JSME International Journal Series A Solid Mechanics and Material Engineering
Online ISSN : 1347-5363
Print ISSN : 1344-7912
ISSN-L : 1344-7912
Volume 48 , Issue 4
Special Issue on Recent Advances in Materials and Processing [I]
Showing 1-50 articles out of 50 articles from the selected issue
PAPERS
  • Koji FUJIMOTO, Tadashi SHIOYA
    2005 Volume 48 Issue 4 Pages 178-182
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Fracture experiments were conducted using glass tubes by pressurizing internally with high pressure water and the paths of the crack propagations were observed. As the results, it has been clarified that regular wavy cracks often appear in glass tubes and that the shapes of the wavy cracks are approximately similar to one another. Monitoring crack propagations by a high-speed video camera system revealed that a crack snakes sinusoidally only when the crack propagation velocity is sufficiently small comparing with the elastic wave velocity of glass and that the wavy crack never appears when the crack tip velocity is large. Therefore, it can be concluded that the mechanism of the wavy crack propagation is not due to the dynamic effect resulting from the rapid crack propagation. Furthermore, by observing the fracture surface, it was found that the anti-plane shear stress plays an important role in the formation of wavy cracks.
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  • Akira KOBIKI, Hiroyuki KAWADA
    2005 Volume 48 Issue 4 Pages 183-188
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The effect of water on fiber bridging of polymer matrix composites (PMCs) has been studied for stress-corrosion cracking (SCC). The fiber bridging during crack propagation in the PMC was observed directly using a transparent polymer matrix. Specimens were immersed and weighed just before conducting the crack propagation test. The contribution of mechanical degradation caused by the water to the bridging was measured as a function of weight gain due to water absorption. The critical energy release rate of the matrix decreased with increase of the water absorption. The energy release rate of a bridged crack varied with the water absorption. To investigate the variation in the bridging mechanism under the water environment, we calculated the bridging stress the σt and the bridging contribution to crack propagation resistance ΔG based on a single-fiber bridging mechanism with the interfacial debonding length and the interfacial debonding energy. The debonding length was measured directly, and the debonding energy was obtained in a fragmentation test. The calculation showed that the increase in the interfacial debonding length influenced the fiber bridging mechanism.
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  • Go YAMAMOTO, Mamoru OMORI, Yoshinori SATO, Toru TAKAHASHI, Kazuyuki TO ...
    2005 Volume 48 Issue 4 Pages 189-193
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Single-walled carbon nanotubes (SWCNTs) are often produced in a form of bundles during their synthesis process. However, the bundles could slide easily on each other as they are held together by a weak van der Waals interaction. This weak cohesion is one of the major obstacles in the preparation of strong macroscopic solid structures composed of SWCNTs. Here, we have attempted to improve the stability of the links between SWCNTs within and between the bundles by introducing polycarbosilane (PCS) (10 mass%) to purified SWCNTs. Then, the SWCNT-PCS composite was prepared by the hot-pressing the SWCNT-PCS mixture at temperatures between 1000 and 1800°C under a pressure of 120MPa. The effect of processing temperatures on the mechanical properties of the composites was examined by conducting three-point bending tests. For comparison, SWCNT solids were also prepared without addition of PCS. In the case of the SWCNT-PCS composite prepared at 1000°C, the specific strength and specific modulus were about two and four times higher than that of the binder-free SWCNT solid, respectively. The reason for the increment is believed due to the stable PCS links formed between SWCNTs within and between the bundles.
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  • Tetsuya MORIMOTO, Satoshi NAKAGAWA, Shinji OGIHARA
    2005 Volume 48 Issue 4 Pages 194-198
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    It is known that the single-modal Weibull model describes well the size effect of brittle fiber tensile strength. However, some ceramic fibers have been reported that single-modal Weibull model provided biased estimation on the gauge length dependence. A hypothesis on the bias is that the density of critical defects is very small, thus, fracture probability of small gauge length samples distributes in discrete manner, which makes the Weibull parameters dependent on the gauge length. Tyranno ZMI Si-Zr-C-O fiber has been selected as an example fiber. The tensile tests have been done on several gauge lengths. The derived Weibull parameters have shown a dependence on the gauge length. Fracture surfaces were observed with SEM. Then we classified the fracture surfaces into the characteristic fracture patterns. Percentage of each fracture pattern was found dependent on the gauge length, too. This may be an important factor of the Weibull parameter dependence on the gauge length.
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  • Kazuya OKUBO, Toru FUJII, Naoya YAMASHITA
    2005 Volume 48 Issue 4 Pages 199-204
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Current study presents one of effective techniques to improve mechanical properties of PLA (Poly-Lactic Acid)-based bamboo fiber composite. Commercially available Micro-Fibrillated Cellulose (MFC) obtained from wood pulp was applied as an enhancer to the composite. The bamboo fibers were extracted by steam explosion method and they were also rubbed in water to remove xylem (soft-wall cells). The liquid-based MFC, PLA and the bamboo fiber were mixed in water for several minutes and they were filtrated under vacuum pressure. To fabricate the composite, remained sheets were then hot pressed after dry. Three-point bending strength and Mode I fracture toughness of the composite were significantly improved, even when 10% of the MFC was added into the PLA/BF composite in weight. If small amount of MFC added into the bamboo fiber composite, tangled MFC fibers prevented the growth of micro crack along the interface between bamboo fiber and matrix.
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  • Kuang-Chih CHANG, Kazuhiro MATSUGI, Gen SASAKI, Osamu YANAGISAWA
    2005 Volume 48 Issue 4 Pages 205-209
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Surface structure of carbon fiber and interfacial reaction between fiber and aluminium in carbon fiber reinforced aluminium composites were investigated by high-resolution transmission electron microscopy. Low and high graphitized carbon fiber reinforced pure aluminium composites were prepared by ultrasonic liquid infiltration. Vapor grown carbon nano fiber (VGCF) reinforced pure aluminium composites were prepared by hot-pressing. Heteroatoms, which existed abundantly in the surface of low graphitized carbon fiber, caused carbon lamellar structure in the fiber surface pronounced curvature. VGCF surface structure appeared regular and linear graphitic lamellae. Low graphitized fiber reinforced pure aluminium composites revealed serious interfacial reaction produced crystalline aluminium carbides (Al4C3), compared to composites reinforced by high graphitized fiber. On the other hand, Al4C3 crystalline reactants were not found at the interface of VGCF reinforced pure aluminium composites, but formation of interlayer was observed. In order to promote Al4C3 growth, carbon fiber reinforced composites were heat-treated at 573K and 873K for 1.8ks. Al4C3 interfacial phases in low and high graphitized fiber reinforced aluminium composites grew with the rise in the temperature. The heat-treatment resulted in the formation of non-crystalline Al4C3 interlayer by energy dispersive X-ray spectroscopy analysis of electron microscopy. At high temperature, Al4C3 was not grew and increased merely at the interface between carbon fiber and pure aluminium matrix, and moreover, the formation of new Al4C3 crystal occurred in this interlayer.
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  • Takayuki BESSHO, Toshio OGASAWARA, Takuya AOKI, Takashi ISHIKAWA, Yasu ...
    2005 Volume 48 Issue 4 Pages 210-214
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The present work investigates the transient creep behavior of a plain woven Tyranno™ Lox-M (Si-Ti-C-O) fiber/SiC matrix composite at 1473K in air. Tensile creep tests were carried out under a constant load between 80 and 160MPa. A creep strain rate is generally represented by ε∝ σn with a constant stress exponent, however the stress exponent decreased with time for this composite material. Monotonic tensile tests were also conducted for loading rates of 0.03, 0.3, and 3kN/min in order to investigate the effect of creep strain on tensile stress/strain behavior. Based on the empirical transient creep equation and creep-hardening model, stress/strain curves under monotonic tensile loading were predicted. A good correlation was obtained between the predicted and measured composite stress/strain curves using strain-hardening model.
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  • Tsutomu UMEDA, Hideo UMEKI, Koji MIMURA
    2005 Volume 48 Issue 4 Pages 215-221
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The high measurement accuracy in dynamic tension testing is required for designs and numerical simulations based on the accurate modeling of stress-strain relations at various strain-rates. The non-coaxial Hopkinson bar method (NCHBM) is one of the recently proposed methods for dynamic tension tests. In this study, the accuracy of the stress-strain relations obtained on the basis of NCHBM is investigated by FEM. The finite element models of NCHBM apparatus and plate type specimens of various dimensions are made in detail. The target material employed in this study is mainly the mild steel that is proper for the investigation of measurement accuracy. On the other hand, SUS316 stainless steel and A7075 aluminum alloy are modeled as specimen materials for the comparison with the experiments. The effects of the bending, the constraint condition, the rising time, the size and geometry of specimen, and the strain rate are examined systematically.
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  • Masaaki ITABASHI, Shigeru NAKAJIMA, Hiroshi FUKUDA
    2005 Volume 48 Issue 4 Pages 222-227
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    After unexpected failure of metallic structure, microscopic investigation will be performed. Generally, such an investigation is limited to search striation pattern with a SEM (scanning electron microscope). But, when the cause of the failure was not severe repeated stress, this investigation is ineffective. In this paper, new microscopic observation technique is proposed to detect low cycle fatigue-impact tensile loading history. Al alloys, 6061-T6 and 2219-T87, were fractured in dynamic tension, after severe pre-fatigue. The side surface of the fractured specimens was observed with a SEM. Neighboring fractured surface, many opened cracks on the side surface have been generated. For each specimen, the number of the cracks was counted together with information of individual sizes and geometric features. For 6061-T6 alloy specimen with the pre-fatigue, the number of the cracks is greater than that for the specimen without the pre-fatigue. For 2219-T87 alloy, the same tendency can be found after a certain screening of the crack counting. Therefore, the crack counting technique may be useful to detect the existence of the pre-fatigue from the dynamically fractured specimen surface.
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  • Kinya OGAWA, Hidetoshi KOBAYASHI, Fumiko SUGIYAMA, Keitaro HORIKAWA
    2005 Volume 48 Issue 4 Pages 228-233
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Thermal activation theory is well-known to be a useful theory to explain the mechanical behaviour of various metals in the wide range of temperature and strain-rate. In this study, a number of trials to obtain the lower yield stress or flow stress at high strain rates from quasi-static data were carried out using the data shown in the report titled “The final report of research group on high-speed deformation of steels for automotive use”. A relation between the thermal component of stress and the strain rate obtained from experiments for αFe and the temperature-strain rate parameter were used with thermal activation theory. The predictions were successfully performed and they showed that the stress-strain behaviour at high strain rates can be evaluated from quasi-static data with good accuracy.
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  • Masatoshi FUTAKAWA, Takashi NAOE, Hiroyuki KOGAWA, Hidefumi DATE, Yuji ...
    2005 Volume 48 Issue 4 Pages 234-239
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    High-power spallation targets for neutron sources are being developed in the world. Mercury target will be installed at the material science and life facility in J-PARC, which will promote innovative science. The mercury target will be subjected to the pressure wave caused by proton bombarding in the mercury. The pressure wave propagation induces the cavitation in mercury that imposes localized impact damage on the target vessel. The impact erosion is a critical issue to decide the lifetime of target. An electromagnetic impact testing machine, MIMTM, was developed to reproduce the localized impact erosion damage and evaluate the damage formation. Additionally, droplet impact analyses were carried out to investigate the correlation between isolate pit profile and micro-jet velocity. We confirmed that the value of depth/radius was applicable to estimate micro-jet velocity, and the velocity at 560W in MIMTM equivalent to 1MW proton beam injection was ∼ 102m/s approximately.
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  • Samadder LITON KUMAR, Yoshio ARAI, Eiichiro TSUCHIDA
    2005 Volume 48 Issue 4 Pages 240-245
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Characteristics of singular fields around an interface edge between ceramic and soft metallic interlayer were investigated experimentally and theoretically. Displacement fields around the interface edge were measured by means of high-sensitivity moiré interferometry. The measured singular fields around the elastic/elastic-plastic interface edge were compared with theoretical results (an elastic/linear hardening materials interface edge prediction and an elastic/power-law hardening materials interface edge prediction). Intensification of stress concentration around the interface edge due to the plastic deformation of the interlayer was clearly observed experimentally and illustrated based on the analysis. A controlling factor for the evolution of singular fields around the elastic/elastic-plastic materials interface edge was proposed and its validity was examined.
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  • Toshio HATTORI, Minoru YAMASHITA, Naoya NISHIMURA
    2005 Volume 48 Issue 4 Pages 246-250
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    In this paper we present the estimation methods of fretting wear process and fretting fatigue life using this wear process. Firstly the fretting-wear process was estimated using contact pressure and relative slippage. And then the stress intensity factor for cracking due to fretting fatigue was calculated by using contact pressure and frictional stress distributions, which were analyzed by the finite element method. The S-N curves of fretting fatigue were predicted by using the relationship between the calculated stress intensity factor range (ΔK) with the threshold stress intensity factor range (ΔKth) and the crack propagation rate (da/dN) obtained using CT specimens of the material. Finaly fretting fatigue tests were conducted on Ni-Mo-V steel specimens. The S-N curves of our experimental results were in good agreement with the analytical results obtained by considering fretting wear process. Using these estimation methods we can explain many fretting troubles in industrial fields.
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  • Tadao KAGIWADA, Hiroyuki HARADA
    2005 Volume 48 Issue 4 Pages 251-255
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Loosening of the wheel nuts, which fix the disk wheels of automobiles to the wheel hub, may be the cause of accidents where the wheel falls off while the automobile is running. When the transverse force of wheel bolts exceeds a certain proportion of the bolt shaft force, the wheel nut begins to loosen. Further, the force on the bolt shaft may also be influenced by the loads acting to the wheel through the moment caused by the offset of the wheel. This study determined the 3-dimensional deformation of the disk wheels and the transverse forces on the wheel bolt by 3-dimensional numerical analysis. The results established that the transverse force was influenced by the bolt shaft force caused by the bolt fastening and was superposed on that due to the load, and that it fluctuated greatly during the revolution of the wheel. This phenomenon may be a large factor in the loosening of wheel nuts.
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  • Masaaki IWASA
    2005 Volume 48 Issue 4 Pages 256-263
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The adhesive strengths of glass fiber reinforced plastics/metal adhesive joints reinforced with glass mat under tensile shear loads and tensile loads were investigated analytically and experimentally. First, the stress singularity parameters of the bonding edges were analyzed by FEM for various types of adhesive joints reinforced with glass mat. The shear stress and normal stress distributions near the bonding edge can be expressed by two stress singularity parameters. Second, tensile shear tests were performed on taper lap joint and taper lap joint reinforced with glass mat and tensile tests were performed on T-type adhesive joint and T-type adhesive joint reinforced with glass mat. The relationships between the loads and the crosshead displacements were measured. We concluded that reinforcing adhesive joints has a greater effect on strength under tensile load than under tensile shear load. The adhesive joints strength reinforced with glass mat can be evaluated by using stress singularity parameters.
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  • Katsuyoshi KONDOH, Takashi YAMAGUCHI, Tadashi SERIKAWA, Hideki OGINUMA
    2005 Volume 48 Issue 4 Pages 264-268
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Surface modification technology on magnesium alloys has been developed by using Mg-Si thin films via a glow discharge sputtering process, in employing Mg2Si bulky materials fabricated by powder metallurgy (PM) process as targets. This is because Mg2Si sintered materials have high hardness and Young’s modulus, in particular, a superior corrosion resistance to the conventional stainless steel. The Mg-Si thin film, having 1-2µm thickness, deposited on the AZ31 substrate improved the mechanical properties, wear and corrosion resistance compared to the conventional magnesium alloys. In particular, the effect of crystalline/amorphous structures of Mg-Si thin films on these properties was investigated in detail.
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  • Yasunori HARADA
    2005 Volume 48 Issue 4 Pages 269-274
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    In the present study, lining of the metal with foils using shot peening was investigated to improve the surface layer characteristics. In the shot peening experiment, the foils set on the metal are pelted with hard particles traveling at a high velocity. The foils are bonded to the metal surface due to plastic deformation induced by the collision of the particles. The foils and the metal are heated to heighten the bondability because of the reduction of flow stress. Lining the metal with the hard powder sandwiched between two aluminum foil sheets was also attempted. In this experiment, a centrifugal shot peening machine wite an electrical heater was employed. The metals are commercially aluminium alloys and magnesium alloys, and the foils are commercially aluminum, titanium and nickel. The effects of shot speed and the heating temperature on the bondability were examined. Wear resistance was also evaluated by grinding. The foils were successfully bonded to the metal surface. It was found that the present method is effective in improving of surface layer characteristics.
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  • Naomichi SAKAMOTO, Yasuo KOGO, Takuya YASUNO, Jun TANIGUCHI, Iwao MIYA ...
    2005 Volume 48 Issue 4 Pages 275-279
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The influence of heat treatment on the mechanical properties of DLC deposited by FIB-CVD was examined. To evaluate the mechanical properties, Young’s modulus and Vickers hardness were measured by the nano indentation tester. For the characterization of DLC structure, Raman scattering was used. The microstructures of samples were characterized by HRTEM equipped with EELS. From results of the indentation experiments, it was found that Young’s modulus and Vickers hardness decreased with increasing heat treatment temperature. Analysis of Raman and EELS spectra indicated that the decrease of Young’s modulus and hardness was caused by the decrease of sp3 fraction.
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  • Takashi NAOE, Masatoshi FUTAKAWA, Akira NAITO, Hiroyuki KOGAWA, Yujiro ...
    2005 Volume 48 Issue 4 Pages 280-285
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Target vessel materials used in spallation neutron source will be exposed to proton and neutron irradiation and mercury immersion environments. In order to evaluate the surface degradation of the vessel candidate materials due to such environment, the triple-ion beam irradiation taking the spallation reaction into account and mercury immersion tests were carried out. Mechanical properties of the gradient surface layer were evaluated by the inverse analysis with multi-layer model that considers distribution of surface characteristic was applied to the load and depth curves measured by using the instrumented indentation machine. Transmission electron microscopic observations were performed to evaluate the changes of microstructure in irradiated surface layer using focused ion-beam cut micro-specimen. The mechanical properties distributions in the surface layer were evaluated quantitatively and the changes in microstructures were correspondent to the property distribution. It was confirmed that the ductility loss is enhanced by the irradiation and mercury immersion, and simulated stress and strain curves of the ion-irradiated surface layer were adequately in good agreement with the curves of experimental equivalent neutron-irradiated material.
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  • Kuniaki DOHDA, Hiroyuki KUBOTA, Yoshinari TSUCHIYA
    2005 Volume 48 Issue 4 Pages 286-291
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The possibilities of application of DLC-Si coating to the die in dry ironing process have been investigated by strip-ironing type tribometer. Alloy tool steel and high speed steel were used as substrate material for ironing dies. Two types of substrate surface texture were prepared by lapping and grinding. And two types of die edge angle were prepared. High tensile strength steel and brass were tested as workpieces. The surface appearance of die, friction coefficient during ironing and surface roughness of ironed workpiece were measured. The friction coefficient of DLC-Si coated die in the dry ironing process is relatively low. Galling does not occur on the die surface. In case of high tensile strength steel, the damage grows with the number of tests. The surface roughness of a brass workpiece does not increase with repeat ironing. The DLC-Si coating could be applied to the dry ironing process in this investigated condition.
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  • (Effect of Substrate Temperature on Structure and Properties of Modified Layer)
    Sergey ZHEREBTSOV, Katsuhiro MAEKAWA, Terutake HAYASHI, Masatoshi FUTA ...
    2005 Volume 48 Issue 4 Pages 292-298
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The effect of varying temperature of the type 316 stainless steel substrate on the structure and properties of laser alloyed layer was investigated. The material for alloying (Al-Si powder mixture) was placed on the surface of stainless steel substrate by pasting. The surface was scanned by a pulsed Nd: YAG laser beam to achieve surface alloying. The temperature of substrate continuously increased during laser treatment to about 830°C. The microstructure, chemical and phase composition and microhardness of the modified layer were studied then. It has been found that four different types of structure were formed in the alloyed zone depending on the temperature of the substrate. These structures differ from each other in phase composition, microhardness and relation to cracking. Based on the results, optimal parameters for the production of a uniform, crack-free layer with a high hardness were developed.
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  • Ikuo YARITA, Takashi NAOI, Tsuyoshi HASHIZUME
    2005 Volume 48 Issue 4 Pages 299-304
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Most of magnesium alloy products are manufactured by die casting or thixo-molding processes. However, there is extremely little use of the products by metal forming due to high resisting plastic deformation in normal temperature and their expensive cost. In this study, to make clear the plastic deformability, stress and strain behaviors of Mg alloy AZ31 hot rolled sheet in plane strain compression in the temperature from 20°C to 250°C have been discussed. Tension test and plane strain compression test have been performed to obtain the equivalent stress and equivalent plastic strain relations. The plane strain compression tests with some lubricants have been performed, and the effect of friction between die and deforming material on plastic deformation behaviors has been investigated by the elastic-plastic finite element analysis. Optical microstructures of deformed materials are also observed.
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  • Teruie TAKEMASU, Hiroshi MIYAHARA
    2005 Volume 48 Issue 4 Pages 305-310
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    It has already been proven that bolt fasteners based on the double thread mechanism have an excellent anti-loosening performance. The purpose of this study is to establish a mass production method for these double thread bolts (DTBs) by thread rolling. The pitch ratio of the coarse thread and the fine thread of the target DTB is set as 2 to 1. A two-die roller with a plunge feed is employed as the rolling method due to its fine processing precision. The roller dies used in the experiments have special grooves on the external surface which follow the same outline as the thread profiles of the DTB. Using these special dies, the DTB can be successfully formed in the same process as single thread bolts. The deformation of a workpiece during rolling is examined, and the examination shows that the formed material smoothly fills the die grooves in each cross section. The rolled DTBs completely pass the loosening test with extremely severe vibration and impact, as specified in NAS3354. The tensile fatigue strength of the rolled DTB is about 100% greater than that of the cutting DTB.
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  • Hisashi IMAI, Shin-ichi MATSUOKA
    2005 Volume 48 Issue 4 Pages 311-316
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The ultrasonic welding method has been expected to replace other welding and brazing processes, and this paper is concerned with an experimental study on the ultrasonic welding of an aluminum alloy onto other three aluminum alloys. In this study the relation between energy density and welding pressure in welding certain types of aluminum alloys was clarified. For example, the ultrasonic welding of an aluminum alloy can be accomplished under the condition E=K1Pn1<f(P, E)<E=K2Pn2 (E: energy density, P: welding pressure, K, n: coefficients). The welding energy increases with an increasing in welding pressure, and decreases with a decrease in the size of the material on the anvil side. The welding energy is effectively used in the ultrasonic welding of a flexible, narrow material with a narrow pressurization area. Weldability can be evaluated by observing the amount of subduction of the welding material. Furthermore, the oxide film and organic coating are periodically removed from bonded interfaces by ultrasonic wave vibration.
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  • Tomoaki ISHIKURO, Shin-ichi MATSUOKA
    2005 Volume 48 Issue 4 Pages 317-321
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    This paper describes an experimental study of ultrasonic welding of thin ceramics and metals using inserts. Ultrasonic welding has enable the joining of various thick ceramics, such as Al2O3 and ZrO2, to aluminum at room temperature quickly and easily as compared to other welding methods. However, for thin ceramics, which are brittle, welding is difficult to perform without causing damage. In this study, aluminum anodized oxide with different anodizing time was used as thin alumina ceramic. Vapor deposition of aluminum alloys was used to create an effective binder layer for welding at a low pressure and within a short duration in order to prevent damage to the anodic oxide film formed with a short anodizing time. For example, ultrasonic welding of thin Al2O3/Al was accomplished under the following conditions: ultrasonic horn tip amplitude of 30µm, welding pressure of 5MPa, and required duration of 0.1s. However, since the vapor deposition film tends to exfoliate as observed in the anodic oxide film formed with a long anodizing time, welding was difficult.
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  • Tsutomu YAMASHITA, Kazunari YOSHIDA
    2005 Volume 48 Issue 4 Pages 322-328
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The general method of reducing curving or bending for midsize wires or sheets is straightening using rollers and/or levelers. For superfine wires, similarly, high straightness is needed. However, it is very difficult to deal with superfine wires due to their fineness and low tensile strength. In our study, warm tensile straightening processes for superfine gold wire, which is widely used as bonding material between leads and IC chips in semiconductors, were examined. Furthermore, finite element analyses of drawing and tensile straightening of superfine wires were carried out. The correlation between straightness and axial residual stress, which was calculated using the curve width when half of the wire was removed by sputtering with a focused ion beam (FIB), was studied. As a result of our studies, the improvement of straightness by tensile straightening of superfine gold wire was demonstrated, and the relationship between axial residual stress and straightness of wires was clarified.
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  • Takayuki HAMA, Motoo ASAKAWA, Masato TAKAMURA, Akitake MAKINOUCHI, Cri ...
    2005 Volume 48 Issue 4 Pages 329-334
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Treatment of contact problems between sheet and tools is one of the most difficult problems to deal with in sheet metal forming simulations. This paper describes a new algorithm for the discretization of the change of the “averaged tool normal” which is calculated by averaging the normals defined on all adjacent elements. The proposed algorithm was implemented into STAMP3D, which is a static explicit program dedicated to sheet metal forming simulations. Simulations of draw bending process were performed and the normalized norm of the non-equilibrated forces due to the change of the tool normals was compared between the original result and the result obtained with the proposed algorithm. It was found that the normalized norm of the non-equilibrated forces was drastically reduced by applying the proposed algorithm. This result shows the improvement of the accuracy of the simulation and the efficiency of the proposed algorithm.
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  • Tetsuo SHINOHARA, Kazunari YOSHIDA
    2005 Volume 48 Issue 4 Pages 335-340
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The surface flaw of a drawn wire has a significant influence on the quality of a product. High-surface-quality drawn wires and rods have been required for the manufacture of automobiles and machines. Wire breaks due to large surface defects are common problems in wire drawing. The authors carried out rolling and multi-pass drawing of a stainless-steel wire with an artificial scratch, and investigated the growth and disappearance of a scratch from both sides by experiments and Finite Element Analysis (FEA). When the scratch angle is small, the scratch side surfaces are pushed toward each other and the scratch becomes an overlap defect. In contrast, when the scratch angle is large, the bottom of the scratch rises, and the scratch is recovered satisfactorily. Furthermore, the scratch shape and the drawing conditions were varied, and the deformation state of a scratch was clarified.
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  • Ken-ichi MANABE, Yosuke YAMAUCHI, Tetsuya YAGAMI
    2005 Volume 48 Issue 4 Pages 341-345
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Recent global efforts to resolve environmental issues are required in sheet metal forming. For this reason, some research projects have been focused on unlubricated processes as well as on the use of volatile lubricants. However, low formability due to poor lubrication conditions is still a matter of concern. In this study, in order to improve the friction conditions, a new algorithm for controlling blank holding force (BHF) and punch speed (SPD) was proposed. The concept is to separate the wrinkle eliminating process from drawing process. That is, the process proceeds with an extremely low BHF until a wrinkle sufficiently grows, and the wrinkle is eliminated by BHF loading without punch penetration. Its effectiveness was investigated by finite element (FE) simulation, in which two blank models (0.5mm and 1.0mm thickness) were used. As a result, the maximum forming forces decreased by 5.33%(0.5mm) and 1.55%(1.0mm) compared with those of the uncontrolled model at a constant minimum BHF. In addition, a thinner blank sheet is better for the algorithm on the basis of the result that cup height decreases and thickness distribution increases in the case of 0.5mm thickness.
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  • Toshi-Taka IKESHOJI, Yuki WATANABE, Akio SUZUMURA, Takahisa YAMAZAKI
    2005 Volume 48 Issue 4 Pages 346-351
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    During the brazing process of the rocket engine’s nozzle skirt assembly made from Fe-Ni based super alloy pipes with Pd based brazing filler, the erosion corrosion pits were sometimes engraved on those pipes’ surface. The corrosion is considered to be assisted by the dynamic flow of the molten brazing filler. In order to estimate the amount of erosion corrosion and to prevent it, the solubility and the dissolution rate of Ni to the molten Ag-Cu-Pd brazing filler are measured experimentally. The Ni crucible poured with the Ag-Cu-Pd brazing filler was heated up to 1320K and quenched after the various keeping time. The microstructure of the solidified brazing filler part’s cross sections was observed, and the amount of the dissolved Ni was estimated using the image processing technique. The solubility was about 5.53mass%and the initial dissolution rate was 6.28 × 10-3mass%/s. Using these data, more elaborate dynamic flow simulation will be able to conduct.
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  • Kenji HIROTA, Yorifumi MORI
    2005 Volume 48 Issue 4 Pages 352-357
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    This paper deals with a new method to bend sheet metals at a small angle precisely, in which a sheet metal is slightly bent by shear deformation at negative punch-die clearance. Deformation behavior and key factors affecting on the bend angle were studied in detail with pure aluminum sheets. It was proved that the bend angle was changed in proportion to both punch penetration and negative punch-die clearance within a certain range. The same was true for high-strength steel and phosphor bronze, which are difficult to bend precisely by conventional methods due to large springback after unloading. By using this relationship as a control law, four kinds of sheet metals were precisely bent within a few degrees. This method was applied to correct the angular errors in U-bend products of high-strength steel and to bend leaf springs of phosphor bronze at an arbitrary small angle.
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  • Kazunari SHINAGAWA
    2005 Volume 48 Issue 4 Pages 358-363
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Effects of material properties and layered structures on internal stress generation in metal/ceramic graded powder compacts during firing process, which can be the cause of cracking, are studied by numerical analysis. Nonlinear variation of the sintering rate or the thermal shrinkage through the layers, due to mixing different materials, generates tensile internal stresses on the surface of the top ceramic layer. To extinguish the tensile stresses in both sintering and cooling periods together by adjusting the graded structure, a way of modifying the sintering properties is clarified. The multilayer is converted into the equivalent, essential three layers on calculation, for ease. Decreasing tensile bending stress and increasing compressive mismatch stress on the surface, by relatively gaining the sintering rate as well as the thickness of the middle layer, can be a solution for surface cracking during sintering, and may not conflict with design for thermal stress relief.
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  • Takuji OKABE, Takahide KANAMEDA
    2005 Volume 48 Issue 4 Pages 364-368
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Mechanical alloying (MA) of Ti-48mol%Al powder mixtures was performed for relatively short milling times (10.8-86.4ks) by planetary ball mill. The MA powders were hot-pressed at relatively low temperatures (673-873K) and pressures (200-600MPa). The influence of hot press temperature and pressure on consolidation (densification, reactive synthesis, etc.) in the MA powders was investigated. In this experiment, some non-reactive Ti powders remained in the consolidated materials, but the optimum hot press conditions for consolidation by reactive sintering were determined by the MA conditions (milling duration, etc.). Subsequently, the hot-pressed specimens were tested for hot-working by compressive creep testing at 1273K and initial pressure of 50MPa. The hot workability was excellent for superplasticity-like deformation. The densification and alloying did not alter the ultra-fine grain size, and the highest density and greatest change in density by hot-working was obtained by the powders milled for longest time.
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  • Terutake HAYASHI, Katsuhiro MAEKAWA, Masashi TAMURA, Kenichi HANYU
    2005 Volume 48 Issue 4 Pages 369-375
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The present paper investigates the laser sintering of titanium sheets toward the fabrication of porous artificial bones. The novelty lies in the use of a titanium powder sheet mixed with an organic binder and the application of selective laser sintering to the fabrication of a laminated porous structure. Alternating irradiation of Nd: YAG pulses with short scanning paths results in the suppression of distortion of the sintered part as well as enhanced mechanical properties. Under the appropriate conditions identified in the experiment, a bending strength of 63MPa and a Young’s modulus of 1.5GPa are attained when the load is applied parallel to the lamination direction, whereas load vertical to the lamination direction yields 79MPa and 1.8GPa, respectively. The size of pores varies from 200 to 300µm, and the porosity is approximately 65%. These values, other than Young’s modulus, are almost equivalent to those of human bones.
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  • Wiwat TANWONGWAN, Anchalee MANONUKUL, Julaluk CARMAI
    2005 Volume 48 Issue 4 Pages 376-380
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    In the past, the most common assumption in every explicit modelling of individual powders for compaction is that powders have only one single size which are arranged uniformly. However, all powders used in practice have a distribution of particle size and random initial arrangement. In this work, a systematic theoretical study of the effects of initial powder arrangement and distribution of size has been investigated using numerical analysis tool. Various types of elements have been considered first. Considering the accuracy and the effort required, the two-dimensional plane strain element has been employed for the rest of the investigation. The initial arrangement of powder and the distribution of powder size were considered separately. The results show that the initial arrangement has significant influence on the macroscopic behaviour while the powder size has little influence. Both factors have noticeable influence on the microscopic behaviour.
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  • Hideki OGINUMA, Eiji YUASA
    2005 Volume 48 Issue 4 Pages 381-386
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    For making the functional alloy powder from magnesium alloy scrap, Mg-Zn and Mg-Al-Zn powder mixtures, which aluminum and zinc powder were added with various contents to machined chips of AZ31 alloy, were mechanically alloyed for various milling times using planetary ball mill. Crystal phase formed in the obtained powder was investigated by X-ray diffraction and Vickers hardness of the powder particles was measured for confirmations of the formed phases. In the case of Mg-2.5mol%Zn powder mechanically alloyed for long milling time, super-saturated α-Mg phase with 2.5mol%Zn concentration forms. The structures of Mg-28 and 52mol%Zn powder consist of Mg2Zn2 or MgZn2, Mg7Zn3 phases and then these phases become to amorphous phase by milling for prolonged time. In the ternary Mg-Al-Zn system of composition range, which were (30-50)mol%Mg with Al/Zn=(90/10-60/40) molar ratio, Mg-(30-50)mol%Al-20mol%Zn and Mg-(10-30)mol%Al-40mol%Zn, icosahedron Mg49 (Al, Zn) 32 phase as called the quasi crystal forms by the mechanical alloying for 72ks.
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  • Tsunehisa MIKI, Norio TAKAKURA, Takashi IIZUKA, Katsuhiko YAMAGUCHI, H ...
    2005 Volume 48 Issue 4 Pages 387-392
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    This study is aimed at exploring possibilities to improve the injectability of wood powder and the mechanical properties of the injected product while keeping the amount of binder to its minimum. In the preliminary experiment, injection moulding of Japanese cedar wood powder was conducted. The effects of binder content (PE; pellet-size) and nozzle temperature on the tensile strength and strain at break of the product were investigated. Results showed that under such conditions, injection moulding of wood powder only was not possible due to insufficient fluidity. Increasing the binder content and the nozzle temperature resulted to a decrease in the maximum injection pressure and improvement in the fluidity of the powder. Using the same PE content, increasing the temperature resulted to an increase in tensile strength of the injected product. However, the strain at break was decreased. Moreover, at PE content below 50%, the strength and strain decreased considerably.
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  • Yukinori TANIGUCHI, Kuniaki DOHDA, Zhrgang WANG
    2005 Volume 48 Issue 4 Pages 393-398
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Density distribution in powder compact caused by frictional force at die wall has been estimated. The pressure transmission ratio λ was defined for the estimation of the magnitude of frictional force occurrence on die wall. The density gradient α was also defined for the estimation of density distribution. The iron and pre-alloyed stainless steel powder were tested, and the performance of zinc stearate and paraffin wax applied as internal lubricant or die wall lubricant has been investigated in various conditions. The die wall lubrication becomes effective way to increase λ in comparison with the internal lubrication. Admixed lubricant prevents the occurrence of density distribution and uniform green compact is obtained in the critical amount of lubricant. Paraffin wax shows higher performance as a die wall lubricant compared with zinc stearate, and remarkable increase of lubrication effect is observed in the combination between zinc stearate as internal lubricant and paraffin wax as wall lubricant.
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  • Masaaki KIMURA, Masahiro KUSAKA, Kenji SEO, Akiyoshi FUJI
    2005 Volume 48 Issue 4 Pages 399-405
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    This report describes the improvements in the joint properties of friction welded joint of 780MPa class high tensile steel. Welded joint made by a continuous drive friction welding machine, the conventional method, had not obtained 100% joint efficiency despite applying forge pressure. This was due to the softening of the welded interface zone for heat input during braking times. Therefore, we developed a continuous drive friction welding machine with an electromagnetic clutch to prevent heat input during braking time. We proposed the process as “The Low Heat Input Friction Welding Method (the LHI method).” In this case, the joint had the same tensile strength as the base metal at friction time when the friction torque reached the initial peak torque. That is, the welded joint obtained 100% joint efficiency by using only the friction stage up to the initial peak torque without the forge (upsetting) stage, despite the existence of a slightly softened region adjacent to the welded interface. Furthermore, the softened region was hardly generated when this joint was made by applying forge pressure at the initial peak torque. In conclusion, a welded joint of high tensile steel made by only the friction stage of the LHI method had excellent joint properties. The LHI method has a lot of advantages for joining such materials as super fine grain steel with which conventional fusion welding processes have difficulty.
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  • Toshi-Taka IKESHOJI, Akio SUZUMURA, Takahisa YAMAZAKI
    2005 Volume 48 Issue 4 Pages 406-412
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The strength of the brazed joint of the four-pipe-brazed specimen (4PB), which imitates the rocket nozzle skirt’s wall, is analyzed numerically. The 4PB specimen comprises four pipes brazed side by side with JIS BPd-6 palladium brazing filler metal. The effect of the fillet geometry to the joint strength of the 4PB specimen is investigated. The numerical analysis is conducted for the 4PB of 10mm diameter with various root gaps from 0.05 to 3.0mm and various apparent fillet widths from 1.0 to 4.0mm. The nominal rupture strain is obtained by the comparison of von Mises’ equivalent stress of the fillet and the pipes with their maximum tensile stress. The results show that the fracture of the 4PD specimens always occurs at the fillet. The nominal rupture strain tends to have weak correlation with the root gap, but in positive proportion to the apparent fillet width.
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  • Yohei INAGAKI, Akio SUZUMURA, Toshi-Taka IKESHOJI, Takahisa YAMAZAKI
    2005 Volume 48 Issue 4 Pages 413-419
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Braze Pressure Welding (BPW) with high frequency induction heating is a newly developed pressure welding technique using interlayer metals for welding the general steel pipes for pipe arrangement in buildings. BPW enables to make joints by solid-state welding in air with relatively small deformation. In this method, the interlayer metal is expected to play the primary role in making high performance joints. It removes contaminations from the joining surface of the base metal and forms fillets at the gaps around the joint. It had been revealed by some experiments and/or numerical analyses in previous research that the BPW joint had higher tensile strength than the brazed joint, and that the fillet can improve the joint strength. In this study, in order to investigate the cleaning effect of interlayer metal more closely, a low carbon steel plate specimen was brazed mainly by Ni-based brazing filler using a tungsten spacer. The microscopy and EPMA analysis on the joints made by various brazing temperatures and durations confirmed that the oxide films on the joining surfaces were removed and discharged from the joining region by the interlayer metal.
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  • Shuying LIU, Akio SUZUMURA, Toshi-Taka IKESHOJI, Takahisa YAMAZAKI
    2005 Volume 48 Issue 4 Pages 420-425
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Brazing of a stainless steel to various aluminum alloys was carried out using an Al-Si filler metal and a fluoride-active flux in air. The brazeability was remarkably different by the aluminum alloys and the brazing conditions. It was considered that the differences were originated with the compositions of base metals and the filler metal, the solidus temperature and the partially melting behavior of the aluminum alloys, and the behavior of the surface oxide film layers of both base metals. On the other hand, the obstruction of brazeability was identified as the rapid reaction between the aluminum alloys and the brazing filler metal, which makes the molten brazing filler metal disappear at the joining interface before the wetting occurs to the stainless steel. Taking this phenomena into consideration, it was attempted to make previous wetting of the brazing filler to the stainless steel before brazing to the aluminum alloys. This method provided the successful brazed joints for the most combinations of the stainless steel and the aluminum alloys.
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  • Seiji KUMAGAI, Masahiko ARANAI, Koichi TAKEDA, Yukio ENDA
    2005 Volume 48 Issue 4 Pages 426-431
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    We attempted to optimize both drying time and temperature for stem chips and bark of Japanese cedar in order to obtain the largest release of combustion heat. Moisture release rates of the stem and bark during air-drying in an oven were evaluated. Higher and lower heating values of stem and bark, dried at different temperatures for different lengths of time, were also evaluated. The drying conditions of 180°C and 30min resulted in the largest heat release of the stem (∼ 4%increase compared to conditions of 105°C and 30min). The optimal drying conditions were not obvious for bark. However, for the drying process in actual plants, the conditions of 180°C and 30min were suggested to be acceptable for both stem and bark.
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  • Hiroshi IMANISHI, Naho SOMA, Osamu YAMASHITA, Tsunehisa MIKI, Kozo KAN ...
    2005 Volume 48 Issue 4 Pages 432-436
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The effect of production conditions of wood powder on the bending properties of wood powder molding material was investigated. Wood powder was produced by milling wood into powder under conditions of different temperatures (25°C, 100°C) and moisture contents (0%MC, about 30%MC). Molding materials were produced from wood powder in stream atmosphere of high temperature and high pressure (175°C, 900kPa) using self-bonding ability of the wood powder. Adhesives, such as a synthetic resin, were not used. To evaluate the bending properties of the molding materials, the modulus of elasticity and the bending strength were examined by static three-point bending test. As for the characteristic of wood particle, in case of wood particle produced by milling wood under a condition of high temperature and high moisture content (100°C and about 30%MC), tendencies for intercellular layer to be exposed on surface of a particle and for the aspect ratio of particles to be large were confirmed. And in that case, the molding material showed the highest value in modulus of elasticity and bending strength. It is highly probable that the inprovement of the self-bonding ability of wood powder and the increase of the aspect ratio of wood particle take part in the improvement of strength properties of molding material.
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PAPERS
  • Seog-Young HAN, Choon-Ho BAEK
    2005 Volume 48 Issue 4 Pages 437-442
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The growth-strain method was applied to shape optimization of cutouts in a composite plate. In this study, of particular interest was whether the growth-strain method developed for shape optimization in isotropic media would work for composite plates. Since the growth-strain method optimizes a shape by generating the bulk strain to make the distributed parameter uniform, the distributed parameter was chosen as Tsai-Hill failure index. Both volume control and stress control of the growth-strain method were performed to obtain optimal shapes under predetermined volumes and target Tsai-Hill values. The Tsai-Hill values of the optimal shapes were compared with those of the initial shapes for the various load conditions, and predetermined volumes and target Tsai-Hill values. As a result, it was verified that the growth-strain method worked very well for shape optimization of cutouts in a composite plate.
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  • Masataro AMANO, Yoji OKABE, Nobuo TAKEDA
    2005 Volume 48 Issue 4 Pages 443-450
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    A Ti-Ni shape memory alloy (SMA) foil and a small-diameter fiber Bragg grating (FBG) sensor were embedded simultaneously into a CFRP cross-ply laminate. When the specimen was heated, the recovery compressive force was generated from the embedded SMA foil, which homogenized the non-uniform strain distribution caused by cracks in the 90° ply. Then, the tensile stress in the 90° ply was relaxed and the occurrence of new transverse cracks was suppressed. This effect was evaluated with the embedded FBG sensor. When the specimen was heated, the deformed reflection spectrum of the FBG returned to its original shape, which suggested that Ti-Ni SMA foil was effective to suppress the damage. However, relaxation of thermal residual tensile stress in the 90° ply was also effective. The result of the 3D FEA suggested that the suppression of damage occurrence and growth was mainly caused by the relaxation of thermal residual tensile stress.
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  • Takashi SAKAI, Sodai HOSHIAI, Eiji NAKAMACHI
    2005 Volume 48 Issue 4 Pages 451-457
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Titanium (Ti) thin films were created on glass and Pb(Zr, Ti)O3 (PZT) substrates using magnetic RF sputtering apparatus. Nano-indentation tests were carried out to study the influence of the Ti thin layer on piezoelectric properties. The piezoelectric properties of the PZT plate and a Ti sputtered one were also measured by laser Doppler vibrometer. Furthermore, some characteristics, such as crystalline structure, depth profiles, and surface roughness of the films were observed by means of an atomic force microscope (AFM). Main conclusions obtained in this study are summarized as follows: (1) From detailed observation and analytical results of AFM, the surface roughness, Ra, tends to increase as Ti film thickness increases. (2) Some of the mechanical properties, such as reduced modulus Er and hardness H obtained from nano-indentation tests, are significantly related to film thickness. (3) The validity of piezoelectric finite element analysis (ANASYS program) for deformation of a piezoelectric material was investigated. As a result, piezoelectric response properties are present in as-received PZT specimens and Ti-sputtered PZT specimens. Experimental and FE analytical results indicate that the piezoelectric coefficient is significantly influenced by Ti layer.
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  • Haruo SAKAMOTO, Kenji HIRAKAWA
    2005 Volume 48 Issue 4 Pages 458-464
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Using a steel material for forging, development of new discs for the next Shinkansen had been started. However, a fracture in a forged disc occurred in a durability test. Subsequently, from the viewpoint of higher fracture toughness, material improvement to an extent sufficient to withstand such a fracture due to tensile residual stress accumulation became the goal of further development. Among the candidate materials, modified AISI 4330 was selected and evaluated in laboratory and field tests. Following the subsequent durability test in the field, modification for bolt sticking and forging formability was conducted. This new brake disc, which proved to be satisfactory for Shinkansen vehicles, is capable of running at high speeds of more than 270km/h and therefore suitable for current vehicles such as the Nozomi and Tsubasa.
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  • Haruo SAKAMOTO, Masahiro HANAI
    2005 Volume 48 Issue 4 Pages 465-471
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    In Japan, lightning damage to FRP blades for wind power generators is increasing, together with the increase in wind power generator installation in recent years. Lightning damage is a big issue in Japan since lightning in Japan seems to be severer than in Europe and the US. In Kochi, Shikoku, Japan, six 600-750kW grade generators have been installed, and some of them have been damaged by lightning several times. In order to solve this issue, the Kochi University of Technology received a research request of lightning protection, sponsored by the Kochi prefecture in 2002. After surveying the literature and questioning related organizations such as NREL (National Renewable Energy Laboratories) and Toray USA, experiments to reproduce lightning damage to FRP specimens were planned. The specimens prepared for this research are 1/2 size models and a 2/4 part of the full size blade. In the previous experiment, flat plate specimens of 450mm width × 2.5m length × 4mm thickness were used, and the experiments produced the damage by lightning. However, the damages were not exactly the same as the ones in the actual field. Therefore, this experiment aims to reproduce the blade failure in the actual field and to clarify the failure mechanism, using the 1/2 size blade model and full size blade specimens. The experiments were conducted mainly in the Toshiba Hamakawasaki High Voltage High Power Testing Laboratory as was made in the previous experiments. This Testing Laboratory is one of the biggest test laboratory for experiments involving high electric voltage and large current. The results showed the reproduction of the failed blades in fields, and clarified the failure mechanism.
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  • Jong Heon KIM, Mitsuo NIINOMI, Toshikazu AKAHORI, Junji TAKEDA, Hiroyu ...
    2005 Volume 48 Issue 4 Pages 472-480
    Published: 2005
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Despite its clinical importance in developing artificial bone, limited information is available regarding the microstructure with respect to the fatigue characteristics of bones. In this study, the fatigue characteristics of the bovine humerus and femur were investigated with respect to microstructures. Fatigue tests were conducted on the bovine humerus and femur at a stress ratio of 0.1 and a frequency of 10Hz. The fatigue strength of the plexiform bone is slightly greater than that of the haversian bone. This is because the volume fraction of voids in the haversian bone, which is the site of stress concentration, is higher than that of voids in the plexiform bone. Several microcracks are observed on the fatigue fracture surface of the haversian bone. The microcracks are short and their propagation directions are random. However, the number of the microcracks in the plexiform bone is very small. The microcracks are relatively long and their propagation directions are parallel to the longitudinal direction of the lamellar bone. Therefore, the crack requires relatively more energy to propagate across the lamella in the plexiform bone.
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