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13 pages, 3223 KiB

Open AccessArticle

A Novel Silicon Allotrope in the Monoclinic Phase

by Chaogang Bai, Changchun Chai, Qingyang Fan, Yuqian Liu and Yintang Yang

Materials 2017, 10(4), 441; https://doi.org/10.3390/ma10040441 - 22 Apr 2017

Cited by 18 | Viewed by 5668 | Correction

Abstract

This paper describes a new silicon allotrope in the P2/m space group found by first-principles calculations using the Cambridge Serial Total Energy Package (CASTEP) plane-wave code. The examined P2/m-Si belongs to the monoclinic crystal system. P2/m [...] Read more.

This paper describes a new silicon allotrope in the P2/m space group found by first-principles calculations using the Cambridge Serial Total Energy Package (CASTEP) plane-wave code. The examined P2/m-Si belongs to the monoclinic crystal system. P2/m-Si is an indirect band-gap semiconductor with a band gap of 1.51 eV, as determined using the HSE06 hybrid functional. The elastic constants, phonon spectra and enthalpy indicate that P2/m-Si is mechanically, dynamically, and thermodynamically stable. P2/m-Si is a low-density (2.19 g/cm³) silicon allotrope. The value of B/G is less than 1.75, which indicates that the new allotrope is brittle. It is shown that the difference in the elastic anisotropy along different orientations is greater than that in other phases. Finally, to understand the thermodynamic properties of P2/m-Si, the thermal expansion coefficient α, the Debye temperature Θ_D, and the heat capacities C_P and C_V are also investigated in detail. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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22 pages, 16452 KiB

Open AccessFeature PaperArticle

Discrete Particle Method for Simulating Hypervelocity Impact Phenomena

by Erkai Watson and Martin O. Steinhauser

Materials 2017, 10(4), 379; https://doi.org/10.3390/ma10040379 - 2 Apr 2017

Cited by 19 | Viewed by 7780

Abstract

In this paper, we introduce a computational model for the simulation of hypervelocity impact (HVI) phenomena which is based on the Discrete Element Method (DEM). Our paper constitutes the first application of DEM to the modeling and simulating of impact events for velocities [...] Read more.

In this paper, we introduce a computational model for the simulation of hypervelocity impact (HVI) phenomena which is based on the Discrete Element Method (DEM). Our paper constitutes the first application of DEM to the modeling and simulating of impact events for velocities beyond 5 kms^-1. We present here the results of a systematic numerical study on HVI of solids. For modeling the solids, we use discrete spherical particles that interact with each other via potentials. In our numerical investigations we are particularly interested in the dynamics of material fragmentation upon impact. We model a typical HVI experiment configuration where a sphere strikes a thin plate and investigate the properties of the resulting debris cloud. We provide a quantitative computational analysis of the resulting debris cloud caused by impact and a comprehensive parameter study by varying key parameters of our model. We compare our findings from the simulations with recent HVI experiments performed at our institute. Our findings are that the DEM method leads to very stable, energy–conserving simulations of HVI scenarios that map the experimental setup where a sphere strikes a thin plate at hypervelocity speed. Our chosen interaction model works particularly well in the velocity range where the local stresses caused by impact shock waves markedly exceed the ultimate material strength. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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16 pages, 3959 KiB

Open AccessArticle

Deformation Modes and Anisotropy of Anti-Perovskite Ti₃AN (A = Al, In and Tl) from First-Principle Calculations

by Kuankuan Chen, Cong Li, Meng Hu, Xun Hou, Chunmei Li and Zhiqian Chen

Materials 2017, 10(4), 362; https://doi.org/10.3390/ma10040362 - 29 Mar 2017

Cited by 11 | Viewed by 5210

Abstract

Deformation modes were studied for Ti₃AN (A = Al, In and Tl) by applying strain to the materials using first-principle calculations. The states of the bonds changed during the deformation process, and the Ti-N bonds remained structurally stable under deformation. The [...] Read more.

Deformation modes were studied for Ti₃AN (A = Al, In and Tl) by applying strain to the materials using first-principle calculations. The states of the bonds changed during the deformation process, and the Ti-N bonds remained structurally stable under deformation. The elastic anisotropy, electronic structures, hardness, and minimum thermal conductivity of anti-perovskite Ti₃AN were investigated using the pseudo potential plane-wave method based on density functional theory. We found that the anisotropy of Ti₃InN was significantly larger than that of Ti₃AlN and Ti₃TlN. All three compounds were mechanically stable. The band structures of the three compounds revealed that they were conductors. The minimum thermal conductivities at high temperature in the propagation directions of [100], [110], and [111] were calculated by the acoustic wave velocity, which indicated that the thermal conductivity was also anisotropic. It is indicated that Ti₃InN is a good thermal barrier material. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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24 pages, 6410 KiB

Open AccessArticle

The Role of Geometrically Necessary Dislocations in Cantilever Beam Bending Experiments of Single Crystals

by Edgar Husser and Swantje Bargmann

Materials 2017, 10(3), 289; https://doi.org/10.3390/ma10030289 - 16 Mar 2017

Cited by 20 | Viewed by 8392

Abstract

The mechanical behavior of single crystalline, micro-sized copper is investigated in the context of cantilever beam bending experiments. Particular focus is on the role of geometrically necessary dislocations (GNDs) during bending-dominated load conditions and their impact on the characteristic bending size effect. Three [...] Read more.

The mechanical behavior of single crystalline, micro-sized copper is investigated in the context of cantilever beam bending experiments. Particular focus is on the role of geometrically necessary dislocations (GNDs) during bending-dominated load conditions and their impact on the characteristic bending size effect. Three different sample sizes are considered in this work with main variation in thickness. A gradient extended crystal plasticity model is presented and applied in a three-dimensional finite-element (FE) framework considering slip system-based edge and screw components of the dislocation density vector. The underlying mathematical model contains non-standard evolution equations for GNDs, crystal-specific interaction relations, and higher-order boundary conditions. Moreover, two element formulations are examined and compared with respect to size-independent as well as size-dependent bending behavior. The first formulation is based on a linear interpolation of the displacement and the GND density field together with a full integration scheme whereas the second is based on a mixed interpolation scheme. While the GND density fields are treated equivalently, the displacement field is interpolated quadratically in combination with a reduced integration scheme. Computational results indicate that GND storage in small cantilever beams strongly influences the evolution of statistically stored dislocations (SSDs) and, hence, the distribution of the total dislocation density. As a particular example, the mechanical bending behavior in the case of a physically motivated limitation of GND storage is studied. The resulting impact on the mechanical bending response as well as on the predicted size effect is analyzed. Obtained results are discussed and related to experimental findings from the literature. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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12 pages, 12932 KiB

Open AccessArticle

Numerical Investigation of the Fracture Mechanism of Defective Graphene Sheets

by Na Fan, Zhenzhou Ren, Guangyin Jing, Jian Guo, Bei Peng and Hai Jiang

Materials 2017, 10(2), 164; https://doi.org/10.3390/ma10020164 - 11 Feb 2017

Cited by 22 | Viewed by 5014

Abstract

Despite the unique occurrences of structural defects in graphene synthesis, the fracture mechanism of a defective graphene sheet has not been fully understood due to the complexities of the defects. In this study, the fracture mechanism of the monolayer graphene with four common [...] Read more.

Despite the unique occurrences of structural defects in graphene synthesis, the fracture mechanism of a defective graphene sheet has not been fully understood due to the complexities of the defects. In this study, the fracture mechanism of the monolayer graphene with four common types of defects (single vacancy defect, divacancy defect, Stone–Wales defect and line vacancy defect) were investigated systematically for mechanical loading along armchair and zigzag directions, by using the finite element method. The results demonstrated that all four types of defects could cause significant fracture strength loss in graphene sheet compared with the pristine one. In addition, the results revealed that the stress concentration occurred at the carbon–carbon bonds along the same direction as the displacement loading due to the deficiency or twist of carbon–carbon bonds, resulting in the breaking of the initial crack point in the graphene sheet. The fracture of the graphene sheet was developed following the direction of the breaking of carbon–carbon bonds, which was opposite to that of the displacement loading. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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9 pages, 11454 KiB

Open AccessArticle

Band Gap Tuning in 2D Layered Materials by Angular Rotation

by Javier Polanco-Gonzalez, Jesús Alfredo Carranco-Rodríguez, José L. Enríquez-Carrejo, Pierre G. Mani-Gonzalez, José Manuel Domínguez-Esquivel and Manuel Ramos

Materials 2017, 10(2), 147; https://doi.org/10.3390/ma10020147 - 8 Feb 2017

Cited by 8 | Viewed by 6791

Abstract

We present a series of computer-assisted high-resolution transmission electron (HRTEM) simulations to determine Moiré patters by induced twisting effects between slabs at rotational angles of 3°, 5°, 8°, and 16°, for molybdenum disulfide, graphene, tungsten disulfide, and tungsten selenide layered materials. In order [...] Read more.

We present a series of computer-assisted high-resolution transmission electron (HRTEM) simulations to determine Moiré patters by induced twisting effects between slabs at rotational angles of 3°, 5°, 8°, and 16°, for molybdenum disulfide, graphene, tungsten disulfide, and tungsten selenide layered materials. In order to investigate the electronic structure, a series of numerical simulations using density functional methods (DFT) methods was completed using Cambridge serial total energy package (CASTEP) with a generalized gradient approximation to determine both the band structure and density of states on honeycomb-like new superlattices. Our results indicated metallic transitions when the rotation approached 8° with respect to each other laminates for most of the two-dimensional systems that were analyzed. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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13 pages, 10186 KiB

Open AccessArticle

Mechanical Properties of Auxetic Cellular Material Consisting of Re-Entrant Hexagonal Honeycombs

by Xiangwen Zhang and Deqing Yang

Materials 2016, 9(11), 900; https://doi.org/10.3390/ma9110900 - 7 Nov 2016

Cited by 87 | Viewed by 8024

Abstract

A preliminary study of the mechanical properties of auxetic cellular material consisting of re-entrant hexagonal honeycombs is presented. For different scales of the honeycombs, the finite element method (FEM) and experimental models are used to perform a parametric analysis on the effects of [...] Read more.

A preliminary study of the mechanical properties of auxetic cellular material consisting of re-entrant hexagonal honeycombs is presented. For different scales of the honeycombs, the finite element method (FEM) and experimental models are used to perform a parametric analysis on the effects of the Poisson’s ratio (cell angle) and the relative density (cell thickness) of honeycombs on bearing capacity and dynamic performance of the auxetic material. The analysis demonstrates that the ultimate bearing capacity of the presented auxetic cellular material is scale-independent when the Poisson’s ratio and the relative density are kept constant. The relationship between the geometric parameters and vibration level difference of the honeycombs is also revealed, which can be divided into two converse parts around the Poisson’s ratio

v = - 1.5

. When

v

is smaller than −1.5, increasing the cell thickness leads to an increase in the vibration level difference of the honeycombs. Moreover, the dynamic performance of thin-walled honeycombs is greatly influenced by the scale of the honeycombs, especially for the ones with small Poisson’s ratio. These conclusions are verified by a frequency response test and a good agreement between the numerical results and experimental data is achieved. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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12 pages, 2007 KiB

Open AccessArticle

First-Principles Investigation of Phase Stability, Electronic Structure and Optical Properties of MgZnO Monolayer

by Changlong Tan, Dan Sun, Xiaohua Tian and Yuewu Huang

Materials 2016, 9(11), 877; https://doi.org/10.3390/ma9110877 - 27 Oct 2016

Cited by 22 | Viewed by 7033

Abstract

MgZnO bulk has attracted much attention as candidates for application in optoelectronic devices in the blue and ultraviolet region. However, there has been no reported study regarding two-dimensional MgZnO monolayer in spite of its unique properties due to quantum confinement effect. Here, using [...] Read more.

MgZnO bulk has attracted much attention as candidates for application in optoelectronic devices in the blue and ultraviolet region. However, there has been no reported study regarding two-dimensional MgZnO monolayer in spite of its unique properties due to quantum confinement effect. Here, using density functional theory calculations, we investigated the phase stability, electronic structure and optical properties of Mg_xZn_1−xO monolayer with Mg concentration x range from 0 to 1. Our calculations show that MgZnO monolayer remains the graphene-like structure with various Mg concentrations. The phase segregation occurring in bulk systems has not been observed in the monolayer due to size effect, which is advantageous for application. Moreover, MgZnO monolayer exhibits interesting tuning of electronic structure and optical properties with Mg concentration. The band gap increases with increasing Mg concentration. More interestingly, a direct to indirect band gap transition is observed for MgZnO monolayer when Mg concentration is higher than 75 at %. We also predict that Mg doping leads to a blue shift of the optical absorption peaks. Our results may provide guidance for designing the growth process and potential application of MgZnO monolayer. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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7 pages, 1752 KiB

Open AccessArticle

Cubic C₃N: A New Superhard Phase of Carbon-Rich Nitride

by Qun Wei, Quan Zhang, Haiyan Yan and Meiguang Zhang

Materials 2016, 9(10), 840; https://doi.org/10.3390/ma9100840 - 17 Oct 2016

Cited by 18 | Viewed by 5933

Abstract

Using the particle swarm optimization technique, we proposed a cubic superhard phase of C₃N (c-C₃N) with an estimated Vicker’s hardness of 65 GPa, which is more energetically favorable than the recently proposed o-C₃N. The [...] Read more.

Using the particle swarm optimization technique, we proposed a cubic superhard phase of C₃N (c-C₃N) with an estimated Vicker’s hardness of 65 GPa, which is more energetically favorable than the recently proposed o-C₃N. The c-C₃N is the most stable phase in a pressure range of 6.5–15.4 GPa. Above 15.4 GPa, the most energetic favorable high pressure phase R3m-C₃N is uncovered. Phonon dispersion and elastic constant calculations confirm the dynamical and mechanical stability of c-C₃N and R3m-C₃N at ambient pressure. The electronic structure calculations indicate that both c-C₃N and R3m-C₃N are indirect semiconductor. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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15 pages, 4834 KiB

Open AccessArticle

Physical Properties of PDMS (Polydimethylsiloxane) Microfluidic Devices on Fluid Behaviors: Various Diameters and Shapes of Periodically-Embedded Microstructures

by Changhyun Roh, Jaewoong Lee and ChanKyu Kang

Materials 2016, 9(10), 836; https://doi.org/10.3390/ma9100836 - 15 Oct 2016

Cited by 14 | Viewed by 5807

Abstract

Deformable polydimethylsiloxane (PDMS) microfluidic devices embedded with three differently-shaped obstacles (hexagon, square, and triangle) were used to examine the significant challenge to classical fluid dynamics. The significant factors in determining a quasi-steady state value of flow velocity (v)_QS and pressure [...] Read more.

Deformable polydimethylsiloxane (PDMS) microfluidic devices embedded with three differently-shaped obstacles (hexagon, square, and triangle) were used to examine the significant challenge to classical fluid dynamics. The significant factors in determining a quasi-steady state value of flow velocity (v)_QS and pressure drop per unit length (∆P/∆x)_QS were dependent on the characteristic of embedded microstructures as well as the applied flow rates. The deviation from the theoretical considerations due to PDMS bulging investigated by the friction constant and the normalized friction factor revealed that the largest PDMS bulging observed in hexagonal obstacles had the smallest (∆P/∆x)_QS ratios, whereas triangle obstacles exhibited the smallest PDMS bulging, but recorded the largest (∆P/∆x)_QS ratios. However, the influence of (v)_QS ratio on microstructures was not very significant in this study. The results were close to the predicted values even though some discrepancy may be due to the relatively mean bulging and experimental uncertainty. The influence of deformable PDMS microfluidic channels with various shapes of embedded microstructures was compared with the rigid microchannels. The significant deviation from the classical relation (i.e., f~1/Re) was also observed in hexagonal obstacles and strongly dependent on the channel geometry, the degree of PDMS deformation, and the shapes of the embedded microstructures. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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12 pages, 3707 KiB

Open AccessArticle

Mechanical and Electronic Properties of XC₆ and XC₁₂

by Qun Wei, Quan Zhang and Meiguang Zhang

Materials 2016, 9(9), 726; https://doi.org/10.3390/ma9090726 - 25 Aug 2016

Cited by 5 | Viewed by 5152

Abstract

A series of carbon-based superconductors XC₆ with high T_c were reported recently. In this paper, based on the first-principles calculations, we studied the mechanical properties of these structures, and further explored the XC₁₂ phases, where the X atoms are from [...] Read more.

A series of carbon-based superconductors XC₆ with high T_c were reported recently. In this paper, based on the first-principles calculations, we studied the mechanical properties of these structures, and further explored the XC₁₂ phases, where the X atoms are from elemental hydrogen to calcium, except noble gas atoms. The mechanically- and dynamically-stable structures include HC₆, NC₆, and SC₆ in XC₆ phases, and BC₁₂, CC₁₂, PC₁₂, SC₁₂, ClC₁₂, and KC₁₂ in XC₁₂ phases. The doping leads to a weakening in mechanical properties and an increase in the elastic anisotropy. C₆ has the lowest elastic anisotropy, and the anisotropy increases with the atomic number of doping atoms for both XC₆ and XC₁₂. Furthermore, the acoustic velocities, Debye temperatures, and the electronic properties are also studied. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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16 pages, 7787 KiB

Open AccessArticle

A New Superhard Phase and Physical Properties of ZrB₃ from First-Principles Calculations

by Gangtai Zhang, Tingting Bai, Yaru Zhao and Yanfei Hu

Materials 2016, 9(8), 703; https://doi.org/10.3390/ma9080703 - 22 Aug 2016

Cited by 30 | Viewed by 6955

Abstract

Using the first-principles particle swarm optimization algorithm for crystal structural prediction, we have predicted a novel monoclinic C2/m structure for ZrB₃, which is more energetically favorable than the previously proposed FeB₃-, TcP₃-, MoB₃-, [...] Read more.

Using the first-principles particle swarm optimization algorithm for crystal structural prediction, we have predicted a novel monoclinic C2/m structure for ZrB₃, which is more energetically favorable than the previously proposed FeB₃-, TcP₃-, MoB₃-, WB₃-, and OsB₃-type structures in the considered pressure range. The new phase is mechanically and dynamically stable, as confirmed by the calculations of its elastic constants and phonon dispersion curve. The calculated large shear modulus (227 GPa) and high hardness (42.2 GPa) show that ZrB₃ within the monoclinic phase is a potentially superhard material. The analyses of the electronic density of states and chemical bonding reveal that the strong B–B and B–Zr covalent bonds are attributed to its high hardness. By the quasi-harmonic Debye model, the heat capacity, thermal expansion coefficient and Grüneisen parameter of ZrB₃ are also systemically investigated. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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13 pages, 2637 KiB

Open AccessArticle

Crystal Structures and Mechanical Properties of Ca₂C at High Pressure

by Qun Wei, Quan Zhang and Meiguang Zhang

Materials 2016, 9(7), 570; https://doi.org/10.3390/ma9070570 - 14 Jul 2016

Cited by 16 | Viewed by 7015

Abstract

Recently, a new high-pressure semiconductor phase of Ca₂C (space group Pnma) was successfully synthesized, it has a low-pressure metallic phase (space group C2/m). In this paper, a systematic investigation of the pressure-induced phase transition of Ca₂ [...] Read more.

Recently, a new high-pressure semiconductor phase of Ca₂C (space group Pnma) was successfully synthesized, it has a low-pressure metallic phase (space group C2/m). In this paper, a systematic investigation of the pressure-induced phase transition of Ca₂C is studied on the basis of first-principles calculations. The calculated enthalpy reveals that the phase transition which transforms from C2/m-Ca₂C to Pnma-Ca₂C occurs at 7.8 GPa, and it is a first-order phase transition with a volume drop of 26.7%. The calculated elastic constants show that C2/m-Ca₂C is mechanically unstable above 6.4 GPa, indicating that the structural phase transition is due to mechanical instability. Both of the two phases exhibit the elastic anisotropy. The semiconductivity of Pnma-Ca₂C and the metallicity of C2/m-Ca₂C have been demonstrated by the electronic band structure calculations. The quasi-direct band gap of Pnma-Ca₂C at 0 GPa is 0.86 eV. Furthermore, the detailed analysis of the total and partial density of states is performed to show the specific contribution to the Fermi level. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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17 pages, 2048 KiB

Open AccessArticle

Structural Transitions in Nanosized Zn_0.97Al_0.03O Powders under High Pressure Analyzed by in Situ Angle-Dispersive X-ray Diffraction

by Chih-Ming Lin, Hsin-Tzu Liu, Shi-Yao Zhong, Chia-Hung Hsu, Yi-Te Chiu, Ming-Fong Tai, Jenh-Yih Juang, Yu-Chun Chuang and Yen-Fa Liao

Materials 2016, 9(7), 561; https://doi.org/10.3390/ma9070561 - 12 Jul 2016

Cited by 4 | Viewed by 5481

Abstract

Nanosized aluminum-doped zinc oxide Zn_1−xAl_xO (AZO) powders (AZO-NPs) with x = 0.01, 0.03, 0.06, 0.09 and 0.11 were synthesized by chemical precipitation method. The thermogravimetric analysis (TGA) indicated that the precursors were converted to oxides from hydroxides near [...] Read more.

Nanosized aluminum-doped zinc oxide Zn_1−xAl_xO (AZO) powders (AZO-NPs) with x = 0.01, 0.03, 0.06, 0.09 and 0.11 were synthesized by chemical precipitation method. The thermogravimetric analysis (TGA) indicated that the precursors were converted to oxides from hydroxides near 250 °C, which were then heated to 500 °C for subsequent thermal processes to obtain preliminary powders. The obtained preliminary powders were then calcined at 500 °C for three hours. The structure and morphology of the products were measured and characterized by angle-dispersive X-ray diffraction (ADXRD) and scanning electron microscopy (SEM). ADXRD results showed that AZO-NPs with Al content less than 11% exhibited würtzite zinc oxide structure and there was no other impurity phase in the AZO-NPs, suggesting substitutional doping of Al on Zn sites. The Zn_0.97Al_0.03O powders (A₃ZO-NPs) with grain size of about 21.4 nm were used for high-pressure measurements. The in situ ADXRD measurements revealed that, for loading run, the pressure-induced würtzite (B4)-to-rocksalt (B1) structural phase transition began at 9.0(1) GPa. Compared to the predicted phase-transition pressure of ~12.7 GPa for pristine ZnO nanocrystals of similar grain size (~21.4 nm), the transition pressure for the present A₃ZO-NPs exhibited a reduction of ~3.7 GPa. The significant reduction in phase-transition pressure is attributed to the effects of highly selective site occupation, namely Zn²⁺ and Al³⁺, were mainly found in tetrahedral and octahedral sites, respectively. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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10 pages, 2038 KiB

Open AccessArticle

Mechanical Properties and Atomic Explanation of Plastic Deformation for Diamond-Like BC₂

by Baobing Zheng, Meiguang Zhang and Shaomei Chang

Materials 2016, 9(7), 514; https://doi.org/10.3390/ma9070514 - 24 Jun 2016

Cited by 3 | Viewed by 5766

Abstract

Motivated by a recently predicted structure of diamond-like BC₂ with a high claimed hardness of 56 GPa (J. Phys. Chem. C 2010, 114, 22688–22690), we focus on whether this tetragonal BC₂ (t-BC₂) is superhard [...] Read more.

Motivated by a recently predicted structure of diamond-like BC₂ with a high claimed hardness of 56 GPa (J. Phys. Chem. C 2010, 114, 22688–22690), we focus on whether this tetragonal BC₂ (t-BC₂) is superhard or not in spite of such an ultrahigh theoretical hardness. The mechanical properties of t-BC₂ were thus further extended by using the first principles in the framework of density functional theory. Our results suggest that the Young’s and shear moduli of t-BC₂ exhibit a high degree of anisotropy. For the weakest shear direction, t-BC₂ undergoes an electronic instability and structural collapse upon a shear strain of about 0.11, with its theoretically ideal strength of only 36.2 GPa. Specifically, the plastic deformation under shear strain along the (110)[001] direction can be attributed to the breaking of d1 B–C bonds. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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8 pages, 4905 KiB

Open AccessArticle

A Stress-Induced Martensitic Transformation in Aged Ti₄₉Ni₅₁ Alloy after High-Velocity Impact

by Yingying Zhu, Haizhen Wang, Zhiyong Gao and Wei Cai

Materials 2016, 9(7), 500; https://doi.org/10.3390/ma9070500 - 23 Jun 2016

Cited by 1 | Viewed by 5002

Abstract

The effects of a high-velocity impact on the microstructure, phase transformation and mechanical property of aged Ti₄₉Ni₅₁ alloy are investigated. The transformation behavior and microstructure along the impact direction after impact emerge with regionalization characteristics, including a deformed region near [...] Read more.

The effects of a high-velocity impact on the microstructure, phase transformation and mechanical property of aged Ti₄₉Ni₅₁ alloy are investigated. The transformation behavior and microstructure along the impact direction after impact emerge with regionalization characteristics, including a deformed region near the crater (0–4 mm) and an un-deformed region of the distal crater (5–6 mm). Stress-induced martensite is the main deformation mechanism in the deforming region of aged Ti₄₉Ni₅₁ alloy under high-velocity impact. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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15 pages, 2488 KiB

Open AccessArticle

A Reinvestigation of a Superhard Tetragonal sp³ Carbon Allotrope

by Mengjiang Xing, Binhua Li, Zhengtao Yu and Qi Chen

Materials 2016, 9(6), 484; https://doi.org/10.3390/ma9060484 - 17 Jun 2016

Cited by 18 | Viewed by 6372

Abstract

I \bar{4}

–carbon was first proposed by Zhang et al., this paper will report regarding this phase of carbon. The present paper reports the structural and elastic properties of the three-dimensional carbon allotrope

I \bar{4}

–carbon using first-principles density functional [...] Read more.

I \bar{4}

–carbon was first proposed by Zhang et al., this paper will report regarding this phase of carbon. The present paper reports the structural and elastic properties of the three-dimensional carbon allotrope

I \bar{4}

–carbon using first-principles density functional theory. The related enthalpy, elastic constants, and phonon spectra confirm that the newly-predicted

I \bar{4}

–carbon is thermodynamically, mechanically, and dynamically stable. The calculated mechanical properties indicate that

I \bar{4}

–carbon has a larger bulk modulus (393 GPa), shear modulus (421 GPa), Young’s modulus (931 GPa), and hardness (55.5 GPa), all of which are all slightly larger than those of c-BN. The present results indicate that

I \bar{4}

–carbon is a superhard material and an indirect-band-gap semiconductor. Moreover,

I \bar{4}

–carbon shows a smaller elastic anisotropy in its linear bulk modulus, shear anisotropic factors, universal anisotropic index, and Young’s modulus. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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9 pages, 2952 KiB

Open AccessArticle

The Lateral Compressive Buckling Performance of Aluminum Honeycomb Panels for Long-Span Hollow Core Roofs

by Caiqi Zhao, Weidong Zheng, Jun Ma and Yangjian Zhao

Materials 2016, 9(6), 444; https://doi.org/10.3390/ma9060444 - 3 Jun 2016

Cited by 29 | Viewed by 9607

Abstract

To solve the problem of critical buckling in the structural analysis and design of the new long-span hollow core roof architecture proposed in this paper (referred to as a “honeycomb panel structural system” (HSSS)), lateral compression tests and finite element analyses were employed [...] Read more.

To solve the problem of critical buckling in the structural analysis and design of the new long-span hollow core roof architecture proposed in this paper (referred to as a “honeycomb panel structural system” (HSSS)), lateral compression tests and finite element analyses were employed in this study to examine the lateral compressive buckling performance of this new type of honeycomb panel with different length-to-thickness ratios. The results led to two main conclusions: (1) Under the experimental conditions that were used, honeycomb panels with the same planar dimensions but different thicknesses had the same compressive stiffness immediately before buckling, while the lateral compressive buckling load-bearing capacity initially increased rapidly with an increasing honeycomb core thickness and then approached the same limiting value; (2) The compressive stiffnesses of test pieces with the same thickness but different lengths were different, while the maximum lateral compressive buckling loads were very similar. Overall instability failure is prone to occur in long and flexible honeycomb panels. In addition, the errors between the lateral compressive buckling loads from the experiment and the finite element simulations are within 6%, which demonstrates the effectiveness of the nonlinear finite element analysis and provides a theoretical basis for future analysis and design for this new type of spatial structure. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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18 pages, 3544 KiB

Open AccessArticle

Two Novel C₃N₄ Phases: Structural, Mechanical and Electronic Properties

by Qingyang Fan, Changchun Chai, Qun Wei and Yintang Yang

Materials 2016, 9(6), 427; https://doi.org/10.3390/ma9060427 - 30 May 2016

Cited by 35 | Viewed by 7306

Abstract

We systematically studied the physical properties of a novel superhard (t-C₃N₄) and a novel hard (m-C₃N₄) C₃N₄ allotrope. Detailed theoretical studies of the structural properties, elastic properties, density [...] Read more.

We systematically studied the physical properties of a novel superhard (t-C₃N₄) and a novel hard (m-C₃N₄) C₃N₄ allotrope. Detailed theoretical studies of the structural properties, elastic properties, density of states, and mechanical properties of these two C₃N₄ phases were carried out using first-principles calculations. The calculated elastic constants and the hardness revealed that t-C₃N₄ is ultra-incompressible and superhard, with a high bulk modulus of 375 GPa and a high hardness of 80 GPa. m-C₃N₄ and t-C₃N₄ both exhibit large anisotropy with respect to Poisson’s ratio, shear modulus, and Young’s modulus. Moreover, m-C₃N₄ is a quasi-direct-bandgap semiconductor, with a band gap of 4.522 eV, and t-C₃N₄ is also a quasi-direct-band-gap semiconductor, with a band gap of 4.210 eV, with the HSE06 functional. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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13 pages, 4468 KiB

Open AccessArticle

Discrete Element Method Modeling of the Rheological Properties of Coke/Pitch Mixtures

by Behzad Majidi, Seyed Mohammad Taghavi, Mario Fafard, Donald P. Ziegler and Houshang Alamdari

Materials 2016, 9(5), 334; https://doi.org/10.3390/ma9050334 - 4 May 2016

Cited by 9 | Viewed by 6904

Abstract

Rheological properties of pitch and pitch/coke mixtures at temperatures around 150 °C are of great interest for the carbon anode manufacturing process in the aluminum industry. In the present work, a cohesive viscoelastic contact model based on Burger’s model is developed using the [...] Read more.

Rheological properties of pitch and pitch/coke mixtures at temperatures around 150 °C are of great interest for the carbon anode manufacturing process in the aluminum industry. In the present work, a cohesive viscoelastic contact model based on Burger’s model is developed using the discrete element method (DEM) on the YADE, the open-source DEM software. A dynamic shear rheometer (DSR) is used to measure the viscoelastic properties of pitch at 150 °C. The experimental data obtained is then used to estimate the Burger’s model parameters and calibrate the DEM model. The DSR tests were then simulated by a three-dimensional model. Very good agreement was observed between the experimental data and simulation results. Coke aggregates were modeled by overlapping spheres in the DEM model. Coke/pitch mixtures were numerically created by adding 5, 10, 20, and 30 percent of coke aggregates of the size range of 0.297–0.595 mm (−30 + 50 mesh) to pitch. Adding up to 30% of coke aggregates to pitch can increase its complex shear modulus at 60 Hz from 273 Pa to 1557 Pa. Results also showed that adding coke particles increases both storage and loss moduli, while it does not have a meaningful effect on the phase angle of pitch. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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10 pages, 2438 KiB

Open AccessArticle

The Mechanical and Electronic Properties of Carbon-Rich Silicon Carbide

by Qingyang Fan, Changchun Chai, Qun Wei and Yintang Yang

Materials 2016, 9(5), 333; https://doi.org/10.3390/ma9050333 - 30 Apr 2016

Cited by 24 | Viewed by 7090

Abstract

A systematic investigation of structural, mechanical, anisotropic, and electronic properties of SiC₂ and SiC₄ at ambient pressure using the density functional theory with generalized gradient approximation is reported in this work. Mechanical properties, i.e., the elastic constants and elastic modulus, [...] Read more.

A systematic investigation of structural, mechanical, anisotropic, and electronic properties of SiC₂ and SiC₄ at ambient pressure using the density functional theory with generalized gradient approximation is reported in this work. Mechanical properties, i.e., the elastic constants and elastic modulus, have been successfully obtained. The anisotropy calculations show that SiC₂ and SiC₄ are both anisotropic materials. The features in the electronic band structures of SiC₂ and SiC₄ are analyzed in detail. The biggest difference between SiC₂ and SiC₄ lies in the universal elastic anisotropy index and band gap. SiC₂ has a small universal elastic anisotropy index value of 0.07, while SiC₂ has a much larger universal elastic anisotropy index value of 0.21, indicating its considerable anisotropy compared with SiC₂. Electronic structures of SiC₂ and SiC₄ are calculated by using hybrid functional HSE06. The calculated results show that SiC₂ is an indirect band gap semiconductor, while SiC₄ is a quasi-direct band gap semiconductor. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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8 pages, 3101 KiB

Open AccessArticle

Si₉₆: A New Silicon Allotrope with Interesting Physical Properties

by Qingyang Fan, Changchun Chai, Qun Wei, Peikun Zhou, Junqin Zhang and Yintang Yang

Materials 2016, 9(4), 284; https://doi.org/10.3390/ma9040284 - 13 Apr 2016

Cited by 32 | Viewed by 7431

Abstract

The structural mechanical properties and electronic properties of a new silicon allotrope Si₉₆ are investigated at ambient pressure by using a first-principles calculation method with the ultrasoft pseudopotential scheme in the framework of generalized gradient approximation. The elastic constants and phonon calculations [...] Read more.

The structural mechanical properties and electronic properties of a new silicon allotrope Si₉₆ are investigated at ambient pressure by using a first-principles calculation method with the ultrasoft pseudopotential scheme in the framework of generalized gradient approximation. The elastic constants and phonon calculations reveal that Si₉₆ is mechanically and dynamically stable at ambient pressure. The conduction band minimum and valence band maximum of Si₉₆ are at the R and G point, which indicates that Si₉₆ is an indirect band gap semiconductor. The anisotropic calculations show that Si₉₆ exhibits a smaller anisotropy than diamond Si in terms of Young’s modulus, the percentage of elastic anisotropy for bulk modulus and shear modulus, and the universal anisotropic index A^U. Interestingly, most silicon allotropes exhibit brittle behavior, in contrast to the previously proposed ductile behavior. The void framework, low density, and nanotube structure make Si₉₆ quite attractive for applications such as hydrogen storage and electronic devices that work at extreme conditions, and there are potential applications in Li-battery anode materials. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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1 pages, 140 KiB

Open AccessCorrection

Correction: A Novel Silicon Allotrope in the Monoclinic Phase. Materials 2017, 10, 441

by Chaogang Bai, Changchun Chai, Qingyang Fan, Yuqian Liu and Yintang Yang

Materials 2017, 10(5), 561; https://doi.org/10.3390/ma10050561 - 22 May 2017

Cited by 2 | Viewed by 3454

Abstract

The authors would like to make the following correction to their paper[1]. In this paper,we wrongly listed the coordinates of the new silicon allotrope [...]
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(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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