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Carbon nanotube (CNT) networks enable CNTs to be used as building blocks for synthesizing novel advanced materials, thus taking full advantage of the superior properties of individual CNTs. Multiscale analyses have to be adopted to study the load transfer mechanisms of CNT networks from the atomic scale to the macroscopic scale due to the huge computational cost. Among them, fully resolved structural features include the graphitic honeycomb lattice (atomic), inter-tube stacking (nano) and assembly (meso) of CNTs. On an atomic scale, the elastic properties, ultimate stresses, and failure strains of individual CNTs with distinct chiralities and radii are obtained under various loading conditions by molecular mechanics. The dependence of the cohesive energies on spacing distances, crossing angles, size and edge effects between two CNTs is analyzed through continuum modeling in nanoscale. The mesoscale models, which neglect the atomic structures of individual CNTs but retain geometrical information about the shape of CNTs and their assembly into a network, have been developed to study the multi-level mechanism of material deformation and microstructural evolution in CNT networks under stretching, from elastic elongation, strengthening to damage and failure. This paper summarizes the multiscale theories mentioned above, which should provide insight into the optimal assembling of CNT network materials for elevated mechanical performance.

The low-yielding-strength (LYS) steel is promising for energy-absorbing devices due to its outstanding plasticity. Although the mechanical properties of LYS steel for quasi-static and ultra-high-rate were studied, the link between them has not been established yet. Here we report both experiments and numerical simulations on the dynamic behavior of a LYS steel (quasi-static yielding stress > 225 MPa, LYS225) under moderate dynamic loadings, which covers the typical range of strain rate in engineering applications. Our results quantify the rate effect of LYS225 under moderate loading speed, and the strain-rate dependent constitutive and damage models are proposed. Moreover, the stress and strain concentration for elliptic-holed LYS225 plate is numerically analyzed based on the proposed constitutive model, which shows significant difference compared to the static solutions. This work could bridge the gap between their quasi-static and ultra-high-rate properties, thereby improve the designing precision of LYS steel-based energy-absorbing structures.

The manufacturing industry has a large volume and a wide range of energy consumption. It is the main body of energy consumption in the industrial field. In recent years, a great challenge has been posed to the manufacturing industry to improve sustainable development for low energy consumption and high efficiency. The energy efficiency of manufacturing systems has become an important research hotspot in the sustainable development of the world’s manufacturing. Aiming at the problem of low energy efficiency in the current machining process, this paper considers the relationship between tool geometric angles and energy consumption, and on the basis of the current energy consumption model establishes an energy consumption model with independent variables including cutting parameters and tool geometric angles. In order to achieve energy-saving and high efficiency, a multi-objective optimization model was established with cutting parameters and tool geometric angles as optimization variables, combined with actual machine tool and process parameter constraints. The model is solved by the elitist non-dominated sorting genetic algorithm (NSGA-II), and an optimized combination of cutting parameters and tool geometric angle is obtained. Through the comparison experiments conducted with the processing methods that are respectively based on the experience and simply optimize the cutting parameters in the actual milling test, the practivity and validity of the method proposed are verified. The test results show that integrated optimization of cutting parameters and tool geometric angles can reduce energy consumption by 8.77% at least.

The interfacial shear coupling (ISC) governs the relative in-plane deformations of layered two-dimensional (2D) van der Waals (vdW) materials, which is significant for both the fundamental theory of solid mechanics and the stability design of 2D devices. Here we study the representative ISC of 2D vdW stacks using bilayer graphene (BLG) and isotope-labeled Raman spectroscopy. The results show that under uniaxial tensile strain, the ISC between two graphene layers evolves sequentially with bonding, sliding and debonding process, and the corresponding interfacial shear strength is inversely proportional to the sample size. Molecular dynamics (MD) simulations demonstrate the origin of this inverse proportionality as stronger interlayer vdW interaction induced by the edge lattices and atoms of BLG that have more degrees of freedom. These results not only provide new fundamental insights into the multiscale interpretation of macroscopic interfacial shear properties of 2D vdW stacks but also have great potential in guiding the design of graphene-based composite materials and flexible 2D electronics.

As exhaust emission standards become increasingly stringent, the requirements for diesel exhaust post-treatment systems become increasingly demanding. This research focuses on the optimisation of a new hybrid structure to improve the performance of exhaust post-treatment systems. First, a short pitch spiral mixing chamber with sufficient mixing space and low temperature loss was designed to improve the evaporation of liquid droplets. Additionally, a conical plate mixer was used to conduct secondary mixing of the gas to improve the flow characteristics further. The ammonia uniformity and crystallisation risk of the new hybrid structure were simulated using Computational Fluid Dynamics, and the optimal hybrid structure was verified by tests. The results showed that ammonia leakage, low temperature crystallisation and NOX conversion efficiency could effectively be improved by optimally designing the new hybrid structure. This research is of great significance for reducing exhaust pollution and optimising diesel exhaust post-treatment systems.

In this study, water soluble CuO nanostructures having nanobelt, nanorod, or spindle morphologies were synthesized using aqueous solutions of Cu(NO3)2·3H2O and NaOH by adjusting the type of surface modifier and reaction temperature. The effect of morphologies of these various CuO nanostructures as water-based lubricant additives on tribological properties was evaluated on a UMT-2 micro-friction tester, and the mechanisms underlying these properties are discussed. The three different morphologies of CuO nanostructures exhibited excellent friction-reducing and anti-wear properties. Tribological mechanisms differed in the initial stage of frictional interactions, but in the stable stage, a tribochemical reaction film and adsorbed lubricious film on the rubbing surfaces played important roles in hindering direct contact between friction pairs, leading to improved tribological properties.

A vibratory erosion test rig is used to study the cavitation erosion of 6061 alloy. Some craters and material fracture are found on the specimen surface at the beginning of test. A cavitation model in an ultrasonic field is developed by applying the bubble–bubble interaction effect into Keller–Miksis equation to obtain the bubbles dynamic characteristics. The results reveal that the bubble cloud configuration is suitable for the explanation of cavitation erosion, and the erosion surfaces of the specimen were subjected to the effect of both massive bubbles collapsing, occurring in the thin liquid layer between the horn and the specimen. It is concluded that the optimal coupling strength of bubbles increases with the decrease of the bubble initial radius, and stable cavitation only occurs when the acoustic pressure amplitude is higher than a threshold value, which can well predict the experimental results.

The dynamic mechanical behaviors of the [Formula: see text] fiber-reinforced composite laminates subjected to double-position low-velocity impacts are investigated by finite element method. Two impact positions symmetrical about the center of the laminates are impacted sequentially with three impact distances (10 mm, 20 mm, and 40 mm) under three impact energies (5 J, 10 J, and 20 J) to study the interference effect of impact damage. For comparison, plastic damage model (PDM) and elastic damage model (EDM) are established to describe the intra-laminar constitutive, respectively. Compared with available experimental data, the mechanical responses calculated by PDM are more accurate, especially at high energies. Affected by the impact interference, the oscillation of force-time curve for the second impact rather than the first impact is relatively weaker, while the severity of impact damage is reversed. The results show that the maximum displacement is more suitable for characterizing the degree of damage interference than bending stiffness, peak force, and energy dissipation.

Good air flow and heat dissipation performance are important factors in ensuring the reliability of emergency power supply cabin (EPSC) equipment. Accordingly, the airflow and temperature fields of...

Purpose The disbonding of DLC coating is a main failure mode in the high-speed cavitation condition, which shortens the service life of the bearing. This study aims to investigate influence of adhesion strength on cavitation erosion resistance of DLC coating. Design/methodology/approach Three DLC coatings with different adhesion strengths were grown on the 304 steel surfaces by using a cathodic arc plasma deposition method. Cavitation tests were performed by using a vibratory test rig to investigate the influence of adhesion strength on cavitation erosion resistance of a DLC coating. The cavitation mechanism of the substrate-coating systems was further discussed by means of surface analyses. Findings The results indicated that, the residual stress decreased and then increased with the increasing DLC coating thickness from 1 µm to 2.9 µm, and the lower residual stress can improve the adhesion strength of the DLC coating to the substrate. It was also concluded that, the plastic deformation as well as the fracture occurred on the DLC coating surface at the same time, owing to higher residual stress and poorer adhesion strength. However, lower residual stress and better adhesion strength could help resist the occurrence of the coating fracture. Originality/value Cavitation tests were performed by using a vibratory test rig to investigate the influence of adhesion strength on cavitation erosion resistance of the DLC coating. The plastic deformation and the fracture occurred on the DLC coating surface at the same time, owing to higher residual stress and poorer adhesion of coating. Lower residual stress and better adhesion of coating could resist the occurrence of the DLC coating fracture.

Centimetres-long carbon nanotube (CNT) bundles with tensile strength over 80 GPa have been fabricated and tested recently [Nat. Nanotechnol. 13, 589–595 (2018)], but it is still a tremendous challenge to predict their nonlinear mechanical behaviors by full-atom molecular dynamics (MD) due to the huge computational cost, particularly for carbon nanotube networks. We completely established here the explicit expressions of the chirality-dependent higher-order nonlinear coarse-grained stretching and bending potentials based on the full-atom Reactive Empirical Bond-Order interatomic potential of second generation (REBO potential). In particular, the coarse-grained non-bonded potentials are improved by using the 18–24 Lennard-Jones potential. By comparison with available experimental results and full-atom MD simulations as well as our analytical results, the present nonlinear coarse-grained potentials have high accuracy. The obtained nonlinear coarse-grained potentials can be used to efficiently characterize the nonlinear mechanical behaviors and understand the failure mechanism of the CNT bundles and networks with 2∼5 orders of magnitude reduction in computing time, which should be of great help for designing and assembling CNT-based flexible microdevices.

Recently, Shang et al. (Angew Chem Int Ed 57(3):774–778, 2018) have developed a method to synthesize ultrathin (around 1.9 nm) graphyne nanosheets. We reported here the mixed-mode I–II fracture toughnesses and crack growth angles of single-layer graphyne sheets using molecular dynamics (MD) simulations and the finite element (FE) method based on the boundary layer model, respectively. The various carbon–carbon bonds of graphyne sheets in the FE method are equated with the nonlinear Timoshenko beams based on the Tersoff–Brenner potential, where all the parameters of the nonlinear beams are completely determined based on the continuum modeling. All the results from the present FE method are reasonable in comparison with those from our MD simulations using the REBO potential. The present results show that both the critical stress intensity factors (SIFs) and the crack growth angle strongly depend on the chirality and loading angle $$\varphi $$ ( $$\varphi =90^{\circ }$$ and $$\varphi =0^{\circ }$$ representing pure mode I and pure mode II, respectively). Meanwhile, the fracture properties of single-layer cyclicgraphene and supergraphene sheets are also studied in order to compare with those of the graphyne sheets. The critical equivalent SIFs are derived as $$1.55

Energy consumption of machining systems has been a great concern of many manufacturing enterprises. It is pointed out that complex properties of sculptured surface have important influence on CNC machining process where energy consumption and machining efficiency are treated as two evaluation indicators of machining system performance. This paper studies the impact of Surface Machining Complexity (SMC) on energy consumption and efficiency in CNC machining. By analyzing critical factors that influence machining power and efficiency, a pentagon model that refers to the workpiece, equipment, cutter, goal, and process is provided. Based on the pentagon model, a model for calculating SMC, which reflects the difficulty level of CNC machining, is developed. Furthermore, a detailed process of the solution using Fuzzy c-means clustering algorithm is introduced with a case study. Finally, the impact of SMC on energy consumption of machining system is discussed via a group of experiments. The experiments verified the effectiveness of the proposed method and present the increased trend between surface machining complexity and energy consumption, in particular considering the effect of surface curvature on machining energy consumption.

Low-yield-strength (LYS) steels possess ultra-high ductility and low yield ratio which indicates a wide prospect of the application for energy absorption. When a LYS steel-based damper or buffer is activated by a seismic wave or a crash impact, the structural integrity usually has a high risk of failure. Hence, the fracture resistance of LYS steels should be a key parameter for their structural design and integrity assessment. Here, we report both an experimental and a numerical investigation on the fracture behavior of an LYS steel with the yield stress of 100 MPa (LYS100), where a part-through corner or surface crack is machined in specimens and the critical loading capacities of the specimens are determined by our experiments. The suitable material parameters of the extended finite element method for LYS100 are determined based on our experimental results, which can be used to describe the fracture behavior of LYS100. Our results show that the fracture toughness of LYS100 can be up to around 1019 N/mm, which is almost twice as high as that of Q235 and one order bigger than that of gray cast iron. These findings will be a great help toward understanding the fracture properties of LYS steels and designing high-performance damping structures.

Truncated carbon nanocones (CNCs) can be taken as energy suppliers because of their special structures. In this paper, we demonstrate the stability of truncated CNCs under compression and the escape behavior of a fullerene catapulted from a compressed CNC by molecular dynamics simulations and theoretical models. The strain energy of a CNC and cohesive energy between a fullerene and the CNC (due to their van der Waals interactions) dominate the stability and catapulting capability of the cone, which strongly depend on geometrical parameters (apex angle, top radius and height) of each CNC and axial distances between them. In particular, the additional transverse vibration of buckled CNCs after released plays a significant role in their catapulting abilities and efficiencies. Finally, finite element method and experiments are further performed to validate the escape mechanism. This study should be of great importance to providing a theoretical support for designing novel nanodevices in mico/nanoelectromechanical systems.

Interfacial water has been estimated to mediate the thermal coupling at the interface between biological tissues and graphene/graphene oxide (GO)-based bio-nano devices, while the interfacial energy transfer is limited by the extreme thermal resistance between graphene and water due to the inherent vibration mismatch and the weak interaction. Oxygen-containing functional groups on the surface of GO form hydrogen bonds (H-bonds) with water, which enhances interfacial interaction and promotes thermal transport at the interface, thereby GO/water model is used to investigate the effects of H-bonds on the thermal boundary conductance (TBC). The results reveal that both the density and distribution of hydroxyl groups affect the interfacial H-bonds and further affect the thermal transport at interface. TBC increases initially with the increased H-bond density and then reaches a plateau when H-bond density reaches saturation. The homogeneously distributed hydroxyl groups form more H-bonds with water molecules than the clustered pattern, and results in more efficient interfacial thermal transfer. The variation of TBC with oxidation concentration can be explained by the mass density depletion length and the density of interfacial H-bonds. Our study highlighted the key role of H-bonds in regulating interfacial thermal transfer and provides theoretical basis and guiding methodology for thermal dissipation of graphene and GO-based bioelectronic devices.

Purpose The purpose of this paper is to provide additive manufacturing-based solutions for preparation of elastomeric foam with broaden compressive stress plateau. Design/methodology/approach Mechanic models are developed for obtaining designs of foam cell units with enhanced elastic buckling. An experimental approach is taken to fabricate the foams based on direct ink writing technique. Experimental and simulation data are collected to assist understanding of our proposals and solutions. Findings A simple tetragonal structured elastomeric foam is proposed and fabricated by direct ink writing, in which its cell unit is theoretically designed by repeating every four filament layers. The foam exhibits a broader stress plateau, because of the pronounced elastic buckling under compressive loading as predicted by the authors’ mechanic modeling. A two-stage stress plateaus as observed in the foam, being attributed to the dual elastic buckling of the cell units along two lateral directions of the XY plane during compression. Research limitations/implications Future work should incorporate more microscopic parameters to tune the elastomeric foam for mechanic performance testing on linear elastic deformation and densification of polymer matrix. Practical implications Additive manufacturing offers an alternative to fabricate elastomeric foam with controlled cell unit design and therefore mechanics. Our results comment on its broad space for development such superior cushioning or damping material in the fields of vibration and energy absorption. Originality/value This work has contributed to new knowledge on preparation of high performance elastomeric foam by providing a better understanding on its cell structure, being printed using direct ink writing machines.

In this paper, we present a new constitutive model to estimate the effective mechanical behaviors of the incompressible neo-Hookean materials with randomly distributed spherical voids under finite deformations. The volumetric multiplicative decomposition is employed to decompose the deformation gradient of a general finite deformation into the corresponding hydrostatic and isochoric part. By deriving and then superposing the strain energy density functions of the hydrostatic and isochoric deformation, we deduce the constitutive model of the porous neo-Hookean materials. The cubic units, which are randomly embedded with equal-sized spherical voids, are constructed as the representative volume element (RVE) models to numerically validate the proposed constitutive model. Various finite deformations are simulated and all the numerical results show that the proposed constitutive model can offer good estimates on the effective mechanical behaviors of the porous neo-Hookean materials. The constitutive model developed by Danielsson et al. (2004) is studied and compared with our model. The results suggest that our model can better capture the comprehensive mechanical behaviors of the porous neo-Hookean materials than the DPB model. The strain energy density function proposed is assessed to be strongly elliptic, which implies the macroscopic mechanical stability of the porous materials.

The thickness- and chirality-dependent mixed-mode I-II critical stress strength factors (SIFs) and crack growth angles of single-crystal silicon (SCS) [10 0] and [1 1 0] plates are investigated using molecular dynamics (MD) simulations and finite element (FE) method based on the boundary layer model, respectively. The silicon-silicon (Si Si) bond in the FE method is modeled as a nonlinear Timoshenko beam based on the Tersoff potential (T3) for the first time, where all the parameters of the nonlinear beam are completely determined based on the continuum modeling. The present MD and FE results show that both critical SIFs and crack growth angles obviously depend on chiral angles, thicknesses and loading angles of SCS plates. Our FE results agree well with those from present MD simulations using the modified Tersoff potential. Checking against the SIFs of available results shows that present MD and FE results are reasonable. This study should be of great help for understanding thickness- and chirality-dependent fracture properties of SCS and designing silicon-based nanodevices.

Efficient and sustainable use of water-based lubricants is essential for energy efficiency. Therefore, the use of water-lubricated mechanical systems instead of conventional oil lubricants is extremely attractive from the viewpoint of resource conservation. In this study, water-soluble Cu nanoparticles of size approximately 3 nm were prepared at room temperature (around 25 °C) via in-situ surface modification. The tribological behavior of the as-synthesized Cu nanoparticles as an additive in distilled water was evaluated using a universal micro-tribotester. The results show that the as-synthesized Cu nanoparticles, as a water-based lubricant additive, can significantly improve the tribological properties of distilled water. In particular, the lowest friction coefficient of 0.06 was obtained via lubrication with a concentration of 0.6 wt% of Cu nanoparticles in distilled water, which is a reduction of 80.6% compared with that obtained via lubrication with distilled water alone. It is considered that some Cu nanoparticles entered the contact area of the friction pairs to form a complex lubricating film and prevent direct contact of the friction pairs. Furthermore, some Cu nanoparticles in the solution accelerate the heat transfer process, which also results in good tribological properties.

The dynamic crack growth in a full-scale gas pipeline of API X80 steel is analyzed using the finite element method with the cohesive zone model. Based on the simulation, it is revealed that for the moderate steady-state crack growth, the crack-tip-opening angle strongly depends on the crack growth speed. In addition, the threshold initial crack sizes under different internal pressures are analyzed, which show a significant three-dimensional effect due to the wall thickness of the pipeline. The presented model offers a feasible way to study some details of the dynamic fracture of full-scale pipelines when tests are difficult or expensive.

A closed-form expression of the interface strength between a fiber and a matrix is obtained using a continuum approach based on van der Waals interactions. The explicit solution of the interface delamination of fiber-reinforced composites with functionally graded interphase under three-dimensional load is derived. The present analytical results indicate that the delamination behavior of the fiber-reinforced composites highly depends upon the interphase thickness, the fiber radius, the Young's moduli and Poisson's ratio of the fiber and the matrix. The present analytical solution provides a sufficient support for the later research on the mechanical behaviors of fiber-reinforced composites and finally for developing new micro-composites.

Elastic T -stress and stress intensity factor (SIF) solutions for through-wall-cracked pipes under internal pressures have been investigated by three-dimensional (3D) finite element (FE) calculations. The distribution of normalized SIFs (mode I K I and mode II K II ) and T -stresses along the crack front for different crack lengths, crack orientations, thickness ratios and Poisson's ratios has been obtained in detail. Our FE results show that the T -stresses increase with increasing Poisson's ratio and crack angle, respectively. The normalized K I increases while K II decreases with increasing Poisson's ratio, respectively. The normalized K I decreases with increasing crack angle, while K II increases with increasing crack angle from 0° to 45° and then decreases from 45° to 90°. Finally, the empirical formulae of the three-parameter K I , K II and T -stress have been derived by fitting present FE results with the least-squares method for the convenience of engineering applications.

The loading direction-dependent shear behavior of single-layer chiral graphene sheets at different temperatures is studied by molecular dynamics (MD) simulations. Our results show that the shear properties (such as shear stress–strain curves, buckling strains, and failure strains) of chiral graphene sheets strongly depend on the loading direction due to the structural asymmetry. The maximum values of both the critical buckling shear strain and the failure strain under positive shear deformation can be around 1.4 times higher than those under negative shear deformation. For a given chiral graphene sheet, both its failure strain and failure stress decrease with increasing temperature. In particular, the amplitude to wavelength ratio of wrinkles for different chiral graphene sheets under shear deformation using present MD simulations agrees well with that from the existing theory. These findings provide physical insights into the origins of the loading direction-dependent shear behavior of chiral graphene sheets and their potential applications in nanodevices.

The increasing penetration of intermittent renewable energy has introduced great risks to energy systems and markets. As a result, extensive research on energy storage systems (ESS) has been undertaken to address the risks caused by renewable energy. Among different types of ESSs, the power-to-gas (P2G) storage devices are of great potential. Thus, P2G has been used in this paper as a storage device to provide gas fuel for gas power generators. The aim of this paper is to investigate a portfolio strategy for gas generators to earn profits and hedge risks in three different electricity markets, namely, the spot, the ancillary, and the financial markets. The presented approach is to apply energy storage and financial derivatives to hedge the market risks of gas generators, including short put option and short call option, and the option value deduction process is also involved. Simulations are carried out based on the real historical data from 2016 to 2018 in Australian electricity markets. Three cases are presented, namely, the traditional model, the individual market case, and the proposed portfolio model. Based on the comparison of the three cases, simulation results show that the proposed portfolio model will help gas generators to earn a return of 1.0429 and hedge risks down to 0.0018. It has been found that the returns of the proposed model from 2016 to 2018 are 26.3% higher, whereas the risks are 88.1% lower on average comparing with the traditional model and the individual market case.

In this paper, water-soluble CuS nanoparticles as water-based lubricant additives were synthesized by a simple surface modification method. Bis (2-hydroxyethyl) dithiocarbamic acid (HDA) was used as a modifier to ensure water solubility of nanoparticles, also acted as a reactant to offer sulfur source in this synthesis reaction of CuS. The tribological properties and thermal conductivity of as-prepared CuS nanoparticles modified by HDA (HDA-CuS) in distilled water were studied using UMT-2 micro friction tester and thermal conductivity meter. The results show that the as-prepared HDA-CuS nanoparticles can effectively improve the tribological behaviors and coefficient of thermal conductivity of distilled water. When the additive concentration is 0.8 wt%, the friction coefficient and wear rate are reduced by 78.3% and 93.7%, respectively, and the coefficient of thermal conductivity can be increased by 3%. The three-dimensional surface profiler, scanning electron microscope, and X-ray photoelectron spectroscopy were used to analyze the worn surface. It was found that a complex lubricating film was generated on the surface of the friction pairs during the friction process.

As an important way of addressing energy and environmental challenges, the market share of wind power generation has increased dramatically in the past decade and has introduced significant challenges to power system operation. In this article, the tail correlation between multiple wind farms is studied. The joint probability distribution of multiple wind farms is estimated by employing the Gumbel copula function. Based on the estimated joint probability distribution, a stochastic optimal dispatch model is proposed to take into account the chance constraints of energy utilization from multiple wind farms in the power system. The sample average approximation method is employed to handle the chance constraints in the proposed model, so as to transform stochastic optimal dispatch into a deterministic non-linear optimization problem. The quantum-inspired evolutionary algorithm is used to solve the proposed model. The proposed model and algorithm are tested with comprehensive case studies to demonstrat...

Buckling behaviors of single-walled carbon nanotubes (SWCNTs) inserted with a linear carbon-atom chain (CAC) (the composite structures are also called carbon nanowires (CNWs)) under torsion and bending as well as compression are studied using molecular dynamics (MD) simulations, respectively. Our MD results show that the critical buckling angles (or strains) of CNWs under the three presented kinds of loading patterns can be two times those of corresponding independent SWCNTs for long CNWs, while the buckling improvement is not obvious for short ones. The main reason is that the radial van der Waals force between the CAC and the SWCNT is very small for a short CNW, while it increases with increasing length and then tends to a constant for a long CNW. The obtained MD results agree well with those from available theoretical models. These findings will be a great help towards understanding the stability and reliability of the special CNT structures, and designing flexible CNT-based devices.

Surfactant-free and binder-free antimony-doped tin oxide (ATO) transparent conducting thin films were fabricated through spin coating and rapid annealing processes, in which nanosheets were assembled into a compact structure via self-contracting high pressure. The mechanism of this compact thin film formation was further proposed and analyzed. The compact ATO thin film had a low root mean square (RMS) roughness of 5.03 nm. This surfactant-free and binder-free compact ATO thin film delivered low resistivity of 3.04 × 10−2 Ω cm, stable resistivity which only increased 13% after exposing in 65% RH air for half a month, high transmittance of 92.70% at 550 nm, and high band gap energy of 4.07 eV. This effective strategy will provide new insight into the synthesis of low-cost and high-performance compact thin films.

A nonlinear continuum model of van der Waals interactions is established to relate the size-dependent nonlinear properties of crystalline polyethylene. The explicit formulas are derived from the Lennard-Jones potential function for the van der Waals force between any two polymer chains. The present results are in reasonable agreement with those from present united-atom molecular dynamics simulations. This work is a new effort to establish nonlinear analytical models of molecular mechanics for crystalline polymers, and it should be helpful to provide an efficient route for mechanical characterization of crystalline polymers and related materials.

We develop the coarse-grained (CG) potentials of single-walled carbon nanotubes (SWCNTs) in CNT bundles and buckypaper for the study of the static and dynamic behaviors. The explicit expressions of the CG stretching, bending and torsion potentials for the nanotubes are obtained by the stick-spiral and the beam models, respectively. The non-bonded CG potentials between two different CG beads are derived from analytical results based on the cohesive energy between two parallel and crossing SWCNTs from the van der Waals interactions. We show that the CG model is applicable to large deformations of complex CNT systems by combining the bonded potentials with non-bonded potentials. Checking against full atom molecular dynamics calculations and our analytical results shows that the present CG potentials have high accuracy. The established CG potentials are used to study the mechanical properties of the CNT bundles and buckypaper efficiently at minor computational cost, which shows great potential for the design of micro- and nanomechanical devices and systems.

Nanoscale defects (such as cracks, holes) often occur in graphene nanoribbons (GNRs). However, it is still a big challenge to accurately predict crack-hole interactions in them. In this study, the nanocale crack-hole interactions in chiral GNRs are investigated under mode-I loading using molecular dynamics (MD) simulations and finite element (FE) analysis. The carbon-carbon (C C) bond in the FE method is modeled as a nonlinear Timoshenko beam based on the full-atom Reactive Empirical Bond-Order interatomic potential of second generation (REBO potential) for the first time. The present MD and FE results show that the shielding effects on the crack tip stress field are dominated by the angle is θ, the hole-to-crack tip spacing r and the chirality of the GNRs. Checking against the linear-elastic fracture mechanics (LEFM) predictions of some crack-hole configurations shows that the present FE method and MD simulations have high accuracy. This study should be of great help for understanding nanoscale crack-hole interactions in GNRs and providing physical insights into the origins of defect engineering of GNRs.

The main advantages of the direct ink write (DIW) printed strain gauge are capable of achieving both the high sensitivity and the large stretchability. The performance of the DIW-printed strain gauge is mainly determined by the design parameters and fabrication process . However, it is still a big challenge for parametric design and precision manufacturing of the DIW-printed strain gauge due to the lack of universal analytical model and optimized process parameters. Here we propose an analytical model for designing widely used sandwich-structure strain gauges with coating-filament-base layers on substrates. The resistive strain gauges with a commercial carbon paste are fabricated by the DIW technology on polyimide and aluminium alloy substrates, respectively. Both its high sensitivity and large stretchability are designed from the present analytical model and reproduced well by the DIW-based fabrication. Our analytical model and DIW-based fabrication will be of great help for designing and fabricating other sandwich-structure gauges.

The failure modes of ZnO nanowires (NWs) with hexagonal cross section subjected to a uniaxial load are systematically investigated by using molecular dynamics (MD) simulations and two theoretical models considering the surface effect. Our results show that two different failure modes of the phase transition and buckling are triggered when the NWs are under uniaxial compression along the [0001] direction, in which the transformation between the two modes is related to the slenderness ratios of the NWs. Such slenderness-ratio-dependent mode transformation is mainly attributed to the competition between the critical stresses of phase transition and buckling. The Euler and Timoshenko models considering surface effect are further proposed to derive the critical slenderness for such mode transformation. The obtained analytical threshold values agree well with those of present MD simulations. Our results should be of great help for shedding some light on the design and application of functional devices based on ZnO NWs.

A complete three-parameter K–T–Tz description of the mixed-mode I/II three-dimensional (3D) crack-tip stress fields has been proposed, in which the stress intensity factor K, T-stress and out-of-plane constraint factor Tz around mix-mode I/II crack front in compact-tension-shear specimens are all the functions of the Poisson ratio v, thickness ratio zB and load angle φ. By fitting the numerical results with the least squares method, empirical formulae have been obtained to accurately describe the 3D distributions of the three parameters for the convenience of engineering applications, which can be used to characterize the 3D crack-tip stress fields completely and establish the three-parameter dominated stress fields.

In this study the frictionless contact of a power-law hardening elastic–plastic sphere in contact with a rigid flat has been investigated by the finite element method. The strain hardening exponent n varied from 0 to 1, with material properties changing from elastic–perfectly plastic to elastic. Parameters such as contact load, contact area under both loading and unloading have been calculated for a wide range of contact interferences. Based on the finite element results, analytical and dimensionless expressions of these contact parameters versus the contact interferences during loading have been presented. In addition, the load–deformation equations at unloading and the residual interference after complete unloading for a large range of maximum interferences are given.

Pristine and Al-doped zinc oxide nanopowders were synthesized via a surfactant-assisted complex sol-gel method, possessing a pure ZnO phase structure and controllable grain size which was characterized by X-ray diffraction and scanning electron microscopy. Using these nanopowders, the pristine and Al-doped ZnO magnetron sputtering targets were prepared following a mold-press, cold isostatical-press and schedule sintering temperature procedure. The relative density of these as-prepared targets was tested by Archimedes’ method on densitometer. All of the results were above 95 theory density percents, and the resistivity was tested on four-probe system at a magnitude of 10-2Ω cm. Related pristine ZnO thin films and Al-doped ZnO thin films were fabricated by magnetron sputtering method, respectively. The pristine and Al-doped ZnO films deposited on the quartz glass by dc sputtering owned a (002) orientation with a thickness of 350 nm at a deposition power of 100 W for two hours under an argon plasma. A good optical transparency above 80% and low resistivity of 1.60×10-3Ω cm were obtained with a deposition temperature of 573 K. The optical energy bandgap could be tailored by Al doping at 4 at.% Al.

In this paper, hierarchical Sn3O4 microflowers self-assembled by nanosheets were successfully synthesized via a simple one-pot hydrothermal route. The crystalline phase and morphology of the as-prepared sample were characterized using X-ray diffraction, field-emission scanning electron microscope and transmission electron microscope. UV-vis absorbance and Raman scattering behavior of the Sn3O4 microflowers were also investigated. Electronic density of states calculation using DFT method revealed that the upper valance band of Sn3O4 was dominated by O 2p. (C) 2014 Elsevier B.V. All rights reserved.