1,724,739 research outputs found
The effect of poling treatment and crystal structure of PZT on fracture toughness and fatigue resistance
No full textEmpirical measurements of fracture toughness and fatigue strength were conducted for piezoelectric Pb(Zr-x,Ti1-x)O-3 of various compositions such as tetragonal, MPB, and rhombohedral. Before the poling treatment the rhombohedral showed the highest fracture toughness, while the tetragonal revealed the lowest fracture toughness. After poling treatment, the fracture toughness measured by the pre-cracked SENB method decreased in all three compositions. The most remarkable decrease was observed in the tetragonal composition. However, when the indentation strength method was used the highest fracture toughness was observed in the tetragonal. The stress intensity factor relief due to microcracks around the indentation marks and the anisotropic internal stresses caused by domain alignment during the poling treatment were proposed as explanations for the comflicting results. Fatigue resistance was lowered by the compressive stress introduced during the poling treatment. The highest fatigue resistance was observed in the rhombohedral composition of low tetragonality, which exhibited low internal stress. (C) 2003 Kluwer Academic Publishers.X113sciescopu
AEROELASTIC ANALYSIS OF A FLEXIBLE CONTROL SURFACE WITH STRUCTURAL NONLINEARITY
No full textThis article is concerned with a time domain approach to the nutter analysis of a night vehicle control surface with concentrated nonlinearities, In this study, an elastic model of a control surface with root freeplay nonlinearity in pitch is considered. A finite element structural model is used for structural analysis and a doublet lattice unsteady aerodynamic model is used for the calculation of aerodynamic loads, In approximating the frequency domain aerodynamic forces, the least-square rational function approximating method is used with an optimizing algorithm, To transform the frequency domain aerodynamic forces to the time domain forces, the method of Brace and Eversman is used. To reduce the problem size and the computation time, the fictitious mass modal approach is used, which can afford the possible local change of structural properties, The effects of the initial conditions and the magnitude of nonlinearity on the aeroelastic characteristics are examined. The aeroelastic responses are sensitive to initial conditions, Limit cycle oscillation and chaotic motion are observed in this study. The presence of freeplay makes the divergent nutter speeds larger than those of a linear case.
Phase-shifted transmission/reflection-type hybrid extrinsic Fabry-Perot interferometric optical fiber sensors
No full textConventional interferometric optical fiber sensors, including the extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensor, have the drawback of ambiguous measurement directions and direction changes, because their signal processing using only fringe counting cannot present measurement direction information, such as tension/compression of strain or increment/decrement of temperature. An EFPI optical fiber sensor constructed with a transmission-type structure (TEFPI optical fiber sensor) can successfully compensate for this problem. However, it has low interferometric fringe visibility and requires somewhat sophisticated signal processing to detect the measurement direction changes. In this research, a hybrid EFPI optical fiber sensor is presented from which transmission-type and reflection-type sensor signals can be simultaneously acquired. The linear combination of the actual transmission-type and reflection-type signals is shown to have a shifted phase from the reflection-type signal according to measurement directions, and thus the phase behavior of lead/lag can present the measurement direction information. Because the hybrid sensor uses separated signals for the measurement quantity and direction, its signal processing is more robust than that of the TEFPI sensor. The sensor and signal processing algorithm were verified with the strain. measurement experiments
Optimum finite element for simulation of elasto-plastic bending of sheet metal
No full textThis paper concerns the optimum condition of finite elements in simulation of elasto-plastic bending. The effect of the integration scheme and the number of finite element layers on calculation of the stress and the strain is thoroughly investigated and some remedies are suggested. As a benchmark problem, an elasto-plastic bending problem is studied for the calculation of the stress and the strain. The calculation directly estimates stress and strain distribution along the thickness direction and shows the oscillatory behavior of the stress and the incompatible behavior of the strain. The results fully demonstrate that the finite element simulation in the usual way is sometimes very dangerous since it could lead to a fatal pitfall. This study proposes the optimum condition of finite elements especially in simulation of elasto-plastic bending with a proper integration scheme
Effects of post-annealing temperature on structural, optical, and electrical properties of ZnO and Znl-xMgxO films by reactive RF magnetron sputtering
No full textZnO and Zn1-xMgxO thin films were deposited on (0 0 0 1) sapphire substrates by a reactive RF magnetron sputtering. The effect of post-annealing temperature on structural, optical, and electrical properties was investigated over the annealing temperatures from 400 to 800 degrees C. The crystallinity of ZnO film grown at 600 degrees C was significantly improved by annealing treatment while the film grown at 700 degrees C showed little improvement with annealing. The near band edge emission peak of ZnO films grown at 600 and 700 degrees C appeared at 3.26 eV after thermal annealing, which was not observable in as-grown film. The ratio of near band edge emission intensity to deep level emission intensity increased with annealing temperatures below 700 degrees C but thereafter decreased. The optical transmittance in the visible region was not influenced much by annealing treatment, showing around 85% for both as-grown and annealed films. The annealed ZnO films exhibited an n-type characteristics whereas high insulator characteristics were observed for as-grown samples. The superior carrier concentration, mobility, and resistivity were achieved with an annealing treatment. An optimum annealing treatment was found to be at 600 degrees C. The ZnO film grown at 600 degrees C followed by the optimum post annealing shows the most improved structural, optical, and electrical properties even better than those of the film grown at a higher growth temperature (700 degrees C) with post-annealing. With Mg doping into ZnO film, blue shift of 150-200 meV was observed, depending on the annealing temperature. The reactive RF magnetron sputtering coupled with an optimum annealing treatment would provide a promising and economically feasible method for optoelectronic device fabrication. (c) 2005 Elsevier B.V. All rights reserved.X1149sciescopu
Thermodynamic aspects of steel reoxidation behavior by the ladle slag system of CaO-MgO-SiO2-Al2O3-FetO-MnO-P2O5
No full textThe reoxidation behavior of steels by slag in the secondary steelmaking process was addressed by investigating the thermodynamic equilibria between the liquid iron containing Mn and P and CaO-MgO-SiO2-Al2O3-P2O5-MnO-FetO ladle slag at 1873 K. The activity coefficient of FetO shows a maximum value in the vicinity of the basicity ((X-CaO + X-MgO + X-MnO)/(X-SiO2 + X-Al2O3 + X-P2O5)) = 2.5 at the specific mole fraction range of FetO, while that of MnO seems to increase gradually with increasing the basicity. However, the values of gamma(FetO) and gamma(MnO) showed minima with respect to P2O5 content of slag. In addition, the values of gamma(FetO) and gamma(MnO) increased as (pct CaO)/(pct Al2O3) ratio increased at given SiO2, MgO, and P2O5 contents. The conversion equations between the FetO and MnO activities and their calculated activities via regular solution model were derived by the correlation between the measured and calculated activities over the limited ranges of FetO and MnO contents. The regular solution model was used to estimate the oxygen potential in the slag. For MgO saturated slags, a(FetO(l)) = 0.864a(FeO(R.S.)), a(Mno(l)) 6.38a(MnO(R.S)). For Al2O3 saturated slags, a(FetO(l)) =2.086(aFeO(R.S.)), a(MnO(l)), = 14.39a(MnO(R.S.)).open1115sciescopu
EFFECTS OF ION-BEAM IRRADIATION ON THE PROPERTIES AND EPITAXIAL-GROWTH OF ALUMINUM NITRIDE FILM BY THE ION-BEAM-ASSISTED DEPOSITION PROCESS
No full textAluminium nitride thin films were grown on Si(111) substrates by ion beam assisted deposition. Epitaxial growth of the AlN films was obtained at the low temperature of 450 degrees C. Characterization of the AlN epitaxial layer was carried out by grazing-incidence diffraction (GID) and high resolution transmission electron microscopy (HRTEM). GID analysis showed two kinds of epitaxial orientation between AlN epitaxial layer and Si substrate. An amorphous layer was observed at the interface between AlN film and Si by cross-sectional HRTEM analysis. The amorphous layer could release the misfit strain between the AlN film and the Si substrate in an early stage of growth. The AlN epitaxial layer formed despite the large lattice mismatch. In addition, the optical properties of AlN films including transmittance, energy band gap, and refractive index were determined and discussed.X1112sciescopu
Epitaxial growth of GaN using reactive neutrals extracted from the nitrogen Helicon wave plasma
No full textA GaN epilayer on sapphire (0001) was grown using the N-2 Helicon wave plasma assisted evaporation deposition process. Various methods to reduce the N-2 ion impingement energy were attempted. The addition of inert gas (Ar, Ne) into the N-2 plasma decreased the impingement of N-2 ions and generated a higher quantity of activated nitrogen. In addition, the installation of mirror-type magnets effectively reduced the ion impingement energy. Although the ion impingement energy was less than the threshold (similar to 25 eV) for damaging GaN, the high flux of ion impingement during the growth of GaN induced a considerable strain in the epilayer. GaN film synthesized under direct ion impingement onto the growing surface has poor luminescent properties, despite its relatively good crystallinity. When the neutral nitrogen was utilized for GaN epilayer growth, the crystallinity and luminescent properties were greatly improved. Furthermore, with the decreasing of kinetic energy of fast neutral nitrogen, the in-plane crystallinity of GaN was improved and thus, an enhancement of luminescent properties was attained. (C) 2000 American Vacuum Society. [S0734-2101(00)01906-0].open114sciescopu
The sulphide capacity of CaO-SiO2-Al2O3-MgO(-FeO) smelting reduction slags
No full textThe effects of MgO and FeO contents on the sulphide capacity of Corex slags were investigated at 1773 K using gas/slag equilibrium technique as a fundamental study for stabilising Corex operational conditions. The gradual substitution of MgO for CaO at a fixed basicity [B = {(%CaO)+(%MgO)}/(%SiO2)] decreased the sulphide capacities of CaO-SiO2-Al2O3-MgO slags. The addition of FeO into the CaO-SiO2-Al2O3-MgO slags at the fixed (%CaO)/(%SiO2) ratio, MgO and Al2O3 contents significantly increased the sulphide capacities. The sulphide capacity decreased according to the increasing Al2O3 content at the fixed (%CaO)/(%SiO2) ratio, MgO and FeO content. Based on the previously reported and present values of sulphide capacities, the sulphide capacity as a function of slag composition on the mole fraction base at 1773 K was expressed by the formula of log C-S = X-CaO - 3.89 X-SiO2 - 3.18 X-Al2O3 - 0.55 X-MgO + 2.43 X-FeO - 2.61. In addition, the relationship between the sulphide capacity and optical basicity could be represented as the formula of log C-S = 12.51 Lambda - 2.24 and the theoretical optical basicity of FeO was found be 0.94 from the correlation. The effect of FeO on the sulphur distribution ratio was estimated using the present sulphide capacity values and the oxygen activity in liquid iron, which could be determined with the help of Fe/FeO equilibrium. FeO activity in slag was well described by the quadratic formalism based on the regular solution model. The sulphur distribution ratio according to FeO content varies in an opposite way, compared with that of the sulphide capacity.X1119sciescopu
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