关键词： Molecular dynamics simulation   mechanical properties   nanocomposite   epoxy   functional group   defect type  

摘要： In this article, several thermoset epoxy-based nanocomposites are simulated using molecular dynamics (MD) simulation. Epoxy resin with 75% crosslinking ratio is modeled first and its properties are used as the matrix material mechanical properties. The effects of defects and functional groups on carbon nanotube- and nanographene-reinforced epoxy nanocomposites are investigated. To achieve our goals, various types of defects and functional groups are created on graphene and nanotube in the MD models. The defects consist of Stone-Wales, vacancy, and Adatom. In addition, functional groups consist of O, OH, COOH, and NH2. Mechanical properties of nanocomposites are determined and compared. Moreover, nanocomposites consisting of continuous and short reinforcements are modeled to investigate the effects of reinforcement length on nanocomposite mechanical properties. Numerical results show that defects and functional groups reduce the elastic modulus of the nanofillers and nanocomposites in continuous nanofiller-reinforced epoxy. However, in nanocomposites consisting of short nanofillers, defects and functional groups have mixed effects on nanocomposite mechanical properties.

ISBN: (纸本)9787564379322

关键词： Crystal structure   Semimetal   Electronic structure   Ductility   Lattice thermal conductivity   First-principles calculations  

摘要： We have studied the origin of the semimetallic pseudo gap and the role of site preference in the L(2)1-type Heusler compound Ru2TaGa. A detailed account of the structural stability, phonon-dependent properties, electronic structure, and thermoelectric properties of the host compound is presented herein. Stability assessments have been made on the basis of phonon band structure, formation energy, mechanical criteria, and hull energy calculations. From the calculated density of states (DOS) and band structure, a semimetallic scenario is evident, with the Fermi level trapped in the pseudo gap. HSE calculations provide a decisive picture, with an indirect overlap between electron and hole pockets near the Fermi level of Ru2TaGa being responsible for the formation of a negative or pseudo gap. Comparison of the Ru e(g) and Ta t(2g) states reveals the role of d-d hybridization in pseudo gap formation in Ru2TaGa-like compounds. Additionally, we endeavor to discuss the transport coefficients of Ru2TaGa. The room temperature Seebeck coefficient calculated for Ru2TaGa is 66.42 mu V/K, considerably larger than those of other semimetallic compounds of the same family. Considering the lattice thermal conductivity (kappa(L) = 2.5 W/mK) at 800 K, we obtain a significant figure of merit of ZT = 0.025 in Ru2TaGa. Although the absolute thermoelectric figure of merit (0.002) is relatively low in Ru2TaGa, it is still the highest among the non-doped full Heuslers of the same family hitherto reported.

关键词： Aerodynamic characteristics   Betula platyphylla Sukaczev leaf   Fluid-solid coupling   Particle image velocimetry   Vortex shedding   Wind deflection angle  

摘要： It is necessary to examine the aerodynamic behaviour of leaves in wind in order to understand wind-induced tree disasters. The effect of the wind deflection angle on the aerodynamic characteristics of leaves remains relatively unexplored. Thus, the reconfiguration, vibration and wake characteristics of the Betula platyphylla Sukaczev leaves at various wind deflection angles and vegetative Cauchy numbers were investigated in a wind tunnel. Wind deflection angle (theta) is defined as the angle between the wind direction and the normal vector of the lamina, and a vegetative Cauchy number characterises the reconfiguration of an elastic structure under flow and is defined as the ratio of the product of the dynamic pressure and the third power of the slenderness ratio to the elasticity modulus. The results showed that at the different cases with an increase of Cauchy number, all the leaves mainly experience three states, a static bending of the laminas, and an opening and closing vibration of the laminas on left and right sides and a reconfiguration of the leaf. Except for the leaves with theta = 0, the leaves with theta = pi/6, pi/3 and pi/2 also experience torsional motion. Four critical Cauchy numbers were defined corresponding to the four reconfigurations and vibration states. The mean critical Cauchy numbers for the torsional motion of the leaves were at theta = pi/6, pi/3 and pi/2 this decreased with the increasing theta. The reconfigured mean Cauchy numbers of leaves for theta = pi/6, pi/3 and pi/2 were significantly larger than those in theta = 0. Furthermore, compared with the case for theta = 0, the cases with theta = pi/6, pi/3 and pi/2 proved to be disadvantageous for the reduction of vortex-induced vibrations through reconfiguration. (C) 2021 IAgrE. Published by Elsevier Ltd. All rights reserved.

关键词： Waves   Currents   Macroalgae   Breakage   Extensibility   Strength   Thickness  

摘要： Sessile organisms such as macroalgae located in the intertidal and shallow subtidal zones are subject to a hydrodynamically diverse environment, controlling the variation of intraspecific morphology and distribution. Kelp forests experience both waves and/or currents, yet, how kelp blade material mechanically differs between these various hydrodynamic environments and what drives the variation in strength and extensibility are not fully understood. Here, the mechanical properties, cellular composition and blade tissue thickness of the meristematic region and distal tips of the kelp Laminaria digitata blades were quantified and compared between seasons and among three hydrodynamic environments: wave dominated, current dominated and a benign hydrodynamic environment. Kelps associated with energetic environments, generally tended to be stronger yet more extensible than those growing in the benign hydrodynamic environment. Higher extensibility was located at the meristematic region whereas tissue was stronger in the distal tip of the blade. Linking both cellular composition and mechanical properties, results suggest enhancement of medulla cells in the meristematic region increases extensibility, potentially protecting the thallus during increased storm activity while growing in a wave/current exposed habitat. Investment in cortex cells towards the tip of the blade suggests an increase in strength of the region, which is susceptible to breakage. However, the lack of variation in the proportion of medulla and cortex cellular layers between distinct hydrodynamic environments revealed that the potential overall strategy for avoiding breakage in energetic hydrodynamic environments is that of investing energy into the increased thickness of blade tissue.

关键词： Carbide free bainitic steel   Isothermal treatments   Isothermal transformation kinetics   Mechanical properties   Microstructure  

摘要： The isothermal transformation kinetics, microstructure, and mechanical properties of a 0.23C high silicon steel, which is isothermally treated both below and above the martensite start temperature (Ms) are investigated. Results show that the small amount of athermal martensite (AM) in below Ms treated sample gives the additional nucleation sites for bainitic transformation, which accelerates the kinetics of bainitic transformation. The nucleation rate accelerates by two orders of magnitude at below Ms compared to above Ms. The microstructural analysis identifies the isothermal decomposition product formed in below and above Ms treated sample as bainitic ferrite. Furthermore, as compared to above Ms, below Ms isothermal treatment shows higher stability of austenite, giving rise to much improved ductility. Moreover, the below Ms isothermal treatment refines the bainitic lath more effectively.

关键词： epoxy resin   graphene oxide   molecular dynamics   penetration  

摘要： The penetration of salt solution into graphene oxide/epoxy resin (GO/EP) will cause structural damage, decrease in mechanical properties, and reduce service life. In this study, molecular dynamics method was used to simulate the penetration of the 3.5% NaCl solution through the GO/EP. In order to understand the effect of GO surface functional groups on the barrier properties of the GO/EP, a pure graphene model and three kinds of GO models modified with oxygen-containing functional groups (ether, hydroxyl, and carboxyl) were established, respectively. The penetration resistance of GO/EP was analyzed. The type of oxygen-containing functional group affects the penetration rate of the salt solution and the GO/EP interface performance. The spatial distribution and kinetic behavior of the salt solution were studied. The results show that the salt solution molecules trapped in GO/EP were mainly concentrated at the interface between GO and EP, which is the main reason for the degradation of the GO/EP interface performance. Affected by GO, the penetration process of ions can be divided into multiple stages, and its motion state was different depending on the type of functional group.

关键词： galaxolide (HHCB)   photodegradation processes   advanced oxidation processes   DFT study  

摘要： Studies on kinetics of galaxolide (HHCB) degradation under influence of UV, simulated sunlight and some advanced oxidation processes (H2O2, UV/H2O2, and Vis/H2O2) were conducted. Galaxolide appeared to be a photolabile compound. The first-order kinetics model was assumed for all studied processes. It was observed that basic pH favored HHCB degradation. The influence of natural matrices (river water and artificial sweat) on direct photolysis of HHCB was examined. It was stated that the process of the photodegradation proceeded slower at the presence of each matrix. HHCB lactone was identified using the GC-MS technique. The recorded chromatograms showed that apart from the lactone, other degradation products were formed that we could not identify. In order to deeper understand the HHCB degradation process, DFT calculations were performed. The results pointed out that OH radicals play a key role in HHCB decomposition, which mainly proceeds via H abstractions as well as OH additions. It follows from the calculations that the visible light is sufficient to initiate the advanced oxidation processes (AOP(s)) under the oxidative conditions, whereas UV irradiation is needed to start decay with no oxidative agents.

关键词： kinetics of austenite phase transitions   alloying elements   overheating zone   mechanical properties  

摘要： The effect of vanadium and molybdenum on the kinetics of phase transitions of austenite and the mechanical properties of the overheating zone of low-carbon high-strength steels has been investigated. Changes in the structure and mechanical properties of the alloys upon cooling with rates typical of various welding methods are shown.

关键词： Graphene   Coarse-grain   Molecular dynamics   Mie potential   Multilayer  

摘要： Graphene-based structures have found widespread applications in the fabrication of superior composite materials, conductors, and sensors owing to their excellent properties. Molecular dynamics (MD) simulation is often used to gain an in-depth understanding of the mechanical behaviors of those structures. However, MD simulation of mesoscale graphene structures faces great challenges due to its limited model size or high computation cost. In this work, we proposed a multilayer coarse-grained (CG) MD model which coarsens graphene layers in both planar and thickness directions. We systematically investigated the effect of coarse-graining on simulation accuracy in the CG-MD model. The optimal coarse-graining parameters for simulating the mechanical behaviors of graphene in tension, shearing, adhesion, bending, and self-folding were obtained. Our optimal CG-MD model enabled the simulation of relatively large-scale graphene structure with 1-2 orders of magnitude increase in length and 3-4 orders of magnitude reduction in computational time compared with the all-atom (AA) model, offering a valuable tool for designing and exploring graphene-based novel materials. (C) 2021 Elsevier Ltd. All rights reserved.