Advanced Materials Research Vols. 79-82

Abstract: Numerical simulation of dense-phase pneumatic conveying flow field was carried out by using k-ε-ks-εs two-fluid model in horizontal pipe on the basis of kinetic theory of granular flow. The coupling issue between gas phase and solid phase was taken into account in the process of simulation. Such characteristics of flow field along pipe as pressure distribution, concentration distribution, gas and particle velocity distribution were obtained. The results of numerical simulation showed the tends of pressure, gas velocity, particle concentration in pipeline. The results of numerical simulation were compared with experimental results, and it showed that the simulation results were validated by the experimental data, which indicate that the model and the corresponding algorithm have higher accuracy and better prediction. Thus the numerical simulation method can reveal the basic characteristics of dense phase pneumatic conveying in horizontal pipe.

Abstract: Molecular simulations of the interfacial properties of (1) a composite with an epoxy(EP) matrix and a carbon nanotube(CNT)/carbon fiber(CF) multi-scale reinforcement and (2) a traditional CF/EP composite were performed employing Materials Studio 4.0 software. Results indicate that the interfacial atom concentration of material 1 is higher that that of material 2 by interfacial molecular structure analysis, and there are many benzene rings in both material 1 and material 2 which are parallel to the crystal layers of CF. The contact layer thickness of material 1 and material 2 is 0.25 and 0.10 nm, respectively. The concentration distribution calculation of EP molecules in the interface shows that the most concentrated part of EP in material 2 appears in the carry-forward area of the contact layer, while it is more close to the contact layer in material 1.

Abstract: This paper presents research work relating to design method and mechanical properties of functionally-graded composite (FGC) beams, in which a kind of strain hardening material UHTCC is used as a replacement for the concrete material that surrounds the longitudinal reinforcements. According to mechanical models of materials and a series of assumptions, a simplified design method of such FGC beams is proposed. On the basis of superposition, the determination and the influencing factors of the thickness of UHTCC layer in FGC beams is discussed. Compared with theoretical and experimental results, simplified method shows conservation and guarantees the safety of structures. During the whole flexural loading process, it is found that the opening of cracks in flexural members can be greatly restricted by the introduction of UHTCC. The possibility of steel corrosion therefore can be evidently reduced.

Abstract: In this study, finite element analysis was made to predict the tensile and compressive behaviors of aluminum foam material. The predicted tensile and compressive behaviors were compared with those determined from the tensile and compressive tests. X-ray imaging technique was used to determine internal structure of aluminum foam material. That is, X-ray computed tomography (CT) was used to model the porosities of the material. Three-dimensional finite element modeling was made by stacking two-dimensional tomography of aluminum foam material determined from CT images. The stackings of CT images were processed by three-dimensional modeling program. The results showed that the tensile stress-strain curve predicted from the finite element analysis was similar to that determined by the experiment. The simulated compressive stress-strain curve also showed similar tendency with that of experiment up to about 0.4 strain but exhibited a different behavior from the experimental one after 0.4 strain. The discrepancy of compressive stress-strain curves in a high strain range was associated with the contact of aluminum foam walls broken by the large deformation.

Abstract: Functionally graded materials (FGMs) have recently been fabricated under gradient magnetic fields via slip casting, based on the distinct difference in magnetic susceptibility between the components in a suspension comprised of both magnetic particles (MPs) and nonmagnetic particles (NPs). In this work, a physical model of a mixed suspension comprised of both MPs and NPs under a gradient magnetic field is built, base on which the distributions of particles in the suspension under gradient magnetic fields are studied using two-dimensional Monte Carlo simulations, and the effects of magnetic field gradient on the distributions of particles are investigated. The results show that a gradient distribution of MPs is formed along field direction, which is attributed to the translation of MPs. As the magnetic field gradient is increased, the distribution gradient of MPs increases.

Abstract: In this paper, the dynamic characteristic of an ionic polymer-metal composite (IPMC) cantilevered beam near resonant frequencies is investigated. A dynamic model is formulated on the basis of beam vibration, charge distribution and charge interactions. Experimental tests are conducted with an IPMC cantilevered beam actuated in frequency domain. Comparison with experimental results shows that the theoretical model is able to predict the dynamic responses of IPMC near resonant frequencies.

Abstract: Molecular simulation can provide mechanism insights into how material behaviour related to molecular properties and microscopic details of the arrangement of many molecules. With the development of Graphics Processing Unit (GPU), scientists have realized general purpose molecular simulations on GPU and the Common Unified Device Architecture (CUDA) environment. In this paper, we provided a brief overview of molecular simulation and CUDA, introduced the recent achievements in molecular simulation based on GPU in material science, mainly about Monte Carlo method and Molecular Dynamics. The recent research achievements have shown that GPUs can provide unprecedented computational power for scientific applications. With optimized algorithms and program codes, a single GPU can provide a performance equivalent to that of a distributed computer cluster. So, study of molecular simulations based on GPU will accelerate the development of material science in the future.

Abstract: This paper deals with nonlinear finite element analysis of smart structures with integrated piezoelectric layers. Two geometrically nonlinear finite plate elements incorporating piezoelectric layers are applied based either on first- or third-order transverse shear deformation theory. Nonlinear strain-displacement relations are used that are valid for small strains and moderate rotations. Numerical tests are performed for the time histories of the tip displacement and sensor output voltage of a thin beam with a piezoelectric patch bonded to the surface.

Abstract: Modeling of Pd/ZnO Schottky diode has been performed together with a set of simulations to investigate its behavior in current-voltage characteristics. The diode was first fabricated and then the simulations were performed to match the IV curves to investigate the possible defects and their states in the bandgap. The doping concentration measured by capacitance-voltage is 3.4 x 1017 cm-3. The Schottky diode is simulated at room temperature and the effective barrier height is determined from current voltage characteristics both by measurements and simulations and it was found to be 0.68eV. The ideality factor obtained from simulated results is 1.06-2.04 which indicates that the transport mechanism is thermionic. It was found that the recombination current in the depletion region is responsible for deviation of experimental values from the ideal thermionic model deployed by the simulator.

Abstract: Diamond-like carbon (DLC) films have attracted great interest due to their outstanding mechanical, biocompatibility, thermal, optical and electrical properties. The DLC films can be produced by microwave plasma chemical vapor deposition (MPCVD) using Argon, methane and hydrogen mixed gases. The film properties depend strongly on the experimental parameters such as substrate temperatures; microwave power, process pressure and hydrogen concentration (H2/Ar+CH4+H2). In this study, the properties of nanomechanics of DLC films with various experimental parameters are firstly discussed which include hardness and Young’s modulus characterizing by depth-sensing nanoindentation technique. The nanoindentation is an excellent method for measuring nanomechanical properties of both bulk and thin films. The probe was conducted using a Berkovich diamond tip. To find the optimized process parameters, the statistical and mathematical response surface methodology (RSM) is used to model and analyze the effect of substrate temperature (T), microwave power (W), process pressure (P) and hydrogen concentration (H) on the properties of nanomechanics of DLC films. The central composite experimental design (CCD) is used to evaluate the interaction parametric effects of multiple experimental variables on process response (hardness and Young’s modulus). The predictive quadratic model proposed herein considering the analysis of variance (ANOVA) are proved to fit and predict values of the hardness and Young’s modulus close to those readings recorded experimentally. The most significant influential factors for maximizing the hardness and Young’s modulus have been identified from the ANOVA table. The RSM technique is demonstrated to be a powerful tool in exploration of the manufacturing parameters space of complex physical process of DLC films deposition by MPCVD.