ideal shear data shifted feature importance rankings. • Effect of alloying on ideal shear translates to predicted stress–strain response. The present work examines the effect of alloying elements (denoted X) on the ideal shear strength for 26 dilute Ni-based alloys, Ni 11 X, as determined by first-principles calculations of pure alias shear deformations. The variations in ideal shear strength are quantitatively explored with correlational analysis techniques, showing the importance of atomic properties such as size and electronegativity. The shear moduli of the alloys are affirmed to show a strong linear relationship with their ideal shear strengths, while the shear moduli of the individual alloying elements were not indicative of alloy shear strength. Through combination with available ideal shear strength data on Mg alloys, a potential application of the Ni alloy data is demonstrated in the search for a set of atomic features suitable for machine learning applications to mechanical properties. As another illustration, the calculated Ni ideal shear strengths play a key role in a predictive multiscale framework for deformation behavior of single crystal alloys at large strains, as shown by simulated stress–strain curves. [ABSTRACT FROM AUTHOR]

The structural, elastic and electronic properties of four nitrides M 2 N 3 (M = Zr, Hf, W and Re) with U 2 S 3 structure are investigated by plane-wave pseudopotential density functional theory by the generalized gradient approximation in this paper. The calculated elastic constants show that the nitrides are mechanically stable at ambient conditions, except Re 2 N 3 . The calculated bulk modulus B and shear modulus G indicate that Zr 2 N 3 , Hf 2 N 3 and W 2 N 3 are potential candidates for hard materials. [ABSTRACT FROM AUTHOR]

Molecular statics simulations are conducted on single-crystal copper nanofilms subjected to shear loading to examine the effect of thickness on the mechanical properties of nanofilms. Simulation results show that not only the yield strength but also the shear modulus increases with decreasing film thickness. In order to better relate the yield strength of a copper nanofilm to its thickness, a Hall–Petch-like fitting function is proposed to predict the variation of yield strength with film thickness. The initial yield is found to be associated with the nucleation of dislocations. The energy required for the first nucleation of dislocations is calculated and plotted as a function of film thickness to elucidate the origin of the thickness effect on yield strength. In addition, the production of vacancy clusters is also found to depend on film thickness and three new patterns of vacancy clusters are observed in our simulations. [ABSTRACT FROM AUTHOR]

First principles calculations are used to focus on the phase stability of N substituted Li 2 FeSiO 4 . The ground state structures of Li 2− x FeSiO 4− y N y ( x = 0, 1, 2; y = 0.5, 1) are determined by including the site-exchange of Li and Fe, on the basis of the Pmn2 1 structure of Li 2 FeSiO 4 . Calculated B / G (quotient of bulk to shear modulus) values of delithiated FeSiO 4− y N y are 1.33 ( y = 0.5) and 0.94 ( y = 1) lower than the critical value 1.75 which separates ductile and brittle materials. The elastic–brittle FeSiO 4− y N y would induce a structural collapse and a capacity fading of Li 2 FeSiO 4− y N y during the charge/discharge cycles, under a significant volume change of more than 32.0%. The calculated results suggest that the phase stability is important for the electrochemical performance of Fe-based silicates as well as the deinsertion voltage. [ABSTRACT FROM AUTHOR]

In the extraction of elastic constants of cubic crystals from first-principles calculations of energy or stress, the relative deviation of the adopted lattice-constants from true values ( Δ a / a 0 ) is inevitably added to the diagonal components of the applied elastic strains, which might lead to sizeable inaccuracy of bulk modulus B and tetragonal shear modulus C ′. This paper suggests an arithmetic scheme that dramatically decrease the error transfer from Δ a / a 0 in the extraction of B and C ′ from first-principles calculations of stress. By using this scheme, we compute the elastic constants of α -Fe, which are all in good agreement with those extracted by least-squares scheme from the same level first-principles calculations of energy and stress. The computed Young’s modulus E and polycrystalline shear modulus G of Fe-base binary alloys at alloy concentration of 0.78 at.% are both satisfactorily consistent with the data at 0 K deduced from the available experimental measurements. Theoretical basis and tests both indicate that the suggested scheme is accurate and efficient in extracting elastic constants of cubic crystals at equilibrium. [ABSTRACT FROM AUTHOR]

Highlights: [•] Shear stress–shear strain curves perform periodic along direction. [•] Microtwins arose during shearing along direction. [•] Shear modulus decreases with increasing temperature. [•] Shear modulus is insensitive to the size of shear model and shear direction. [•] The classical description of shear modulus is still efficient at the nanoscale. [Copyright &y& Elsevier]

Highlights: [•] Molecular modelling was used to study interfacial interactions of CNTs/epoxy matrix. [•] Different geometrical factors of the CNTs were taken into account. [•] An effective shear transfer length of 1000nm was obtained. [•] An increase of a factor of 10 was found in the matrix shear modulus at the interface. [•] Geometrical factors of the modelled CNT affect the interfacial shear strength. [ABSTRACT FROM AUTHOR]

[Display omitted] • Orientation-dependent twinning/detwinning in NiTi is investigated by uniaxial tension and nanoindentation. • The mechanical response of stress-induced martensite variants during uniaxial tension has been discussed by DFT. • The BCO → B19″ → B19′ and B19′ → B19 are the best-behaved path of 〈0 1 0〉 and NiTi 〈1 1 0〉, respectively. • The radius of the twinned/detwinned region boundary increases in the order of 〈1 1 1〉 < 〈1 0 0〉 < 〈1 1 0〉. • 〈1 1 1〉 possessed the more fracture toughness due to lowest twin boundaries form. Understanding the effect of crystallographic orientation on the twinnin/detwinning mechanisms in NiTi shape memory alloys at an atomistic scale can help to control and tune the mechanical properties and failure behavior of such materials. In this work, we employed classical molecular dynamics (MD) and density functional theory (DFT) computational methods to better understand how twinning and detwinning occurs through a combination of slip, twin, and shuffle on 〈0 1 0〉, 〈1 1 0〉, and 〈1 1 1〉 crystallographic orientations under uniaxial tensile test. Elastic constants including Young's Modulus (E), Bulk modulus (B), Poisson's ratio (ν), and Shear Modulus (G) are obtained and computed for resultant stress-induced martensite variants as a function of crystallographic orientation using DFT calculations. In addition, computational nanoindentation tests are carried out using MD simulations to evaluate the effect of crystallographic orientation on the twinning and detwinning characteristics in martensite in NiTi alloys under sphere indenter, both qualitatively and quantitatively. Based on a careful polyhedral template matching (PTM) and dislocation analysis (DXA) by taking into account the textures, it is determined that the microscopic stress-strain and load-displacement responses strongly depend on the crystallographic orientation. Our findings reveal that the size of twinned and detwinned zones in martensite increases in the order of 〈1 1 1〉 < 〈0 1 0〉 < 〈1 1 0〉. Based on DFT results, against 〈1 1 1〉 direction, abrupt changes in the free energy-strain curves occurs at 4% strain in 〈0 0 1〉, and 8% strain in 〈1 1 0〉 directions. The twinning and detwinning mechanisms are controlled by monoclinic martensite (B19′) → orthorhombic martensite (B19) phase transformation in 〈1 1 0〉 orientation and by body-centered orthorhombic martensite (BCO) → an intermediate structure (B19″) → monoclinic martensite (B19′) phase transformation in 〈0 0 1〉 orientation. Finally, the predicted orientation-dependent critical energy release rate is analyzed to examine the effect of the twinning and detwinning process on the fracture toughness of the material. Our results show that reducing the density of twins results in increasing the critical energy release rate. Therefore, the fracture stress intensity increases in the order of 〈0 0 1〉 < 〈1 1 0〉 < 〈1 1 1〉. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the molecular structural mechanics method is employed to calculate the mechanical properties of a double-layered carbon graphene sheet more accurately. For this purpose, covalent bonds are modeled using nonlinear beam elements and van der Waals interactions are replaced by nonlinear truss elements. Morse potential and Lennard–Jones potential equations are used to simulate the covalent bonds and van der Waals interactions, respectively. For each atom, van der Waals forces are considered with respect to all the other atoms located in its cut-off radius. In addition to in-plane mechanical properties of single and double-layered graphene sheets some out-of-plane properties like the thickness-wise stiffness and shear modulus are studied. The results indicate that Young’s modulus of a double-layered carbon graphene sheet decreases linearly with strain while Poisson’s ratio is independent from it. Also it is noted that the thickness-wise stiffness significantly increases while the distance between the two layers declines however the shear modulus is independent from shear strain. [Copyright &y& Elsevier]

Abstract: Carbon nitride in the form of C3N4 was speculated nearly 22years ago. It has various structural forms ranging from layered graphitic to superhard structures. Using first principles calculations, we investigate the structural and elastic properties of these graphitic and superhard structures. The independent elastic constants of cubic, hexagonal, rhombohedral, buckled as well as orthorhombic phases of C3N4 are reported in this work. We also examine the bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio. From the work it is evident that although the compressibility of some of the superhard phases may surpass diamond, the shear modulus indicates that C3N4 is not harder than diamond, as had been speculated earlier. [Copyright &y& Elsevier]

Abstract: In this paper we report theoretical ab initio study of the elastic and piezoelectric properties of LiMX2 (M=Ga,In; X=S, Se) by means of density functional theory (DFT). Other relevant quantities such as shear modulus, Young’s modulus, sound velocity, Poisson’s ratio, anisotropy factors, and Debye temperature have been calculated. The calculated Debye temperatures for LiInS2 and LiInSe2 are very close to experimental counterparts. Moreover, we present for the first time the investigation of the piezoelectric properties of LiGaS2, LiGaSe2 and LiInSe2 using the density-functional perturbation theory (DFPT). The calculated piezoelectric tensors for LiInS2 are in good agreement with the experimental data. These compounds that have reached crystal growth maturity show good piezoelectric property. For example, the calculated d 15 and d 33 piezoelectric coefficients of LiGaSe2 are 5.02pN/C and 3.17pN/C respectively. [Copyright &y& Elsevier]

Abstract: Using particle swarm optimization technique on crystal structural prediction, a universal hexagonal MoB4-type structure was uncovered for WB4, TcB4, and ReB4. This MoB4-type structure is energetically much superior to the previously proposed WB4-type structure and stable against decomposition into the mixture of TM and B at ambient conditions. The Young’s modulus and shear modulus as a function of crystal orientation for the TMB4 (TM=W, Tc, and Re) have thus been systematically investigated. TMB4 within this hexagonal structure are found to be ultra-incompressible and hard due to their high bulk modulus and large hardness. Especially, they exhibit an unusual incompressibility along the c axis, close to that of diamond. Their ultra-incompressibility is attributed to a staking of B–TM–B “sandwiches” layers linked by strong covalent TM–B bonding, which is manifested by the PDOS and ELF analysis. [Copyright &y& Elsevier]

Abstract: First principles calculations are performed to investigate the structural, mechanical, electronic, and thermodynamic properties of BeB2C2. Our calculated lattice parameters are in good agreement with the experimental data. Orthorhombic BeB2C2 phase is found to be mechanically stable at ambient pressure. The Young’s modulus and shear modulus as a function of crystal orientation for the BeB2C2 have been systematically investigated. Further mechanical properties demonstrated that BeB2C2 is strongly prone to brittle and possesses high Vickers hardness of 26.5–28.6GPa. Density of states and electron topological analysis show that chemical bonding among Be, B, and C atoms in BeB2C2 is a complex mixture of covalent and ionic characters. Based on the quasi-harmonic Debye model, the dependence of Debye temperature, Grüneisen parameter, heat capacity, and thermal expansion coefficient on the temperature and pressure are systematically explored in the whole pressure range from 0 to 20GPa and temperature range from 0 to 1200K. [Copyright &y& Elsevier]

Abstract: Molecular dynamics simulations and geometry optimizations based on the Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field were performed to understand the effect of Single Wall Carbon Nanotubes (SWCNTs) on the mechanical properties of Poly(vinylidene fluoride) (PVDF). In particular, the Young’s modulus, bulk and shear modulus, pullout energy, pullout force, interfacial shear stress and interfacial bonding energy were calculated. The presence of the SWCNTs can increase the Young’s modulus of the systems studied here by 1GPa in the direction of the SWCNT axis, although this depends on the distance between neighboring SWCNTs. The calculated interfacial shear stress was between 100 and 129MPa, which is in agreement with results obtained for other SWCNT-polymer systems. The results, and in particular those obtained for the bulk and shear modulus, show that SWCNTs do not have a significant effect on the bulk mechanical properties. Functionalizing the SWCNTs may yield stronger adhesion between the nanotube and the polymer, thereby achieving improved mechanical properties. [Copyright &y& Elsevier]

The effect of glass stability on the yielding transition and mechanical properties of periodically deformed binary glasses is investigated using molecular dynamics simulations. We consider a binary mixture first slowly cooled below the glass transition temperature and then mechanically annealed to deeper energy states via small-amplitude oscillatory shear deformation. We show that upon increasing glass stability, the shear modulus and the yielding peak during startup continuous deformation increase towards plateau levels. It is found that during the strain amplitude sweep, the yielding transition occurs at higher amplitudes and it becomes more abrupt in deeply annealed glasses. The processes of initiation and formation of a shear band are elucidated via the spatiotemporal analysis of nonaffine displacements of atoms. These results are important for thermo-mechanical processing of highly stable amorphous alloys. [Display omitted] • Periodic subyield shear deformation leads to a logarithmic decay of the potential energy. • Under amplitude sweep, more stable, thermal glasses yield at higher strain amplitudes. • Before shear band formation, the size of plastic events is smaller in deeply annealed glasses. [ABSTRACT FROM AUTHOR]

[Display omitted] Shape optimization techniques are utilized to develop an optimal shear specimen for polymer matrix composites (PMCs) in which shear stresses result from simple uniaxial extension. An expanding array of composite applications means certification and damage tolerance are critical design factors. This methodology improves the ease of characterization for classically challenging material properties, such as shear failure. Numerical simulations were conducted using IM7/977-3 unidirectional prepreg mechanical properties. Large shear strain concentrations in the region of interest led to predicted failure in the region of interest under conditions consistent with shear. The geometry generated by the shape optimization should continue to be explored due to its capability generating a geometry which can measure the shear modulus and shear strength of a laminate. The shape optimization method's ability to tailor a sample geometry for a desired strain state and failure mode leads the authors to recommend exploration of additional optimized test geometries for other failure modes and materials, in addition to the experimental investigation of the geometry generated for shear. [ABSTRACT FROM AUTHOR]

[Display omitted] • CuZr MGs were rejuvenated following thermal-pressure treatments. • Rejuvenation pressures in the range of 0–50 GPa were considered. • The shear modulus showed the largest reduction among the mechanical properties. • Solid-like polyhedra contributed to the increase of potential energy. • Transition and liquid-like polyhedra contributed to the increase of free volume. Thermal-pressure treatments have proved to bring metallic glasses (MGs) to rejuvenated states. However the knowledge regarding their effect on the mechanical properties and atomic structure is still limited. Here, molecular dynamics simulations were performed on Cu 50 Zr 50 MGs rejuvenated at pressures in the range of 0–50 GPa. The Young, bulk, and shear moduli decreased as the pressure increased, while the Poisson's ratio increased. The shear modulus showed the largest variation, with a loss of ~ 8.5%. Compression tests revealed that the transition from localized to homogeneous deformation occurred in the 20–32 GPa range. The contribution of different Voronoi polyhedron types to MGs rejuvenation were also explored. Voronoi analysis delivered that solid-like polyhedra contributed to the increase of potential energy, whereas transition and liquid-like polyhedra contributed to the increase of atomic volume. Overall, our results elucidate the change of several properties at the atomic scale, adding new insights regarding thermal-pressure treatments in MGs. [ABSTRACT FROM AUTHOR]

[Display omitted] The present manuscript explores application of machine learning methods for determining elastic constants and other derived mechanical properties of multi-component alloys. A number of machine learning models, including linear regression, neural network and random forest based models, are trained and tested on a dataset of binary alloys generated using density functional theory (DFT) calculations and spanning over a large number of elemental species in the periodic table. Starting with a wide range of simple and easily accessible compositionally-averaged elemental features, a correlation-based feature selection strategy was used to systematically down-select a set of most relevant features towards the prediction of the elasticity tensor components. The true predictive performance and the associated uncertainties of the models were established by testing on unseen data and bootstrapping, respectively. A single and pair-wise feature partial dependence analysis was performed to visualize the average property trends in the multi-dimensional feature space in order to further understand the achieved predictive performance. The utility of the trained model is further demonstrated by obtaining sufficiently accurate yet highly efficient approximations for bulk modulus, Young's modulus, shear modulus and Poisson's ratio for alloys beyond the binary space (i.e., two-component alloys) on which the model was originally trained. More importantly, we test and validate the predictive performance of the developed model directly against the experimentally measured elastic constants of technologically relevant multi-component alloys (such as, Ni- and Ti-based alloys). Finally, utility of such a data-enabled route is demonstrated by predicting the possible range of various elastic properties for vast composition space available within the five component Ni-Cr-Fe-Mo-W alloy system in a high-throughput manner. [ABSTRACT FROM AUTHOR]

[Display omitted] This paper presented a comprehensive study of structural and mechanical properties of HfC-TaC and HfC-HfN based ceramics. Using evolutionary algorithm and first-principles method, we firstly explored crystal structures of ternary Hf 1- x Ta x C and HfC 1- x N x compounds. Besides those known structures, several new structures were predicted to be thermodynamically stable or metastable. The simulated X-ray diffraction patterns and structural analysis has shown that ternary Hf 1- x Ta x C and HfC 1- x N x compounds all belong to be rock salt structure with [Hf 6- x Ta x C], [Hf 6 C] or [Hf 6 N] octahedra as structural basis. Then, the mechanical properties of ternary Hf 1- x Ta x C and HfC 1- x N x along with binary HfC, TaC, and HfN compounds were calculated by a first-principles method. We found that the maximum shear and elastic moduli, Vickers hardness and fracture toughness of ternary Hf 1- x Ta x C and HfC 1- x N x compounds were higher than those of binary HfC, TaC, and HfN compounds due to alloying strengthening; our present finding agrees well with those previous experimental studies. Finally, the relationship between the mechanical properties and valence electron concentration (VEC) of Hf 1- x Ta x C and HfC 1- x N x compounds was studied. We show that both Hf 1- x Ta x C and HfC 1- x N x compounds have the maximum Vickers hardness at VEC around 8.3. But for other mechanical properties, there is no general rule for predicting their maximum values. [ABSTRACT FROM AUTHOR]