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

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Language：Japanese   Publisher：日本材料学会  

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

Many guide parts of Al2O3 ceramics are used as mechanical components in the hot environment of textile machines. Some guide parts are occasionally fractured via fatigue failure due to thermal stress in service. The analysis of thermal stress requires knowledge of the heat transfer coefficients between a ceramic guide and cold airflow, as well as of the hot environment in service, because a continuous string running at a high speed of 10m/s carries cold room-temperature air to the ditch bottom of guide parts in the hot environment. However, for the heat transfer coefficients in such a situation, there has been no example of practical direct measurement in the past. Therefore, the heat transfer coefficients were estimated using an inverse analysis method, in which suitable heat transfer coefficients were estimated through trial and error, considering the correspondence of the fracture mode and strength between analytical fracture and actual fracture in service. From the analytical results for the thermal stress using the estimated heat transfer coefficients, the cause of fracture of some ceramic guides was clarified through fracture mechanics of a surface crack in a thermal stress field. The lifetime of ceramic guides was estimated probabilistically also from the viewpoint of fracture lives in long-term service.

DOI： 10.2472/jsms.51.12Appendix_225

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmezairiki.2002.0_253

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmezairiki.2002.0_759

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DOI： 10.1299/jsmezairiki.2002.0_755

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：JAPAN INST METALS  

We have developed a now technology of cold working by which a collar can be formed in the middle of a round mild steel bat Keeping a constant axial-compressive stress about the yield strength of the material used, giving the round bar repeatedly an alternate stress of tension and compression by a bending moment, the local collar is formed in the round bar in the process of superplasticity-like deformation advances. One of the merits for this processing method is to obtain a superplasticity-like compressive deformation by a lower compressive load without the mechanical damage produced by strain accumulation. Another is to rise only within 15 K in temperature on the collar in the processing regardless of the presence of lubricant. The third is to prevent materials from being wasted due to die cutting work Therefore, this technology of cold working leads to the saving of both energy and resource and to the prevention of environmental pollution due to lubricant. Through this study, the processing conditions that have a large influence on the collar-forming processing are clarified by means of the experiment and the calculation model analysis. Moreover, the temperature change in the collar is measured by an infrared thermometer along with the superplasticity-like deformation in this collar-forming processing.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmezairiki.2000.0_381

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Shape memory alloy has the properties of the pseudoelasticity and the shape memory effect, therefore, shape memory alloy is applied to various fields such as industrial and medical materials. The objective of this work is to invastigate to investigate the effect of Cu content and heat temperature on pseudoelasticity of TiNiCu shape memory alloys. The results show that the transformation start and finish stress and strain energy are affected by heat temperature and Cu content.

DOI： 10.1299/jsmemecjo.2000.3.0_327

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

Low cycle fatigue tests using smooth specimens of Mar-M247 are conducted at room temperature to simulate the fracture under out-of-phase thermal fatigue and the behavior of initiation and growth of small cracks is identified. Three kinds of specimen are cut from a cast plate such that their axes possess angles of 0°, 45° and 90° with respect to the &lt
001&gt
orientation that is parallel to the solidification direction
these specimens being denoted the specimen 0°, the specimen 45° and the specimen 90°, respectively. The results are discussed in connection with the anisotropic and composite microstructures. They are summarized as follows. (1) Transgranular cracks are initiated in all specimens. The first crack in Specimen 0° nucleates at 8000 cycles and those in other two specimens at about 1000 cycles. Cracks of Specimen 0° are initiated from casting defects at surface of the specimen, whereas cracks of Specimens 45° and 90° originate mostly in slip bands and the number of cracks per unit area is 200 times as large as that of Specimen 0°. (2) Cracks in Specimen 0° grow each other independently. On the other hand, cracks in Specimens 45° or 90° coalesce frequently. Grain boundaries, dendrite arms and γ′-phase precipitates do not work as barriers to the crack growth unlike the creep fatigue crack. However, the direction of crack growth has a strong dependence on the crystallographic orientation of the γ-matrix. (3) The crack growth rate tends to be the lowest in Specimen 0° for the same half crack length. This is caused by the smallest Young's modulus, the largest resistance for slip band formation, and the lowest crack density and hence the crack growth without coalescence.

DOI： 10.2472/jsms.48.1281

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

This paper deals with the initiation and growth of small cracks in a directionally solidified superalloy, Mar-M247. An experimental investigation was done under creep-fatigue conditions at the test temperature of 1273 K (1000 degrees C) in air. Specimens were subjected to push-pull loading along the [001] crystal orientation, parallel to the solidification direction. The results observed are summarized as follows: although the grain boundaries are macroscopically parallel to the solidification direction, they are wavy or serrated microscopically. A crack nucleates along a parr of the grain boundary, being nearly perpendicular to the stress axis. The intergranular crack stops growing when the tip reaches a bend in the grain boundary just after the initiation phase. Most cracks remain arrested in this phase until the specimen Fails. Some of the cracks overcome the barrier and their tips go into the neighbouring grains (phase II). They grow quickly along the secondary dendrite boundary, while they grow very slowly in the matrix. This dendrite-boundary crack is arrested for a while when the tip reaches the primary dendrite. When the crack is small, it grows so as to avoid the primary dendrite, but after the crack grew large, being accompanied with frequent coalescence with other small cracks, it cuts through the dendrite (phase III). The large crack grows smoothly and monotonously, regardless of the microstructure.

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

Experimental investigation was done to characterize the low cycle fatigue (LCF) in an as-cast Ti-34wt.%Al with near 0 degrees-oriented lamellar structure by using the smooth bar specimens subjected to push-pull loading. Effects of test temperatures, strain waveforms and lamellar and/or grain boundaries on the crack initiation, propagation and the failure life are shown in this paper. It is pointed out that the TiAl tested is inferior to other heat resistant alloys in the LCF resistance over 0.5% total strain range at room temperature, whereas it has a satisfactory grade at high temperatures or under creep-fatigue conditions.

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

This paper deals with the initiation and growth of small cracks in a directionally solidified superalloy, Mar-M247. An experimental investigation was done under creep-fatigue conditions at the test temperature of 1273 K (1000°C) in air. Specimens were subjected to push-pull loading along the 〈001〉 crystal orientation, parallel to the solidification direction. The results observed are summarized as follows: although the gram boundaries are macroscopically parallel to the solidification direction, they are wavy or serrated microscopically. A crack nucleates along a part of the grain boundary, being nearly perpendicular to the stress axis. The intergranular crack stops growing when the tip reaches a bend in the gram boundary just after the initiation phase. Most cracks remain arrested in this phase until the specimen fails. Some of the cracks overcome the barrier and their tips go into the neighbouring grains (phase II). They grow quickly along the secondary dendrite boundary, while they grow very slowly in the matrix. This dendrite-boundary crack is arrested for a while when the tip reaches the primary dendrite. When the crack is small, it grows so as to avoid the primary dendrite, but after the crack grew large, being accompanied with frequent coalescence with other small cracks, it cuts through the dendrite (phase III). The large crack grows smoothly and monotonously, regardless of the microstructure.

DOI： 10.1046/j.1460-2695.1998.00540.x

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

This paper deals with the effect of anisotropy on fracture processes of a directionally solidified superalloy, Mar-M247, under a push-pull creep-fatigue condition at high-temperature. Three kinds of specimen were cut from a cast plate such that their axes possess angles of 0°, 45° and 90° with respect to the 〈001〉 orientation that is aligned parallel to the solidification direction (also to the grain boundaries and primary dendrite axis)
these specimens being denoted the 0° specimen, the 45° specimen, and the 90° specimen, respectively. The tests were conducted at 1273 K (1000°C) in air under equal magnitudes of the range of a ΔJ-related parameter, ΔHc, which represents the driving force for crack growth in creep-fatigue. Although the gram boundaries are macroscopically parallel to the solidification direction, they are wavy or serrated microscopically. Small cracks nucleate along parts of the grain boundaries perpendicular to the stress axis in all specimens. The 90° specimen has the shortest crack initiation life and the 0° specimen has the longest. In the 90° and 45° specimens, intergranular cracks continue to nucleate and a mam crack is formed along the grain boundary due to the frequent coalescence of small cracks. In the 0° specimen, cracks grow into the grain, and transgranular cracks coalesce along the primary dendrite or grain boundary. The 0° specimen exhibits the slowest crack growth rate and the 90° specimen the fastest. These differences in the initiation and growth behaviour of small cracks cause the longest failure life in the 0° specimen and the shortest in the 90° specimen.

DOI： 10.1046/j.1460-2695.1998.00454.x

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

In order to elucidate the fracture process in high-temperature low-cycle fatigue of a cast Ti-34wt.%Al with lamellar structure and to derive the life law of smooth specimens, the behavior of initiation and growth of microcracks is observed in detail. The results obtained are summarized as follows. (1)Microcracks, which originate from casting defects at and/or beneath the specimen surface, begin to initiate at less than 15% of the failure life. (2) The transgranular microcracks grow perpendicularly to the stress axis and transversely to the lamellar boundaries. They are neither blocked nor decelerated by the grain boundary. (3) Although the growth rate of microcracks has a large scatter, the average rate coincides with the fracture mechanics law which is characterized by the relationship between the crack growth rate, dc/dN, and the fatigue J-integral range, Delta J(f). (4) The crack initiating at the earliest stage of many distributed cracks tends to grow up to be a main crack for the failure. (5) The fatigue life of smooth specimens, N-f, is successfully correlated with Delta (W) over tilde(f)-parameter which is derived by integrating fracture mechanics law of dc/dN vs. Delta J(f) relation.

DOI： 10.2472/jsms.46.3Appendix_37

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

High-temperature fatigue crack propagation tests were conducted on Ti-34 wt% Al intermetallic compound with lamellar structure, in order to elucidate the effects of lamellar boundaries and creep on the resistance to translamellar cracking. The results obtained are summarized as follows. (1) Slow crack growth during fatigue is found to traverse the lamellae, and its rate is independent of whether the cracking direction is perpendicular to the lamellae or along them. (2) The fatigue crack propagation;ate, dl/dN, at 1073 K is correlated well with the effective stress intensity factor range, Delta K-eff. (3) The fatigue crack propagation rate at room temperature is little slower than that at 1073 K. (4) Under creep-fatigue conditions, the crack propagation exhibits a time-dependence and its rate per cycle, dl/dN, is governed by the creep J-integral range, Delta J(c). (5) In transverse crack propagation, the dl/dN-Delta J(c) relationship is independent of the crack direction to the lamellar surface. (6) Compared with some heat-resisting steels and alloys, the resistance of the present TiAl to fatigue crack propagation is remarkably low at high levels of stress amplitude while the resistance to creep-fatigue crack propagation is almost the same. Copyright (C) 1996 Elsevier Science Ltd

DOI： 10.1016/0966-9795(96)00011-8

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The effects of total strain range and test temperature on the fatigue life of a cast intermetallic compound, Ti-34 wt.%Al, which possesses a lamellar structure,γ+α2,were investigated. The behaviors of initiation and propagation of small cracks were observed in the smooth bar specimens subjected to push-pull cyclic loading. The results observed are summarized as follows. (1) A small amount of inelastic strain is observed even in fatigue under high strain range up to 1%. The fatigue life is sensitive to the total strain range. (2) The fatigue life shows a positive temperature dependency. (3) Small cracks observed on/near the surface of specimens are classified into three types, Type A cracks which initiate from defects introduced during casting process and form a main crack in fatigue below 1073K. Type B cracks which initiate along an interface of lamellae being parallel to the stress axis and are blocked by grain boundaries never to grow as a long crack. Type C cracks which initiate from the cracking of the surface oxide-layer and bring numerous fracture sites in the matrix over 1173K. (4) Although the initiation and early propagation of Type A cracks show an eminent fluctuation caused by the distribution of casting defects and the orientation of lamellar structure, they follow by a continuous propagation with an increase in crack length. Therefore, Type A cracks are typical of this material where by the fatigue fracture is brought about at the early stage of life. © 1995, The Society of Materials Science, Japan. All rights reserved.

DOI： 10.2472/jsms.44.769

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

The behavior of initiation and growth of small cracks were investigated in creep fatigue at 1273K (1000°C) using a smooth round-bar specimen of an oxide (Y<SUB>2</SUB>O<SUB>3</SUB>) dispersion-strengthened (ODS) superalloy, Inconel MA 754, produced by means of the mechanical alloying process. The elongated grain structure was attained by extrusion and isothermal annealing. The experimental results are summarized as follows : (1) Multiple traverse cracks (Type A) were initiated on the surface along grain boundaries perpendicular to the stress axis from the early stage to the middle stage of life. However, most of them were arrested immediately after the initiation by the grain boundary along the stress axis. (2) Transgranular cracks (Type B) began to appear from the middle stage of life. Although the grain boundary along the stress axis interfered with the growth of the Type B crack, the crack broke through the barrier and formed a main crack which brought about failure of the specimen. (3) While the elongated grain structure worked to prevent the growth of Type A cracks, it showed little effect on that of Type B cracks.

DOI： 10.1299/kikaia.59.933

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

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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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The fracture tests of porous ceramics were carried out under tensile and bending conditions, and a formula model of fracture process was investigated in order to clarify the fracture properties. As the formula model, the assemblies of pore-element and matrix-element were proposed, and the experimental results were estimated using an inverse analysis method. As the results, the stress-strain behaviors of porous ceramics under tensile load were successfully simulated using our devisal formula model.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Shape memory alloys have the properties of the pseudo-elasticity and the shape memory effect. Therefore, shape memory alloys are applied to the components as industrial and medical materials in various fields. The objective of this work is to formulate about the effect of Cu content and heat temperature on the pseudo-elasticity properties of Ti-Ni-Cu shape memory alloys and to develop how to simulate the pseudo-elasticity behaviors. It was clarified to though the simulations that the pseudo-elasticity behaviors are largely affected heat temperature and Cu content.

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Though porous ceramics are low strength materials, their damage tolerances are superior to conventional monolithic ceramics. However their strength properties are not clarified enough to make a strength design. In this study, the fracture tests of porous ceramics were carried out under tensile and bending conditions, and a formula model of fracture process was investigated in order to clarify the fracture properties. The formula model of mixture elements of pore and matrix was proposed, and the experimental results were estimated using an inverse analysis method. As the results, non-linear behaviors of porous ceramics were successfully simulated using our formula model.

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The fractures of ceramics-metal joint body semiconductor substrate are caused by the thermal stress and the residual stress due to the thermal stress produced in the manufacturing process and thermal cycle. In this study, the thermal cyclic test and four-point bending test were carried out. Moreover, residual stress was analyzed and strength deterioration due to the thermal cyclic stress was discussed, and the fracture strength of the substrate was evaluated on the basis of fracture mechanics.

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Language：English   Presentation type：Oral presentation (general)  

The fracture tests of porous ceramics were carried out under tensile and bending conditions, and a formula model of fracture process was investigated in order to clarify the fracture properties. As the formula model, the assemblies of pore-element and matrix-element were proposed, and the experimental results were estimated using an inverse analysis method. As the results, the stress-strain behaviors of porous ceramics under tensile load were successfully simulated using our devisal formula model.

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Al_2O_3 ceramics are used for mechanical components such as guide parts in high temperature atmosphere of a machine and the failures due to thermal stress have occurred often in service. The heat transfer coefficients between atmosphere and ceramics in service are necessary for analysis of thermal stress. Thus, in this work the heat transfer coefficients were estimated using an inverse analysis method, by which several property parameter are determined so that fracture due to stress intensity factor at the thermal stress field may agree with the fracture in a practical service. Using the heat transfer coefficients obtained, thermal stresses in the guide part were analyzed by FEM, and fracture lives of the guide part in service were predicted inversely.

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