Applied Mechanics and Materials Vols. 764-765

Abstract: Capture and reforming fume gases from atmosphere became an ultimate task recently. Photocatalytic reduction to useful compounds is a key to the future. Photoinduced reduction of carbon dioxide and ammonia aqueous solution into amine compounds at room temperature and atmospheric pressure using transition metal doped titanium dioxide is reported in this paper. UV-visible spectra showed a high absorbance at 200 nm wavelength which is a characteristic of urea. High Performance Liquid Chromatography revealed presence of amine compounds and urea was found a main product of photocatalytic reaction.

Abstract: Present study investigates the microstructural evolution and in-situ formation of Ti/(TiB+TiC) composite. The sintered compacts are having near theoretical density. The relative density of Ti/(TiB+TiC) composites decreases with increasing TiB and TiC content.The phase evolutions of TiB and TiC according to the in-situ reactions are analyzed by X-Ray diffraction technique (XRD). Optical microscope (OM) and Energy dispersive spectroscope (EDS) observations of the Ti/(TiB+TiC) composites shows the presence of TiC and TiB reinforcements as equiaxed and needle like structures respectively.

Abstract: In this study, texture evolution during high pressure torsion (HPT) of aluminum single crystal is predicted by the crystal plasticity finite element method (CPFEM) model integrating the crystal plasticity constitutive theory with Bassani & Wu hardening model. It has been found by the simulation that, during the HPT process, the lattice rotates mainly around the radial direction of the sample. With increasing HPT deformation, the initial cube orientation rotates progressively to the rotated cube orientation, and then to the C component of ideal torsion texture which could be remained over a wide strain range. Further HPT deformation leads to the orientation towards to the ideal texture component.

Abstract: Retaining pins are generally used as the parts of automobile gears, axes, crankshafts, and seat belts, which are proceeded three-stage forming and then drilling processing in the original manufacturing procedure. However, the fixture seizing in the drilling processing could result in rod surface damage and dent, and the depth tolerance exceeding the drawing specifications after the drilling causes the major defects in product manufacturing. This study attempts to modify the cold forging process by adding one stage and replacing the original mechanical drilling processing with backward extrusion and forging engineering. In the research process, Finite Element Method is utilized for analyzing and simulating the forming load at each stage. The analysis results show that increasing the original 3-stage forging process to 4-stage could assist in solving the problems of rod dent and depth tolerance exceeding the drawing specifications after the drilling. Although the die cost would increase with an increasing stage, the new process allows the forging force being more even and the die life being prolonged, in consideration of the overall production costs.

Abstract: Polymer/Carbon nanotube nanocomposites have attracted major research and commercial interests due to their superior mechanical and electrical properties. Characterizing mechanical properties of these nanocomposites has been always a challenge. The present study is to develop representative volume element method for modeling of nanoindentation behavior of Epoxy/Single wall carbon nanotubes (SWCNTs) nanocomposites that have nonlinear elastic reponse using finite element analysis. A series of two dimensional simulations were done to obtain stress-strain curve and load-displacement response of elastic-plastic material. The results indicated that the nanoindentation finite element models were able to simulate the loading-unloading responses of the Epoxy/SWCNTs nanocomposites. Besides, the relative influences on the load-displacement response are investigated, including mesh geometry, indenter radius and friction coefficient. Furthermore, these simulated results show good agreement with experimental data from literature. The reasearch results are very useful for studying the nanosize scale material properties such as hardness as well as elastic modulus of Polymer/Carbon nanotube nanocomposite in the future.

Abstract: To maximize the fundamental frequency of composite laminates, a hybrid optimization algorithm which combines the respective merits of the genetic algorithm and the simulated annealing algorithm is adopted. This hybrid algorithm also incorporates adaptive mechanisms designed to adjust the probabilities of the cross-over and mutation operators. Then, this algorithm is applied to optimize the fiber angle of each layer of a composite laminate such that its fundamental natural frequency is maximized. The results indicate that this hybrid optimization algorithm could quickly find the optimal fiber angles and maximize the fundamental frequency, even under complicated choices of fiber angle and boundary conditions.

Abstract: The eutectic structure in Mg-6Gd-3.7Nd based alloy was characterized to be result of a 'quasibinary eutectic reaction' L→ α-Mg + β-Mg₅RE. The ST temperature applied was apparently sufficient to melt the GB regions of the as-cast Mg-Gd-Nd based alloy, and transform the eutectic structures to a globular liquid phase enriched with RE elements. High supersaturation of Mg matrix by rare earth (RE) elements after quenching of solution treated Mg-Gd-Nd alloy provides sequential precipitation of different metastable phases: α-Mg (S.S.S.S.) → β'' (Mg₃RE, DO₁₉)→ β' (Mg₇RE, BCO) → β₁ (Mg₃RE, FCC) → β (Mg₅RE, FCC). The stable β precipitates grew from the eutectic structure in the form of needle-like precipitates. These needles seem to be a continuation of the β phase presented in the eutectic structure. These β precipitates grow at the expense of smaller β₁ and β precipitates presented in the α-Mg matrix. The combination of HRTEM, TEM with SAED and JEMS simulation was carried out to characterize the nanometer-scale precipitates. Microhardness measurements were performed to reveal the effect of precipitation on the mechanical properties of the alloys.

Abstract: The testing of functional properties of asphalt mixtures started in Czech Republic already in 1976, when the first device for the determination of stiffness modulus was put into operation. At the moment Czech Republic is one of the 5 EU-countries, where the standards for functional testing have been introduced and where the compact system with various functional tests exists. The presented paper shows the practical use of the newly introduced above mentioned functional tests. The paper describes the results of an experiment, in which the change of chosen functional parameters of asphalt mixture was investigated by adding of two additives. These additives enable the reduction of production temperatures of these mixtures.

Abstract: In this work, metal/oxide/metal capacitors were fabricated and investigated using transparent boron-doped zinc oxide (ZnO:B) films for nonvolatile memory applications. Both top and bottom electrodes are tungsten. The average value of transmittance of ZnO:B films grown on silicon substrates is found to be about 91% in the visible light region. According to the relationship between transmittance and wavelength, the optical band gap of ZnO:B films is determined to be about 3.26 eV. The temperature dependent current-voltage curves show that the current density increases with increasing temperature in low-resistance state (LRS), meanwhile, the current density decreases with increasing temperature in high-resistance state (HRS). From the resistive switching behavior of the W/ZnO:B/W memory devices, the reset voltage which triggers the memory devices from an LRS to an HRS is independent of temperature. On the other hand, the set voltage which triggers the memory devices from an HRS to an LRS is increased with temperature.

Abstract: Arthrospira (Spirulina) platensis contains large quantities of γ-linolenic acid (GLA). GLA is an essential omega-6 unsaturated fatty acid made in the human body from linoleic acid. It can be metabolized to various important eicosanoids such as prostaglandins, thromboxanes, leukotrienes, prostacyclins, and lipoxins. The aim of this study was to investigate the optimal extraction parameters of GLA from A. platensis using supercritical CO₂ technology. Results showed that operating temperatures and pressures were important factors in the extraction of GLA. A maximum GLA yield of 161.98 μg/g could be obtained at a pressure of 30 MPa, a temperature of 60°C, and a CO₂ flow rate of 6 mL/min. Conversely, only a yield of 104.16 μg/g could be obtained at a pressure of 10 MPa, a temperature of 40°C, and a CO₂ flow rate of 6 mL/min. The correlation between pressure and yield could be explained by an increase in collision rates between CO₂ molecules and carrier affinity under a high pressure. Therefore, an operating temperature between 50 and 60°C and a pressure of 30 MPa should be used to maximize the yield of GLA from A. platensis using supercritical CO₂ technology.