Applied Mechanics and Materials Vols. 479-480

Abstract: In the present study, various quantities of Bi₂O₃ were added into 0.98(Na_0.5K_0.5)NbO₃-0.02Bi(Na_0.93K_0.07)TiO₃ (0.98NKN-0.02BNKT) ceramics. It was found that 0.98NKN-0.02BNKT with the addition of 0~0.5 wt.% Bi₂O₃ exhibit relatively good piezoelectric properties. For 0.98NKN-0.02BNKT ceramics, the electromechanical coupling coefficients of the planar mode k_p and the thickness mode k_t reach 0.40 and 0.47,respectively. For 0.98NKN-0.02BNKT ceramics with the addition of 0.3 wt.% Bi₂O₃, the electromechanical coupling coefficients ofthe planar mode k_p and the thickness mode k_t reach 0.50 and 0.53, respectively. It is obvious that 0.98NKN-0.02BNKT solid solution ceramics by adding low quantities of Bi₂O₃ is one of the promising lead-free ceramics for electromechanical transducer applications.

Abstract: Grain size and lubricating conditions influence material flow behaviours in micro metal forming processes. In this study, the brass (JIS C2700) tubes with 1.1 mm outer diameter and 0.5 mm inner diameter were treated by annealing at 400 °C, 500 °C and 600 °C to obtain various microstructures with the grain sizes of 20 μm, 34 μm and 80 μm, respectively. The treated tubes were machined and grounded to be 0.6 mm length specimens for the experiments of micro forward and backward hollow extrusion. Three lubricating conditions, which were dry, full and punch lubricated conditions, were carried out in the experiments. By comparing the upper cup height and rod length of the extruded specimens with the calibration curves established by finite element simulations, it is possible to estimate the friction factors in the processes. The results show that the dry conditions lead to stronger friction effects and thus larger friction factors. Moreover, the friction factor increased with grain size and stroke for all conditions.

Abstract: This study is aim to evaluate the natural frequency variation of the scale-down reinforced concrete containment vessel specimen under accelerated corrosion conditions. A plastic ring was sealed around the perimeter of the cylindrical vessel bottom with the 3.5 % NaCl solution to achieve the accelerated corrosion test. Concrete resistivity, open circuit potential, corrosion rate and natural frequencies were tested and discussed in this study. Test results presented that the accelerated corrosion method with a direct 60 voltage applied was a suitable method for estimating and accelerating the concrete vessel specimen. Therefore, the changes in natural frequencies were consistent with the material degradation of the concrete vessel specimen. The natural frequencies decreased with the increasing corrosion rate or decreasing resistivities for the specimen at higher mode, but would be no change for the specimen at the natural frequency of 1^st mode.

Abstract: The paper deals with the preparation of cobalt nanoparticles dispersed multi walled carbon nanotube buckypaper by the dispersion and filtration method to study the electromagnetic (microwave) absorption properties. From the X-ray diffraction the crystallite size of the cobalt nanoparticles of 33.04 nm was calculated. FESEM image clearly indicates the presence of cobalt nanoparticles in the buckypaper. Microwave-absorbing properties were investigated in terms of measuring the transmission coefficient (S₂₁) with MWCNT-buckypaper as the absorber using microstrip line in a frequency range of 2–20 GHz. Compared to the pure buckypaper the absorption peak of the Co-CNT composites move to the lower frequency by dispersing the Co nanoparticles into the MWCNT-BP.

Abstract: This paper reports a simple and effective method to increase heating efficiency and decrease heating time that renders direct heating billet within die using resistance heating system during hot forging process. The apparatus employs resistance equipment set into the forging die, and the billet was directly resistance heating by the forging die. Base on the approach, the die as a forming condition on direct heating and forging was also researched. The result of experiments shows that the billet could be heated quickly to 1000°C in about 5 seconds and the high strength material (AISI4140) was successfully formed to the shape of bolt head. With this mechanism, the rapidly heating and isothermal deformation during the hot forging process can be achieved.

Abstract: This study introduces a new forming concept for hot forging by using soft die. The soft die (AISI1050) was employed not only to heating the billet, but also to forming the billet. In this proposed method, the soft die can be used as the electrode to raise the temperature of billet directly by resistance heating. The temperature of the billet is higher; the flow stress of the billet is become lower. Then the billet is easier to press into the cavity of the soft die. In addition, the soft die itself could not be heated by the electrifying and the temperature raise of soft die was occurred by the heat transfer from the heated billet. Therefore, the soft die can be carried out on hot forging process, and to achieve the purpose of forming. The result of experiments shows that the billet could be heated quickly to 1000°C in about 5 seconds, and a spur gear was successfully formed. With the proposed method, it was simple enough to hot forging high-alloy metals with poor workability.

Abstract: Carbon nano tube(CNT) possesses excellent electrical, mechanical and thermal properties. Therefore, it has been applied in a variety of fields. In this study, we added CNT in Al₂O₃ to improve the characteristics. The composite of CNT(1.5 wt%), Al₂O₃(∅=20nm), zirconia(90g) and ethanol(20ml) is deconcentrated with planetary ball mill for 1hr, 3hr, 5hr under 200rpm, 300rpm, respectively. The prepared powder was pressed under 14MPa uniaxialy after the composite was dried in the oven at 90°C, and then the powder is pressed again by Cold Isostatic Press(CIP) with 200MPa. Then reinforced alumina matrix composites with CNT was sintered by high temperature furnace at 1525 °C

Abstract: In this work, GZO thin films were prepared by sol-gel process and spin coating technique. The XRD results showed the preferential c-axis orientation of the crystallites and the presence of the wurite phase of ZnO and it were suggested that the presence of Ga might be changed the d-spacing of ZnO to formation the Ga-doped zinc oxide. The effects of Ga amount on the conductivity and transparency were studied. The electrical resistivity for the GZO film doped 2 at% of Ga could be lowered to be 7.510-3Ω-cm with the calcination temperature was 550°C and hydrogen treatment was conducted in the Ar/H2 (97/3) atmosphere at 500°C. In addition, the optical transmittances of GZO thin films were higher than 90% in visible wavelength region.

Abstract: Roll coating is widely used to apply a thin liquid film to a continuous, flexible substrate. It is known that macroscopic instabilities of the film system can result in a non-homogenous film growth to fluid flow. The influence of the Rossby number, the viscoelastic parameter, and the roller radius on the nonlinear hydrodynamic stability of a thin viscoelastic polymer fluid film coating flow down a rotating vertical roller is investigated. In contrast to most previous studies, the solution scheme employed in this study is based on a numerical approximation approach rather than an analytical method. The size of the explosive supercritical instability region increases significantly as the roller rotates. It is shown that the stability of the liquid film is enhanced by reducing the viscoelastic effect or decreasing the speed of the rotating roller. At higher values of the Reynolds number, the tendency of the rotation effect to prompt thin-film instability increases with an increasing roller radius.