The color of sintered body from incinerated ash of sewage and the chemical state of iron in the body were studied. The ash was pressed into a rectangular body under 100MPa, and the body was fired at 1000°C for 3h in air or Ar-O2 (Po2: 0.1-0.4kPa) atmospheres at various heating rates. The formation of porous black core was observed in the body fired either Po2=0.1-0.3kPa at the heating rate of 5°C/min or at under 0.1kPa at the rate of 2.0-5.0°C/min. Reflectance spectra, ESR, and XRD analyses indicated that iron oxide in the black core was mainly in the form of FeO. The results obtained seem to confirm that the formation of black core occurs when the oxidation of residual carbon in the body is not completed at the temperature where the reduction of ferric oxide to ferrous oxide takes place.
The internal-friction (IF) of superconductor RBa2Cu3Oy (R=Y, Er, Ho and Dy) was measured by a torsional vibration method in the frequency range of 0.032-10Hz. IF peaks were observed in the temperature range 410-520K. The peak-temperatures were influenced by the kind of rare-earth ions in R-site as well as the measured frequencies. The relaxation process was characterized by an average activation enthalpy of H=1.17±0.05eV and a pre-exponential factor of log(τ0)=-13.0±0.5 for YBa2Cu3Oy, H=1.17±0.05eV and log(τ0)=-13.0±0.6 for ErBa2Cu3Oy, H=1.24±0.01eV and log(τ0)=-14.2±0.1 for HoBa2Cu3Oy, H=1.17±0.03eV and log(τ0)=-13.5±0.3 for DyBa2Cu3Oy, respectively. The relaxation time (τ) decreased with increasing the ionic radius of rare-earth ion in Re-site. The activation enthalpy, however, was little affected by the ionic radius of R-site cation in RBa2Cu3Oy.
Fracture toughness and other mechanical properties of alumina matrix composite reinforced with nickel particles were measured. Nickel/alumina composites up to 25vol% of nickel contents were prepared by sintering in fine graphite powder bed under N2 gas atmosphere. Vibration was also applied during sintering to promote the dispersion of nickel particles in alumina matrix, using a high-frequency apparatus. Decrease in Young's modulus and three-point bending strength was observed with increasing nickel content. The fracture toughness, on the other hand, measured by SEVNB method increased with increasing nickel content. The fracture energy of composite was estimated by Griffith equation according to the observed fracture toughness and Young's modulus. The fracture energy increased in proportion to the total surface area of nickel particles comprized in the unit volume of composite. Increase in fracture energy corresponded to the formation of microcracks, which generated on nickel particles in the frontal process zone of composite. Decrease in bending strength was explained by the formation of large defects in composite, due to the large pore, decreasing of interparticle spacing or aggregation of nickel particles.
Solid solution ceramics of the system xPb (Yb1/2Nb1/2) O3-yPbTiO3-zPbZrO3, where x=0.1-0.7, y=0.2-0.7, z=0.1-0.7, and x+y+z=1, were prepared by the solid state reaction of powder materials. Ceramic, dielectric and piezoelectric properties and crystal structures of the system were studied. The system is composed of three crystal phases at room temperature: the monoclinic, tetragonal and rhombohedral. Sintering of the system xPb (Yb1/2Nb1/2) O3-yPbTiO3-zPbZrO3 is much easier than that of each terminal compositions and well sintered ceramics were obtained for the compositions near the morphotropic transformation. Piezoelectric ceramics with high dielectric constants and high radial coupling coefficient, kr, and low mechanical quality factor were obtained for the compositions near the morphotropic transformation. The composition Pb (Yb1/2Nb1/2)0.1Ti0.5Zr0.4O3 showed the highest kr of 0.46.
Surface modification was applied to silicone elastomers via ultrasonic implantation of bioactive 50CaO·50SiO2 (mol%) glass particles (<45μm in diameter). Silicone elastomers with different hardness, which were sampled from an appropriate stage of their hardening process, were immersed in the bioactive glass-ethanol suspension and subjected to irradiation of ultrasonic energy. The glass particles wholly covered and well adhered to the surface of silicone elastomers when the glass was implanted in the silicone elastomer at the stage of hard gel. Thus the resulting composite formed apatite, which is essential for bone-bonding, in Kokubo solution within 7 days. The cross-sectional analysis of the composite soaked in Kokubo solution indicates that the composite is covered with a complexed layer consisting of the bioactive glass and the in situ formed apatite.
The effect of micronsize-B4C dispersion on the sintering behavior of SiC was investigated for SiC/B4C composites prepared by hot-pressing method. By use of 4wt% carbon and 1wt% boron as sintering additives, nearly fully dense SiC/B4C composites were hot-pressed in an argon atmosphere at 2150°C for 1h of holding time. The effects of B4C dispersion on the grain size and microstructure of SiC/B4C composite were also studied by SEM and TEM. The incorporation of micronsize-B4C into SiC matrix inhibited the sinterability of SiC up to the addition of 10vol%-B4C for SiC/B4C composites hot-pressed at 2200°C. However, in the case of adding 20% B4C, the microstructure consisted of relatively large SiC matrix grains and their morphology was relatively round. Some mechanical properties, Vickers hardness and fracture toughness, were evaluated for the hot-pressed SiC/B4C composites. The relation between microstructure and mechanical properties was investigated for SiC/B4C composites.
MgAl2O4 spinel precursor was synthesized from heterogeneous alkoxide solution containing MgO powder with average particle size of 0.1μm. The obtained precursor was very stable and identified as a material consisting of MgO, AlOOH and Mg4Al2(OH)14·3H2O. However, calcination of this precursor at 1200°C did not yield monolithic spinel powder. MgO from the starting material remained in the calcined powder. In order to eliminate the remaining MgO, an attempt was made to mill the precursor under various conditions by the planetary ball-milling equipment. It was recognized that such milling results in the elimination of the MgO and the synthesizing the same constituents of a precursor by using MgO powder with average particle size of 0.01μm. The obtained powder was sintered at a temperature from 1300°C to 1600°C for 3h. Sintering temperature of 1500°C was enough to obtain polycrystalline spinel with more than 99% of the oretical density.
He ion yield XAFS measurements under He atmosphere at ambient pressure have been adopted for analyzing the local structure of several metal nitride thin films. XANES spectra and EXAFS parameters for zinc blend-type iron nitride, obtained by the yield XAFS, have coincided with those obtained using the conventional transmission XAFS. The yield XAFS measurements employing the grazing incidence technique have been presented for the determination of chemical species on the surface of Ti-Al-N films after the erosion experiment, showing the followings; the corrosion products on the film surface after heating at 600°C under O2 gas flow were Ti based oxides, either TiO2 or Al2TiO5. Al2TiO5 was slightly yielded not only on Al-rich Ti1-xAlxN but also on Ti-rich Ti1-xAlxN films after aging in a distilled water for 2 weeks. The local structure around Fe for Si-Fe-N films before and after annealing in an H2 atmosphere at several temperatures has been investigated. The as-deposited Si-Fe-N film contained Fe with local structure similar to that of FeNy (y>0.5) and such local structure was not broken against the annealing at 300°C. Annealing at 500°C changed the local structure around Fe, i.e., N bonded to Fe was almost eliminated and Fe formed a fine particle similar to α-Fe.
Application range of Stören-Rice Method is discussed which is used for estimating the formability in stretch forming of sheet metals. One of the famous methods for analyzing localized necking had been proposed by Hill. But, the application of his analysis must be confined in the bi-axial forming where there is at least the direction with no stretching, ie, εtt=0 in the forming sheet. Hence, this condition becomes an obstacle for its application in biaxial stretch forming. Stören-Rice proposed Δεtt=0, in place of εtt=0, where Δ denotes difference between the regions separated by necking plane. This proposal is suggesting that the condition εtt=0 might be removed, but it has not been proved whether the removal of the condition is realized or not. Then, on the equilibrium condition proposed in their analysis, the range of applicable forming is examined where the existence of multiple solution can be made sure. Consequently, it is found that it is possible to have multiple solution in the only forming condition satisfying εtt=0. Therefore, the forming limit obtained in biaxial stretching are in the outside of the application range, and they are an imaginary solution.
In order to simulate the deep-draw forming process for composite materials with complex microstructure, a novel computational method that takes the microscopic large deformation into consideration is proposed. The microstructure of composite materials affects the deep-draw forming process. The proposed method decouples this complicated problem into macro- and microscopic problems by means of homogenized nonlinear material properties, which contributes much to the computational cost effectiveness. First, using the large deformation analysis and homogenization, the homdgenized nonlinear properties considering the microstructural geometrical nonlinearity are obtained by microscopic analyses. Secondly, the deep-draw forming analysis is carried out macroscopically with precalculated material database. This material database consists of 21 independent parameters given by microscopic analyses, and is referred with respect to three macroscopic strain parameters. An example of deep-draw forming simulation for a formed core is shown.
Quasi-isotropic Carbon/Epoxy laminates under tensile loading are investigated to understand the effects of temperature on stress-strain response and damage progress including the interlaminar delamination growth behavior. The material system used is T800H/3631 and the stacking sequence is quasi-isotropic [0°/45°/-45°/90°]s. The transverse crack behavior is microscopically observed and its density is quantitatively measured by using an optical microscope under various loads at different temperatures, i.e., low (-100°), room (25°) and high (150°) temperatures. The interlaminar delamination growth behavior is non-destructively examined by a scanning acoustic microscope (SAM). It is found that nonlinearity observed in the stress-strain response is caused by the large scale interlaminar delamination throughout the length of the specimen. The transverse crack propagation and interlaminar delamination growth behavior are obviously affected by the temperature environments. Characteristic transverse crack formation at the edge of -45° layer under -100°C is pointed out and its mechanism is discussed with the use of shear coupling of an off -axis lamina.
Relation between fracture toughness and pressure condition in autoclave molding of GF composite laminates is investigated. Glass/epoxy prepregs are molded under different curing pressures, and UD laminates of T and T are fabricated. The results of the double cantilever beam (DCB) test show that the curing pressure has certain influences on the interlaminar fracture toughness via the change in morphology of matrix resin and fibers between laminae, and via the change in interfacial strength of fiber and matrix. It is also found that the fiber/matrix interfacial strength increases as the curing pressure increases by SEM photographs of the fracture surface in GF UD laminates.
The general aim of this study is to establish the modeling technique of interphase, which is the interfacial region between fiber and matrix, and to investigate the effects of interphase properties on the stress transfer mechanism and the fracture behavior in single fiber pull-out test. The finite element analytical model, which was divided independently with each element of fiber, matrix and interphase, has been applied. The interphase was assumed as orthotropy, because it can be dealt with the stress transfer and the stress bearing separately. The influence of interfacial shear stiffness on stress transmissibility was evaluated by the stress transferred from fiber to matrix by passing through the interphase. Also the effects of thermal stress which occurred at post-curing of resin, and meniscus which formed at the edge between fiber and matrix surface were investigated by FEM. From the analytical results, the following points were obtained; (1) the interphase shearing modulus strongly affected the interfacial stress transmissibility, (2) the degree of stress concentration occurring at matrix surface was varied by interphase shear modulus, meniscus size and thermal stress, (3) the meniscus size largely affects both a success of pull-out testing and an appearance of the interfacial properties.
This paper reports the experimental results of frictional properties of carbon fiber unidirectionally reinforced epoxy with a counter part of mild steel and the effect of fiber orientation is investigated. It is shown that the coefficient of friction increases with increasing fiber orientation, where 0 degree means that the fiber is parallel to the contact surface, and that this tendency is enhanced with the roughness of the contact surface increasing. The contact surface structures are studied before and after friction by OM, SEM, EPMA and roughness analyzer, and the effects of fiber orientation on the original and frictionally damaged surfaces are mentioned in detail including the discussion on the distribution process of each element. Several mechanisms based on the experimental analyses are presented to explain the effect of fiber orientation on the coefficient of friction of carbon fiber unidirectionally reinforced epoxy.
In this paper, a fracture model for polycrystalline ceramics is proposed. In the model, it is assumed that fracture toughness along a crack front has a distribution and that the fracture toughness for the macro-material is the mean value of those. It follows from the model that the probability distribution of fracture toughness for polycrystalline ceramics with a crack of the same configuration can be approximated by a normal distribution and that the coefficient of variation of fracture toughness for polycrystalline ceramics with a crack of the similar figure is inversely proportional to the root of the crack front length. In order to examine the theoretical results, indentation fracture tests of alumina ceramics are carried out. The experimental results agree with the theoretical results.
It is known that bending strengths of glued laminated beams (glulams) may be dominated by tensile strengths of outer layers of glulams. Since compressive strengths as well as tensile strengths of laminae should effect the stress distribution through the depth of the beam, the compressive strength may be important to estimate the bending strength of the beam. In the present paper, we considered about the effects of number of laminae on compressive strengths of glulams composed of homogeneous-grade lumbers of Japanese Larch. We conducted compression tests parallel to the grains with various number of laminae and different grades of glulams. The test results showed that the effect of lamina grades on the mean compressive strength (CS) were clear and the correlation between the mean CS and specific gravity (SG) were considerably high. We calculated the ratio of compressive strength to specific gravity, so called “specific strengths” (SCS). The effects of lamination on mean CS and mean SCS were not observed for both high and low grade glulams, then the size effects on CS and SCS were very small. We compared these test results to bending strength (MOR) done in the previous paper.