Alumina cement hardens rapidly and its early-age strength is very high, compared to portland cement. So alumina cement is expected as rapid hardening cement. In spite of the excellent properties of alumina cement, however, the cement has not been widely used, because the cement does not have long-term strength, due to the conversion of crystalline phase. At first, alumina cement reacts with water to form the hydrates of CaO·Al2O3·10H2O and 2CaO·Al2O3·8H2O, resulting in high strength. Then the hydrates subsequently decompose to a mixture of 3CaO·Al2O3·6H2O, Al(OH)3 gel and water. This process causes an increase in porosity, leading to a decrease in strength. In order to examine the effect of additives on crystalline phases and long-term strength, in this paper, consolidated alumina cements containing fumed silica and water-reducing admixture were prepared and evaluated the compressive strength, the changes of crystalline phase and the changes of microstructure with time. The water-reducing admixture was effective to inhibit dissolution of CaO·Al2O3 component in alumina cement. The consolidated alumina cement with both fumed silica and water-reducing admixture didn't form the first hydrate of CaO·Al2O3·10H2O and had long-term high strength. Formation of CaO·Al2O3·10H2O was inferred to be important for strength degradation due to the conversion.
Room temperature (R.T.) resistivity and the positive temperature coefficient of resistivity (PTCR) of Gd-Mn codoped BaTiO3 from powders obtained by hydrothermal synthesis were investigated. Mixtures of Gd(NO3)3, Mn(NO3)2, and BaTiO3 powders (average particle size ; 0.1 to 0.3μm) obtained by hydrothermal synthesis were dried and pressed into pellets with a diameter of 2 cm. Then, the pellets fired at the temperature range of 1230 to 1300°C for 2 h in air. By using BaTiO3 powders obtained by hydrothermal synthesis, relatively low R.T. resistivity and remarkable PTCR characteristics was observed for the samples fired at the temperatures lower than 1300°C. In particular, semiconductive sample was obtained and PTCR jump was more than 2 orders of magnitude for the sample fired at 1230°C by using BaTiO3 powders which have an average particle size of 0.2μm. Results of electron spin resonance indicated that changes of chemical states of Mn in the grain boundary significantly affected the PTCR properties.
Porcelain roof tiles are very popular in Japan. In Kyoto, in particular, smoked roof tiles are preferred for temples, shrines and even home. A volume of roof tiles are taken out as an industrial waste, with building renovation and housing rehabilitation. Such tiles have been discarded in landfills in the past. Decrease in landfills and demand of reduction of such waste promote to recycle the waste roof tile. On the contrary, clay with good quality for roof tile is being depleted. In order to decrease fraction of roof tile clay used in producing the tile, in the preset study, waste roof tile was recycled for the production of the new tile. In consequence, green compacts with waste roof tiles were sintered by conventional method and the mechanical and water-resistant properties were improved. However, smoking process was insufficient. Beautiful smoked tiles could not be prepared, resulting from formation of glassy phase on the tiles. Control of sintering temperature makes it successful to prepare the tiles with almost the same shrinkage and water absorption of tile prepared with only roof tile clay without waste tile.
Wollastonite consolidated by carbonation is one of promising materials as a crystallization-type phosphorous adsorbent. The detailed crystallization mechanism of phosphorous, however, has not been clarified yet. In this study, the crystallization of calcium phosphate on the surface of the consolidated body of wollastonite was examined in detail by SEM, EDX and XRD in order to clarify the detailed mechanism of phosphorous removal by crystallization. It was found that the crystallization of calcium phosphate occurred to a depth of 100μm from the surface of the wollastonite consolidated body, which was the region fully carbonated and mainly composed SiO2 gel-like compound and CaCO3 (calcite and aragonite). Further investigation of crystallization of calcium phosphate using SiO2 gel and CaCO3 powders consolidated by gypsum revealed that a crystallization site of calcium phosphate was probably the surface of CaCO3 crystals generated by the carbonation of wollastonite. Moreover, it was found from the investigation using calcite and aragonite single crystals that the crystallization of calcium phosphate occurred on the surfaces of both crystals and that the surface of aragonite was slightly advantageous for crystallization. XRD analysis showed that Ca-deficient hydroxylapatite (Ca9(HPO4)(PO4)5OH, d-HAP) and dicalcium phosphate dehydrate (CaHPO4·2H2O, DCPD) were mainly crystallized on the surfaces of aragonite and calcite, respectively.
Thermal behavior of γ-Al2O3 coat layer on alloy substrate was examined for forming the catalytic parts used under harsh heat condition. Stable catalytic coat layer was made through a simple dipping-drawing procedure of aqueous γ-Al2O3 slurry. Thermal stability of alumina layer and interface was examined by surface area measurement, XRD, and SEM morphology as well as EDS in the temperature range of 800∼1200°C. The phase trasformation and related microstructural development were observed at the surface of alloy substrate and alumina layer. The coat layer was stable, regarding with metastable phase and surface area, on FeCrAl alloy below the temperature of 1200°C, however macroscopic structure of coated alumina must be improved more.
The crystallization behavior of ZnO-Al2O3-SiO2-ZrO2 glasses was investigated by DTA and XRD in order to prepare transparent glass ceramics containing ZnAl2O4 nano-crystal. The crystallization peak temperature (TC) obtained by DTA was used as a measure of the number of nuclei formed in the glass sample during heat treatment. The increase of nucleation rate was observed with the increase of SiO2 and ZnO content. The effects of SiO2 and ZnO to promote their nucleation are different because their effects on the viscosity of glass melts are opposite. The ratio ZnO/Al2O3 is very important to make transparent glass ceramics containing ZnAl2O4 nano-crystal.
This paper evaluates effect of ply thickness on nonlinear mechanical behavior of angle-plied CFRP laminates. To begin with, stress-strain behavior of unidirectional laminates under off-axis tensile loading is obtained. The laminates have exhibited nonlinear mechanical behavior in all off-axis angles investigated. It has been also shown that this nonlinear behavior can be predicted well by the one-parameter plasticity model. Angle-plied CFRP laminates have been manufactured using 16 plies of 0.15 mm thick prepreg ([(+45)4/(-45)4]S) or 48 plies of 0.05 mm thick prepreg ([(±45)12]S). When neighboring plies in same fiber orientation are regarded as one blocked plies for 16-ply laminates, this ply thickness is 12 times thicker than that in 48-ply laminates. Tensile tests have been demonstrated that 48-ply laminates show complicated nonlinear behavior until maximum strain of about 20% and intense fiber-matrix debondings as with interlaminar delamination. An attempt has been made to predict the stress-strain behavior of the angle-plied laminates by the one-parameter plasticity model in conjunction with classical laminate plate theory. The predicted behavior of the 16-ply laminates has agreed well with the experimental results without any modification. As for the 48-ply laminates, the model has predicted comparable results of the nonlinear behavior in large strain region when changes in fiber orientation angle due to deformation of the plate has been also taken into account.
Asymptotic solutions around an interfacial corner can be obtained by the combination of the Stroh formalism and the Williams eigenfunction method. The H-integral method, which is derived from Betti reciprocal principle, is useful for analyzing the stress intensity factors (SIFs) of cracks and corners. By expanding these theories for an interfacial corner between anisotropic piezoelectric multi-materials, we developed the modified H-integral method. This method has high generality that can deal a jointed corner with various numbers of materials and several boundary conditions on the corner surfaces. We proposed a new definition of SIFs of an interfacial corner between anisotropic piezoelectric multi-materials, which is compatible with the definitions of SIFs of a crack in a homogeneous material and an interfacial crack. The accuracy of obtained SIFs was confirmed by comparing the asymptotic solutions obtained from the SIFs with the stress field directly obtained by the finite element method (FEM). And we proposed a numerical method for degenerate materials, which cause numerical problems in the Stroh formalism.
We investigate the mechanical strength of ceramic/metal composites subjected to cyclic thermal loading. First, test samples of Cu/AlN systems are prepared via brazing. Next, short-term thermal cycle tests (25, 50, and 100cycles) are conducted at temperatures ranging from -40 to 125°C. Four-point bending tests are conducted to evaluate the residual strength. Further, thermal stress analysis is performed using the finite element method in order to examine the thermal stress behaviors during cyclic heating. The results reveal that the residual strength increases during 0∼20cycles because of residual thermal stress relaxation. This relaxation is generated by the cyclic softening of the metals owing to combined hardening. In contrast, relatively long-term thermal cycling (20∼100cycles) reduces the residual strength owing to damage growth to AlN. The AlN plates exhibit variability in residual strength, and the distribution of the residual strength for each cycle number conforms to the two-parameter Weibull curve. The variability in residual strength increases with the cycle number, and it is attributed to variabilities in the pre-existing crack size and damage accumulation. We conclude that the residual strength of the Cu/AlN composites depends on the thermal stress behavior and damage growth to the AlN plates.
The corrosion mechanism and its modeling of Polyamide (PA) in nitric acid (HNO3) solution were investigated. The appearances on specimens in HNO3 solution were changed with discoloration while not happen in distill water (DH). The weight change on wet specimens in nitric acid solution linearly increased after the incubation period. The weight change showed that the diffusion of DH and HNO3 solution into PA obeyed Fickian diffusion model except in HNO3 30mass%. Thus, the diffusion rate of each nitric acid concentration and DH were calculated from weight change with wet specimens. From SEC measurements, it was observed that PA by HNO3 solution degraded gradually in the specimen wholly with increasing immersion time. The reaction rate of each HNO3 concentration was calculated from molecular weight change at the surface of the specimen. The corrosion rate equation between PA and HNO3 solution was estimated with the previous diffusion rate and reaction rate. This equation showed that the calculated molecular weight change agreed well with the experimental ones. From this result, it was observed that the degradation of PA by HNO3 solution was of the corroded layer-forming type in the early immersion stage and of the penetration type in the later stage.
This paper presents a study on cyclic flexural behavior of steel pipes repaired by patch plate subjected to constant axial force. In this study, repaired steel pipes of piled pier are modeled. In FE analyses, steel pipes having various pipe diameters are analyzed under several levels of constant axial compressive stress to understand the buckling behavior of steel pipe repaired by patch plate. It is shown that a required thickness of patch plate is larger than the thickness reduction to achieve the same level of ductility performance in the repaired pipe as in the intact pipe. Furthermore, it is found that the required thickness of patch plate increases with the level of axial force.
It is well known that fatigue strength of bended copper pipes under internal pressure is decreased by flattening and change in thickness at the cross section. It is important to understand fatigue fracture phenomenon of bended copper pipes, because they are significant members utilized in air-condition equipments and hot-water supply systems. In this paper, fatigue tests of bended copper pipe specimens were carried out under internal pressure and stress conditions of these cross sections were calculated by finite element method (FEM), in order to clarify fatigue fracture phenomenon of bended copper pipes. The conclusions are obtained as follows : (1) Origin of fatigue fracture of bended copper pipes was the same as position of maximum stress range (ΔSMAX) obtained by FEM. (2) In tested copper pipe specimens, ΔSMAX/Δσ at the cross section was strongly affected by flattening ratio (DoS/DoL), and ΔSMAX/Δσ was less affected by change in thickness ratio (Tout/Tin). Where, Δσ is an elastic stress range of Lamé's equation. (3) Fatigue fracture phenomenon of bended copper pipes under internal pressure was similar to low-cycle fatigue fracture phenomenon of strain controlled type at stress concentration parts.
In order to investigate effects of a texture and a slip characteristic on fatigue properties of Al alloys in high humidity, rotating bending fatigue tests were carried out using plain specimens of an extruded bar and a drawn one of age-hardened Al alloy 2017-T4 and an Al alloy annealed the extruded one in relative humidity of 25% and 85%. The extruded Al alloy and the annealed one had a marked texture of a (111) plane at the cross section of each bar, but a specified orientation was not observed in the drawn one. In addition, the aged-hardened Al alloys show a planar slip property and the annealed alloy shows a wavy one. In the all Al alloys, the obvious retardation of a small crack growth due to blocking effect of a grain boundary was observed in low humidity, though the retardation disappeared in high humidity. Moreover the acceleration of a crack growth was yielded due to the change in growth mechanism of a crack from a tensile mode in low humidity to a shear mode at high stress levels in high humidity in the extruded alloy, though the effect of humidity on the growth mechanism was very small in the drawn Al alloy and the annealed one. In the extruded Al alloy, the fracture surface yielded by the shear mode crack in high humidity was occupied by many slip planes and voids and was a (100) plane, though the fracture surface formed by the growth of the tensile mode crack in low humidity was covered with striations. In the drawn and annealed Al alloys, fracture surfaces were mainly occupied by striations irrespective of humidity and stress levels.