Applied Mechanics and Materials Vols. 284-287

Abstract: The Ti-6Al-4V alloy were solution heat-treated at 960°C for 1 hour and then cooling by water-quenching immediately and 2 bar argon atmosphere, respectively. After being aged at 550°C for 5 hours, the tensile and Charpy impact test were performed. Based on the results, it is found that the quantity of primary α grains will increasing with decreasing the cooling rate following the solution heat treatment, and which will result in the tensile strength and toughness decreasing. Moreover, the optical and SEM micrographs indicated that the cracks propagated with traversing the prior β grains and propagating along the primary α grain boundaries in both of the tensile and impact fractured specimens. This implies that the strength of α grain boundary is less than that of α grain, which will play an important role on the mechanical properties of tensile strength and toughness.

Abstract: Transparent conducting Al-doped ZnO (AZO) thin films were deposited on soda-lime glass substrates by DC magnetron sputtering with a sintered ceramic target, AZOY® that contains a small amount of Y2O3 in addition to Al2O3 and ZnO. The effect of substrate temperatures (Ts) on the structural, electrical and optical properties of the prepared AZO films was evaluated extensively. By elevating Ts, the electrical conductivity of the films could be effectively improved from 1.68 ×10-3 cm (no substrates heating) to a minimum resistivity of 4.6210-4 cm at Ts = 400oC with an average visible transmittance (400~800nm) of ~80%. It revealed that substrate heating is closely related to the crystallinity and the surface roughness of the deposited films. It is noteworthy that the transmittance in the NIR region was also improved considerably as compared to those using alloy targets by reactive magnetron sputtering and even slightly higher than those using Al-doped ZnO (1 wt.%) ceramic targets by RF sputtering.

Abstract: This study investigates the properties of cement-based composites with addition of various recycled rock wools and compare with the properties of composites containing fly ash and ggbs. The use of recycled rock wool is with a cylindrical and fiber-shape particle less than 75 μm. Based on the chemical composition and particle size distribution, the material properties of recycled rock wool are similar to other pozzolanic materials such as fly ash and ggbs and can be use a supplementary cementitious material. The experimental results show that partially replacing cement with recycled rock wool improves the compressive strength and porestructure, but reduce the flow spread at the high level replacement. Therefore, the test results indicate that recycled rock wool is an effective mineral admixture, with 10 % to 30 % as suitable replacement ratio of cement for the difference water/cementitious ratios.

Abstract: The thin flexible Polyimides (PI) films have desirable properties for use in the electrical and electronics industry because their good thermal stability, high flexibility, low dielectric constants, excellent mechanical strength, low loss tangent, low relative permittivity and electrical insulating properties. In order to determine the process window of the surface metallization of PI, the fine traces with 50 micron pitch (25micron line /space) built on a flexible 50 micron thick PI film using wet fabrication process are reported in this paper. The thick copper (Cu) film was obtained from the Cu plating process using evaporated thin film of Cu as the adhesion layer. The fabricated fanout fine patterns are further investigated using scanning electron microscope (SEM), energy-dispersive spectrometry (EDS) and X-ray spectrometry technologies. The experiment is conducted to study the effect of the process parameters on the Cu film surface properties. The results obtained in this work can be applied to the fabrication of flexible microelectronic devices.

Abstract: High tensile strength steel (HS40R) and galvanized steel (EZNCEN) are extensively used as components of vehicle bodies because they satisfy environmental standards and improve fuel economy. Because vehicle body sheets are becoming thinner and stronger, it is difficult to satisfy the design standards of spot welding joints. This research presents the optimization of the welding condition for various welding variables of a spot welding specimen by genetic algorithm (GA). When the welding condition optimization of spot weldment is performed using finite element method. The fatigue strength prediction method using FEM is useful for the prior evaluation technique that can predict the fatigue strength of spot weldment.

Abstract: This study proposes a new piercing technology with rotating punch; it carries out an FEM simulation on rotating piercing process using DEFORM-3D commercial software. Frictions among the punch, the blank holder, the dies and the work-piece material are assumed as Coulomb friction, but can be different. The surface of the inner diameter, the effective stress, the effective strain, velocity field, damage, burr and the shearing force can be determined form the FEM simulation. In this study, effects of various piercing conditions such as the clearance, the punch nose angle, the frictional coefficient, the rotating angular velocity, the shearing force, and burr on shearing characteristics are explored effectively to realize the feasibility of FEM model.

Abstract: The micromechanical investigation of fiber cross-section shape effect on the rate sensitive nonlinear behavior of a glass/epoxy was performed at 10^-5/s and 1/s, which considering four shapes, square, cross, circle and ellipse. With the strain of different rate loadings measured by Fibre Bragg gratings (FBGs) sensors, the rate-dependent inelastic constitutive relationship of epoxy is built by using an internal state variables viscoplasticity model. Then, through homogenizing the properties of unit cells, the responses of resin and its composites at 30° and 60° off-axis loadings are predicted by a micromechanical model compared with the experiments data. The effect of fiber cross-section fiber on the 30° and 90° off-axis responses are discussed with respect to the viscoplastic parameters of the resin determined. The results indicate that the micromechanical model accurately calculates the behavior of the PMCs employed. The square fiber causes the largest flow stress and plastic strain in the four cases. And the influences on overall responses for the four fiber shapes are enhanced with raising off-axis angles but weaken with the rate increase. However, the elliptical fiber yields the highest modulus in linear elastic stage. The square fiber is the most effective and the elliptical fiber is the least effective in the nonlinear deformation stage. Besides, the elastic properties are unaffected by loading rates when it is less than 1/s.

Abstract: L-cysteine capped Mn2+-doped ZnS quantum dots are prepared as a fluorescence probe for the detection of heavy metal contaminants, such as As2O42-, Cd2+, CrO42-, Ni2+, Zn2+, Ca2+, Fe2+, Cu2+, Pb2+, Co2+ and Mn2+ ions. The results show L-cysteine capped Mn2+-doped ZnS quantum dots exhibit good sensitivity and selectivity for the detection of copper ions. The relationship between the detection limit, linear range and the concentration of quantum dots are examined. The optimum fluorescence sensor is obtained at the L-cysteine-ZnS QDs concentration of 2 mg/mL and pH 7.0 in phosphate buffer. The limit of detection for this sensor system is 0.2 ppm with the linear range between 0.5 and 20 ppm. The effect of foreign ions from Mn2+, Fe2+, Co2+ and Ni2+ for the detection of Cu2+ solution is also evaluated. The results show there is no significant difference on the measurement of quenching effect.

Abstract: CFRP composite material, which is reinforced with carbon fiber, features superior heat and corrosion resistance, and these benefits enables the gradual applications on aerospace industries and sports-entertainment business. However, guarantee on superior strength and rigidity on harsh condition, such as hot moisture environment and collision load is extremely difficult. Therefore, in study moisture absorption test was conducted until complete moisture absorption in test specimen using hygrothermal heat chamber to evaluate strength degradation in CFRP composite under hygrothermal environment. As a result, the effect of moisture absorption and impact loads of approximately 50% reduction in strength are shown.

Abstract: Ultrathin (2 emulsion (SCE). Incomplete coverage of the Cu plate, the working electrode, by electroplated Ni and non-uniform Ni films with defects were obtained when conventional electroplating at 1 A/dm² with 30 sec of deposition time was used. When electroplating with SCE (ESCE) was applied, complete coverage, defect-free and uniform UTNFs were obtained. SEM and AFM showed surface morphology of the UTNFs was covered by spherical-shaped particles with ~10 nm in diameter, which was expected to be individual Ni grains because the size was consistent with grain size of Ni films reported when ESCE was applied. High H₂ solubility in CO₂, periodic-plating-characteristic after applying ESCE, and improved transport efficiency of the reactive species are believed to be the main reasons to cause effects of grain refinement and suppression in formation of the defects. Thickness of the UTNFs was 11.97±1.82 nm when the deposition time was 15 sec, and the thickness increased to 38.45±1.71 nm when the deposition time was increased to 45 sec.