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In molecular dynamics simulations, there are dozens of potentials of different type, which take into account the angular dependence of the potential energy, for describing the interactions in carbon. Each of them describes simultaneously only a part of its physical properties. Meanwhile, a recently developed N-body approach provides the ability to set the required precision of this angular dependence. In particular, in this work we will show how accuracy in describing three-body interactions influences the accuracy of reproduction of physical properties of carbon on the example of one and two basis functions for these interactions. For both potentials, the identical optimization procedure, including fitting database and weights of each target value, was performed. We found that the last one reproduces the structural, elastic and defect properties of diamond, graphite and graphene phases of carbon in better agreement with experimental and theoretical data than the potential with only one basis function. For additional benchmark of this potential we assessed the melting point of graphite, which is predicted in an acceptable agreement with the experimental value. [Display omitted] • A new interatomic potential for carbon was developed. • An increase of basis functions improves the description of carbon structures. • The potential with one functions predicts graphite structures as unstable. • The potential with two functions predicts three main carbon structures as stable. [ABSTRACT FROM AUTHOR]

[Display omitted] • Helical dislocations generate significant normal stress in the direction parallel to their axis within the helix region. • The helix pitch has a greater impact on the intensity of stress within the helicoid dislocation than the helix diameter. • The helix's unfolding is controlled by the self-Peach-Koehler force, which is attributed to the shear stress components. Mutual interaction among microstructural elements, such as dislocations or point defects, through elastic fields plays an important role in understanding the dynamic evolution of microstructures in materials. For example, the ability of a helical dislocation to absorb extra point defects relies on the distribution of vacancy or interstitial around the helical dislocation line, which is determined by the elastic stress tensor. Therefore, to understand the kinetics and thermodynamics of crystallographic defects far from their statistical equilibrium, e.g., under irradiation, one needs to get an insight into the elastic stress field associated with helical dislocations. Using anisotropic linear elasticity theory, we investigate the elastic stress field induced by the helical dislocation line. Helical dislocations generate significant normal stress in the direction parallel to their axis within the helix region, while the other stress components are negligibly small. Furthermore, we elucidate the effect of geometrical parameters of helical structure, such as pitch length, diameter, and chirality, on the magnitude and distribution of the stress field. Atomistic simulation is also conducted to verify the elastic field modeling results further. [ABSTRACT FROM AUTHOR]

Advancements in modern semiconductor devices increasingly depend on the utilization of amorphous materials and the reduction of material thickness, pushing the boundaries of their physical capabilities. The mechanical properties of these thin layers are critical in determining both the operational efficacy and mechanical integrity of these devices. Unlike bulk crystalline materials, whose calculation techniques are well-established, amorphous materials present a challenge due to the significant variation in atomic topology and their non-affine transformations under external strain. This study introduces a novel method for computing the elastic tensor of amorphous materials, applicable to both bulk and ultra-thin films in the linear elastic regime using Density Functional Theory. We exemplify this method with a-SiO 2 , a commonly used dielectric. Our approach accounts for the structural disorder inherent in amorphous systems, which, while contributing to remarkable material properties, complicates traditional elastic tensor computation. We propose a solution involving the inability of atomic positions to relax under internal relaxation, near the boundaries of the computational unit cell, ensuring the affine transformations necessary for linear elasticity. This method's efficacy is demonstrated through its alignment with classical Young's modulus measurements, and has potential for broad application in fields such as Technology Computer Aided Design and stress analysis via Raman spectra. The revised technique for assessing the mechanical properties of amorphous materials opens new avenues for exploring their impact on device reliability and functionality. [Display omitted] [ABSTRACT FROM AUTHOR]

A fundamental understanding of the elastic properties of 2D network structures is highly beneficial for research and applications of 2D materials. In this context, Poisson's ratio has been studied elaborately for different crystallographic structures of crystalline phases of bilayer silica structures. This paper focuses on the elastic structure–property relationship of crystalline and vitreous polymorphs of plane network materials. We generate defective crystalline network states and seven sets of disordered states, each with a different level of network heterogeneity, using a dual Monte Carlo bond switching algorithm. Firstly, uniaxial tensile deformation is applied to a model material in a two-dimensional framework, concentrating only on the in-plane network topologies. Secondly, uniaxial tensile deformation is applied to bilayer silica structures, considering the out-of-plane morphology of the material. Mechanical testing is performed using the athermal quasistatic deformation protocol, which allows one to study the influence of the network topology exclusively without any thermal disturbances. We show that manipulating the network heterogeneity allows one to directly tune the Poisson's ratio of the material, creating possibilities for novel mechanical applications. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Electronic structure, chemical bonding, mechanical properties of AlFe 2 B 2 -based compounds are studied. • B-B forms covalent bonds, TM-B exhibits ionic-covalent bonds, and TM-TM shows metallic bonds. • Adding Cr or V instead of reduced Fe in AlFe 2 B 2 enhances hardness, brittleness, and isotropy. • An increase in isotropy is significantly more influenced by Cr than by V. • Cr-B's higher bond strength than V-B indicates that AlFeCrB 2 has the highest hardness and Young's modulus. MAB phase AlFe 2 B 2 has attracted a lot of attention as a ternary transition metal boride with layered structure due to its near-room temperature magneto-caloric effect (MCE), composed of earth-abundant elements and other properties. In this work the electronic structure, chemical bonding characteristics, mechanical stability, elastic properties, and elastic anisotropy of AlFe 2 B 2 -based compounds (borides) have been investigated using first-principles calculations based on density functional theory (DFT). The substitution effect of transition metals (TM) Cr and V in AlFe (2-x) TM x B 2 (x = 0–1), (TM = Cr, V) compounds have been investigated. It was determined that all the elements added instead of the removed Fe element in the borides increased the mechanical properties such as hardness, brittleness, and isotropy. Moreover, it has been observed that hardness, brittleness, and isotropy increase with the increasing amount of the fourth alloying element. In AlFe (2-x) TM x B 2 , it has been observed that for x = 0.25 and 0.5 values, V causes an increase in stiffness more than Cr; however, for x = 1, while the increase in Cr continues to have an effect, a reverse trend is observed for V. Additionally, it has been observed that an increase in isotropy is significantly more influenced by Cr than by V. Among borides, it has been determined that AlFeCrB 2 exhibits the highest elastic moduli (bulk, shear, and Young's modulus), hardness, and isotropy. [ABSTRACT FROM AUTHOR]

We present AnisoGNNs — graph neural networks (GNNs) that generalize predictions of anisotropic properties of polycrystals in arbitrary testing directions without the need in excessive training data. To this end, we develop GNNs with a physics-inspired combination of node attributes and aggregation function. We demonstrate the excellent generalization capabilities of AnisoGNNs in predicting anisotropic elastic and inelastic properties of two alloys. [Display omitted] • A new graph-neural network predicts anisotropic properties of polycrystals. • Model generalizes to loading directions without training data in those directions. • Model predicts properties in new directions by rigid rotation of microstructure. • Single-crystal tensorial properties as node features enable generalization abilities. [ABSTRACT FROM AUTHOR]

Phase-field modeling is an effective simulation technique for modeling microstructure evolution of elastically anisotropic systems. To introduce the elastic energy contribution in a phase field model, an interpolation scheme is used to define the mechanical properties within the phases and across the continuous interface. Several existing interpolation schemes introduce a potential excess elastic energy at the interface, which undesirable effect on microstructure evolution needs to be evaluated. In this study, we focused on three interpolation schemes including Khachaturyan' scheme (KHS), Voigt–Taylor's scheme (VTS), and Steinbach–Apel's scheme (SAS). Comparisons of these schemes' performances were performed in three configuration types using the MOOSE (Multiphysics Object-Oriented Simulation Environment) framework: bi-crystal, isotropic particle-matrix and anisotropic particle-matrix. The contribution of excess elastic energy on the interface energy as a function of interface width and the computational time to steady-state were evaluated in these three configurations. SAS introduces the lowest excess elastic energy contribution and the VTS has the biggest contribution amongst the considered schemes. Moreover, when modeling precipitation in an anisotropic elastic material, the SAS approach seems to predict more physical convex shapes during growth, making it preferable to KHS and VTS. As currently implemented, SAS requires the largest computational time and KHS requires the smallest time to reach steady-state amongst the considered schemes. [Display omitted] [ABSTRACT FROM AUTHOR]

We propose and characterize a novel 2D material with a perovskite structure, Sr 2 TaO 4 monolayer. Using a first principles approach, we study the stability, elastic and electronic properties of the 2D-Sr 2 TaO 4 system. In this metallic monolayer system, the tantalum atom is surrounded by six oxygen atoms in an octahedral configuration. The rotation of the octahedra structures yields antiferrodistortive distortions favoring a phase transition. We have demonstrated the stability of this perovskite-like monolayer using phonons, molecular dynamics, and elasticity criteria. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] Identifying key descriptors and understanding important features across different classes of materials are crucial for machine learning (ML) tools to both predict material properties and reveal the physics underlying any process of interest. Traditionally, the predictive modeling of elastic properties of materials is limited to only a few classes of materials and a small set of ML tools despite the broad applications of these materials. Users now have a broad choice of ML models ranging from simple regression models to graph neural networks (GNN) for predicting structure–property relationships. While in recent years, GNNs have outshined traditional ML models in terms of predictability, their intensive data requirement and lack of interpretability may limit practical applicability. Here, we develop a domain-segmented feature space using a diverse set of material attributes and perform a predictive analysis using state-of-the-art ML tools using elastic modulus prediction as a representative example. By deducing a model-independent overall ranking based on feature importance learned by each model, the knowledge is then transferred to GNNs. Our findings indicate a threshold limit on the predictability of traditional ML models, but our approach of transferring task-specific feature importance knowledge to the GNNs can enhance their performance by reducing their data requirement while retaining considerable accuracy. [ABSTRACT FROM AUTHOR]

The accuracy of interatomic interaction potentials – also known as force fields – is the main factor determining the physical soundness of classical molecular dynamics (MD) simulations. Here, we present a multi-objective framework to generate embedded-atom-method (EAM) force fields using ab initio data. The EAM force fields were tuned via particle swarm optimization to capture the non-linear association between atomic structures and system energies. Using this framework, 95 standard EAM force fields for zirconium were developed and 45 physical features for each developed force field were tracked. Principal component analysis (PCA) was performed to provide insights into the compromises that must be made when generating EAM force fields. Of note, by assigning large fitting weights to generalized stacking fault energy (GSFE) surfaces, there exist EAM force fields with properly positioned minima on prismatic GSFE surfaces and containing no spurious minima in basal GSFE surfaces. However, while standard EAM force fields achieved this without explicitly taking the angular dependence of atomic interactions into account, they led to a severe mismatch between other important physical properties and benchmarks. Hence, we also constructed two machine-learned tabulated Gaussian approximation potentials (tabGAP) with an additional three-body term, which successfully tackled the aforementioned issue and exhibit acceptable prediction accuracy across many physical properties (lattice parameters, elastic properties, dimer potential energies, melting temperatures, phase stability, point defect formation energies, point defect migration energies, and free surface energies) of Zr. Remarkably, its computational efficiency is only 6 times slower than standard EAM force fields. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] The HCP structure of zinc (Zn) exhibits an anomalous c/a ratio, a factor that traditional empirical potentials find challenging to reproduce accurately, thus impeding thorough investigations of its property and behavior via realistic atomistic simulations. The advent of machine learning interatomic potentials in recent years has ushered in new opportunities for the development of reliable Zn potentials. In this study, we construct a large set of atomic configurations composed of Zn atoms and calculate their energy, atomic forces, and stress tensor through high-throughput density functional theory calculations. Based on the calculated data, a moment tensor potential for Zn is developed, whose fidelity is then thoroughly examined by comprehensive comparison to existing potentials from the literature, density function theory calculations, and/or experimental measurements. It is found that the constructed potential can accurately reproduce the c/a ratio of HCP Zn, the relative stability of different crystal phases, the elastic properties, and defect properties of Zn. It can also describe reliably the structure, thermodynamic, and kinetic properties of Zn melt. This potential therefore offers a reliable tool for further exploration of the property and behavior of Zn at the atomic scale. [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]

[Display omitted] The binary silver-titanium system attracts interest due to its application in the brazing ceramic components as well as a material for the selective electroanalytic conversion of CO 2. The experimental investigation of this system is very difficult due to the big difference between the melting temperatures of silver and titanium and the wide binary phase region that includes liquid and titanium. Taking into account experimental difficulties it makes sense to apply computational methods to determine the thermodynamic properties of the phases in the silver-titanium system. In this work, the ab initio methods were used to calculate formation energy, heat capacity, and elastic properties of the AgTi and AgTi 2 phases. After that, thermodynamic modeling was done and a set of Gibbs energies of all phases in this system was obtained. [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]

This paper presents application of an electronic-based approach to the design of elastically isotropic and metastable β -Ti alloys. A systematic ab initio calculations were performed to predict the elastic properties of binary and ternary alloys, considering the 3 d and 4 d transition metals as solute elements. It was found, that at specific average concentration of valence electron e/a = 4.72, the binary and ternary Ti-based 3 d alloys are elastically isotropic. The same properties are achieved at smaller e/a = 4.59 when 4 d metals are used for alloying. As a result, three lightweight elastically isotropic β -Ti solutions were designed: Ti-46Mo, Ti-17Fe-7Cr and Ti-17Fe-13V wt.% with a significantly reduced concentration of alloying elements relative to the only known elastically isotropic Ti-72V wt.% system. Investigation of the generalized stacking fault energy of two { 1 1 0 } 〈 1 1 1 〉 and { 1 1 2 } 〈 1 1 1 〉 slip modes of body-centered cubic (BCC) lattice indicates that isotropy of elastic properties does not yield the same isotropy in terms of plastic deformation. Analysis of the electronic structure of materials with diversified elastic anisotropy reveals also that isotropic systems display transition of the bond character from direct covalent to more delocalized metallic bond. This transition together with electrostatic ion-ion interaction and number of valence electrons control the elastic anisotropy of BCC transition metals and alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Generated a large dataset of over 5000 polygrain microstructures and properties. • Developed a graph neural network (GNN) model with a property prediction error <1.4% • The optimized GNN model outperforms linear regression and two baseline CNN models. • Identified critical and unwanted input features via sequential forward selection. • Demonstrated excellent transfer learning performance of the pretrained GNN model. We develop a polycrystal graph neural network (PGNN) model for predicting the effective properties of polycrystalline materials, using the Li 7 La 3 Zr 2 O 12 ceramic as an example. A large-scale dataset with >5000 different three-dimensional polycrystalline microstructures of finite-width grain boundary is generated by Voronoi tessellation and processing of the electron backscatter diffraction images. The effective ion conductivities and elastic stiffness coefficients of these microstructures are calculated by high-throughput physics-based simulations. The optimized PGNN model achieves a low error of <1.4% in predicting all three diagonal components of the effective Li-ion conductivity matrix, outperforming a linear regression model and two baseline convolutional neural network models. Sequential forward selection method is used to quantify the relative importance of selecting individual grain (boundary) features to improving the property prediction accuracy, through which both the critical and unwanted node (edge) feature can be determined. The extrapolation performance of the trained PGNN model is also investigated. The transfer learning performance is evaluated by using the PGNN model pretrained for predicting conductivities to predict the elastic properties of the same set of microstructures. : [ABSTRACT FROM AUTHOR]

• The perovskite HoMnO 3 crystal structures are studied in this work. • The simulations using Quantum Espresso are applied and discussed. • The DFT method is applied to understand its properties. • The elastic properties are investigated. • The mechanical behavior is deduced. The structural and elastic properties of the oxide perovskite HoMnO 3 have been investigated by density-functional theory (DFT) implemented on the Quantum ESPRESSO code for the hexagonal, orthorhombic, rhombohedral and cubic crystal structures in the non-magnetic (NM), ferromagnetic (FM) and antiferromagnetic (AFM) configurations. The results show that all these compounds are thermodynamically stable, the hexagonal and the orthorhombic being the most stables in agreement with experimental results. The calculated bulk modulus, B, is about 168.5 ± 1.0 GPa and 178.9 ± 1.0 GPa for hexagonal structure in FM and configurations, respectively, and 188.7 ± 0.6 GPa and 175.6 ± 2.1GPa for orthorhombic structure in FM and AFM configurations, respectively. These values and those of the elastic constants C ij in the present work are comparable to values recently obtained with DFT calculations and experimentally for other perovskites RMnO 3 (R = Eu, Gd, Tb and Dy). The calculated Poisson's ratio is about 0.19; 0.27; 0.23 and 0.3 for hexagonal, orthorhombic, rhombohedral and cubic structure, respectively. The calculated Pugh's ratio is about 1.30; 1.77–1.98; 1.54–1.60 and 2.11, respectively. These results show that the perovskite HoMnO 3 tends to be brittle in hexagonal phase and ductile in cubic phase. In the orthorhombic or rhombohedral phase, it is near brittle-ductile boarder line. [ABSTRACT FROM AUTHOR]

• Impact of the mesoscopic spherulitic structure on the macroscopic elastic properties. • Multiscale workflow to determine the elastic properties of a Semi-Crystalline Polymer. • Molecular Dynamics as inputs for material data in Finite Element calculations. • Validation against experimental data for semi-crystalline Polyethylene. Nowadays, computational resources allow carrying out mechanical calculations on complex multi-scale materials. Finite Element (FE) calculations can especially be directly performed on microstructures of materials. This work is a first attempt to analyse the impact of the crystalline architecture at a mesoscopic scale on the macroscopic elastic properties of Semi-Crystalline Polymers (SCP). Such polymers can be considered biphasic materials, which are composed of an amorphous phase embedded in a crystalline network. The material studied here is Polyethylene (PE). Molecular Dynamics (MD) calculations are carried out on a 100% crystallized Polyethylene model to determine the elastic properties of the crystalline regions of the material. 3D mesostructures of the typical layout of the spherulitic crystalline network of Semi-Crystalline Polymers are then constructed from experimental observations. These material data and this geometrical description are then integrated in computations with the Finite Element method on elementary volumes to finally determine the macroscopic elastic properties of the material. In this work, which is a first attempt to test such a multi-scale workflow, no amorphous phase is considered. Different 3D architectures are compared demonstrating the role of the crystalline arrangement on the stiffness of the material. Three main types of mesostructures have been analysed: crystalline lamellae disposed in a complete random arrangement, crystalline lamellae disposed in a spherulite arrangement, crystalline lamellae with branches disposed in a spherulite arrangement. It appears that the 3D configuration of the lamellae, as well as the presence of branches, have an influence on the macroscopic elastic properties of the material. Then, comparisons with experimental data suggest that the macroscopic elastic properties can be represented with a purely cohesive crystalline network for crystalline degree up to about 50%. This result questions the role of the amorphous phase on the elastic properties of such systems. [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]

[Display omitted] • Applying a length-scale insensitive degradation function to improve the efficiency of Hydrogen-assisted cracking (HAC) simulation. • Reducing the mesh density and enables the simulation of hydrogen-assisted cracking in larger structures. • Decoupling the physical length scale and the phase field length scale. The present paper applies a length-scale insensitive degradation function to accelerate the simulation of hydrogen-assisted cracking processes. In this work, the modified Fick's law is used to compute hydrogen flux. The Langmuir - McLean isotherm is employed to calculate the hydrogen surface coverage that deteriorates failure strength and fracture energy of metallic materials. The solid is treated as linear elasticity and the fractures are represented in fixed mesh by phase field variables. In the phase field model, the length-scale insensitive degradation function is employed to separate the phase field length scale from the physical process zone length scale, which enables the simulation of hydrogen-assisted cracking in larger structures with the same mesh density. Numerical examples are provided to demonstrate the applicability of the present method. [ABSTRACT FROM AUTHOR]

In this work, a combined modelling approach for crack propagation in defective graphene is presented. Molecular dynamics (MD) simulations are used to obtain material parameters (Y oung 's modulus and Poisson ratio) and to determine the energy contributions during the crack evolution. The elastic properties are then applied in phase-field continuum simulations which are based on the Griffith energy criterion for fracture. In particular, the influence of point defects on elastic properties and the fracture toughness are investigated. For the latter, we obtain values consistent with recent experimental findings. Further, we discuss alternative definitions of an effective fracture toughness, which accounts for the conditions of crack propagation and establishes a link between dynamic, discrete and continuous, quasi-static fracture processes on MD level and continuum level, respectively. It is demonstrated that the combination of MD and phase-field simulations is a well-founded approach to identify defect-dependent material parameters. [ABSTRACT FROM AUTHOR]

• Dominance of specific crystallographic direction of CrPS 4 when in-plane cleavage (fracture) occurs. • Elastic anisotropy of monolayer CrPS 4 proved by the oval shape of orientation-dependent Young's modulus. • Low-energy cleavage fracture direction proved as 〈1 1 0〉 by the stress-strain relation of monolayer CrPS 4. • Vulnerability of Cr S Cr bonding (a "glue" for structural motifs of CrPS 4) along the shear direction 〈1 1 0〉. In-plane cleavage directions of two-dimensional (2D) crystals are displayed and often well defined in their flakes exfoliated by the mechanical exfoliation method. Here, we investigate the correlation between dominant in-plane cleavage direction and elastic properties in different directions for CrPS 4. CrPS 4 flakes show a preferential in-plane cleavage direction of 67.5°, corresponding to 〈1 1 0〉 direction. To explain it, we calculated the directional dependence of Young's modulus and fracture energy using first-principles density functional theory calculations. We found that relative fracture energy is directly relevant to the in-plane cleavage direction of CrPS 4. It is also found that in CrPS 4 the rhomboidal Cr S Cr bonds, which are especially vulnerable in 〈1 1 0〉 direction, connect robust structural motifs to each other. Our study can provide a facile approach to figure out the direction of 2D crystals without complex characterization process, which is valuable for material processing of 2D materials. [ABSTRACT FROM AUTHOR]

• Elastic properties of Marval X12 and FeCrNiC steels calculated from DFT. • The main effect of C on elastic constants is due to symmetry change. • 3D phase field model predicts a change from lath to mixed martensite morphology. The effect of the carbon concentration on the elastic properties and martensitic microstructure of Marval X12 steel is studied using first principles calculations and phase-field simulations. The density functional theory (DFT) results predict almost no changes of the elastic moduli with an increase of C content. However, there is a sizeable change of the elastic constants due to cubic to tetragonal martensitic transformation. The elastic constants are used as input data for the 3D elastoplastic phase-field model to study the martensitic microstructure evolution in Marval X12 steel. The results, showing that lath martensite is formed in this steel, are in agreement with experiments. With increasing carbon concentration, we observe formation of mixed morphology predominantly composed of martensite laths and some martensite plates. Our results also suggest that different combinations of martensite variants are formed with increasing carbon content. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The method only requires molecular dynamics to generate models of nanoporous gold. • Geometrical characterizations show that models are realistic. • Mechanical characterizations yields values that are consistent with the literature. Abstract Models that can be used to describe nanoporous gold are often generated either by phase-field or Monte-Carlo methods. It is not ascertained that these models are closely matching experimental systems, and there is a need for other variants. Here is proposed an original approach to generate alternative models, which is solely based on molecular dynamics simulations. Structures obtained with this method are structurally characterized by determining the ligaments diameter distributions, the scaled genus densities and the interfacial shape distributions. Selected mechanical characterizations are also done by deforming the structures in tension and in compression. Structural and mechanical properties are in good agreement with experimental and theoretical published results. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Using the Exact Muffin-Tin Orbitals method within the Perdew-Burke-Ernzerhof exchange-correlation approximation for solids and solid surfaces (PBEsol), we study the single crystal elastic constants of 4 d transition metals (atomic number Z between 39 and 47) and their binary alloys in the body centered cubic (bcc) and face centered cubic (fcc) structures. Alloys between the first neighbors Z (Z + 1) and between the second neighbors Z (Z + 2) are considered. The lattice constants, bulk moduli and elastic constants are found in good agreement with the available experimental and theoretical data. It is shown that the correlation between the relative tetragonal shear elastic constant C ′ fcc -2 C ′ bcc and the structural energy difference between the fcc and bcc lattices Δ E is superior to the previously considered models. For a given crystal structure, the equiatomic Z (Z + 2) alloys turn out to have similar structural and elastic properties as the pure elements with atomic number (Z + 1). Furthermore, alloys with composition Z 1− x (Z + 2) x possess similar properties as Z 1−2 x (Z + 1) 2 x. The present theoretical data on the structural and the elastic properties of 4 d transition metal alloys provides consistent input for coarse scale modeling of material properties. [ABSTRACT FROM AUTHOR]

Graphical abstract Heat capacity of binary uranium aluminides predicted by ab initio quasiharmonic phonon approach. Abstract The structural, elastic, electronic, vibrational and thermodynamic properties of uranium aluminides UAl x (x = 2, 3, 4) were studied by density functional theory calculations. The single crystal elastic constants of UAl x were predicted using the stress-strain method, which were further used to calculate the polycrystalline aggregate properties of UAl x , including bulk modulus, shear modulus, Young's modulus, and Poisson's ratio, etc. The calculated electronic density of states confirm that UAl x compounds are metallic phases with majority states at the Fermi level contributed by U 5 f electrons. The phonon dispersion relations and density of states show that the low frequency acoustic phonon modes of UAl x are dominated by the lattice vibration of uranium atoms while high frequency optical phonon modes are from the vibration of aluminum atoms. Using quasiharmonic approximation, thermodynamic properties of UAl x , including Gibbs free energy, entropy, heat capacity, and linear thermal expansion coefficient, were predicted by including both lattice vibrational and thermal electronic contributions. The thermal electronic energy was found to be crucial for the description of the temperature dependence of the thermodynamic properties. The derived Gibbs energy functions of UAl x are expected to be useful to the thermodynamic modeling of the ternary U-Mo-Al system. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract In this work, structural transformation, elastic behaviors, phonon spectra, and thermodynamic properties upon hydrostatic compression of hafnium are investigated by using first-principle density functional theory. Our calculated equilibrium structural parameters and the transition pressures of α → ω → β are well consistent with experiments. At ambient pressure, the elastic constants indicate that the α and ω phases are mechanically stable while the β phase is unstable. The thermal properties including bulk modulus, entropy, and heat capacity in wide range of pressure and temperature for α -Hf are predicted. We present results of the phonon spectra and phonon density of states for the three experimentally observed phases and discuss the effects of pressure and temperature on those properties. The β -Hf is mechanically and dynamically stable at high pressure or at high temperature. Employing the quasiharmonic approximation as well as the Debye model, we calculate the Gibbs free energy and predict the pressure-temperature phase diagram. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Uniform pattern transformation can be observed in some structures with periodic arrays of pores at a critical compressive load because of buckling of the constituents of the structures. This pattern transformation can be exploited to design structures for various potential applications. Previous studies have focused on the instability of periodic porous structures of which the base materials were elastomers, and applications of these structures may be narrow because of the elastomer limitations of low melting temperature and stiffness. In addition, material failures such as plasticity and fracture were rarely discussed in previous studies. Here, we introduce metals as the base materials for some periodic metallic porous nanostructures (PMPNs). Our molecular dynamics simulation results show that PMPNs can exhibit pattern transformation at a critical strain because of buckling. In addition, we develop a simple formulation by incorporating the effect of surface on the Euler–Bernoulli beam theory to predict the critical load for the buckling of nanostructures. The prediction of our model is in good agreement with the molecular dynamics simulation results. When the applied strain is sufficiently large, the nanoscale metals experience dislocation-medicated plasticity. We also show that the pore shape of the PMPNs strongly affects the characteristics of the periodic metallic structures including the effective Young's modulus, critical strain for micro-buckling, and critical strain for plasticity. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The elastic and electronic properties of BNNTs containing vacancies are reported. • Zigzag BNNTs show slightly higher elastic properties compered to armchair ones. • The effect of atom vacancies becomes more prominent for the smaller diameter BNNTs. • Distribution of vacancy pores influences the elastic properties of BNNTs. • Application of different loadings changes the band gaps of BNNTs significantly. Abstract Molecular dynamics (MD) simulations were carried out with a three-body Tersoff potential force field to predict the transversely isotropic elastic properties of pristine and defected BNNTs. This is accomplished by imposing uniaxial tension, twisting moment, in-plane shear and in-plane biaxial tension to the BNNTs. Effects of various factors such as chirality and diameter of BNNTs, vacancy concentration, and distribution of vacancy pores along the length and circumference of BNNTs were critically examined. Our study reveals that the elastic coefficients of BNNTs decrease as their diameter increase, except axial Young's modulus. Young's modulus of BNNT increases with the diameter and reaches its maximum value when the tube diameter is ∼14 Å and then it starts decreasing. We also found that the axial Young's modulus of a BNNT increases as its aspect ratio increases and stabilizes at a particular value of aspect ratio (L/D ∼ 15). The vacancies greatly affect the elastic properties of BNNTs; for instance, the vacancy concentration of 2% in (10, 10) BNNT reduce its axial Young's, shear, plane strain bulk and in-plane shear moduli by 14%, 25%, 14% and 18%, respectively. Furthermore, we studied the electronic properties of pristine and defective BNNTs under four transversely isotropic loading conditions using the strain effective method. The results reveal that the electronic properties of BNNTs can be altered via different routes: loadings conditions, diameter and vacancy concentration. Our fundamental study highlights the critical role played by vacancy defected BNNTs in determining their elastic and electronic properties as they are vastly being used in multifarious applications such as nano-electronic devices and reinforcements in multifunctional nanocomposites. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • W 2 N 3 _mC30_8CM and W 2 N 3 _oP20_62PNMA was predicted for the first time. • r-W 2 N 3 is unstable due to partial occupancy of 3a Wyckoff site for W atoms. • W 2 N 3 _oP20_62PNMA is a potential ultra-incompressible and hard candidate. • Physical properties and elastic anisotropy are explored for W 2 N 3. Abstract Searching new materials with novel properties is always desirable for material innovation. Based on particle swarm optimization (PSO) and first-principles, the ground state W 2 N 3 _mC30_8CM and high pressure state W 2 N 3 _oP20_62PNMA were predicted for the first time. The mechanical, dynamical and electronic properties, and elastic anisotropy of synthesized h-W 2 N 3 and r-W 2 N 3 , and predicted W 2 N 3 _mC30_8CM and W 2 N 3 _oP20_62PNMA have been investigated by first-principles. W 2 N 3 _mC30_8CM, W 2 N 3 _oP20_62PNMA and h-W 2 N 3 are mechanically and dynamically stable. For r-W 2 N 3 , its mechanical and dynamic instability might be due to partial occupancy of 3a Wyckoff site for W atoms. Due to finite states at Fermi level, they are metallic. Our results enriched the crystal structures for W 2 N 3 and provided some information to further understand their properties. [ABSTRACT FROM AUTHOR]

Abstract Phase-field studies of solid-state precipitation under strong chemo-mechanical coupling are performed and benchmarked against the existing analytical solutions. The open source software packages OpenPhase and DAMASK are used for the numerical studies. Solutions for chemical diffusion and static mechanical equilibrium are investigated individually followed by a chemo-mechanical coupling effect arising due to composition dependence of the elastic constants. The accuracy of the numerical solutions versus the analytical solutions is quantitatively discussed. For the chemical diffusion benchmark, an excellent match, with a deviation < 0.1 % , was obtained. For the static mechanical equilibrium benchmark Eshelby problem was considered where a deviation of 5 % was observed in the normal component of the stress, while the results from the diffuse interface (OpenPhase) and sharp interface (DAMASK) models were slightly different. In the presence of the chemo-mechanical coupling, the concentration field around a static precipitate was benchmarked for different coupling coefficients. In this case, it is found that the deviation increases proportional to the coupling coefficient that represents the strength of coupling concentration and elastic constants. Finally, the interface kinetics in the presence of the considered chemo-mechanical coupling were studied using OpenPhase and a hybrid OpenPhase–DAMASK implementation, replacing the mechanical solver of OpenPhase with DAMASK's. The observed deviations in the benchmark studies are discussed to provide guidance for the use of these results in studying further phase transformation models and implementations involving diffusion, elasticity and chemo-mechanical coupling effect. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Semi-coherent cube-on-cube miscible U–Zr interfaces were studied using molecular dynamics simulations. The misfit accommodation of such semi-coherent phase boundaries was characterized by a two-dimensional dislocation network model utilizing a combination of theoretical predictions and analysis of the atomic system. The dislocation networks were discussed for various stacking orientation of the adjoining phases in terms of the composition of the dislocation sets, the partitioning between edge and screw components and the associated residual elastic fields. These analyses showed that the patterning of the network of dislocations forming these phase boundaries results from the competition between a structurally-driven process (i.e., function of the lattice misfit) and a chemically-driven process (i.e., due to the miscibility between U and Zr). [ABSTRACT FROM AUTHOR]

Graphical abstract (a) 3D computational domain for the concurrent continuum-atomistic simulation with a crack embedded in it, (b) expanded view of the crack-tip boost region, (c) contour plot of stress showing crack advance. Highlights • Coupled concurrent atomistic-crystal elasticity model is developed for modeling crack propagation. • Strain-boost Hyperdynamics developed to bridge time scales of continuum and atomistic domains. • Low strain-rates of continuum models are achievable by this model. • Brittle crack propagation rate in a nickel single crystal is quantified using a parametrized evolution law. • Phase field energies are developed from concurrent model. Abstract Concurrent multiscale models that couple atomistic and continuum calculations are useful for extending the spatial limitations of atomistic models, as well as for deriving effective continuum models. This paper develops a concurrent atomistic-continuum computational model with an embedded crack in the atomistic domain. Molecular dynamics (MD) simulations are conducted in the atomistic domain, while the continuum domain is modeled using the finite element (FE) method. A major limitation of concurrent models is the time-scale mismatch between the continuum and atomistic domains that causes the two sub-domains to experience different strain-rates. To bridge the time scale difference, the MD model is augmented by a novel strain-boost hyperdynamics accelerated time marching scheme. The concurrent model is used to study strain-rate and temperature effects on crack propagation in a nickel single crystal. The continuum domain uses a nonlinear anisotropic elasticity constitutive model. Crack propagation rate is represented by a parametric continuum model, whose strain-rate and temperature dependencies are investigated. Finally, the concurrent model is used to evaluate the free energy density function for phase field modeling of crack propagation. Validation studies elucidate the potential of the concurrent model as a modeling tool for large scale continuum fracture models. [ABSTRACT FROM AUTHOR]

Object kinetic Monte Carlo and finite-element calculations have been used to calculate the sink strength of low-angle symmetric tilt grain boundaries (STGBs) in Cu. It is shown that saddle point anisotropy of vacancies increases their absorption by STGBs, making these interfaces nearly neutral sinks. The continuous model, which includes point defect anisotropy at saddle point, is able to reproduce OKMC calculations, provided the exact value of the diffusion tensor is retained. The use of elastodiffusion tensor is not valid, due to the large strains ( ε ∼ 10 - 2 ) created by STGBs. The low numerical cost of the continuous model could allow for a more systematic investigation of radiation tolerance due to interfaces. [ABSTRACT FROM AUTHOR]

A comprehensive, critical study of the vibrational, thermodynamic and thermoelastic properties of bcc iron is presented, using well established semi-empirical embedded-atom method potentials available in the literature. Classical molecular dynamics simulations are used to address temperature effects, where dynamical matrices are constructed as a time average of the second moment of the atomic displacements. The C 11 , C 44 , C ′ elastic constants are then obtained from the sound velocities along high symmetry directions in reciprocal space. Results are compared to ultrasonic measurements and highlight the limitations of the potentials considered here in describing thermoelastic properties. [ABSTRACT FROM AUTHOR]

Porosity can play an important role in altering the phase transformation characteristics of NiTi shape memory alloys (SMA), thus changing its shape memory as well as its superelasticity properties. This work, based on atomistic simulations of binary NiTi SMA, documents the effects of porosity at the nanometer length scale on phase fraction evolution kinetics, transformation temperatures, and stress-strain response. Classical molecular dynamics simulations are performed using a well-examined and verified Finnis-Sinclair type embedded-atom method interatomic potential. Simulation results for the nano-porous NiTi with various porosity configurations are compared to non-porous NiTi. The martensite phase fraction and transformation temperatures increase noticeably with increasing porosity, and the stress-strain response shows noticeable variation with porosity. The residual strain and hysteretic energy dissipation capacity increase significantly with increasing porosity. [ABSTRACT FROM AUTHOR]

By establishing some atomistic simulation cells with the same size but different numbers of grains, molecular dynamics simulations are performed to investigate the super-elasticity of nanocrystalline NiTi shape memory alloy subjected to a cyclic tension-unloading and its dependence on the grain size. The effect of grain boundaries on the martensite transformation stress as well as the nucleation and growth of martensite phase is addressed. The degeneration of super-elasticity and the initiation and growth of defects in the nanocrystalline NiTi SMA during the cyclic tension-unloading are discussed. The results show that the super-elasticity degeneration occurs during the cyclic deformation of nanocrystalline NiTi SMA, and the residual strain accumulates progressively with the increasing number of cycles, which becomes more significant with the decrease of grain size. The grain boundaries can enhance the martensite transformation stress of nanocrystalline NiTi SMA and suppress the instability occurred during the martensite transformation. It is revealed that the interstitial atoms and plastic deformation are mainly concentrated within the grain boundaries. [ABSTRACT FROM AUTHOR]

In this work, we study effects of neutron irradiation and elastic tensile loading on microstructure evolution in polycrystalline tungsten by using a phase field modeling based approach. The proposed model involves the interaction of point defects with grain boundaries (GBs), thermal resistance of GBs, and voids. The void evolution analysis shows that the elastic energy field affects the shape and growth rate of voids. The overall trend of porosity evolution during irradiation follows the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. Voids nucleation and growth can reduce both elastic strain energy and chemical free energy in the system. In addition, increase of porosity could significantly degrade the effective thermal conductivity of analyzed tungsten polycrystalline microstructures. The observations comply with the predictions from the theoretical models. [ABSTRACT FROM AUTHOR]

[Display omitted] Refractory high entropy alloy (RHEA) is an important family of alloy with excellent mechanical properties and broad industrial applications. Different chemical and stoichiometric compositions make RHEA a highly tunable material with a huge space for optimization. However, the virtual screening of RHEA is extremely nontrivial, considering the high cost of conventional first-principles calculations. In this work, we compute the ground state and the elastic properties of 2487 RHEAs using exact muffin-tin orbital method combined with coherent potential approximation (EMTO-CPA). Using these data, we train an accurate and robust random forest model that can predict the elastic properties of RHEA systems much more efficiently. Furthermore, we also examine the correlation between seven independent input features and the elastic properties of the alloy. Through this analysis, we identify the most important features that control the elastic properties of RHEA, paving the road to a rational design of the RHEA materials. [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 objective of the current study was to design titanium alloys by optimizing tensile strength, yield strength, modulus of elasticity and biocompatibility using the artificial neural network (ANN) and recursive partitioning (RP) models. The database of 308 titanium alloys served as the basis of the model with alloy composition and processing parameters as inputs and each property to be optimized as the target. Levenberg-Marquardt back propagation was used to train the ANN model. RP model was used to elucidate different thresholds of alloying elements that are decisive of biocompatibility. The sensitivity analysis of ANN model revealed that Ta and Nb when used at very high concentrations (30–35%), their tensile and yield strength are higher. With the increase in the concentration of Ta and Nb, the modulus of elasticity was shown to decrease and at high concentrations, modulus of elasticity reaches to that of cortical bone. The RP model showed that these two alloys are safe. Hence, we have generated ANN simulations of Ti-xNb-yTa ternary system to ascertain the optimal combination of Ta and Nb that can provide higher tensile and yield strengths and lower modulus of elasticity. These simulations were compared with already developed alloys with these combinations. To conclude, ANN-based optimization of prerequisite properties facilitated timely and cost-effective solutions in the design of biocompatible titanium alloys. [ABSTRACT FROM AUTHOR]

We present the second set of benchmark problems for phase field models that are being jointly developed by the Center for Hierarchical Materials Design (CHiMaD) and the National Institute of Standards and Technology (NIST) along with input from other members in the phase field community. As the integrated computational materials engineering (ICME) approach to materials design has gained traction, there is an increasing need for quantitative phase field results. New algorithms and numerical implementations increase computational capabilities, necessitating standard problems to evaluate their impact on simulated microstructure evolution as well as their computational performance. We propose one benchmark problem for solidification and dendritic growth in a single-component system, and one problem for linear elasticity via the shape evolution of an elastically constrained precipitate. We demonstrate the utility and sensitivity of the benchmark problems by comparing the results of (1) dendritic growth simulations performed with different time integrators and (2) elastically constrained precipitate simulations with different precipitate sizes, initial conditions, and elastic moduli. These numerical benchmark problems will provide a consistent basis for evaluating different algorithms, both existing and those to be developed in the future, for accuracy and computational efficiency when applied to simulate physics often incorporated in phase field models. [ABSTRACT FROM AUTHOR]

Different descriptions used to model a point-defect in an elastic continuum are reviewed. The emphasis is put on the elastic dipole approximation, which is shown to be equivalent to the infinitesimal Eshelby inclusion and to the infinitesimal dislocation loop. Knowing this elastic dipole, a second rank tensor fully characterizing the point-defect, one can directly obtain the long-range elastic field induced by the point-defect and its interaction with other elastic fields. The polarizability of the point-defect, resulting from the elastic dipole dependence with the applied strain, is also introduced. Parameterization of such an elastic model, either from experiments or from atomic simulations, is discussed. Different examples, like elastodiffusion and bias calculations, are finally considered to illustrate the usefulness of such an elastic model to describe the evolution of a point-defect in a external elastic field. [ABSTRACT FROM AUTHOR]

The present work deals with first-principles calculations on chemical bonding characteristics, elastic properties, and ideal strengths under both shear and tensile deformations of MoAlB and WAlB nanolaminated MAB phases. Diverse chemical bonds were found in MoAlB and WAlB, including strong B B covalent bonds, Al B covalent-ionic bonds, Mo B bonds and metallic Mo Al and Al Al bonds. Elastic properties of MoAlB and WAlB are not highly anisotropic with shear modulus of (0 1 0)[1 0 0], (0 1 0)[0 0 1], (0 0 1)[1 0 0] similar to each other. Nevertheless, ideal strengths display significant anisotropy. The results show that ideal shear strength τ m of basal plane shears are lower than those of non-basal plane shears, while ideal tensile strength σ m of the basal plane is lower than those of non-basal planes. In addition, ideal tensile strength of the basal plane is also much lower than ideal shear strengths of basal plane shears. The basal plane cleavage and shear failure both take place along the weakly bonded Al Al layers. Moreover, the basal plane shear failure is found accompanied by remarkable expansion of the Al Al layers, which reduces the resistance against basal plane shears. It suggests that MoAlB and WAlB tend to cleavage along the Al Al layer or dislocations tend to multiply and slip in the Al Al layer, which is similar to MAX phases. [ABSTRACT FROM AUTHOR]

Local lattice instability analysis based on the atomic elastic stiffness (AES), B ij α = Δ σ i α / Δ ε j ( i , j = 1 – 6 in Voigt notation), is applied to mode I crack tip in covalent binary crystal β -SiC of Tersoff interatomic potential. The application limit of the AES is disclosed at the discontinuous local energy surface of disordered broken bonds in the discrete binary system; however, we also captured interesting results with the 1st eigenvalue η α ( 1 ) of B ij α as follows, (1) the atomic stress of C atoms coincides with the stress singularity in the linear fracture mechanics, when the minimum eigenvalue of C atom shows the first sudden drop or the first instability, (2) but the crack doesn’t propagate nor there is no remarkable change in the stress–strain curve, (3) bond breaking and reconstruction occurs in the vicinity of crack tip at the second instability in the eigenvalue, (4) C atoms in the disordered configuration show extraordinary large negative eigenvalue (possibly due to discontinuity of energy surface), while Si atoms show third drop in the eigenvalue just before unstable crack propagation, (5) linear fracture mechanics fails to predict the stress singularity at the crack propagation, (6) the principal axes of the eigenvector of η α ( 1 ) < 0 atoms reveal the deformation mode for local slip and cracking on the multiple (1 1 1) planes in the unstable domain at the forefront of the propagating crack. [ABSTRACT FROM AUTHOR]

The structural, elastic properties, hardness and electronic structure of Mo 2 FeB 2 alloyed with Cr and Ni have been investigated by using first-principles calculations. The doping concentrations of 2.5 at. %, 5.0 at. %, 10.0 at. % and 20.0 at. % are analyzed systematically in this paper. From the calculated impurity formation energy, it is found that all the structures can retain good structural stability with the doping concentrations of Cr, Ni up to 20.0 at. %. According to the calculated elastic constants, it is observed that Cr can increase the Young’s modulus and hardness and reduce the ductility of Mo 2 FeB 2 markedly with the increasing of alloying concentration. In contrast, Ni can decrease the hardness but improve the ductility of Mo 2 FeB 2 obviously. The calculated electronic structure indicates that the increase of elastic modulus is attributed to the formation of B Cr bond for Cr-doped and B Ni bond for Ni-doped. The Mo Cr and Mo Ni metallic bonds weaken the shear modulus of Mo 2 FeB 2 . When the doping concentration is 20.0 at. %, it is obvious that the alloying elements Cr and Ni can significantly affect the moduli of Mo 2 FeB 2 . [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) are a class of metallic smart materials which possess pseudoelasticity (PE) and shape memory effect (SME), depending on the ambient temperature. The unique thermomechanical properties of SMAs originate from the temperature-induced as well as stress-induced martensitic transformations (MTs). Former research work has shown that the thermomechanical properties of polycrystalline SMAs are grain size and rate dependent. In order to explore the physical mechanisms behind this phenomenon, a phase field (PF) model is developed in this paper to study the microstructure evolution and the thermomechanical responses of polycrystalline SMAs under dynamic loadings. The inertial effect, the latent heat release and conduction during the phase transformation are simultaneously considered. The grain boundary energy change during the phase transformation is also accounted for in the PF model. Numerical simulations are then conducted to study the temperature-induced MT as well as the stress-induced martensite reorientation of nanocrystalline SMAs with different grain sizes. The influences of the grain size, the latent heat effect and the loading rate on the microstructure evolution process and the stress–strain curves are systematically discussed. [ABSTRACT FROM AUTHOR]

We investigated the process of twin boundary migration to clarify the origin of pseudoelasticity by twinning in D0 3 -type Fe 3 Ga using first-principles calculations. We calculated the energy profile of twin boundary migration and found that although energy barriers appear during twin boundary migration in bcc Fe and bcc Mo, there was no energy barrier for twin boundary migration in D0 3 -type Fe 3 Ga. Analysis of the shear strain at each twin layer revealed that twin boundary migration in D0 3 -type Fe 3 Ga proceeded not in a layer-by-layer fashion but by the sliding of more than two layers that include the twin boundary, which led to the flat energy profile in D0 3 -type Fe 3 Ga. This sliding mechanism originated from shear strain introduced near the twin boundary to accommodate the lattice distortion induced by the difference in the atomic arrangement between the D0 3 matrix and the pseudo twin layers. [ABSTRACT FROM AUTHOR]

Diffusion of point defects during irradiation is simulated via a two-way coupling between mechanical stress and defect diffusion in iron. This diffusion is based on a modified chemical potential that includes not only the local concentration of radiation-induced defects, but also the influence of the residual stress field from both the microstructure (i.e. dislocations or grain boundaries) and the eigenstrain caused by the defects themselves. Defect flux and concentration rates are derived from this chemical potential using Fick’s first and second laws. Mean field rate theory is incorporated to model the annihilation of Frenkel pairs, and increased annihilation near grain boundaries is included based on the elastic energy of each grain boundary. Mechanical equilibrium is coupled with diffusion by computing eigenstrain from point defects and adding this to the total strain. Intrinsic stresses associated with the dislocations and grain boundaries are calculated using dislocation and disclination mechanics. Through this two-way-coupled model, regions of low concentration are seen near grain boundaries, and sink efficiency is calculated for different types of microstructure. The results show that the two-way mechanical coupling has a strong influence on sink efficiency for dislocation loops. The results also suggest that misorientation is a poor metric for determining sink efficiency, with sink density and elastic energy being much more informative. [ABSTRACT FROM AUTHOR]

The structural stabilities, mechanical and thermodynamic properties of pure and alloyed Ni 3 Al systems have been investigated systematically, based on density functional theory and Debye-Grüneisen model. Close attentions are paid to alloying elements W and Re by studying the strengthening effects of single-alloying element W, Re, Mo, Ta, Ru and co-alloying elements WRe, WMo, ReMo, WTa, ReTa, WRu, ReRu, which substitute the Al site and the nearest neighboring Al-Al sites, respectively. The calculated formation energies and elastic constants show that all the alloyed Ni 3 Al are thermodynamically and mechanically stable. It is found that alloying elements W has similar effects on the mechanical and thermodynamic properties of Ni 3 Al to those of Re, which suggests a possibility of replacing Re with W in Ni-based single crystal superalloys. In addition, co-alloyings with different elements have no distinct synergistic enhancement but simple combined effect on the mechanical properties of Ni 3 Al. The enhanced chemical bondings between the alloying atoms W/Re and the neighboring host atoms Ni are considered to be the main strengthening mechanisms in W/Re alloyed Ni 3 Al systems. [ABSTRACT FROM AUTHOR]