Prediction of forming limit in hydro-mechanical deep drawing of steel sheets using ductile fracture criterion

It has been observed that the forming limit curve at fracture (FLCF) of steel sheets, with a relatively higher ductility limit have linear shapes, similar to those of a bulk forming process. In contrast, the FLCF of sheets with a relatively lower ductility limit have rather complex shapes approaching the forming limit curve at neck (FLCN) towards the equi-biaxial strain paths. In this study, the FLCFs of steel sheets were measured and compared with the fracture strains predicted from specific ductile fracture criteria, including a criterion suggested by the authors, which can accurately describe FLCFs with both linear and complex shapes. To predict the forming limit for hydro-mechanical deep drawing of steel sheets, the ductile fracture criteria were integrated into a finite element simulation. The simulation, results based on the criterion suggested by authors accurately predicted the experimetal, fracture limits of steel sheets for the hydro-mechanical deep drawing process.     

Effect of ZrO<Subscript>2</Subscript> coating on<Emphasis Type="Italic">in vitro</Emphasis> formation of calcium phosphate

We prepared zirconia thin films on (100) Si wafer by using a chemical solution deposition with a zirconium naphthenate as a starting material. The films were pyrolyzed at 500°C for 10 min and finally annealed for 30 min in air at 500°C. Amorphous films after annealing had no distinct structure and were uniform along the cross section line.In vitro formation of the calcium phosphate was evaluated by the field emission-scanning electron microscope, energy dispersive X-ray spectrometer and Fourier transform infrared spectroscopy.     

Prediction model for surface temperature of roller and densification of iron powder during hot roll pressing

The hot roll pressing of iron powder with several rotating speeds was carried out on a pilot-plant scale. From these experiments, it was confirmed that the surface temperature of roller was increased with increasing its rotating speed. It was also known that the heat transfer coefficient between the iron powder and the roller surface is closely related with the rotating speed of roller. These results were quantitatively described by using a mathematical model which was derived based on the steady-state heat transfer during hot roll pressing. In addition, the densification behavior of iron powder during the hot roll pressing was simulated by a finite element model based on the arbitrary Lagrangian and Eulerian (ALE) method and a yield criterion for metal powder. From these models, the maximum critical rotating speed of roller during the hot roll pressing, in which the roller could hold out against the thermal fracture, could be determined.     

Analysis of deformation texture inhomogeneity and stability condition of shear components in f.c.c. metals

The texture of cold rolled aluminum sheet has been known to vary through the thickness due to inhomogeneous deformation during rolling. The copper texture is obtained in the center layer that is plane strain compressed while the shear texture in the surface layer, which is approximated by major 001 011 and minor 111 112 and 111 110 components. The stability condition of these components was calculated based on the full constraint Taylor-Bishop-Hill theory and could be described by a parameterdɛ₁₃/dɛ₁₁ with the suffixes 1 and 3 indicating the rolling and thickness directions, respectively.     

Microstructure and mechanical property of irradiated Zr−2.5Nb pressure tube in Wolsong unit-1

With the aim of assessing the degradation of Zr−2.5Nb pressure tubes operating in the Wolsong unit-1 nuclear power plant, characterization tests are being conducted on irradiated Zr−2.5Nb tubes removed after 10-year operation. The examined tube had been exposed to temperatures ranging from 264 to 306°C and a neutron fluence of 8.9×10²¹ n/cm² (E>1 MeV) at the maximum. Tensile tests were carried out at temperatures ranging from RT to 300°C. The density of a-type and c-type dislocations was examined on the irradiated Zr-2.5Nb tube using a transmission electron microscope. Neutron irradiation up to 8.9×10²¹ n/cm² (E>1 MeV) yielded an increase in a-type dislocation density of the Zr−2.5Nb pressure tube to 7.5×10¹⁴ m⁻², which was highest at the inlet of the tube exposed to the low temperature of 275°C. In contranst, the c-component dislocation density did not change with irradiation, keeping an initial dislocation density of 0.8×10¹⁴ m⁻² over the whole length of the tube. As expected, the neutron irradiation increased mechanical strength by about 17–26% in the transverse direction and by 34–39% in the longitudinal direction compared to that of the unirradiated tube at 300°C. The change in the mechanical properties with irradiation is discussed in association with the microstructural change as a function of temperature and neutron fluence.     

Mechanical properties of porous titanium compacts prepared by powder sintering

Porous Ti compacts for biomedical applications are successfully fabricated in the porosity range from 5.0 to 37.1 vol% by controlling sintering conditions and Ti powder sizes. Young’s modulus and bending strength at the porosity of around 30 vol% are found to be similar to those of human cortical bone.     

Low-energy ion beam treatment of α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>(0001) and improvement of photoluminescence of ZnO thin films

A low energy N₂ ^? ion beam impinged on a α-Al₂O₃(0001) single crystal surface in the range of fluence 5×10¹⁵/cm²?1×10¹⁸/cm² at room temperature. After ion bombardment, chemical bonding on the modified sapphire surface was investigated by x-ray photoelectron spectroscopy. Below a fluence of 1×10¹⁵/cm², only a non-bonded N1s peak at the binding energy 398.7 eV was found, but further irradiation up to 2×10¹⁷/cm² induced Al?O?N bonding at around 403 eV. The occurrence of Al?N bonding was identified at ion fluence higher than 5×10¹⁷/cm² at 396.6 eV. II–VI ZnO thin films were grown on an untreated/ion-beam-induced sapphire surface by pulsed laser deposition (PLD) for the investigation of the modified-substrate effect on photoluminescence. The ZnO films grown on modified sapphire containing Al?O?N bonding only, and both Al?O?N and Al?N bonding showed a significant reduction of the peak related to deep-level defects in photoluminescence. These results are explained in terms of the formation of Al?N?O and Al?O?N layers and relaxation of the interfacial strain between Al₂O₃ and ZnO.     

Advanced compensation technologies for large‐sized UHD OLED TVs

In this paper, we present novel organic light‐emitting diode (OLED) display panel compensation technologies for large‐sized ultra‐high‐definition OLED TVs considering variations of threshold voltage, mobility, channel size, OLED efficiency, and OLED uniformity. Using these technologies, we have successfully launched 55‐, 65‐ and 77‐in. ultra‐high‐definition OLED TVs.     

Note: Interpolation for evaluation of a two-dimensional spatial profile of plasma densities at low gas pressures

An interpolation algorithm for the evaluation of the spatial profile of plasma densities in a cylindrical reactor was developed for low gas pressures. The algorithm is based on a collisionless two-dimensional fluid model. Contrary to the collisional case, i.e., diffusion fluid model, the fitting algorithm depends on the aspect ratio of the cylindrical reactor. The spatial density profile of the collisionless fitting algorithm is presented in two-dimensional images and compared with the results of the diffusion fluid model.