共查询到20条相似文献,搜索用时 15 毫秒
1.
A. R. Alian S. A. Meguid 《International Journal of Mechanics and Materials in Design》2018,14(4):551-563
In this paper, we develop an efficient multiscale molecular dynamics (MD)–finite element (FE) modeling scheme capable of determining the elastic and fracture properties of polycrystalline graphene. The local elastic properties of a grain boundary (GB) connecting two adjacent graphene grains, with different lattice orientations, were first determined using MD simulations. In a two-dimensional medium, randomly distributed grains connected with GBs were then created using the Voronoi tessellation method. The constructed Voronoi diagrams were used to create FE models of the polycrystalline graphene, where the GBs were represented by interphase regions with their local properties determined using MD. The grains were modeled as pristine graphene and the accuracy of the polycrystalline FE model was validated with MD simulations of a geometrically identical polycrystalline graphene. The results reveal good agreement between MD and FE simulations. They further show that the elastic and fracture properties of polycrystalline graphene are greatly influenced by the grain size and the misorientation angle. They also indicate that the predicted elastic properties are in agreement with earlier reported experimental and MD results. We believe that this newly proposed multiscale scheme could be easily integrated into current design software to model graphene based nano- and micro-devices. 相似文献
2.
Atefeh Nabavi Alexander Capozzi Samuel Goroshin David L. Frost Francois Barthelat 《Journal of Materials Science》2014,49(23):8095-8106
Ceramic–metal composites (cermets) offer unique combinations of hardness and toughness, which make them attractive for a variety of applications. In this study, we propose a new method for the preparation of the metal–sulfur precursor mixture based on the ability to melt-cast the precursor mixture. We have used self-propagating high-temperature synthesis to produce a chromium/chromium sulfide cermet, exploiting the fact that this mixture of metal and sulfur can support the propagation of reactive waves. This ability, together with the properties of the reaction products (low gas evolution and liquid sulfide products), enables the net-shape synthesis of dense, near theoretical density product with a relatively simple and low-cost set-up. While the thermochemical calculations predict near-zero gas production for the chromium–sulfur system, the actual cermets showed a large amount of porosity (about 70 %), when synthesized at atmospheric pressure. The possible sources for porosity were identified, and the process improved to bring the porosity down to about 7 %. We also investigated the physical properties of the produced cermet with optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction techniques. 相似文献
3.
We report a comparative study of graphene nanoplatelets (GNPs)–epoxy nanocomposites with enhanced electrical conductive properties obtained with two different processing techniques. In the first one (TEC1), the epoxy monomer was added to a previously produced GNP–chloroform suspension and after the evaporation of the solvent, the hardener was added. In the second technique (TEC2), the hardener was added to a GNP–tetrahydrofuran suspension and after the evaporation of the solvent, the epoxy monomer was added. Although there was good dispersion of GNPs in the epoxy matrix with both techniques, the nanocomposite based on TEC1 showed a slightly better dispersion than the one based on TEC2. Electric and dielectric characterization showed that it is possible to reach the electrical percolation threshold at reasonably low GNP contents. 相似文献
4.
Polyimide/reduced graphene oxide (PI/r-GO) core–shell structured microspheres were fabricated by in-situ reduction of graphene oxide (GO), which was coated on the surface of PI microspheres via hydrogen bonding and π–π stacking interaction. The highly ordered 3D core–shell structure of PI/r-GO microspheres with graphene shell thickness of 3 nm was well characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and Raman spectra. The glass transition temperature (Tg) of PI/r-GO microspheres was slightly increased because of the interaction of r-GO and PI matrix while the temperature at 5% weight loss (T5%) of PI/r-GO microspheres was decreased due to the side effect of reductant hydrazine hydrate. The PI/r-GO nanocomposites exhibited highly electrical conductivity with percolation threshold of 0.15 vol% and ultimate conductivity of 1.4 × 10−2 S/m. Besides, the thermal conductivity of PI/r-GO nanocomposites with 2% weight content of r-GO could reach up to 0.26 W/m K. 相似文献
5.
An investigation is conducted on the effect of the hybrid of multi-wall carbon nanotubes (MWCNTs) and graphene oxide (GO) nanosheets on the tribological performance of epoxy composites at low GO weight fractions of 0.05–0.5 phr. The MWCNT amount is kept constant at 0.5 phr, which is typical for CNT/epoxy composites with enhanced mechanical properties. Friction and wear tests against smooth steel show that the introduction of 0.5 phr MWCNTs into the epoxy matrix increases the friction coefficient and decreases the specific wear rate. When testing the tribological performance of MWCNT/GO hybrids, it is shown that at a high GO amount of 0.5 phr, the friction coefficient is decreased below that of the neat matrix whereas the wear rate is increased above that of the neat matrix. At an optimal hybrid formulation, i.e., 0.5 phr MWCNTs and 0.1 phr GO, a further increase in the friction coefficient and a further reduction in the specific wear rate are observed. The specific wear rate is reduced by about 40% down to a factor of 11 relative to the neat epoxy when the GO content is 0.1 phr. 相似文献
6.
Xuecheng Chen Chengyi Hou Qinghong Zhang Yaogang Li Hongzhi Wang 《Materials Science and Engineering: B》2012,177(13):1067-1072
Co1−xNixFe2O4/graphene nanocomposites were synthesized through a one-step solvothermal method. The as-synthesized products were characterized by X-ray powder diffraction, field emission scanning microscopy, transmission electron microscope, and high-resolution transmission electron microscope. The results show that the Co1−xNixFe2O4 nanoparticles are uniformly dispersed on graphene sheets. The dependence of structure, magnetic and electrical properties of Co1−xNixFe2O4/graphene nanocomposites on the Ni2+ concentration and the graphene content were also studied. The saturation magnetization and electrical conductivity of the as-prepared products reached 51.82 emu/g and 1.00 × 102 S/m, respectively. 相似文献
7.
A novel method for the preparation of epoxy/silver nanocomposites was developed by in-situ formation of silver nanoparticles within the epoxy matrix. The silver–imidazole complex was synthesized by silver acetate and 2-ethyl-4-methylimidazole (2E4MZ). During the cure of epoxy resin, silver nanoparticles were in-situ generated through thermal decomposition of the silver–imidazole complex which was capable of reducing Ag+ to Ag0 by itself. The simultaneously released imidazole could cure the epoxy. In addition, the in-situ generated silver nanoparticles could be stabilized by the formed epoxy network. Therefore, by using the thermal decomposition method, uniformly dispersed silver nanoparticles of size of around 11.6 nm were in-situ generated in epoxy matrix. 相似文献
8.
9.
《Materials Research Bulletin》2004,39(7-8):881-886
A novel and convenient reduction–hydrolysis method was developed to make high-purity VO2 nanopowders. The products have been studied with XRD, IR, XPS, and DTA. The nanopowders exhibited a strong crystallographic transition to the rutile-type structure around 68–72 °C. The XRD patterns and TEM images of products showed that the average size of samples was in the range of 30–40 nm. The XPS results demonstrated that the vanadium exists as V4+ ions in the products. We also found that the phase transition temperature of products decreased by tungsten doping. 相似文献
10.
11.
12.
A novel approach for electrical circuit modeling of Li-ion battery is proposed in this paper. The model proposed in this paper is simple, fast, not memory intensive and does not involve any look-up table. The model mimics the steady-state and dynamic behavior of battery. Internal charge distribution of the battery is modeled using two RC circuits. Self-discharge characteristic of the battery is modeled using a leakage resistance. Experimental procedure to determine the internal resistance, leakage resistance and the value of RC elements is explained in detail. The variation of parameters with state of charge (SOC) and magnitude of current is presented. The internal voltage source of the battery model varies dynamically with SOC to replicate the experimental terminal voltage characteristics of battery. The accuracy of model is validated with experimental results. 相似文献
13.
14.
Mahua Ghosh Chaudhuri Rajib Dey Manoj K Mitra Gopes C Das Siddhartha Mukherjee 《Science and Technology of Advanced Materials》2008,9(1)
Silicon nitride (Si3 N4) nanowires have been prepared by carbothermal reduction followed by the nitridation (CTRN) of silica gel containing ultrafine excess carbon obtained by the decomposition of dextrose over the temperature range of 1200–1350 °C. This innovative process involves repeated evacuation followed by purging of nitrogen gas so that the interconnected nanopores of the gel are filled with nitrogen gas prior to heat treatment. During heat treatment at higher temperatures, the presence of nitrogen gas in the nanopores of the gel starts the CTRN reaction simultaneously throughout the bulk of the gel, leading to the formation of Si3 N4 nanowires. The in situ generated ultrafine carbon obtained by the decomposition of dextrose decreases the partial pressure of oxygen in the system to stabilize the nanowires. The nanowires synthesized by this process are of ∼500 nm diameter and ∼0.2 mm length. The product was characterized by scanning electron microscope (SEM), energy dispersive x-ray analysis (EDX), x-ray diffraction (XRD) and infrared (IR) spectra. 相似文献
15.
AbstractSilicon nitride (Si3 N4) nanowires have been prepared by carbothermal reduction followed by the nitridation (CTRN) of silica gel containing ultrafine excess carbon obtained by the decomposition of dextrose over the temperature range of 1200–1350 °C. This innovative process involves repeated evacuation followed by purging of nitrogen gas so that the interconnected nanopores of the gel are filled with nitrogen gas prior to heat treatment. During heat treatment at higher temperatures, the presence of nitrogen gas in the nanopores of the gel starts the CTRN reaction simultaneously throughout the bulk of the gel, leading to the formation of Si3 N4 nanowires. The in situ generated ultrafine carbon obtained by the decomposition of dextrose decreases the partial pressure of oxygen in the system to stabilize the nanowires. The nanowires synthesized by this process are of ~500 nm diameter and ~0.2 mm length. The product was characterized by scanning electron microscope (SEM), energy dispersive x-ray analysis (EDX), x-ray diffraction (XRD) and infrared (IR) spectra. 相似文献
16.
Yan Zhang Fu-cheng Zhang Li-he Qian Tian-sheng Wang 《Computational Materials Science》2011,50(5):1754-1762
Phase boundaries play significant roles in the crack initiation and propagation behavior of duplex phase materials such as nanoscale bainite–austenite (α/γ) microstructures. Simulation of α/γ-iron phase boundary interacting with crack propagation was carried out using molecular dynamics method. Bi-phase systems consisting of α-iron with body-centered cubic structure and γ-iron with face-centered cubic structure, were constructed. Phase boundaries were created using Nishiyama–Wasserman and Kurdjumov–Saches (K–S) orientation relationships, respectively. Eight orientations of cracks in α- or γ-phase were analyzed to illustrate the orientation dependence of crack growth. Finnis–Sinclair potential for Fe fit by Mendelev was used to describe interatomic potentials. Tensile load was applied normal to the crack surface. Simulation results reveal that in most cases phase boundary provides an obstacle to slip and dislocation motion during crack propagation, except in two orientations with K–S relation. New-cracks always nucleate phase boundary as a result of slip blocking and dislocation pileups. Bcc/fcc iron phase boundary is therefore demonstrated to be a great contribution to the strengthening of nanoscale duplex steel. 相似文献
17.
Mihaela D. Lazar Alexandru R. Biris Gheorghe Borodi Cezara Voica Fumiya Watanabe Enkeleda Dervishi Alexandru S. Biris 《Journal of Materials Science》2013,48(21):7409-7421
Magnesia supported Au, Ag, and Au–Ag nanostructured catalysts were prepared, characterized, and used to synthesize few-layer graphene–metal nanoparticle (Gr–MeNP) composites. The catalysts have a mezoporous structure and a mixture of MgO and MgO·H2O as support. The gold nanoparticles (AuNPs) are uniformly dispersed on the surface of the Au/MgO catalysts, and have a uniform round shape with a medium size of ~8 nm. On the other hand, the silver nanoparticles (AgNPs) present on the Ag/MgO catalyst have an irregular shape, larger diameters, and less uniform dispersion. The Au–Ag/MgO catalyst contains large Au–Ag bimetallic particles of ~20–30 nm surrounded by small (5 nm) AuNPs. Following the RF-CCVD process and the dissolution of the magnesia support, relative large, few-layer, wrinkled graphene sheets decorated with metal nanoparticles (MeNPs) are observed. Graphene–gold (Gr–Au) and graphene–silver (Gr–Ag) composites had 4–7 graphitic layers with a relatively large area and similar crystallinity for samples prepared in similar experimental conditions. Graphene–gold–silver composites (Gr–Au–Ag) presented graphitic rectangles with round, bent edges, higher crystallinity, and a higher number of layers (8–14). The MeNPs are encased in the graphitic layers of all the different samples. Their size, shape, and distribution depend on the nature of the catalyst. The AuNPs were uniformly distributed, had a size of about 15 nm, and a round shape similar to those from Au/MgO catalyst. In Gr–Ag, the AgNPs have a round shape, very different from that of the Ag/MgO catalyst, large size distribution and are not uniformly distributed on the surface. Agglomerations of AgNPs together with large areas of pristine few-layer graphene were observed. In Gr–Au–Ag composites, almost exclusively large bimetallic particles of about 25–30 nm, situated at the edge of graphene rectangles have been found. 相似文献
18.
In this study, a novel rare-earth complex, dithio-aminomethyl-lysine samarium (DALSm), was prepared and then was employed as activator, accelerator, cross-linker and interfacial modifier to improve the mechanical properties of SBR/silica nanocomposites. The results showed that 6 phr DALSm performed a higher vulcanization efficiency than the combination of 5 phr activator zinc oxide (ZnO), 2 phr stearic acid (SA), and 2 phr accelerator diethyl dithiocarbamate zinc (EDCZn). Meanwhile, the XPS and FTIR analysis of DALSm/silica model compounds confirmed that hydrogen bonds and coordination bonds could be formed between DALSm and silica during vulcanization process, which can effectively facilitate the homogenous dispersion of silica particles into SBR matrix and enhance the interface adhesion between rubber matrix and filler. As a consequent, the mechanical properties of SBR/DALSm/silica nanocomposites were substantially improved and much more excellent than those of the SBR/EDCZn/silica nanocomposites containing equivalent filler content. Based on the results of immobilized polymer layer, the reinforcing mechanism of DALSm in SBR/silica nanocomposites was analyzed. 相似文献
19.
Compacted powders of titanium (Ti) and carbon (C) in form of pellets were exposed to a massive amount of heat generated from the thermite reaction of Fe2O3 and Al in a graphite–steel tube mounted in a developed centrifugal accelerator machine. The centrifugal force facilitated the formation of multi-component products during the process. Titanium carbide (TiC) product is joined to an Al2O3–Fe layer, which are the products of the thermite reaction. The existence of centrifugal acceleration had a significant effect on both metallurgical alloying and mechanical interlocking between different layers of the sample to form a functional material. A mathematical model developed for this experiment to describe the speed rate of iron infiltration inside the TiC product as well as viscosity rate variation was presented. The composition, microstructure and mechanical properties confirmed the model. 相似文献
20.
Xiulin Shu Qingshan Shi Jing Feng Xiaobao Xie Yiben Chen 《Journal of Materials Science》2014,49(22):7742-7749
In order to improve biocompatibility and cell growth, poly-γ-glutamic acid (γ-PGA) was used as an additive, and a series of γ-PGA/hydroxyapatite (γ-PGA/HAp) nanocomposites were prepared. Then the morphology, water uptake and retention abilities, in vitro degradation properties in the simulated medium, and cytotoxicity of these γ-PGA/HAp nanocomposites were investigated. The results show that the γ-PGA/HAp nanocomposites have homogenous nano-sized grains, hydrophilicity, biocompatibility, and controlled in vitro degradation, suggesting that the γ-PGA/HAp nanocomposites are novel nanostructure composites with great potential application in the field of bone tissue engineering. 相似文献