AMORPHOUS-FORMING ABILITY AND ITS EVALUATION BASED ON THERMAL STABILITY OF GLASS AND AMORPHOUS CERAMICS
Rikuo OTA and Takashi WAKASUGI
Review Paper (Vol.1 No.4)
AMORPHOUS-FORMING ABILITY AND ITS EVALUATION BASED ON THERMAL STABILITY OF GLASS AND AMORPHOUS CERAMICS |
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Rikuo OTA and Takashi WAKASUGI |
201 |
General Papers (Vol.1 No.4)
PRESSURELESS-SINTERED BORON NITRIDE WITH LIMITED CONTENT OF BORIC OXIDE |
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Milan HUBACEK and Masanori UEKI |
209 |
EXAMINATION OF A WAKE-DILATATION MODEL OF MICROCRACK TOUGHENING IN CERAMICS |
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Noboru MIYATA and Naoshi OZAWA |
213 |
EFFECT OF INITIAL DRY AND WET CONDITIONS OF CONCRETE ON FREEZING AND THAWING RESISTANCE AND MATHEMATICAL ANALYSIS OF DETERIORATION |
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Kiyoshi KATO, Naoki KATO and Tadashi KAWAI |
221 |
INFLUENCE OF WATER ON MECHANICAL PROPERTIES AND FRACTURE MECHANISM OF CFRP/HONEYCOMB CORE SANDWICH BEAM |
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Kenjiro KOMAI, Sohei SHIROSHITA and Gilles KILIDJIAN |
226 |
CYCLIC INELASTIC DEFORMATION AND LIFE PREDICTION OF CFRP |
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Katsuhiko SASAKI and Hiromasa ISHIKAWA |
232 |
EFFECT OF INTERNAL CREEP MICROCRACKS ON FATIGUE MACROCRACK PROPAGATION AT HIGH TEMPERATURES |
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Ryuichi OHTANI, Takayuki KITAMURA and Weisheng ZHOU |
238 |
CONSTITUTIVE MODELING OF PROPORTIONAL/NONPROPORTIONAL CYCLIC PLASTICITY FOR TYPE 316 STAINLESS STEEL APPLICABLE TO A WIDE TEMPERATURE RANGE |
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Yasuaki OHMI, Eiichi TANAKA, Sumio MURAKAMI, Morio JINCHO and Tetsuya SUZUKI |
247 |
PLANE-STRAIN FLOW LOCALIZATION IN TENSION BLOCKS OBEYING STRAIN-GRADIENT-DEPENDENT CONSTITUTIVE EQUATION |
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Yoshihiro TOMITA and Takehiro FUJIMOTO |
254 |
EXPERIMENTAL STUDY ON PERFORMANCES IN Cu-BASED SHAPE MEMORY ALLOY UNDER MULTI-AXIAL LOADING CONDITIONS |
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Masataka TOKUDA, Petr SITTNER, Masayoshi TAKAKURA and Ye MEN |
260 |
Short comunication (Vol.1 No.4)
MEASUREMENT OF OXYGEN POTENTIAL IN Na2SO4-CONTAlNING Na2O-B2O3-Al2O3 MELTS BY ZrO2 SENSOR | |
Takashi WAKASUGI, Rikuo OTA, Shin-ichiro OGUNI and Jiro FUKUNAGA |
266 |
Vol.1 No.4 ABSTRACT
Rikuo OTA and Takashi WAKASUGI
Abstract:Relation between glass-forming regions and amorphous-forming regions were discussed among the various multi-component systems according to the preparation methods and experimental conditions. It was concluded that melt-quenching technique can yield comparatively small range of amorphous composition since obtainable quenching rate is limited. Sputtering technique on the other hand is regarded as a most powerful technique to produce amorphous materials. This sol-gel technique is another most promising technique to obtain wide range of amorphous materials as long as the gels formed are water resistant. Sol-gel method can transform high melting point compounds such as Al2O3 and TiO2 into amorphous. TC/TL ratio can be regarded useful for the evaluation of amorphous-forming ability despite the different preparation techniques. In conclusion it can be stated that amorphous-forming ability is intrinsic to the constituents, only slightly dependent on the preparation technique. Key Words:Melt-quenching, Sol-gel method, Sputtering, Crystallization, Thermal stability
PRESSURELESS-SINTERED BORON NITRIDE WITH LIMITED CONTENT OF BORIC OXIDE
Milan HUBACEK and Masanori UEKI
Abstract:Elemental boron and boron nitride powders were mixed and pressureless-sintered in nitrogen. The structure and mechanical parameters of the ceramics were investigated and compared with those obtained from boron nitride powder free of the elemental boron. A positive effect of the addition of boron was found in increasing density, mechanical strength and refractoriness, and in suppressing growth of boron nitride grains. The reason of these changes has been explained by the formation of a refractory suboxide with a formula B6O as a consequence of a boron-controlled extraction of boric oxide (@B2O3). The extraction of the sesquioxide being originally adhered to the surface of boron nitride grains allowing a more effective formation of boron nitride ceramic skeleton. From the morphology of the ceramics, it has been suggested that the formation of volatile boron suboxide (B2O2) precedes to localization of oxygen in B60 grains. Key Words:Hexagonal boron nitride, Boric oxide, Boron, Pressureless sintering, Crystallization, Grain growth
Noboru MIYATA and Naoshi OZAWA
Abstract:An attempt was made to examine the validity of a wake-dilatation model of microcrack toughening in ceramic matrix composites. Model two-phase, particulate composite system was chosen for study. Spheroidized alumina particles with average size 25 and 12 mm, respectively, were dispersed in a soda lime silica glass having thermal expansion coefficient greater than the expansion coefficient of alumina. The composite containing 25-um alumina particles was formulated by selecting a combination of differential thermal expansion and particle size, whereby microcrack toughening is expected to occur most effectively. Another composite containing 12 mm alumina particles was designed as a reference material, in which the condition for the occurrence of microcracking is not met. For both composites, specimens containing 30 vol% of alumina particles were prepared by hot-pressing technique. Fracture toughness and R-curve measurements were carried out on each of the composites. Glass-alumina (25 mm) composite exhibited a rising R-curve behavior. The experimental results were interpreted on the basis of a wake-dilatation model of microcracking. By evaluating physical parameters involved in the model, its validity was discussed. Key Words:Ceramics, Particulate composites, Brittle matrix composites, Microcrack toughening, Crack-tip shielding, Zone shielding, Wake-dilatation model, R-curve behavior, Fracture toughness.
Kiyoshi KATO, Naoki KATO and Tadashi KAWAI
Abstract:The authors have already made clear the deterioration mechanism of durability of concrete structures due to the meteorological action, especially, the fundamental mechanism of deterioration due to the dry and wet action and the freezing and thawing action, and the effect of the concrete factors on them. This Paper furthermore deals with the effect of the initial moisture content of concrete on the freezing and thawing resistance and analyzed mathematically the concrete factors dominating the elastic modulus of elasticity. Key Words:Durability, Water content, Freezing and thawing action, Wet and dry actin, Surface deterioration
Kenjiro KOMAI, Sohei SHIROSHITA and Gilles KILIDJIAN
Abstract:Carbon fiber reinforced facing/aramid honeycomb core sandwich beams were studied through three point bending test. In order to clarify the influences of water on the stiffness and strength, the dry and wet specimens were used. At the same time, the fractured specimens were inspected by a scanning electron microscope (SEM) and a scanning acoustic microscope (SAM) to observe the fracture surfaces and interior damages of the specimens, respectively and the fracture mechanism was discussed. The experimental results showed the following. (1) With 6 wt.% water absorption the flexural stiffness of the sandwich composites rises a little while the shearing stiffness falls by 11%. (2) The core shearing strength is more sensitive to water absorption than the facing one. For a 3 wt.% absorption ratio, the facing strength and core shearing strength are 9% and 18% lower, respectively. However, the decrease has a tendency to level off over 4 wt.% absorption ratio. (3) The bonding strength between the facing and the core is larger than the matrix. (4) The buckling axes observed in the compressive fracture surfaces are more seen in wet specimens than dry ones, which shows that the fibers are liable to buckle in wet specimens. (5) At a small span length (< 200 mm), the wet specimens deflect more than the dry specimens, which is due to the degradation of the aramid fiber paper of the cell wall. Key Words:Sandwich material, CFRP, Aramid honeycomb, Three point bending test, Bonding, Delamination, Strength, Stiffness, Water absorption, SEM, SAM
CYCLIC INELASTIC DEFORMATION AND LIFE PREDICTION OF CFRP
Katsuhiko SASAKI and Hiromasa ISHIKAWA
Abstract:Fiber reinforced composite materials are widely used in many structures. It is well known that composite materials inelastically deform. Although there are some researches on fatigue failure, damage and crack propagation of composite materials, Cyclic inelastic behavior of composite materials subjected to cyclic loadings whose direction is different from that of the fiber has not been investigated in detail. In this paper, in order to investigate the cyclic inelastic behavior and the fatigue failure of composite materials, cyclic tension-compression loading under several conditions are carried out using laminated graphite/epoxy tubular specimens. The definition of fatigue failure is also discussed based on the test results. It is found that the CFRP subjected to cyclic loading shows the characteristic cyclic inelastic deformation. Moreover, using the concept of the plastic strain energy density and the concerned definition of fatigue failure, the relationship between the number of fatigue failure and the plastic strain energy density can be expressed by a formula. Key Words:CFRP, Cyclic loading, Inelasticitiy, Plastic strain energy density, Fatigue failure
EFFECT OF INTERNAL CREEP MICROCRACKS ON FATIGUE MACROCRACK PROPAGATION AT HIGH TEMPERATURES
Ryuichi OHTANI, Takayuki KITAMURA and Weisheng ZHOU
Abstract:The cycle-dependent pure fatigue crack propagation and the time-dependent creep-fatigue one, in general, were scarcely accompanied with microcracks and voids or cavities in the vicinity of the tip of propagating cracks inside the material when subjected to relatively high strain rate cycles at intermediate temperatures. In very low strain rate and/or high temperature conditions, however, diffusion-controlled creep cavities and microcracks tend to be generated along grain boundaries at the mid-thickness. These cavities and microcracks affect the macrocrack propagation in high temperature fatigue in two ways; one is the decease in the Hack propagation resistance and the other is the decrease in the crack driving force, i.e., the J-integral. Consequently, the Weep-fatigue crack propagation is accelerated by several times and the succeeding fatigue crack propagation in the pre-creep damaged material by ten times at most for a given J-integral range, D J. Key Words:High temperature fatigue, Crack propagation, Creep cavity, Microcrack, Pre-creep damage
Yasuaki OHMI, Eiichi TANAKA, Sumio MURAKAMI, Morio JINCHO and Tetsuya SUZUKI
Abstract:A constitutive model of cyclic plasticity is formulated to describe proportional and nonproportional hardening of type 316 stainless steel in the range from room temperature to 973K. For this purpose, we first examine the evolution of the size of isotropic and kinematic hardening range based on the experimental results performed previously by the present authors. It is elucidated that the complicated behavior of cyclic hardening under proportional cycles is induced by the evolution of kinematic hardening variable. Then, new evolution equations of kinematic hardening variables are established by incorporating this information into the nonlinear kinematic hardening rule. In particular, the dependence of cyclic hardening on the history of strain amplitude is taken into account. The final model is established by incorporating these evolution equations into the nonproportional viscoplastic model proposed by one of the present authors. It is elucidated that the proposed model can describe the behavior of proportional and nonproportional cyclic hardening under various loading conditions including strain cycles with amplitude variation in the range from room temperature to 973K. Key Words:Constitutive equation, Plasticity, Cyclic hardening, Nonproportional cycles, High temperature
Yoshihiro TOMITA and Takehiro FUJIMOTO
Abstract:Plane-strain dynamic now localization in tension blocks under a wide range of deformation rates has been investigated numerically. The material is characterized by a thermo-elasto-viscoplastic constitutive evaluation with strain-gradient-dependent flow stress. The mixed type variational principle for the corresponding materials is developed to satisfy this continuity requirement of the higher-order derivative of velocity. In this variational principle, the velocity and representative strain rate arc regarded as independent variables. The finite element method developed using the variational principle has been employed to explore the effects of deformation rate applied, and shape and size of the blocks on the now localization behavior. Key Words:Mixed type variational principle, Thermo-elasto-viscoplastic material, Strain-gradient-dependent constitutive model, Flow localization behavior.
Masataka TOKUDA, Petr SITTNER, Masayoshi TAKAKURA and Ye MEN
Abstract:This paper reports several interesting features in the shape memory alloy observed experimentally under multi-axial complex loading conditions including some temperature changes (the general loading condition). The experiments were performed systematically by applying the combined loads of axial force and torque to thin-wailed tubular specimen made of a Cu-based polycrystalline shape memory alloy. In these systematic experiments, the strong path dependency of pseudo-elastic phenomenon was observed, and moreover this dependency was disappeared completely only when the materials went back to the stress free state. This kind of unique behaviour of shape memory alloy may be quite interesting from a view point of new engineering applications of shape memory alloy. Key Words:Shape memory alloy, Pseudo-elastic behavior, Experimental study, Thin-walled tube, Combined load of axial force and torque, Path dependency, Temperature change, Intelligent material