Thin Cu film was deposited on the (0001) surface of α-Al2O3 by a pulsed-laser deposition technique at substrate temperature of 800°C. The atomic structure of Cu/Al2O3 (0001) interface was characterized by high-resolution transmission electron microscopy (HRTEM). It was found that the interface was atomically sharp and the following orientation relationship (OR) was existed; (111)Cu//(0001)Al2O3, Cu//Al2O3. In contrast, the OR with geometrically high coherency across the interface was evaluated by the coincidence of reciprocal lattice points method, and the result showed that the preferred OR was (111)Cu//(0001)Al2O3, Cu//Al2O3. This OR is not consistent with the experimental results, and suggests that interfacial chemical bonding plays an important role to form the actual OR. In order to understand the nature of the chemical bonding at the interface, HRTEM image simulations were performed and their results were compared with the experimental images. It was found that the Cu(111)/Al2O3 (0001) interface terminated at oxygen-layer, which indicates that Cu-O bonds determine the stability of the interface.
TiO2 photocatalytic filters are utilized for various fields of environmental purification, such as decomposition of stench substances and harmful chemicals, etc. However, it turned out that the decomposition rate of sulfide chemicals, such as hydrogen sulfide (H2S) and methylmercaptan (CH3SH), were very slow to react on TiO2 under UV irradiation. In order to improve the decomposition ability of sulfide chemicals, this Ag-deposited Photocatalytic filter has been developed. The Ag-deposited photocatalytic filter was fabricated by coating TiO2 on the porous ceramics body, and successively depositing nano-sized Ag particles on TiO2 by means of photodeposition method. It was observed that Ag deposition on TiO2 improved the adsorption ability for H2S gas and CH3SH gas. Consequently, the Ag-deposited photocatalytic filter could remove H2S gas and CH3SH gas with an 8.0 times, and an 8.7 times effectiveness, respectively, in comparison with conventional TiO2 photocatalytic filter.
Hydroxyapatite ceramics were attempted as a scavenger for the magnetic separation process. In the present paper, some hydroxyapatites, pure hydroxyapatite and cattle bone, were ion-exchanged by mixing in a Fe salt solution for 2 hours. After drying ion-exchanged hydroxyapatites, they Were heat-treated in an air atmosphere at 500°C for 2 hours for magnetic seeding on the magnetic separation. Especially the ability of Cd2+ removal of magnetic-seeded hydroxyapatites was investigated through an ICP equipment. Hydroxyapatites with magnetic seeding treatments were carried out by the magnetic separation.
The consolidation mechanism of calcium silicate with water under carbonation was investigated. CaSiO3 powder was activated by mechano-chemical treatment for 24h in air with a vibration ball-mill. The cakes of the vibration ball-milled CaSiO3 added with a fair amount of water were carbonated at 50°C in 0.33MPa CO2 for 0.5 to 6hrs. in order to obtain the specimens carbonated to different degrees. The microstructural development in this carbonation process was observed by transmission and scanning electron microscopy and 29Si-MAS NMR, and the pore size distributions of the consolidated bodies were evaluated by mercury intrusion and N2 gas adsorption methods. By this carbonation treatment, dense consolidated bodies were obtained which exhibited high compressive strength. In the carbonated specimen, needle like crystals of aragonite precipitated to fill up macro-pores, and particles coalesced to form continuous matrices. The results of 29Si-MAS NMR showed that Q2 structure of SiO2 component assignable to single silicate chains transformed into Q4 structure indicative of three-dimensional SiO2 networks. These experimental results suggest that carbonation-induced consolidation would be caused by poly-condensation of SiO2 component in CaSiO3.
Charcoal has been recognized as new carbon resource because it is reproducible and good for earth resource drain and environmental problems. For production of SiC ceramics, in the present study, charcoal was utilized as a carbon source. In order to examine the usefulness of charcoal powder, three kinds of carbon, charcoal, carbon black and graphite were used for the reaction of SiC formation and the reactivity with silicon was investigated. SiC from charcoal had good crystallinity. Charcoal powder showed better reactivity with silicon due to the characteristic porous structure. Charcoal was found to become carbon source for ceramics production. Porous SiC was prepared utilizing the characteristic structure of charcoal by Si-infiltration technique. The infiltration was carried out at 1450°C for 2h under a flow of Ar gas. Obtained specimen was almost reacted to SiC but a little bit of silicon was observed via XRD. However, the characteristic structure of charcoal was maintained after the reaction with Si. The mechanical properties of the porous SiC materials were improved compared with as-received charcoal.
he essential requirement for an artificial material to show bone-bonding ability (bioactivity) is the formation of a bonelike apatite layer on its surface in the living body. An acellular simulated body fluid (SBF) with ion concentrations nearly equal to those in human blood plasma was shown to reproduce in vivo bonelike apatite formation on bioactive materials. Recently, new bone-repairing materials with bioactivity and mechanical properties analogous to those of natural bone have been strongly desired to be developed. Therefore, inorganic-organic composites are considered to be suitable for this purpose. It has been reported that titanium oxide with an anatase structure (TiO2) shows high bioactivity, and that ultra-high molecular weight polyethylene (PE) shows good biocompatibility. In the present study, bioactive PE/TiO2 composites were prepared by hot press. The composites were prepared from the powder mixtures of PE (90 vol%) and TiO2 (10 vol%) obtained by three different mixing processes, 1) an agate mortar mixing, 2) ball milling and 3) Theta-composer mixing. Their bioactivity and the effects of the mixing on the mechanical properties of the composites were investigated. The Theta-composer can prepare the composite particles of PE covered uniformly with the TiO2 powders without any agglomerations of TiO2. After hot press, the composites prepared from Theta-composer powder mixture gave the most uniform distribution of the TiO2 powder in the PE matrix. All of these composites formed the apatite layer on their surfaces after soaked in SBF. The composite prepared from Theta-composer powder mixture showed the highest bending strength. These composites show high extensibility. These composites are considered to be useful as bone-repairing materials.
Porous lanthanum strontium manganite (LSM) for the cathode in solid oxide fuel cells (SOFCs), was prepared with the fine perovskite oxide powder and organic PMMA particles as the pore-former. After calcination of organic particles, porous LSM with different porosity was synthesized at 1673K for 1hr by pressureless sintering. Porosity and microstructure of porous LSM were characterized. At room temperature or at 1273K of operating temperature, fracture strength was estimated by three-point bending test and Young's modulus was by the strain under bending test. The fracture toughness was also measured by SEVNB method. Electrical conductivity at operating temperature was confirmed by the four-terminal method, using the specimen similar to that measured mechanical properties. With addition of PMMA particles, the uniformly spherical and isolated pores with approximetely 10μm in diameter were observed below 0.25 porosity. Above 0.25, continuous pores were mainly observed. The fracture strength decreased with the increase of the porosity independent of testing temperature. Isolated or continued pores in LSM matrix changed the decreasing rate of strength. Normalized strength, strength for porous LSM divided by that for dense LSM, was agreed at each porosity, though strength at operating temperature was higher than that at room temperature. Apparent Young's modulus for porous LSM also showed similar tendency. Slightly decrease of fracture toughness for porous LSM at operating temperature was observed due to the healed wake zone or enlarged the frontal process zone. Electrical conductivity at operating temperature and thermal conductivity at room temperature decreased similarly with porosity. These properties of porous LSM were discussed using the effective volume of solid phase.
Submicron-sized diamond particles having hydrophilic groups on the surface were heated either in an atmosphere of hydrogen or inert gas. The surface variation of the diamond during heating was observed by means of TG-mass spectrometry and TEM obsavation. The hydrophilic diamond particles had an atoms-deep disordered zone near the outer surface. This structure was not affected significantly by heating in hydrogen at 1473K, while it increased significantly in depth after heating in nitrogen at 1473K. It is thus estimated that the removal of oxygen or oxygen-containing functional group could trigger the graphitization of the surface of diamond.
Isothermal DTA was performed at various temperatures for nucleated Li2O·2SiO2 glasses and the time neccesary to obtain crystallization peak, t0, was measured. The number density of nuclei in the glass was evaluated from crystallization peak temperature, TC, obtained by DTA with the heating rate of 10°C/min. The crystal growth rate of Li2O·2SiO2 glass was calculated from t0 and TC. By this method, crystal growth rate was measured more conveniently than by the traditional method based on the observation by micsroscope. The accuracy of crystal growth rate obtained was discussed, and it was found that good accuracy is attainable by using the glass samples with proper number density of nuclei.
The porous fly-ash ceramics with various porosity were prepared using colloidal process with molten wax. Polyethylene terephthalate powders were used combustible pore-forming agents. The total porosity of porous fly-ash increased with the polyethylene terephthalate powder content. The flexural strength of porous fly-ash drastically decreased as the total porosity increased. By the treatment of the sintered fly-ash with 3mol/dm3 NaOH solution at 383K for 15h, phillipsite, a kind of zeolite, was formed on the sintered fly-ash surface. The flexural strength of sintered fly-ash decreased to half of the original value by the zeolitization treatment.
The stress distribution of anisotropic multilayer filament-wound composite pipes was analyzed. Based on the three-dimensional anisotropic elasticity and the classical laminated-plate theory, exact elastic solutions of stress and deformation were presented for the filament-wound pipes subjected either to internal pressure, axial force or torsion. The shear coupling effect is considered in the analysis. The influence of winding angle and winding sequence on stress distribution in pipes was investigated. The ratio of hoop-to-axial stress is 2:1 in orthotropic pipes; however, the ratio proved to be not 2:1 in anisotropic pipes due to the coupling effect. The stress and deformation of filament-wound pipes strongly depend on the winding angle and the winding sequence.
In the present study, a widely acceptable buckling analysis was proposed for the symmetrically laminated composite plates by introducing both the pb-2 Ritz displacement functions to represent an arbitrary edge condition and the higher-order shear deformation theory. At the same time, the bucking analysis was conducted for the angle-ply symmetric laminates subjected to biaxial compression, shear or combined loading. As a result, it was confirmed that the proposed method for bucking analysis was effective one, and the very accurate result of buckling load was obtained due to the consideration of the higher-order shear deformation. Then, based on the proposed method the effects of loading conditions, boundary supports, material anisotropy and plate thickness on the buckling load were investigated and the optimum lamination angle for the buckling load was calculated. Furthermore, the buckling mode with three dimensional representation was obtained, and this provided a useful way for the buckling analysis and buckling prediction.
The allowable load or yield load in the various joint methods of wood constructions was prescribed by revision of the Building Standard Law. The allowable load of full pinned mortise-and-tenon joint which is one of traditional joint methods was provisionally specified to the numerical value of 3.81kN. This study was intended to estimate the effects of end (edge)-distance, tenon thickness and dowel shape on pull up resistance of full pinned mortise-and-tenon joints. The relationship between maximum load, yield load and end (edge)-distance did not show a clear tendency. In all examination conditions, the ratio of maximum load and yield load was 1.5-2.0. The experimental result is leading yield load can be evaluated as the allowable load. Although allowable loads with round dowel showed no remarkable effect on tenon thickness, allowable loads with square dowel depended on tenon thickness remarkably. The allowable load of 40mm tenon thickness exceeded the standard value of 3.81kN on all conditions. However, in the case of 30mm tenon thickness, values less than the standard value were also measured under some experimental conditions.
Slip-band formation and crack-initiation processes in α-brass under cyclic shear stress were examined by means of atomic force microscopy (AFM), and the slip-direction was identified with orientation imaging microscope (OIM). From AFM observations, it was found that slip-bands were not always formed along the maximum resolved shear stress directions, and slip-systems could be activated in the direction whose angles from the surface were larger than 22°. The depth of an intrusion increased linearly with the logarithm of the number of cycles, and the increasing rate of the intrusion depth drastically increased with its outgrowth to a crack. By combining the intrusion depth and the slip direction, those were measured with AFM and OIM, respectively, the value of slip distance could be evaluated, and the critical values of the slip distance for the initiation of transgranular crack was found to be constant for all crack initiation sites, while the intrusion depth was not constant. The critical value of the slip distance for cyclic shear stress (torsion) was identical for cyclic normal stress (bending). A unique relationship between shear stress amplitude in the slip direction and number of cycles to failure was obtained for cyclic torsion and bending loadings.
Creep damage analysis method of welded joint on the basis of the random fracture resistance model was proposed and was applied to the creep damage evaluation of welded joint of low alloy steel. Firstly a random fracture resistance of grain boundaries, an initiation and a growth driving forces of small defects, which were necessary in the above model, were determined considering the stress-dependent damage progress of the fine-grain HAZ material of 21/4Cr-1Mo steel. Secondly a procedure combining both the stress distribution in the welded joint and the random fracture resistance model was concretely proposed and was applied to the creep damage evaluation of the model test and the actual power piping. Experimental results of both the time history and the distribution of the number density of small defects in the welded joint were successfully reproduced by the proposed method.
Fatigue tests were conducted at both 893K and room temperature for ZrO2-8Y2O3-sprayed and Al2O3-sprayed type 304 stainless steel. Surface strain during the fatigue test was monitored to examine the delamination of a subsurface layer using a laser speckle strain gauge. Surface strain was found to decrease when subsurface delamination occurred. The number of cycles to delamination was decided by the surface strain behavior. It was found that delamination lives of a ZrO2-8Y2O3-sprayed specimen with an Atmospheric Plasma Sprayed (APS)-bond-coating and that with a thermal aged Low Pressure Plasma Sprayed (LPPS)-bond-coating were longer than those of a ZrO2-8Y2O3-sprayed specimen with a non-thermal aged LPPS-bond-coating and an Al2O3-sprayed specimen with an APS-bond-coating. The strength of an APS-bond-coating was so low that multiple cracks occurred, while the strength of a LPPS-bond-coating was so high that a single crack occurred near the fracture surface. In case of the specimen with an APS-bond-coating, the fatigue fracture life of an Al2O3-sprayed specimen was longer than that of a ZrO2-8Y2O3-sprayed specimen. The reason was that the crack initiated at a bond-coating penetrated into a substrate with no delamination between a bond-coating and a substrate for a ZrO2-8Y2O3-sprayed specimen. In case of the specimen with a LPPS-bond-coating, the fatigue fracture life of a specimen with a thermal aged bond-coating was longer than that with a non-thermal aged bond-coating and the fatigue lives of these specimens were longer than those with an APS-bond-coating. The improvement of the fatigue fracture life was caused by the restriction of a crack initiation into the substrate due to the LPPS-bond-coating with a relatively higher strength. It was concluded that a bond-coating with high strength and high adhesive strength was effective on the improvement of fatigue fracture lives of plasma sprayed materials.
Stepwise S-N curves were obtained under rotating bending fatigue tests at high temperatures for an low alloy steel, as well as fatigue tests at room temperature for surface hardened specimens by shot peening or carburizing treatment. In the high cycle region, internal fracture with fish-eye pattern was dominant. As for mechanisms of internal fatigue fracture for 1Cr-0.5Mo steel, under high cycle region at high temperatures, following results can be obtained. (1) Oxidized surface layer itself has no effect on preventing fatigue crack from initiating at the specimen surface. (2) Specimen surface hardens during rotating bending fatigue test at 673K due to dynamic strain aging. Because of this phenomenon, it is difficult for Stage I cracks to initiate at specimen surface. (3) Effects of surface improvement by dynamic strain aging on fatigue strength can be recognized.
Hydrogen behavior in fatigue crack growth of lamellar TiAl intermetallic compounds has been studied by means of hydrogen microprint technique. We can visualize the hydrogen in metal using the silver reduced by the hydrogen. Hydrogen was introduced to specimens by cathodic charging technique, and then metal-hydride on the charged specimen surface were removed by electropolishing. For the hydrogen microprint technique, specimen surface was covered with collodion and photographic emulsion before pre-cracking. Fatigue crack growth tests were performed by using the hydro-servo testing machine in a darkroom. The relationship between the stress intensity factor range and crack growth rate was studied, and region of reduced silver particles was detected for all test conditions. The fatigue crack growth was accelerated with hydrogen-charged specimens as compared with non-charged specimens. In parallel type specimens, in which cyclic load was applied perpendicular to the lamellar boundaries, the main crack grew along lamellar boundaries and large amount of silver precipitates was observed in charged specimens. It was deduced that hydrogen reduced the strength of lamellar boundaries. In perpendicular type charged specimens, in which cyclic load was applied parallel to the lamellar boundaries, it was observed that silver precipitates accumulated on the slip lines and the main crack grew partially along the slip lines. Based on the observation, it was deduced that the hydrogen promoted slip and reduced the strength of slip plane.
The hydrogen microprint technique is one of the candidate method for visualizing hydrogen in metallic materials. We can visualize the hydrogen in metal using the silver reduced by the hydrogen. In the present study, the hydrogen behavior in sustained-load crack growth of a lamellar TiAl intermetallic compounds has been studied by means of hydrogen microprint technique. The crack growth was accelerated by the hydrogen. The hydrogen accumulated region was well visualized by the hydrogen microprint technique. It was proven that large amount of hydrogen was accumulated in the high stress field at the crack tip. The hydrogen content at the crack tip depended on the crack arresting time. Also it was confirmed that hydrogen content was dependent on the hydrostatic stress.
Three point bending specimen was made from commercial alumina and Al2O3/SiC composite ceramics. A semielliptical surface crack up to 500μm in diameter (aspect ratio≈0.9) was introduced on the test specimens. Basic crack-healing behavior was systematically studied as a function of crack-healing temperature, environment and crack size. Three point bending strength was measured at room temperature and elevated temperatures up to 1500°C. The crack-healing behavior of monolithic alumina was compared with that of Al2O3/SiC. Main conclusions obtained are as follows; (1) Bending strength of pre-cracked specimens of alumina recovered due to crack-healing. A surface crack of 100μm could be healed by the crack-healing above 1400°C for 1h. Difference of annealing environment had no significant effect on the crack-healing behavior of monolithic alumina above 1400°C. (2) The recovery of strength in monolithic alumina was caused by the sintering process or the removal of tensile residual stress near the pre-crack. Above 1400°C, the sintering mechanism is assumed to be dominant, however, below 1300°C, annealing mechanism is dominant. (3) The crack-healing of Al2O3/SiC occurs due to oxidation mainly, which is quite different from that of monolithic alumina. (4) The specimens which was crack-healed above 1400°C had similar bending strength to base material up to 1200°C.
Engineering ceramics are superior in strength than metal at high temperature. However, they are brittle and sensitive to flaws. As a result, the structural integrity of a ceramics component may be seriously affected. Whereas, some engineering ceramics have the ability of crack-healing. If this ability could be used in engineering ceramics components, their reliability will be increased and their life time will also prolonged. This study focuses on the crack-healing behavior of commercial SiC ceramics. Three point bending specimen was made from commercial SiC ceramics. A semi-elliptical surface crack of 50μm to 700μm in diameter (aspect ratio≈0.9) was made on each specimen. Basic crack-healing behavior as a function of crack-healing time and fracture behavior of crack-healed member were systematically studied. The main conclusions obtained were following; (1) Recommended crack-healing condition by this study was 1h at 1773K in air. (2) Maximum crack size which can be healed completely was semi-elliptical surface crack of 450μm in diameter. (3) Heat resist proof temperature of crack-healed zone for bending strength was about 878K. (4) Base material is not sensitive to static fatigue, but crack-healed zone is quite sensitive to static fatigue at room temperature.
A sintered SiC polycrystalline fiber, which has been developed by UBE Industries, Ltd., possesses high modulus, excellent thermal stability and oxidation resistance. A SiC matrix composite reinforced by the sintered SiC fiber was fabricated by polymer impregnation and pyrolysis (PIP) method. The composite consisted of 26vol% 3-D sintered SiC fabric and polymer-derived SiC matrix. Carbon coating was applied by chemical vapor deposition on the 3-D sintered SiC fabric prior to the matrix densification. Three point flexural tests of the sintered SiC fiber reinforced SiC composite up to 1400°C in Ar were carried out, and the results were compared with a SiC matrix composite reinforced by an amorphous Si-Zr-C-O fiber. The flexural strength of the sintered SiC fiber reinforced SiC composite at 1400°C retained 84% of the strength at room temperature, while that of the amorphous Si-Zr-C-O fiber reinforced SiC composite retained only 56%. In addition, the sintered SiC fiber reinforced SiC composite showed higher stiffness than that of the amorphous Si-Zr-C-O fiber reinforced SiC composite. The higher retention ratio of the strength at 1400°C and higher stiffness of the sintered SiC fiber reinforced SiC composite were attributed to excellent heat resistance and high tensile modulus of the sintered SiC fiber.
In the present study, internal strain monitoring and detection of cure shrinkage in matrix resins by using EFPI optical fiber sensors have been investigated for CFRP during autoclave cure. EFPI sensors were embedded into quasi-isotropic CFRP laminates composed of carbon fiber/heat-resistant tough epoxy resin prepregs for aircraft structures. In order to examine the monitoring ability of EFPI sensors, measured internal strains were compared with specific volume of matrix resins determined by PVT measurement during cure, which indicates their cure shrinkage and thermal expansion/contraction. The results show that the cure shrinkage terminates at a certain degree of cure before the resin cures completely, and the EFPI sensors can detect this phenomenon. From these results, it is found that the EFPI sensors can measure the internal strains corresponding to the specific volume change of the matrix resins after the degree of cure reaches approximately 30%.
This paper studies the position, diameter and depth determination for internal defects by a. c. potential method. Alternative currents from 500Hz to 6000Hz were applied to specimens that have artificial holes with 1.0mm-2.5mm diameter and 0.8mm-5.0mm depth. A. c. potentials from 500Hz to 6000Hz were measured at 13 positions on the specimen surface. The potential difference between 500Hz and 6000Hz depended on the diameter and hole depth. A new a. c. method was proposed for determining the position, diameter and depth of internal holes. The hole position was determined as the symmetric point of the disturbed potential profile by a defect. The diameter and depth of the internal hole were determined by utilizing potential difference and critical frequency. Finite element method analyses were carried out for confirming the reliability of experimental results. The potential differences and critical frequencies obtained in FEM analyses agreed with the experiment results quantitatively.
In this study, dry wear tests were carried out to investigate the friction and wear properties of magnesium alloys by using a pin-on-disk wear testing machine at room temperature. Mg-Al-Zn (AZ31, AZ61 and AZ91) alloys were used as test specimens. Mg-Al-Zn alloys fabricated by extrusion method of processing were tested. Furthermore, two kinds of specimens were prepared by heat treatment: one is solution-treated at 413°C for 48 hours and the other is aging-treated at 150°C for 100 hours after solution treatment. SUJ2 was used as a disk material. Wear rates and coefficients of friction were investigated under constant conditions. The main results obtained were as follows. (1) The coefficient of friction decreased with the increment of aluminum content. In addition, it decreased with aging treatment. (2) The wear resistance of solution-treated Mg-Al-Zn alloys was independent of aluminum content. (3) The wear resistance of an aging-treated AZ61 alloy was same compared with a solution-treated one. On the other hand, the wear resistance of an aging-treated AZ91 alloy deteriorated compared with a solution-treated one. Consequently, the wear resistance of aging-treated Mg-Al-Zn alloys was dependent on aluminum content. It was confirmed that precipitated particles had an influence upon the wear resistance of aging-treated Mg-Al-Zn alloys.