Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

In this study, a series of long-term, intermittent permeability experiments utilizing Berea sandstone and Horonobe mudstone samples, with and without a single artificial fracture, is conducted for more than 1000 days to examine the evolution of rock permeability under relatively high-temperature and confining pressure conditions. Effluent element concentrations are also measured throughout the experiments. Before and after flow-through experiments, rock samples are prepared for X-ray diffraction, X-ray fluorescence, and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy to examine the mineralogical changes between pre and postexperimental samples, and also for microfocus X-ray CT to evaluate the alteration of the microstructure. Although there are exceptions, the observed, qualitative evolution of permeability is found to be generally consistent in both the intact and the fractured rock samples - the permeability in the intact rock samples increases with time after experiencing no significant changes in permeability for the first several hundred days, while that in the fractured rock samples decreases with time. An evaluation of the Damkohler number and of the net dissolution, using the measured element concentrations, reveals that the increase in permeability can most likely be attributed to the relative dominance of the mineral dissolution in the pore spaces, while the decrease can most likely be attributed to the mineral dissolution/crushing at the propping asperities within the fracture. Taking supplemental observations by microfocus X-ray CT and using the intact sandstone samples, a slight increase in relatively large pore spaces is seen. This supports the increase in permeability observed in the flow-through experiments. Key Points: A long-term evolution in rock permeability is measured The increase in permeability in the intact samples is likely due to the formation of flow paths The decrease in permeability in the fractured samples is attributed to the dissolution at the contacting asperities.

DOI： 10.1002/2014WR016427

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© (2015) Trans Tech Publications, Switzerland. We have proposed a new cold processing method to enlarge the diameter of a short section of a metal shaft using a combination of a cyclic bending load and an axial compressive load that is lower than the yield stress of the sample material. We call this cold processing method the diameter-enlargement working method, and refer to the enlarged section of the processed shaft as the diameter-enlargement section. The processing method produces large plastic deformation, and its Key features are as follows: the diameter-enlargement deformation progresses easily under a low axial compressive load at room temperature and the processed part exhibits little temperature increase. However, a crack is generated in the notch near the diameter-enlargement section during processing, and the cause is not yet clearly understood. Therefore, we conducted processing experiments to clarify the crack generation conditions, and simulated the working process using the finite element method to investigate the behaviors of stress and strain during processing. Furthermore, we calculated the low-cycle fatigue damage in the processed shaft using the Manson-Coffin expression. Based on the experiments and analyses, we determined that a fatigue crack is generated because of cyclic axial normal stress in the notch root at the axial-compressive loading side. The experimental and analytical fatigue strength was well described by the Coffin-Manson expression.

DOI： 10.4028/www.scientific.net/KEM.656-657.473

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© (2015) Trans Tech Publications, Switzerland. Metal pipes have a long history as fluid conduits, and are commonly joined with components such as elbows to form bent transport paths. However, with the increasing demands for economy and energy saving, pipes with reduced joints and thinner walls are desired. The number of joints can be reduced by a drawing and bending process that forms a bend section at any position in the pipe. However, this approach incurs problems such as wrinkling and flattening, especially under conditions of large bending angle, decreased bending radius, and thin pipe walls. In this research, applying vibrations to the mandrel was trialed as an approach for controlling the wrinkle depth and flattening. First, processing experiments were performed on thin walled pipes (wall thickness = 0.5 mm; outer diameter = 14 mm). The change of flattening and the number and depths of wrinkles were investigated in the presence and absence of vibrations. Next, simulations were performed using the commercial nonlinear finite element software. Through these simulations, the flatness and appearance of wrinkles were analyzed by modeling the behavior and distribution of stresses and strains in the processing process. The application of vibration to the mandrel appears to be a promising approach for controlling the wrinkling and flattening problems during pipe processing.

DOI： 10.4028/www.scientific.net/KEM.656-657.600

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Silicon dioxide has eight stable crystalline phases at conditions of the Earth's rocky parts. Many metastable phases including amorphous phases have been known, which indicates the presence of large kinetic barriers. As a consequence, some crystalline silica phases transform to amorphous phases by bypassing the liquid via two different pathways. Here we show a new pathway, a fracture-induced amorphization of stishovite that is a high-pressure polymorph. The amorphization accompanies a huge volume expansion of similar to 100% and occurs in a thin layer whose thickness from the fracture surface is several tens of nanometers. Amorphous silica materials that look like strings or worms were observed on the fracture surfaces. The amount of amorphous silica near the fracture surfaces is positively correlated with indentation fracture toughness. This result indicates that the fracture-induced amorphization causes toughening of stishovite polycrystals. The fracture-induced solid-state amorphization may provide a potential platform for toughening in ceramics.

DOI： 10.1038/srep06558

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This paper proposes a new near-net-shape working method to partially enlarge and control shaft's cross section through a metal mold. This study investigates the changes in the sectional area of shafts during the processing under various processing conditions, and evaluates the changes with a filling ratio. We introduce the processing method and the processing conditions, and then we report the results of processing experiments. Lastly, we clarify that processing conditions influence on the geometry of the processed part. © (2014) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/AMM.473.35

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We have proposed a new cold processing method to form a partial diameter-enlargement part in a hollow shaft. Using the processing method, the diameter-enlargement part with a large deformation is formed easily by applying compressive stress at yield stress level and cyclic torsional stress on two ends of specimen. In the present paper, processing experiments were conducted using the processing machine developed originally based on the processing principle, and deformation behaviors on the diameter-enlargement part were measured. In addition, the simulation analysis method in the processing was developed by the finite element method (FEM), the behaviors of stress and strain on processed part were analyzed, and deformation mechanism was investigated. It is clarified that the processing conditions affect the deformation behaviors base on the experiments and analysis. © (2014) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/AMM.473.30

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DOI： 10.1038/srep06558

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

This study experimentally and numerically investigated the damage extension of a brittle monolithic silicon carbide plate in response to the high speed impact of a projectile. An out-of-plane impact of a silicon nitride sphere with a velocity of 50 to 600 m/s induced multiple ring cracks on the contact surface. A crater, a cone crack, and a median crack were observed in the cross section under the contact point. The generation and extension of the damage were numerically studied based on linear fracture mechanics. A dynamic stress analysis using the finite element method demonstrated that the distribution of the principal axis corresponding to the maximum principal stress aligned radically from the contact point to induce a circular crack on the surface. (C) 2014 Published by Elsevier Ltd.

DOI： 10.1016/j.mspro.2014.06.017

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

We proposed a new cold processing method to partially enlarge the diameter of a shaft with a combination of a cyclic bending load and an axial compressive load that is lower than the yield stress of sample material. We call this cold processing method a diameter-enlargement working method, and call this processed part a diameter-enlargement part. Key features of the processing method are chiefly as follows: the diameter enlargement deformation progresses easily under a low axial compressive load at room temperature; the processed part has little temperature increase, although the processing causes large plastic deformation. We have tested the influence of the processing conditions and the mechanical properties of the sample materials in terms of diameter enlargement deformation behavior. However, little is known about the fatigue damage condition in a diameter enlargement part. Therefore, we carried out processing experiments to clarify crack generation conditions, and simulated working processing using finite element method in order to investigate behaviors of stress and strain during the processing. Furthermore, we evaluated low cycle fatigue damage in the processed part by using the Manson-Coffin expression. This paper clarified the mechanism of crack generation during the processing and evaluates the fatigue strength of the processed part. (C) 2014 Elsevier Ltd.

DOI： 10.1016/j.mspro.2014.06.242

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Nanocrystalline bulk stishovite, with pure SiO2 composition, was synthesized under high pressure and temperature. We found that this material has an extremely high fracture toughness (similar to 13 MPa m(1/2)), nearly eight times higher than that of stishovite single crystal. The measured Vickers hardness of this material was similar to 29 GPa and stishovite is known to be one of the hardest oxides. This new material has potential to be used for industrial purposes because of its combination of very high hardness and toughness. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2012.08.028

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Language：Japanese   Publishing type：Research paper (scientific journal)  

We investigate the mechanical strength of ceramic/metal composites subjected to cyclic thermal loading. First, test samples of Cu/AlN systems are prepared via brazing. Next, short-term thermal cycle tests (25, 50, and 100cycles) are conducted at temperatures ranging from -40 to 125°C. Four-point bending tests are conducted to evaluate the residual strength. Further, thermal stress analysis is performed using the finite element method in order to examine the thermal stress behaviors during cyclic heating. The results reveal that the residual strength increases during 0∼20cycles because of residual thermal stress relaxation. This relaxation is generated by the cyclic softening of the metals owing to combined hardening. In contrast, relatively long-term thermal cycling (20∼100cycles) reduces the residual strength owing to damage growth to AlN. The AlN plates exhibit variability in residual strength, and the distribution of the residual strength for each cycle number conforms to the two-parameter Weibull curve. The variability in residual strength increases with the cycle number, and it is attributed to variabilities in the pre-existing crack size and damage accumulation. We conclude that the residual strength of the Cu/AlN composites depends on the thermal stress behavior and damage growth to the AlN plates. © 2012 The Society of Materials Science, Japan.

DOI： 10.2472/jsms.61.530

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Ceramic balls have been used as components of devices, such as those found in high-pressure pumps for automobiles and industrial machines. In the backflow valve, for example, a ceramic ball is in contact with a conical surface. Fractures of ceramic balls are extremely rare. It is important to investigate the cause of these rare fractures to guarantee higher reliability in the backflow valve. In this paper, the fracture mechanism and strength are discussed for an equivalent normal stress seq beneath the contact region and the maximum principal stress sp near the contact boundary using stress intensity from fracture mechanics. The fracture surface of the ceramic ball was formed perpendicular to load direction. We assumed that fracture origins (defect/crack) existed on lines through three high stresses that analysed by finite element method. Actual fracture of a ceramic ball was found to be caused by the equivalent normal stress beneath contact region and not to be caused by the Hertz principal stress. Stress intensity factor (SIF) was clarified to depend on pressure, taper angle, CrN-coating thickness and the friction factor of the inside of the valve hole. A pre-existing defect size involved in failure was estimated by the SIF using three-dimensional elliptic defects and equivalent normal stress. Therefore, the actual fracture of a ceramic ball, which rarely occurs, could be evaluated by considering three-dimensional elliptic defects and the Weibull distribution of defects.

DOI： 10.1111/j.1460-2695.2011.01619.x

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Language：Japanese   Publishing type：Research paper (scientific journal)  

The effects of brazing filler metal diffusion on the mechanical strength of a ceramic/metal composite are described. First, a specimen of a SUS304/Cu/Si 3N 4 system, including brazing filler metals of AgCu and/or AgCuTi, was prepared by brazing in a vacuum furnace. Next, the vicinity of the joint parts was observed using field emission scanning electron microscopy. The brazing filler metals were found to diffuse into the Cu interlayer and ramify. In addition, a crack due to thermal stress resulting from a mismatch in thermal contraction between the materials present was observed around the AgCuTi/Si 3N 4 boundary. Energy-dispersive X-ray spectroscopic analysis revealed that Ag atoms diffused into the Cu interlayer to form the solid solutions of Ag and Cu. Micro-Vickers hardness tests were conducted on the surface of the Cu interlayer in order to examine the effects of brazing alloy diffusion on the hardening of the Cu interlayer. It was found that the diffusion of the brazing filler metals enhanced the hardness of the Cu interlayer. Finally, numerical simulations were performed to verify the increase in thermal stress due to hardening of Cu, and this behavior was discussed using simple equations. The results of the experiments and numerical simulations showed that the mechanical strength of the SUS304/Cu/Si 3N 4 composite is subjected to the diffusion of brazing filler metals. © 2012 The Society of Materials Science Japan.

DOI： 10.2472/jsms.61.197

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This paper experimentally and analytically investigates the fatigue strength and of mechanical damage of the processed shafts. First, we carry out rotary bending fatigue tests and investigate the fatigue stgate strain hardening near the processed part. Finally, we simulate stress and strain distributions of the shaft during the processing using finite element method (FEM) and calculate the stress concentration rate at the notch root of the processed part. Based on the processing experiments and the finite element analyses (FEA), we clarify that the plastic work mechanically does not reduce the fatigue strength of shafts in the processing range. © (2012) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/AMM.217-219.2346

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Language：Japanese   Publishing type：Research paper (scientific journal)  

The effects of thermal loading conditions on the mechanical properties of S45C/Cu/Si 3N 4 composites with brazing filler metals of AgCu and AgCuTi are described. Thermal loading tests were conducted on test samples under various heat conditions, after which the joint parts of the samples were observed with a focus on the Cu interlayers using an optical microscope. Four-point bending tests were conducted on the samples to evaluate the residual strength and stress strain characteristics of the samples. In addition, fracture surfaces and the origins of the fractures were observed using an optical microscope. The results showed that thermal loading of the S45C/Cu/Si 3N 4 composites caused fatigue damage to the Cu interlayers and its amount increased with increases in the cycle number and temperature range of thermal loading. In the case of relatively-mild thermal loading conditions, fracture initiation regions were observed at the Cu/Si 3N 4 boundary. In contrast, fracture initiation regions were observed in the Cu interlayer for the samples subjected to relatively-extreme thermal loading conditions. The increases in the cycle number and temperature range of thermal loading promoted reductions of residual strength, resilient modulus and residual fracture ductility for the samples. The reductions of the mechanical properties of the S45C/Cu/Si 3N 4 composites were affected by the fatigue damage of the Cu interlayers. It was concluded that continuous operation (no start-stop system) is suitable for long-term use of ceramic/metal composites including interlayers in order to minimize reduction of their mechanical strength. © 2012 The Society of Materials Science, Japan.

DOI： 10.2472/jsms.61.292

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This paper presents empirical models for predicting matrix crack density in a carbon fiber reinforced plastic (CFRP) cross-ply laminate under static-fatigue and cyclic-fatigue loadings. First, a modified slow crack growth (SCG) law, that covers the whole range of stress ratio R of tension-tension fatigue (0 ≤ R a;circ 1), was proposed. The modified SCG law and three conventional SCG laws were then combined with Weibull's probabilistic failure concept for predicting fatigue matrix crack density in a cross-ply laminate. Matrix crack density was expressed as a function of R, the maximum stress in the transverse ply and the number of cycles. Next, fatigue tests were performed for R of 0, 0.2, 0.4, 0.6, and 1 to determine the applicability of these four models. Finally, constant fatigue life (CFL) diagrams were investigated based on the modified model. © 2011 Society of Plastics Engineers.

DOI： 10.1002/pc.21192

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This paper aims at quantitative evaluation of residual strength after thermal shock in ceramics. First, a model predicting the residual strength from Young's modulus or crack density after thermal shock was established using a fracture mechanics approach. Next, thermal shock tests were carried out for porous SiC and soda glass. The residual strength and Young's modulus of both materials after thermal shock were measured. Then, the crack density of soda glass also was estimated by observing residual cracks on the surface. The experimental results were compared with the predictions to verify the validity of the model. The model exhibits good agreement with the experimental results. © 2011 The Japan Society of Mechanical Engineers.

DOI： 10.1299/kikaia.77.126

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DOI： 10.1299/kikaia.77.126

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The purpose of this paper is to estimate the fracture strength distribution of porous ceramics under quasi-static load. Four-point bending test was performed for SiC-porous ceramics at room temperature under quasi-static load. Fracture strength distributions obtained in the above test were estimated with the aid of a conventional probabilistic time-dependent fracture model on the basis of the slow crack growth concept in conjunction with two-parameter Weibull distribution. The results showed that the estimated fracture strength distribution curves were not in good agreement with the experimental data at stress rates. Porous ceramics have damage-tolerable property due to failure of a lot of grain boundaries. Therefore, this is because the dispersion of applied stress was not considered in the conventional model. A new probabilistic time-dependent fracture model considered the dispersion of applied stress was proposed based on Markov process in conjunction with local load sharing rule. The fracture strength distribution curves estimated the aid of the new model were in reasonably good agreement. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.engfracmech.2010.06.005

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Effects of loading rate on damage behavior in a pig liver loaded in compression were experimentally investigated. First, we developed a macroscopic damage model of liver cells or hepatocytes. Next, microscopic damage mechanism at the cell level was discussed through in-situ observation. Yield stress and strain were decreased with increasing strain rate. This behavior was ascribed to difference in pressure among individual liver components. The stress in a liver specimen subjected to a constant strain completely disappears after a certain period of time. For low strain rate, all the cells can endure high yield stress and strain because there is enough time for the individual cells to equilibrate the pressure. In contrast, for high strain rate, the yield stress and strain became lower since the cells cannot equilibrate the pressure due to limited intercellular blood flow during a short time. An interlobular connective tissue (Glisson's sheath) of a hepatic lobule was not easily damaged in the compressive field as it is stronger than the internal tissue. Consequently, the first failure occurred in the weakest central vein.

DOI： 10.1299/kikaia.76.625

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This paper discusses high-speed impact damage in a three-dimensionally woven SiC/SiC composite (3D-CMC). The impact damage was introduced by a steel ball projectile in 3D-CMC plates with and without thermal exposure. The surface and internal damages were observed by optical microscopy and X-ray CT. A crater was observed on the collision surface. The X-ray CT measurement revealed that multiple pyramid-shaped cone cracks were generated beneath the crater when the impact speed was relatively low. At an impact speed exceeding the critical speed, a spall fragment was ejected from the back surface, while no internal damage was observed in the fragment. The spall fracture mode differed between the virgin and the thermally-exposed specimens. This difference is the result of embrittlement of the fiber/matrix interface due to oxidation of the carbon coating layer in the thermally-exposed specimen. In addition, it is found that z-yarns improve impact resistance by constraining delamination. © 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.compositesa.2009.12.005

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Language：Japanese   Publisher：JAPAN SOCIETY FOR COMPOSITE MATERIALS  

The purpose of the present study is to obtain the fatigue limit diagram (FLD) and S-N diagram (SND) for transverse cracking in fiber reinforced plastic laminates under fatigue loading on the basis of the probabilistic slow crack growth (SCG) model. First, the deterministic and probabilistic FLD and SND were discussed for formulation. Next, the transverse crack density ρ was measured against number of cycles for various stress ratios <i>R</i> at a constant maximum stress to experimentally determine the parameters associated with the probabilistic SCG model. Finally, the FLD and SND were derived from the relationship among, ρ, <i>R</i> and fatigue life using the above parameters.

DOI： 10.6089/jscm.36.129

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Publishing type：Research paper (international conference proceedings)  

This paper aims at characterizing the high-speed impact damage behavior in CFRP unidirectional (UD) and cross-ply (CP) laminates. First, high-speed (~ 400 m/s) impact damage was introduced by collision of a flying steel sphere (projectile) to CFRP plates with the use of an electric heat gun. The surface and internal damages of the CFRP specimens were observed by using optical microscopy together with radiography. The damage process model was then established on the basis of the experimental result. Next, the dynamic finite element analysis was performed to simulate the damage process. Cohesive elements were introduced in the analysis to express the initiation and propagation of delamination while the maximum stress fracture criteria were employed to express another type of damage such as tensile, compressive and shear failure of the elements. Finally, the simulation was compared with the experimental results to understand the damage evolution mechanism.

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In order to investigate the effects of ball diameters and contact loading rates on ring crack occurrence, static and dynamic contact tests were carried out using ceramic bearing ball. As the results, the scatter of ring crack initiation strength in contact test of same ball diameters is smaller than that of same size. Ring crack occurs at a distance from contact boundary with decreasing ratio of ball diameters. Initiation strength of ring crack is not evaluated by maximum tensile stress on the ball surface, because micro-defects of ball surface doesn't consider. Therefore, the evaluation should apply the stress intensity factor. Since the ring crack occurrences are not dependent on size effect, the scatters of strength are constant even if ball diameters change. In the case of dynamic contact tests, the strengths are increased with decreasing loading time. Then, the scatter is also small. Ring crack strength in dependent loading rates can be evaluated using stress intensity factor and cumulative effective hold time. © 2009 The Society of Materials Science, Japan.

DOI： 10.2472/jsms.58.338

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This paper presents a delayed-fracture model for transverse cracking in CFRP cross-ply laminates under static fatigue loading. First, a delayed-fracture model for a crack in a brittle material was established on the basis of the slow crack growth (SCG) concept in conjunction with a probabilistic fracture model using the three-parameter Weibull distribution. Second, the above probabilistic SCG model was applied to transverse cracking in cross-ply laminates under static fatigue loading. The stress and the length of the unit element in the transverse layers were calculated with the aid of a shear-lag analysis, taking the residual stress into account. The transverse crack density was expressed as a function of applied stress and time with the parameters in the Paris law and the Weibull distribution function specified, in addition to the mechanical and geometrical properties. Unknown parameters were determined from experiment data gathered in static tensile and static fatigue tests. The reproduced transverse crack density at various applied loads agreed well with the experiment results. © 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.compscitech.2008.11.023

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The strength reliability of the ceramics/metal joints in the vacuum interrupters was studied focusing on the thermal stress around the ceramics/metal joints due to mismatch of thermal expansion coefficients between ceramics and metal. It was found from the experiment results that the residual strength of the joint depends on the amount of metal brazing alloy used as a jointing material. Firstly, in the present work, the thermal stress around the ceramics/metal joints was calculated using finite element analysis. Next, the effect of the amount of metal brazing alloy on the residual strength of the joint was investigated on the basis of a fracture mechanical approach. Finally, the amount of metal brazing alloy minimizing the strength reduction of the joint is determined using the results of the numerical analysis.

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Language：Japanese   Publisher：日本材料学会  

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Shear loading tests were executed to ceramics/metal joints used for an electronic device in various temperatures and loading rates. Fracture origin of the joints is formed from ceramics of interfacial neighborhood. According to FEM analysis, it is clarified that the driving force for the failure is not a shear stress but a tensile stress. The tensile stress dramatically decreases from just beneath the surface to interior portion. Slow crack growth behavior in nominal shear stress was estimated using fracture mechanics in the different conditions of loading rates.

DOI： 10.1299/jsmemecjo.2009.6.0_47

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Sphere indentation tests were performed to clarify damage properties on surface of Advanced Pore-Free SiC (APF-SiC) with excellent damage tolerance. The ring crack initiation strength properties were discussed from fracture mechanics viewpoint based on FEM analysis and detailed observations of growth behaviors of the ring crack and the cone crack. As compared to conventional SiC, the initiation strength was nearly equal to regardless of sphere sizes. However, its scatter was increased with increasing sphere sizes. Clusters are formed by uniting some in multi-micro cracks which occur near surface with increasing the contact load, one of that from which the ring crack occurs. Therefore, the strength and the scatter are controlled by the cluster size and its distribution, and the size depends on the generating crack density. It can be explained by the mechanics model which is expressed by the relationship between strength ratio and crack density based on the energy equilibrium theory. © 2008 The Society of Materials Science.

DOI： 10.2472/jsms.57.1138

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人日本機械学会  

In the present study, quench tests were carried out to characterize the fracture behavior of advanced pore-free SiC with damage tolerance during thermal shock. The residual strength of specimens after the quench tests was also measured. It is found that the critical temperature difference and the decrease in residual strength of this material are larger than those of conventional SiC. This is because the fracture is dominated only by flaw size since the wake zone is not generated during thermal shock with high strain rate. The critical temperature difference as well as the crack propagation is calculated with the aid of the unified theory of thermal shock.

DOI： 10.1299/kikaia.74.1156

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Advanced Pore Free SiC (APF-SiC) developed by newly improved reaction sintering method has excellent property such as super-high strength and damage tolerance ability by preceding failure of uniformly dispersing residual metallic silicon particles. In order to clarify effects of damage tolerance on strength property of this material, we have researched by carrying out 4-point bending tests at loading rates. As the result, at above loading rate of 0.5mm/min, it is found that the fracture strengths increase slightly with increasing loading rate. It is considered that delay fracture depended on the time from starting of slip of inclusion to fracture occurs in this material. One the other hand, it is found that the fracture strengths also increase at below loading rate of that. Generally, strength of the residual metallic silicones inviting damage tolerance decreases with decreasing loading rate since slow crack growth occurs. Then a lot of internal energy accumulated by loading is released with decreasing loading rate in this material. Therefore it is considered that resistance toward slip of inclusions increases and this behavior causes damage tolerance in this material, where can be theory explained by effects loading time. Moreover, it is suggested that unified strength estimation method proposed by Okabe et al.10) would be effectively to estimates strength property of material with damage tolerance ability. © 2008 The Society of Materials Science.

DOI： 10.2472/jsms.57.292

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

It had been well known that the fracture of SiC manufactured by conventional reaction sintering method was caused by one of the pores in that. However, according to the recent studies, pore free SiC. so called APF-SiC was developed by improvement of reaction sintering method. As the result, the strength and the damage tolerance ability rise and then the cause of fracture of APF-SiC changed from pores to something else. Therefore we have investigated fracture surface of APF-SiC by using FE-SEM and EDS in order to demonstrate the cause of fracture. As the result, we found the inclusion that consisted of allotropes of Carbon covered with very thin SiO2 and SiN layer. And the size of the inclusion is ten times larger than that of SiC grain. Considering from present results, the inclusion is the one of the cause of fracture of APF-SiC.

DOI： 10.2109/jcersj2.116.126

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In the present study, 4-point bending test was carried out by using porous ceramics to investigate statistical properties of damage-tolerant ceramics. Distribution of the bending strengths plotted on a Weibull probability paper was nonlinear and was very similar to superposed distribution. Consequently, the bending strength distribution was analyzed by cluster fracture probabilistic model with the basis of Markov process assuming the LLS rule. It is found that the probabilistic model agreed well than the 2-parameter Weibull distribution. Therefore this indicates that the bending strength distribution controls cluster size.

DOI： 10.1299/jsmemecjo.2008.1.0_291

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

Stress distributions beneath the contact surface of ceramic plat in contact with round bar were analyzed by 3-D FEM. On the basis of analytical results, the contact strength was evaluated by considering varied sizes and positions of pre-existing defects from a viewpoint of fracture mechanics. The contact rupture occurs from a surface defect that pre-exists in the vicinity of the edge of the plate. If we posit the premise that a defect size and a distance from contact boundary to its defect, the contact rapture load can be evaluated by using the proposed equation.

DOI： 10.1299/jmmp.1.490

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Advanced pore-free SiC (APF-SiC) with uniformly dispersing metal Si particle was developed by new process of manufacture. This ceramic material was investigated for mechanical properties and fracture behavior by evaluating tests such as 4-point bending, static fatigue and indentation at room temperature. It was found that bending strength of APF-SiC indicates about two times of strength for usual reaction-sintering SiC (RS-SiC). In addition, their mechanical properties (such as Poisson's ratio and Fracture toughness) are nearly equal. However, as for Weibull modulus and Young's modulus APF-SiC became smaller than RS-SiC. It is considered to be due to difference of their fracture mechanics. APF-SiC has the dispersing metal silicon particles of about 100 nm instead of the potential defects. As the load given to a specimen increases, a lot of cracks continues to occur in the boundary between metal silicon and silicon carbide and so the strain energy in and around them is released. Some clusters are formed by uniting some cracks. When maximum stress intensity factor around the cluster reached to a critical value, macroscopic fracture occurred with fracturing from some places at same time. The scatter as well as the fracture strength depends on the size of a cluster. In the static fatigue test of APF-SiC, the time dependence was not recognized in fracture strength. In addition, all experimental values obtained were more than the average of bending strength. This fracture strength property can be explained by a conceptual model that the cracks due to a constant bending load had stopped initiating and started uniting on releasing the energy around the cluster of many cracks.

DOI： 10.1299/kikaia.73.926

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Advanced Pore-Free SiC (APF-SiC) with super-high strength is expected to be used as engineering structural materials since it has damage tolerance ability by preceding failure of metallic silicon particles In the present study, thermal shock tests of this material were carried out to characterize the fracture behavior. The residual strength after thermal shock was also measured. It is found that the critical temperature difference ΔT_c of this material is larger than that of conventional SiC due to smaller size of pre-existing flaws. As the result, the validity of the Griffith's theory was experimentally confirmed. In addition, the damage tolerance behavior in thermal-shocked materials is not observed because the metallic silicon particles may he failed by thermal shock.

DOI： 10.1299/jsmemecjo.2007.1.0_647

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The impact damage in a silicon carbide plate caused by a collision of a silicon nitride sphere was characterized through microscopic observations as well as an analysis based on the Hertz's contact theory. The experimental results in the impact tests were compared with those in the quasi-static indentation tests. It was proved that the minimum and maximum radii of multiple ring cracks increased with increasing speed or maximum collision load, and that the corn crack growth also had the collision speed-dependency. The maximum radius of the ring crack agreed well with a theoretical one which was derived based on the Hertz's theory while the minimum radius of the ring crack becomes smaller than theoretical one at high collision speeds where the sphere was broken into pieces due to impact load. It was presumed from the analysis that a ring crack with a minimum radius was generated when the collision load reached 40% of the maximum one.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASME-AMER SOC MECHANICAL ENG  

To minimize surgical stresses including blood loss and operation time to the patients during hepatic resection, we studied the feasibility of a combination of a partial liver freezing technique and shape-memory alloy, which also enables a free-designed resection curve. In this surgical procedure, the region surrounding a tumor in the liver is frozen to excise and prevent hemorrhage. The liver was frozen by a Peltier module. The effects of cooling rate and freezing temperature on the excision force that arise between a scalpel and the liver are carried out experimentally as a basic research for partial freezing surgical procedures. A porcine liver was used as a liver sample. The physical properties were estimated by using the finite element method based on the heat transfer characteristics of the liver. Isolation of the liver was conducted using a scalpel attached to the end-effector of a 3 degrees of freedom robot. In the experiments, the minimum excision force was obtained at a temperature between 272 K and 275 K; therefore, it is preferable that the liver be excised within this temperature range. Lowering of the cooling rate decreases the excision force even if the temperature of the liver remains unchanged. The lower the temperature of the liver is, the larger the increment rate of excision force is with regard to the cooling rate.

DOI： 10.1115/1.2244577

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Ceramics strength under a contact stress with horizontal force was analyzed using finite element method. When ceramic plate was compressed with a ball or round bar, it was found that the occurring position of a surface crack under the compressive condition by round bar becomes further from the contact boundary compared with that by a ball. On the other hand, the surface crack taking part in failure becomes larger. The maximum contact stress and maximum stress intensity factor at tip of a surface flaw slightly outside contact boundary become larger with increasing of horizontal force. And the position of their maximum value approaches the contact boundary. As seen in experimental results, the surface crack ocurrence position was found to approach the contact boundary with increasing of horizontal force.

DOI： 10.1299/kikaia.72.2038

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DOI： 10.1299/kikaia.72.2045

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Language：Japanese   Publishing type：Research paper (scientific journal)  

An actual joint structure of ceramics-metal in the airtight seal parts for a neutron detector was studied on the residual stress generated in the joint process due to the difference of the thermal expansion coefficient between ceramics and metal. The influences of shape and dimension of the joint structure on the residual stress were clarified analytically by finite element method (FEM) and verified experimentally by checking cracks generated in prototype samples. Based on fracture mechanics, equivalent stress intensity factor K Ieq was calculated in consideration of a latent flaw in the residual stress fields, and optimal geometries of the joint structure were proposed for reducing the residual stress. The residual joint strength was discussed by using the difference ΔK Ieq between fracture toughness K IC and K Ieq. The main results obtained are summarized as follows : the residual joint stress increases with the thickness of a Cu-Ti eutectic reaction layer
the residual joint stress decreases with the reduction in taper angle of the end of Cu interlayer
the residual joint stress is hardly influenced by wall thickness in the end of SUS304 pipe. On the basis of these results, the optimization in the structural factors can decrease the residual stress because of reducing stress concentration field near the interface of ceramic and metal, and so the residual joint strength increase with decreasing of the residual stress depending in the structural factors as the thickness of a Cu-Ti eutectic reaction layer, taper angle of the end of Cu interlayer and wall thickness in the end of SUS304 pipe.

DOI： 10.2472/jsms.54.741

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人日本機械学会  

Compressive tests were carried out to measure the mechanical properties such as Young's modulus and strength of a pig's liver. There is no evidence showing macroscopic anisotropy in the liver although blood vessels were distributed in a quasi-transversely-isotropic array. Compression tests of the liver specimens which are not mechanically constrained gave more accurate stress-strain behavior rather than those of the constrained specimens. The Young's modulus and yield stress of a fresh live within 12 h after the slaughter are almost constant regardless of the presence of physiology brine solution. The intestine membrane has higher Young's modulus and maximum strength (or yield stress) than internal tissue of the liver. However, strain for crack initiation of the membrane is almost equal to yield strain of the internal tissue. Yield strain is used as a valid parameter which evaluates mechanical damage of the liver. The tangent modulus of the liver which shows viscoelastic phenomena can be approximated by a binomial function. This function can be applied to not only an soft tissue under compressive loading but also a stiffer membrane loaded in tension.

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Language：Japanese   Publisher：金沢工業大学材料システム研究所  

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmebs.2004.17.0_409

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmebs.2004.17.0_405

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmebs.2004.17.0_407

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Language：Japanese   Publisher：愛媛大学  

Fracture mechanics based considerations were made for investigating the ring-crack formation of ceramic plates contacted with a ceramic sphere under a combined normal and tangential indentation load. The intrnsic tensile strength of the ceramic plate did not dictate the onset of ring-crack formation. The size of pre-existing defects (being less than one micron) that may result in the ring-crack initiation were somwhat smaller than the grain size of the ceramic plate. On the other hand, the stress gradient induced beneath the contact was significantly dependent on the contact angle of normal/tangential combined load; when the contact angle is increased, the mean dimension of defects which lead to ring-crack initiation becomes large, whereas the location of the induced crack is progressively away of the contact circle. The stress gradient induced beneath the contact was taken into account for calculating the stress intensity factor of the pre-existing surface defect. The fracture toughness value thus estimated for the ceramic plates satisfactorily predicted the onset of ring-crack formation of all the ceramic plates examined.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Society of Materials Science Japan  

Fracture mechanics based considerations were made for investigating the ring-crack formation of ceramic plates contacted with a ceramic sphere under a combined normal and tangential indentation load. The intrnsic tensile strength of the ceramic plate did not dictate the onset of ring-crack formation. The size of pre-existing defects (being less than one micron) that may result in the ring-crack initiation were somwhat smaller than the grain size of the ceramic plate. On the other hand, the stress gradient induced beneath the contact was significantly dependent on the contact angle of normal/tangential combined load
when the contact angle is increased, the mean dimension of defects which lead to ring-crack initiation becomes large, whereas the location of the induced crack is progressively away of the contact circle. The stress gradient induced beneath the contact was taken into account for calculating the stress intensity factor of the pre-existing surface defect. The fracture toughness value thus estimated for the ceramic plates satisfactorily predicted the onset of ring-crack formation of all the ceramic plates examined.

DOI： 10.2472/jsms.53.1149

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Language：Japanese   Publisher：一般社団法人 日本機械学会  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Society of Materials Science Japan  

Contact strength tests were carried out in soda lime glass plate with a small ceramic sphere. As the ring crack initiation stress changes with increasing the contact angle, the peculiar tensile strength of glass is not applicable as the criterion of initiation strength. Initiation strength including steep stress distribution was discussed from the view-point of fracture mechanics. Stress inclination changes with increasing the contact angle. Crack lengths which cause the ring crack initiation are extremely short and a submicron order. The ring crack occurs also even at a position away from the contact circle because stress level is high. Arranging the phenomenon by the stress intensity factor, the ring crack was caused in the fracture toughness value of glass. Therefore, the application of the stress intensity factor is appropriate as the evaluation parameter of the ring crack initiation. Furthermore, a probabilistic evaluation equation can be expressed using stress intensity factor and Weibull modulus in which a contact angle and an effective volume are considered.

DOI： 10.2472/jsms.53.175

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BLACKWELL PUBLISHING LTD  

Residual stresses generated by the mismatch of thermal expansion coefficients of ceramics and metals affect the strength of ceramic-metal joints. An interlayer metal can be inserted between the ceramic and metal in order to relax this stress. An analysis was carried out of the residual stresses produced during joint-cooling and in 4-point bending tests. The effects of interlayer thickness on ceramic-metal joint strength were then studied by considering a superimposed stress distribution of the residual stress and the bending stress. Finally, joint strength was estimated from fracture mechanics and strength probability analysis by considering the residual stress distribution, defect size and position of pre-existing defects in the ceramic parts. As a result of this study, we suggest an optimum material selection and interlayer thickness for ceramic-metal joint structures. This approach is generally suitable for the design of electrical and mechanical structures.

DOI： 10.1046/j.1460-2695.2003.00581.x

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To widely use "Residual stress measurement for engineering ceramics by indentation fracture method" industrially, the investigation of detailed magnification factor is indispensable. The influences stress distribution on magnification factor and application and magnification factor of this measuement to several ceramic materials were was discussed. The magnification factor which were almost equal to JSMS-SD-4-01 were obtained by considering indent load dependency under stress field of uniformal compression. The magnification factor is almost equivalent in both Si_3N_4 and Al_2O_3. On the other hand, the magnification factor increased with increasing indent load under gradient stress field.

DOI： 10.1299/jsmemecjo.2003.1.0_317

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this research, packaging structures in which chip parts were bonded to the ceramics substrate of Alumina (Al_2O_3) or nitride aluminum (AIN) with electro-conductive adhesive etc. through a thick film conducting electricity, was studied. For the structures, the bonding remaining strength, considered the residual stress caused in a bonding process based on fracture mechanics, was evaluated, and the influences of both the ceramics substrate and the thick film conductor's thermo-physical property on the strength were examined. Moreover, to examine the decrease behavior of the bonding residual strength by heat cycle loads in-service, thermal cycle tests, the verification tests of a peeling strength, and the simulation analyses of those tests were done, and the peeling fracture strength and the fracture life were predicted. As a result, the mechanism of trouble generated in-service is clarified from the viewpoint of fracture mechanics, the validity of remedies is confirmed, and the present research is useful for the new development of the product.

DOI： 10.1299/jsmemecjo.2003.1.0_315

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC MATERIALS SCIENCE, JAPAN  

Residual stress generated by thermal expansion coefficient mismatch between ceramic and metal is an important problem affecting the strength of ceramic-metal joints. An interlayer, which is a ductile metal, is often inserted between ceramic and metal in order to relax this residual stress. In this study, the residual stress produced in the joint-cooling process is analyzed and 4-point bending tests are carried out. From the viewpoint of experimental observations and fracture mechanics, the effects of interlayer thickness on joint strength in ceramic/metal joints are discussed considering the superimposed stress distribution of the residual stress and the bending stress. Joint strength is then estimated based on fracture mechanics and fracture probability considering the superimposed stress, crack size and position of pre-existing defects in the ceramics. The optimum interlayer thickness for the present specimen is identified, and the estimation method is extended to the analysis of generic joint strength using normalized strength of ceramic by expressing joint strength in terms of normalized strength considering the scatter of joint strength and the effective volume.

DOI： 10.2472/jsms.51.9Appendix_109

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC MATERIALS SCIENCE, JAPAN  

Residual stress generated by thermal expansion coefficient mismatch between ceramic and metal is an important problem affecting the strength of ceramic-metal joints. An interlayer, which is a ductile metal, is often inserted between ceramic and metal in order to relax this residual stress. In this study, the residual stress produced in the joint-cooling process is analyzed and 4-point bending tests are carried out. From the viewpoint of experimental observations and fracture mechanics, the effects of interlayer thickness on joint strength in ceramic/metal joints are discussed considering the superimposed stress distribution of the residual stress and the bending stress. Joint strength is then estimated based on fracture mechanics and fracture probability considering the superimposed stress, crack size and position of pre-existing defects in the ceramics. The optimum interlayer thickness for the present specimen is identified, and the estimation method is extended to the analysis of generic joint strength using normalized strength of ceramic by expressing joint strength in terms of normalized strength considering the scatter of joint strength and the effective volume.

DOI： 10.2472/jsms.51.9Appendix_109

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC MATERIALS SCIENCE, JAPAN  

The ceramics/metal joints in the airtight seal parts for a neutron detector are studied on the reliability for strength and long-term life. Both functions of airtight and insulation are required for the airtight seal parts, which suffer a very bad influence from a viewpoint of long-term reliability as well as strength, because the residual sum is generated in these joints due to die difference of the thermal expansion coefficient between ceramics and metal. The ceramics subjected to neutron irradiation in-serve occurs in swelling (volume expansion) and decreases in strength. Moreover, the copper interlayer rises in yield sum and hardens with increasing the plastic deformation due to the swelling of ceramics, and so lowers in function for stress relaxation. As a result, not only the internal stress in ceramics increases with passing the time in service, but also the facture strength of ceramics lowers, and finally a delayed fracture occurs at the ceramic/metal joints in the airtight seal parts. Therefore, in our study, the residual stress has been analyzed by a simulation model using FEM so that both mechanisms of the increment in internal stress as well as mechanical damage can be clarified for the ceramic/metal jointing parts subjected to the neutron irradiation over long-term. On the other hand, the strength verification against the ceramic/metal joints are performed through simulation model analyses as well as the virtual tensile tests for small mock up specimens. From a viewpoint of fracture mechanics, the reliability for fracture life as well as strength of the airtight seal parts is discussed statistically considering the scatter of strength for Si3N4.

DOI： 10.2472/jsms.51.9Appendix_101

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Society of Materials Science Japan  

To use effectively various strength data of ceramic/metal joints for materials development, structural design, and strength reliability analysis in the future, fracture strength database was constructed by using commercial software of easy operativeness. The database has been collected the strength data of about 1800 or more obtained by bending, fatigue, creep, and heat cycle test, etc. It is equipped with the function of addition/edit and retrieval/extraction of data. Furthermore, as one of utilities of this database, a basic strength properties and strength reliability of joints were mentioned in this paper, and the unified strength estimation method was applied to the joints. As the results, an evaluation equations that were derived by considering scatter of joint strength, can estimate the strength that corresponds to various test situations from basic strength such as bending strength.

DOI： 10.2472/jsms.51.61

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Language：English   Publishing type：Research paper (scientific journal)  

The ceramics/metal joints in the airtight seal parts for a neutron detector are studied on the reliability for strength and long-term life. Both functions of airtight and insulation are required for the airtight seal parts, which suffer a very bad influence from a viewpoint of long-term reliability as well as strength, because the residual stress is generated in these joints due to the difference of the thermal expansion coefficient between ceramics and metal. The ceramics subjected to neutron irradiation in-serve occurs in swelling (volume expansion) and decreases in strength. Moreover, the copper interlayer rises in yield stress and hardens with increasing the plastic deformation due to the swelling of ceramics, and so lowers in function for stress relaxation. As a result, not only the internal stress in ceramics increases with passing the time in service, but also the facture strength of ceramics lowers, and finally a delayed fracture occurs at the ceramic/metal joints in the airtight seal parts. Therefore, in our study, the residual stress has been analyzed by a simulation model using FEM, so that both mechanisms of the increment in internal stress as well as mechanical damage can be clarified for the ceramic/metal jointing parts subjected to the neutron irradiation over long-term. On the other hand, the strength verification against the ceramic/metal joints are performed through simulation model analyses as well as the virtual tensile tests for small mock up specimens. From a viewpoint of fracture mechanics, the reliability for fracture life as well as strength of the airtight seal parts is discussed statistically considering the scatter of strength for Si3N4. Key words: Ceramics/Metal Joints, Mechanical Damage, Strength Reliability, Neutron Irradiation, Residual Stress, Swelling, hardening, Fracture toughness, Fracture Life. © 2002, The Society of Materials Science, Japan. All rights reserved.

DOI： 10.2472/jsms.51.9Appendix_101

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Language：English   Publishing type：Research paper (scientific journal)  

Residual stress generated by thermal expansion coefficient mismatch between ceramic and metal is an important problem affecting the strength of ceramic-metal joints. An interlayer, which is a ductile metal, is often inserted between ceramic and metal in order to relax this residual stress. In this study, the residual stress produced in the joint-cooling process is analyzed and 4-point bending tests are carried out. From the viewpoint of experimental observations and fracture mechanics, the effects of interlayer thickness on joint strength in ceramic/metal joints are discussed considering the superimposed stress distribution of the residual stress and the bending stress. Joint strength is then estimated based on fracture mechanics and fracture probability considering the superimposed stress, crack size and position of pre-existing defects in the ceramics. The optimum interlayer thickness for the present specimen is identified, and the estimation method is extended to the analysis of generic joint strength using normalized strength of ceramic by expressing joint strength in terms of normalized strength considering the scatter of joint strength and the effective volume. © 2002, The Society of Materials Science, Japan. All rights reserved.

DOI： 10.2472/jsms.51.9Appendix_109

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Society of Materials Science Japan  

The residual stress, which generated by thermal expansion coefficient mismatch between ceramics and metals, is an important problem on strength in ceramic/metal joints. An interlayer, which is a ductile metal, is inserted between ceramics and metal in order to relax the residual stress. In this study, first of all, the analysis of the residual stress produced in joint-cooling process and 4-point bending tests were carried out. Next, from a viewpoint of experimental and fracture mechanics, the effects of interlayer thickness on joint strength in ceramic/metal joints were discussed considering the superposed stress distribution of the residual stress and the bending stress. In addition, the estimation of joint strength was tried to do from viewpoints of fracture mechanics and probability of strength by considering the superposed stress, size and position of potential defects in the ceramics. From the above-mentioned, it is found that the optimum thickness is 0.2mm in this specimen. Joint strength in various interlayer thicknesses can be estimated as normalized strength of ceramics by arranging joint strength to normalized strength considering the scatter of joint strength and the effective volume.

DOI： 10.2472/jsms.50.7

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Society of Materials Science Japan  

In order to clarify the extreme strength of spinning fracture, the high-speed spin tests were carried out for two ceramic circular disks till they burst. On the other hand, the spinning fracture strengths were evaluated by theoretically analyzing the centrifugal stress distribution and by using the unified estimation method for ceramic strength. Also, the residual stresses on the surface of the ceramic circular disks were estimated by using the indentation flaw method (IF method) and their influences on the spinning fracture strength were studied from the viewpoint of fracture mechanics. The extreme spinning fracture strengths were successfully estimated from the 4-point bending strength by using the unified strength estimation method. The residual stress had the negligible influence on the spinning fracture strength. The ceramic circular disks were clarified to have sufficient reliability against fracture in practical service of textile machinery.

DOI： 10.2472/jsms.50.284

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

In order to clarify the conditions for fracture morphology of monolithic ceramics subjected to a solid particle collision, the stress analysis of ceramic circle plate subjected to compressive contact load by a small ball was carried out for the various circle plate thicknesses. The maximum stresses of three critical points were compared in the relation with the plate thickness. As fracture criteria the stress intensity factor on the basis of stress distribution were analyzed for each critical points. The behaviors of fracture morphology depending to the plate thickness were successfully clarified by estimating K1 for fracture criteria. On the basis of small ball collision test results, the collision velocity, which converted from impact load, can express the conditions for the fracture morphology. The critical collision velocity is found to change depending to plate thickness and fracture toughness of ceramics.

DOI： 10.1299/kikaia.66.1758

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Soc Mater Sci, Japan  

A major problem in ceramic/metal joint is thermal expansion coefficient mismatch between ceramics and metal. This thermal expansion coefficient mismatch causes serious residual stresses at the interface of the ceramic/metal joint, which generated during joint-cooling process. Then, an interlayer, which is ductile metal such as copper, nickel and so on, is inserted between ceramics and metal because of relaxing the residual stress. It should be considered that thickness of interlayer have significant influence on the joint strength with considering the residual stress. In this study, it paid attention to the thickness of interlayer, and the optimum thickness of interlayer was discussed from a viewpoint of the stresses based on simulation model analysis as well as 4 point bending tests, considering the residual stresses, which were analyzed using three-dimensional plasto-elastic finite element method. As a result of the analysis, residual stress increased with decreasing of the interlayer thickness. The superposing stress of the applied bending stress and the residual stress showed minimum value in the case of the interlayer thickness of 0.2 mm. On the other hand, paying notice to the result of the bending test as well as the analysis, the joint specimen showed the highest bending strength in the case of the interlayer thickness of 0.2 mm. Furthermore, the scatter of joint strength is apparently small in this thickness compared with in the other thickness.

DOI： 10.2472/jsms.49.905

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Soc Mater Sci, Japan  

Room and high temperature four point bend tests for Si3N4/SUS3O4 joints were carried out at various crosshead speeds. Ceramics/metal interface region and brazing zone were analyzed using a vickers hardness tester, SEM and EPMA to discuss the relation between strength of joints and microstructure. Furthermore, the fracture strength and the nature of its scatter were estimated based on the proposed model. Failure of brazed Si3N4/metal joints occurred at a flaw in ceramics near bonding interface. Therefore, the bending strength of the joints was dominated by a magnitude and distribution of stress concentration induced in ceramic region. The magnitude of stress concentration induced in ceramic region was dependent on deformation resistance of interlayer. This buffer effect of interlayer depended on exposed time of the specimen at test temperature, which inversely corresponds to loading rate. The dispersion of strengths of the joints was well described according to the weibull distribution using unified estimation method. The estimation equation was proposed to evaluate the bending strength and its nature of scatter.

DOI： 10.2472/jsms.48.1288

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Soc Mater Sci, Japan  

Cyclic tensile fatigue tests were conducted for Si3N4/S45C joint specimens with copper interlayer at room temperature in order to clarify fatigue strength properties of ceramic/metal joint, considering the influence of residual stress in ceramics induced during joining process. Not only the joining process residual stress but also the residual stress behavior due to cyclic tensile loading was analyzed by using the three-dimensional elastic-plastic finite-element method. All experimental data obtained in this study were tried to arrange as the relationship between the normalized testing stress and the effective loading time by using the unified estimation method with considering effective volume and effective loading time. However, even if using the unified estimation method, the normalized strengths in the cyclic fatigue tests were clearly lower than normalized tensile strength at fracture probability of 50%. The difference of both normalized strengths was caused by the increase of the residual stress redistributed during cyclic fatigue tests. The redistributed residual stress was due to the reversible plastic deformation made in the interlayer of copper, but tended to saturate after second cycles. Then, if modifying not only the effective loading time but also the time-strength by using the unified estimation method against the superposing stress of the testing stress and the redistributing residual stress in cyclic fatigue tests, the cyclic tensile fatigue strengths agreed well with the normalized tensile strength for ceramic/metal joints as well as for monolithic ceramics. All cyclic fatigue strengths containing tensile fracture strength can be estimated well as the normalized strength with scatter properties of Weibull distribution.

DOI： 10.2472/jsms.48.1416

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Society of Materials Science Japan  

Room and high temperature four point bend tests for Si3N4/SUS304 joints were carried out at constant loading. Fracture surfaces of the interlayer of joints were observed using SEM to discuss the fracture mechanism at high temperature. Furthermore, the fracture strength distribution was estimated on the basis of the unified estimation method considering the fracture mechanism. (1) Failure of brazed Si3N4/metal joints in high stress level was occurred at a flaw in ceramics near bonding interface. On the other hand, failure of the interlayer in low stress level was occurred due to creep rupture. Creep rupture of joints was dominated on steady-state creep of the interlayer. Then, creep rupture life also could be predicted from minimum creep strain rate in interlayer by using both equation of Monkman-Grant18) and Norton's law.19) (2) The fracture strength of the joints could be evaluated considering the temperature dependence of strength as follows: σf· teff 1/n, = σ̂f exp[(- Qi/k)(1/T + 273 - 1/Tθ + 273)]m̂,√ln(1 - Pf)-1 (3) Reliability structural design of joints had better determine the stress level and proof life considering failure of the interlayer with small scatter of rupture lives.

DOI： 10.2472/jsms.47.1221

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Bridging and interlocking elements, which are responsible for the stress shielding effect, are frequently observed in the wake of fatigue cracks. The crack growth curves arranged by the crack tip stress intensity factor K<SUB>tip</SUB> (da/dN-K<SUB>tip</SUB> curves), where the stress shielding effect is taken into consideration, almost coincide regardless of loading history, while those arranged by the apparent stress intensity factor K<SUB>app</SUB> (da/dN-K<SUB>app</SUB> curves) significantly depend on the loading history. The fatigue crack growth resistance increases with increasing grain size. The main reason for this grain size dependence is that the stress shielding effect becomes significant with increasing grain size. The crack growth curves arranged by K<SUB>tip</SUB> almost coincide regardless of grain size.

DOI： 10.1299/kikaia.62.1985

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Cyclic fatigue crack growth tests of silicon nitride specimens with surface cracks as well as through-the-thickness cracks were carried out. The surface crack length was measured by a surface film gage technique. The fatigue crack growth rate for surface cracks was less than that for through-the-thickness cracks. From SEM observations, more significant bridging was found in the wake of surface cracks compared to through-the-thickness cracks. From evaluations of the stress shielding effect due to bridging based on the measurements of the crack mouth opening displacement, it was found that the crack growth curve determined from the crack tip stress intensity factor Ktip for surface cracks almost coincided with that for through-the-thickness cracks.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：FATIGUE & FRACTURE ENGINEERINGMATERIALS STRUCTURES LIMITED  

Fatigue crack growth tests of five ceramic materials were carried out in order to investigate the general characteristics of cyclic and static fatigue crack growth in ceramics. A cyclic effect was found in Si3N4, Al2O3 and TiB2, where the main fracture mechanism was intergranular separation, and stress shielding due to grain bridging occurred near the crack tip. On the other hand, no cyclic effect was observed in SiC and ZrO2, where the main fracture mechanism was transgranular fracture. The fatigue crack growth curves reduced to a unique curve by using the parameter K(tip)/E, regardless of the kind of ceramics studied.

DOI： 10.1111/j.1460-2695.1993.tb00126.x

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ENGINEERING MATERIALS ADVISORY SERVICES LTD  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：PERGAMON PRESS LTD  

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Fatigue crack growth tests of several ceramic materials were carried out to investigate the general characteristics of cyclic and static fatigue crack growth in ceramics. The cyclic effect was found in Si<SUB>3</SUB>N<SUB>4</SUB>. Al<SUB>2</SUB>O<SUB>3</SUB> and TiB<SUB>2</SUB>, where the main fracture mechanism was the intergranular fracture. On the other hand no cyclic effect was observed in SiC or ZrO<SUB>2</SUB>, where the main fracture mechanism was the transgranular fracture. The fatigue crack growth curves were found to be reduced to a unique curve by using Δ K<SUB>eff</SUB>/E, regardless of the kind of ceramics.

DOI： 10.1299/kikaia.57.2615

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Fatigue crack growth tests of silicon nitride specimens with long cracks were carried out to investigate the effects of wave form of loading, stress ratio and frequency. The crack growth rate was independent of the wave form of loading and frequency. The effective stress intensity factor range afforded a unique crack growth curve regardless of stress ratio in the range of low growth rate. The fatigue crack growth rate in cyclic fatigue was higher than that in static fatigue. Fatigue tests of smooth specimens with small surface cracks induced by grinding were also carried out in the high frequency range. The S-N curve was predicted by using the both cyclic and static crack growth curves, where the initial surface crack size was defined on the basis of the strength of the specimen and the fracture toughness value. The S-N curve predicted using the cyclic crack growth curve was not in agreement with the experimental results. On the other hand, the predicted S -N curve using the static crack growth curve was in good agreement with the experimental results. Therefore, it is clear that a small crack tends to grow in a static fatigue manner even in the range of high frequency and low crack growth rate, where the cyclic crack growth is dominant for long cracks. © 1991, The Society of Materials Science, Japan. All rights reserved.

DOI： 10.2472/jsms.40.588

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The fracture toughnesses of Si<SUB>3</SUB>N<SUB>4</SUB> (two lots), SiC, TiB<SUB>2</SUB>, ZrO<SUB>2</SUB> and Al<SUB>2</SUB>O<SUB>3</SUB> were obtained by bending precracked specimens in three different ways: by the bridge compression (BC) method, by fatigue precracking from a crack introduced by the BC method (FP method), and by the controlled surface flaw (CSF) method. For comparison, fracture toughness evaluations by the chevron notch (CN) method and the indentation fracture (IF) method were also carried out. Furthermore, the effect of loading rate on fracture toughness of FP specimens was examined together with a crack propagation test under static fatigue. The K<SUB>IC</SUB> values evaluated by FP, CSF and CN methods showed a reasonable agreement with each other for all six of the ceramics tested, while the evaluation by BC and IF methods tended to give considerably lower values than those obtained by the three methods. The normalization of these K<SUB>IC</SUB> and K<SUB>ISCC</SUB> values was done by a theoretical K<SUB>IC</SUB> value, which was derived according to the Griffith criterion for unstable fracture. The different fracture modes of these materials were successfully characterized in correlation to the normalized fracture toughness.

DOI： 10.1299/kikaia.57.1326

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Fuel cell is expected in realizing a low carbon society. However, objective comparison of cell is difficult because cell has been developed by various manufactures. Therefore, strength evaluation method of cell hasn't been established. In the present study, we aimed at the establishment of strength evaluation method about cell. Same models of small punch testing were made by finite element method. Therefore, in the contact state of the plates, change in stress distribution into experiment condition was analyzed by finite element method. As the results, experiment condition that contact stress is higher is found.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

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The mechanical strength properties of ceramic/metal substrates exposed to cyclic thermal loadings were studied in order to discuss the effects of the number of thermal loadings on the residual strength of the substrates. First, thermal stress analysis was performed using the finite element method for an examination of the thermal stress behaviors during the cyclic thermal loading processes. Next, test samples of Cu/AIN substrates, including brazing filler metals of AgCuTi, were prepared by brazing in a vacuum furnace. Thirdly, thermal cycling tests with cycle numbers of 25,50 and 100 were conducted on the test samples. Finally, four-point bending tests were conducted on the thermally-loaded samples to evaluate residual strength. The results showed that residual strength increased after 25 thermal cycles. In contrast, thermal cycling with 25-100 cycles resulted in a reduction of residual strength. These behaviors were discussed in terms of residual stress relaxation and a mechanism for the microscopic damage of sintered materials with polycrystalline structures.

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Porous ceramics is expected to be applied as cleanup filter under high temperature environment since it has high damage tolerance ability. We have investigated effect of damage tolerance ability on fundamental fracture properties by carrying out 4-point bending test under loading rates. As the result, at above loading rate of 0.5mm/min, strengths increased with increasing loading rate. Because it is only depended at slow crack growth of one of the flaws in this material. In contrast, at the loading rates below 0.5mm/min, strengths also increased. It is considered that resistance to crack growth increased due to release of accumulated internal energy since grain boundary markedly fails with decreasing loading rate. These phenomenon was explained by unified strength estimation method considering effect loading rate.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The quantitative estimation is required since the fatal defect called a ring crack will occur when a ceramic ball is used for ceramic bearing. We considered the application of stress intensity factor and effective volume by performing FEM analysis and the contact examination of balls. As the results, it did not depend on ball size for the scatter of ring crack initiation load, and it was clarified that a ring crack progressed aslant to the ball surface. The stress intensity factor was discussed based on these results. It was clearly showed that the crack length involved in the formation of a ring crack was approximately 1.5μm, without dependence of ball size. This analytical result is well agreement with an experimental result. Therefore, it was proved theoretically that it is not necessary to consider the influence of effective volume in ring crack initiation of a ball.

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Language：English   Publisher：一般社団法人日本機械学会  

Advanced Pore-Free SiC (APF-SiC) with super-high strength is developed by reaction sintering method improved newly. Authors had constructed a peculiar fracture mechanism model of this material differing from the fracture mechanism of usual ceramics. The fracture mechanism is that fracture occur at cluster crack (one of the formed some clusters). This fracture is called cluster fracture. In this study, to clarify adequacy of this model, clusters were researched in detail by using mapping analysis and observing some clusters. Crack growth behavior is researched by using AE censer. As the results, it is clarified that some clusters are formed by aggregate of un-reacted substance and the cluster fracture doesn&#039;t occur due to growth of cluster crack. In the case of 4-point bending tests is carried out at low loading rate, nonlinear behavior appeared on stress-strain curve before failure. In addition, bending strength increased with decreasing loading rate. On the basis of these results, fracture mechanism is considered as follows. Some clusters are formed by aggregate of un-reacted substance at near rupture. Cluster fracture occurs at the same time with cluster crack being one of the formed some clusters are formed. Therefore increasing strength is because to forms cluster crack stops by internal energy accumulated by loading was released since residual metallic silicones are preferentially failed.

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Language：English   Publishing type：Research paper, summary (national, other academic conference)  

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Ceramics have the properties of high-stiffness, proof-corrosion, and light-weight superior to metal materials and so have been applied to a ball and a race in high performance ball bearing and etc. As a recent expansion of this application, a ceramics ball has been applied to the backflow valve, which is comprised in automotive fuel supply system. However, it must be considered sufficiently that ceramic balls can maintain a high confidence over long-term without being broken by cyclic contact loadings, which are generated between a ceramic ball and housing on switching a backflow valve. In this investigation, the stress analysis by FEM was conducted for clarifying failure mechanism due to cyclic contact stress. As results of analysis, the place of highest contact stress was seen directly underneath the contact region between a ball and housing. In ceramics of brittle material, the fracture occurs usually from a microscopic latent flaw in materials. Therefore, it was probabilistically clarified from a view-point of fracture mechanics that a latent internal microscopic flaw was a starting point of fracture.

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

Stress distributions beneath the contact surface of ceramic plat in contact with round bar were analyzed by 3-D FEM. On the basis of analytical results, the contact strength was evaluated by considering varied sizes and positions of pre-existing defects from a viewpoint of fracture mechanics. The contact rupture occurs from a surface defect that pre-exists in the vicinity of the edge of the plate. If a defect size and a distance from contact boundary to its defect are assumed, the contact rapture load can be estimated by using the proposed equation.

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Ceramics have the properties of high-stiffness, proof-corrosion, and light-weight superior to metal materials and so have been applied to a ball and a race in high performance ball bearing and etc. As a recent expansion of this application, a ceramics ball has been applied to the backflow valve, which is comprised in automotive fuel supply system. However, it must be considered sufficiently that ceramics balls can be kept a high confidence over long-term without being broken down by cyclic contact loadings, which generate between a ceramics ball and housing on switching of the backflow valve. In this investigation, the stress analysis by FEM was conducted for clarifying failure mechanism due to cyclic contact stress. As result of analysis, high stress place was seen in contact side neighborhood of a ball and housing. Ceramics is brittle material, predominant of the fracture is a microscopic crack in materials. Therefore, author clarified that an initial surface microscopic crack was a starting point of fracture.

DOI： 10.1299/jsmemecjo.2006.1.0_201

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Pore-free ceramics (PFC) material was investigated mechanical properties and fracture behavior such as 4-point bending and static fatigue at room temperature. Arranging by relationship between bending strength and fracture probability, Weibull modulus of PFC decreases compared with regular same ceramics. It is attributable to different fracture mechanics. PFC has binder exists instead of a potential defect and they are distributed minutely and uniformly. When a specimen is loaded, a lot of cracks occur in boundary between binder and ceramic grain and strain energy is released. Some clusters are formed by some cracks&#039; uniting. The scatter of fracture strength that depends on the size of the cluster is caused. As for static fatigue test of PFC, the time dependence fracture wasn&#039;t caused. In addition, all experimental values are more than average of bending strength. Fracture model above can explain this behavior to which crack coalescences stop.

DOI： 10.1299/jsmemecjo.2006.1.0_899

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Language：Japanese   Publisher：日本材料学会  

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DOI： 10.1299/jsmezairiki.2003.0_193

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To execute surgical operations on livers in short time and to reduce the stress on the patients, we propose a soft freezing method for liver surgical procedures. In this surgical procedure, a tumor surrounding the liver is frozen in order to ease the excision and prevent hemorrhage. The effects of cooling velocity and freezing temperation on the excision force by the scalpel on the liver are carried out experimentally as a basic research into partial freezing surgical procedures. In this study, to excise a cancer using free excision curve, the development of the cooling needle and the investigation of the cooling function were carried out using a liver of a pig. The physical properties value was reversely analyzed by using the finite element method based on the heat transfer characteristic data of a mock liver. In addition, the proposed estimation equation can express the relation between arbitrary cooling time and distance and temperature.

DOI： 10.1299/jsmemecjo.2003.7.0_53

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To execute surgical operations on livers in a short time and to reduce the stress on the patients, we propose a soft freezing method for liver surgical procedures. In this surgical procedure, a tumor surrounding the liver is frozen in order to ease the ease the excision and prevent hemorrhage. The effects of cooling velocity and freezing temperature on the excision force by the scalpel on the liver are carried out experimentally as a basic research into partial freezing surgical procedures. In this study, to excise a cancer using free excision curve, the development of the cooling needle and the investigation of the cooling function were carried out using a liver of a big. The physical properties value was reversely analyzed by using the finite element method based on the heat transfer characteristic data of a mock liver. In addition, the proposed estimation equation can express the relation between arbitrary cooling time and distance and temperature.

DOI： 10.1299/jsmemecjo.2002.6.0_15

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A major problem in ceramic/metal joint is thermal expansion coefficient mismatch between ceramics and metal. This thermal expansion coefficient mismatch causes serious residual stresses at the interface of the ceramic/metal joint, which generated during joint-cooling process. Then, an interlayer, which is ductile metal such as copper, nickel and so on, is inserted between ceramics and metal because of relaxing the residual stress. It should be considered that thickness of interlayer have significant influence on the joint strength with considering the residual stress.&lt;br&gt;In this study, it paid attention to the thickness of interlayer, and the optimum thickness of Interlayer was discussed from a viewpoint of the stresses based on simulation model analysis as well as 4 point bending tests, considering the residual stresses, which were analyzed using three-dimensional plasto-elastic finite element method. As a result of the analysis, residual stress increased with decreasing of the interlayer thickness. The superposing stress of the applied bending stress and the residual stress showed minimum value in the case of the interlayer thickness of 0.2mm. On the other hand, paying notice to the result of the bending test as well as the analysis, the joint specimen showed the highest bending strength in the case of the interlayer thickness of 0.2mm. Furthermore, the scatter of joint strength is apparently small in this thickness compared with in the other thickness.

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Language：Japanese   Publisher：愛媛大学工学部  

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DOI： 10.1299/jsmezairiki.2000.0_401

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Language：Japanese   Publisher：The Society of Materials Science, Japan  

Cyclic tensile fatigue tests were conducted for Si&lt;sub&gt;3&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt;/S45C joint specimens with copper interlayer at room temperature in order to clarify fatigue strength properties of ceramic/metal joint, considering the influence of residual stress in ceramics induced during joining process. Not only the joining process residual stress but also the residual stress behavior due to cyclic tensile loading was analyzed by using the three-dimensional elastic-plastic finite-element method. All experimental data obtained in this study were tried to arrange as the relationship between the normalized testing stress and the effective loading time by using the unified estimation method with considering effective volume and effective loading time. However, even if using the unified estimation method, the normalized strengths in the cyclic fatigue tests were clearly lower than normalized tensile strength at fracture probability of 50%. The difference of both normalized strengths was caused by the increase of the residual stress redistributed during cyclic fatigue tests. The redistributed residual stress was due to the reversible plastic deformation made in the interlayer of copper, but tended to saturate after second cycles. Then, if modifying not only the effective loading time but also the time-strength by using the unified estimation method against the superposing stress of the testing stress and the redistributing residual stress in cyclic fatigue tests, the cyclic tensile fatigue strengths agreed well with the normalized tensile strength for ceramic/metal joints as well as for monolithic ceramics. All cyclic fatigue strengths containing tensile fracture strength can be estimated well as the normalized strength with scatter properties of Weibull distribution.

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Language：Japanese   Publisher：愛媛大学工学部  

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Room and high temperature four point bend tests for Si&lt;sub&gt;3&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt;/SUS304 joints were carried out at constant loading.Fracture surfaces of the interlayer of joints were observed using SEM to discuss the fracture mechanism at high temperature. Furthermore, the fracture strength distribution was estimated on the basis of the unified estimation method considering the fracture mechanism.&lt;br&gt;(1) Failure of brazed Si&lt;sub&gt;3&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt;/metal joints in high stress level was occurred at a flaw in ceramics near bonding interface. On the other hand, failure of the interlayer in low stress level was occurred due to creep rupture. Creep rupture of joints was dominated on steady-state creep of the interlayer. Then, creep rupture life also could be predicted from minimum creep strain rate in interlayer by using both equation of Monkman-Grant and Norton&#039;s law.&lt;br&gt;(2) The fracture strength of the joints could be evaluated considering the temperature dependence of strength as follows:&lt;br&gt;&amp;sigma;&lt;i&gt;&lt;sub&gt;f&lt;/sub&gt;&lt;/i&gt;&amp;middot;&lt;i&gt;t&lt;sub&gt;eff&lt;/sub&gt;&lt;/i&gt;&lt;sup&gt;1/&lt;i&gt;n&lt;sub&gt;j&lt;/sub&gt;&lt;/i&gt;&lt;/sup&gt;=&amp;sigma;&lt;i&gt;&lt;sub&gt;f&lt;/sub&gt;&lt;/i&gt;exp[(-&lt;i&gt;Q&lt;sub&gt;i&lt;/sub&gt;&lt;/i&gt;/&lt;i&gt;k&lt;/i&gt;)(1/&lt;i&gt;T&lt;/i&gt;+273-1/&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;&amp;theta;&lt;/sub&gt;+273)]&lt;sup&gt;&lt;i&gt;m&lt;sub&gt;i&lt;/sub&gt;&lt;/i&gt;&lt;/sup&gt;&amp;radic;ln(1-&lt;i&gt;P&lt;sub&gt;f&lt;/sub&gt;&lt;/i&gt;)&lt;sup&gt;-1&lt;/sup&gt;&lt;br&gt;(3) Reliability structural design of joints had better determine the stress level and proof life considering failure of the interlayer with small scatter of rupture lives.

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Advanced Pore-Free SiC (APF-SiC) with super-high strength is expected to be used as engineering structural materials since it has damage tolerance ability by preceding failure of metallic silicon particles In the present study, thermal shock tests of this material were carried out to characterize the fracture behavior. The residual strength after thermal shock was also measured. It is found that the critical temperature difference ΔT_c of this material is larger than that of conventional SiC due to smaller size of pre-existing flaws. As the result, the validity of the Griffith's theory was experimentally confirmed. In addition, the damage tolerance behavior in thermal-shocked materials is not observed because the metallic silicon particles may he failed by thermal shock.

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Fracture mechanics based considerations were made for investigating the ring-crack formation of ceramic plates contacted with a ceramic sphere under a combined normal and tangential indentation load. The intrnsic tensile strength of the ceramic plate did not dictate the onset of ring-crack formation. The size of pre-existing defects (being less than one micron) that may result in the ring-crack initiation were somwhat smaller than the grain size of the ceramic plate. On the other hand, the stress gradient induced beneath the contact was significantly dependent on the contact angle of normal/tangential combined load; when the contact angle is increased, the mean dimension of defects which lead to ring-crack initiation becomes large, whereas the location of the induced crack is progressively away of the contact circle. The stress gradient induced beneath the contact was taken into account for calculating the stress intensity factor of the pre-existing surface defect. The fracture toughness value thus estimated for the ceramic plates satisfactorily predicted the onset of ring-crack formation of all the ceramic plates examined.

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The strength reliability of the ceramics/metal joints in the vacuum interrupters was studied focusing on the thermal stress around the ceramics/metal joints due to mismatch of thermal expansion coefficients between ceramics and metal. It was found from the experiment results that the residual strength of the joint depends on the amount of metal brazing alloy used as a jointing material. Firstly, in the present work, the thermal stress around the ceramics/metal joints was calculated using finite element analysis. Next, the effect of the amount of metal brazing alloy on the residual strength of the joint was investigated on the basis of a fracture mechanical approach. Finally, the amount of metal brazing alloy minimizing the strength reduction of the joint is determined using the results of the numerical analysis.

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Shear loading tests were executed to ceramics/metal joints used for an electronic device in various temperatures and loading rates. Fracture origin of the joints is formed from ceramics of interfacial neighborhood. According to FEM analysis, it is clarified that the driving force for the failure is not a shear stress but a tensile stress. The tensile stress dramatically decreases from just beneath the surface to interior portion. Slow crack growth behavior in nominal shear stress was estimated using fracture mechanics in the different conditions of loading rates.

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It is reported that about 30% of Japanese over 60 years old suffer osteoarthritis of the knee, and a lot of them need knee brace or supporter in daily life. A new type supporter is invented for this disease by one of the authors. In this study, the shape optimization of the frame of a soft type supporter is researched. The design objective is to create holes in the design domain so that the frame can be fixed to the flexible cloth cover strongly and stably. It can also reduce the weight of the supporter, and improve the air permeability. However, the generation of the hole can cause a decrease in the rigidity of the frame. It is also important to guarantee the enough stiffness in load direction so that it can carry out the function. For this purpose, a topology optimization approach is introduced to the design. A FEM model is established, and the boundary condition of FEM model is determined by the experiment of patients with the supporter. The SIMP (Simple lsotropic Material with Penalization), which is a topology optimization technique, is used in numerical analysis. In order to save the computation time, we also improved the SIMP. Numerical example illustrate effectiveness of our approach. © 2008 Society for Experimental Mechanics Inc.

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セラミックス/金属接合部材の接合部近傍に一定負荷速度にてせん断応力を負荷した.接合部材は接合界面ではなくセラミックス側からき裂が発生しており,せん断破壊はセラミックス側での破壊が支配的であった.そこで,従来のき裂進展特性式がモードIIでも成立つと仮定してセラミックスのせん断遅れ破壊モデルを提案した.その結果,両対数グラフに整理されたせん断破壊応力とせん断応力速度は直線関係にあり,ゆえにこのモデルの妥当性が示された.また破壊モードに関わらずき裂進展に対する抵抗値は同等であることが明らかとなった.

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本研究では,損傷許容型セラミックスの熱衝撃破壊特性を明らかにすることを目的としている.著者らは,Hasselmanの熱統一理論に基づき,熱衝撃破壊発生確率を考慮した熱衝撃前後の機械的特性から熱衝撃特性を評価できる確率論的残存強度予測モデルを提唱した.そこで多孔質SiCを用いて液中急冷熱衝撃試験を行い,その後4点曲げ試験により残存強度及びヤング率を評価した.その結果,理論線と良く一致し,評価法の妥当性を明らかとした.またこのことは,損傷許容型セラミックスの熱衝撃破壊もまた,グリフィスの理論に準じており,熱衝撃後の残存強度のばらつきは潜在欠陥のばらつきに支配されていることを示唆している.

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In the present study, 4-point bending test was carried out by using porous ceramics to investigate statistical properties of damage-tolerant ceramics. Distribution of the bending strengths plotted on a Weibull probability paper was nonlinear and was very similar to superposed distribution. Consequently, the bending strength distribution was analyzed by cluster fracture probabilistic model with the basis of Markov process assuming the LLS rule. It is found that the probabilistic model agreed well than the 2-parameter Weibull distribution. Therefore this indicates that the bending strength distribution controls cluster size.

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本研究では損傷許容型セラミックス材料の評価法の確立を目的としている.そこで第一段階として気孔径の異なる多孔質セラミックスを用いて,任意の負荷速度において3点曲げおよび4点曲げ試験を行った.その結果,SL#5では低負荷速度において逆寸法効果が見られた.この原因は,損傷許容性は,寸法効果が大きくまた負荷速度が遅くなれば顕著に創出されるためであると考えられる.

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この論文の目的は損傷許容型脆性固体材料の曲げ強度分布特性を評価することである.実験として,SiC系多孔質セラミックスを用いて常温下での4点曲げ試験を行った後に破壊強度をワイブル線図に整理した.そして従来から提言されている2母数ワイブル分布に基づく確率論的遅れ破壊モデルによって評価したが良い一致を示さなかった.そこで破面観察を行うと,従来のセラミックスとは異なり多くの粒界損傷が見られ,これにより優れた損傷許容性が発現していると考えられる.そこで,粒界損傷の変化を確率過程として表すことを考えマルコフ過程に基づいた確率論的遅れ破壊モデルを提唱して評価した.その結果,実験結果と良い一致を示した.

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In this research, packaging structures in which chip parts were bonded to the ceramics substrate of Alumina (Al_2O_3) or nitride aluminum (AIN) with electro-conductive adhesive etc. through a thick film conducting electricity, was studied. For the structures, the bonding remaining strength, considered the residual stress caused in a bonding process based on fracture mechanics, was evaluated, and the influences of both the ceramics substrate and the thick film conductor's thermo-physical property on the strength were examined. Moreover, to examine the decrease behavior of the bonding residual strength by heat cycle loads in-service, thermal cycle tests, the verification tests of a peeling strength, and the simulation analyses of those tests were done, and the peeling fracture strength and the fracture life were predicted. As a result, the mechanism of trouble generated in-service is clarified from the viewpoint of fracture mechanics, the validity of remedies is confirmed, and the present research is useful for the new development of the product.

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To widely use "Residual stress measurement for engineering ceramics by indentation fracture method" industrially, the investigation of detailed magnification factor is indispensable. The influences stress distribution on magnification factor and application and magnification factor of this measuement to several ceramic materials were was discussed. The magnification factor which were almost equal to JSMS-SD-4-01 were obtained by considering indent load dependency under stress field of uniformal compression. The magnification factor is almost equivalent in both Si_3N_4 and Al_2O_3. On the other hand, the magnification factor increased with increasing indent load under gradient stress field.

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