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舩津, 賢人 ; 伊藤, 一磨 ; 白井, 紘行 ; 高草木, 文雄
概要:
application/pdf<br />Journal Article<br />In order to investigate the effectiveness as a heat shield of SiC-based and carbon-based materials, the ablation experiments were performed in micro-air plasma-jet at an atmospheric
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pressure. Test materials are SiC/SiC, SiC, C/C, and C. These materials were inserted into the plasma-jets and ablation properties were measured, that is weight loss rate and the heat of ablation. In order to investigate the physical behaviors of the materials in the plasma-jets, the ablating C/C and C were observed by a high-speed video camera. In addition, the surface of the ablated materials was observed with a scanning electron microscope and was analyzed quantitatively with an electron probe microanalyzer. It was found that SiC-based materials might be effective as an ablation material because of its small weight loss. The heats of ablation of C/C and C were almost the same. The surface observation and quantitative analyses showed that the ablated surfaces of SiC-based materials were covered with silicon oxides.
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| 2.
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秋山, 繁 ; 天田, 重庚 ; 島田, 道男 ; 千田, 哲也 ; 古谷, 典〓
概要:
application/pdf<br />Journal Article<br />Structural Ceramics have excellent wear- and heat-resistant characteristics. However, in some applications, they are exposed to very high temperatures and high heat-flux environments, and are
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also subjected to repeated thermal loadings that change rapidly with time. Such repeated thermal loadings are causes of material fracture. Therefore, it is important to investigate the thermal shock fatigue characteristics of these ceramics. We present results of thermal shock fatigue strength tests for a machinable structural ceramic called MACOR, composed of SiO_2-MgO-Al_2O_3. The thermal shock fatigue experiments were done using a CO_2 laser, and the crack generation of the specimens was measured from AE (acoustic emission) signals. Consequently, the thermal shock fatigue strength of MACOR was estimated from the critical power density, and it was proposed that the thermal shock strength of ceramics should be cstimated using a minimum value P_<LF> [W/mm^2] of the critical power density below which ceramic fracture is independent of the spot diameter. Finally, the P_<LF> of 0.2 W/mm^2 was obtained from thermal shock fatigue experiments using MACOR.
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| 3.
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AKIYAMA, Shigeru ; AMADA, Shigeyasu
概要:
application/pdf<br />Journal Article<br />Structural ceramics are attracting attention in the development of space planes, aircraft and nuclear fusion reactors because they have excellent wear-resistant and heat-resistant
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characteristics. However, in some applications it is anticipated that they will be exposed to very-high-temperature environments of the order of thousands of degrees. Therefore, it is very important to investigate their thermal shock characteristics. In this report, the distributions of temperatures and thermal stresses of cylindrically shaped ceramics under irradiation by laser beams are discussed using the finite-element computer code (MARC) with arbitrary quadrilateral axisymmetric ring elements. The relationships between spot diameters of laser beams and maximum values of compressive thermal stresses are derived for various power densities. From these relationships, a critical fracture curve is obtained, and it is compared with the experimental results.
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久門, 輝正 ; 池田, 哲也
概要:
application/pdf<br />Journal Article<br />Estimation of friction and wear properties was attempted using the AE count rate in wear tests for three kinds of metal pins rubbed on four kinds of ceramic disks under unlubricated and
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lubricated (oleic acid) conditions. The relationships between the AE count rates emanating from the end of the pins and the specific wear rate, the topographies of micro-roughness of the wear surfaces, and the mode of wear were established. As a result, we found that the sum of the wear rates for the combination of pin and disk increased with an increase in the AE count rate under both unlubricated and lubricated conditions ; thus it is possible to evaluate the specific wear rate from the AE count rate. The specific wear rate and the AE count rate also increased with the increase in the surface damage such as the equivalent cross-sectional area of microgrooves of the pin and disk.
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神宮, 利夫 ; 川端, 一司
概要:
application/pdf<br />Journal Article<br />The misalignment of the flat anvil of a testing machine with the end of a circular rod specimen causes local crushing due to the stress concentration and bending moment, which must be avoided in
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compression tests. When very hard material, such as fine ceramics, is tested using the compression split Hopkinson bar, the hard specimen may be indented into the incident and transmission bars. In this paper, the insertion of a thin metal plate between the bar-specimen interface in the conventional compression split Hopkinson bar system was examined to prevent indentation. The stress pulse in the incident and transmission bars is measured using the thin steel plate (thickness 0.4 and 1 mm), copper (1 mm) and aluminium (1 mm) , and the pulse profile is investigated. The configuration of the wave observed using the thin steel plate (0.4 mm) is the sharpest, and is similar to that without the plate. The rise of pulses using the steel plate (1 mm) is ramplike. With use of a copper plate and aluminium, the two-step profile appears. The stress-strain relationship evaluated from these stress pulses was compared with that obtained in the static test. The dynamic strength of ceramics is less than about half the static strength.
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SENDA, Tetsuya ; TAKAHASHl, Chiori ; UEMATSU, Susumu ; AMADA, Shigeyasu
概要:
application/pdf<br />Journal Article<br />The frictional behavior of alumina ceramics was investigated at various temper
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atures up to 1200℃. The coefficient of friction decreased with increasing temperature and this dependence became more pronounced as higher contact pressure was applled. Wear loss at room temperature could be interpreted as beingcaused by one of two different behavior modes which have a rate difference of anorder of magnitude. At temperatures higher than 800℃, the wear loss was far less than that at lower temperatures and a smooth, flat friction surface, which is probably responsible for both the low friction coefficient and the small wear loss, was observed.
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| 7.
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千田, 哲也 ; 飯野, 千織 ; 植松, 進 ; 天田, 重庚
概要:
application/pdf<br />Journal Article<br />The frictional behavior of alumina ceramics was investigated at various temper
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atures up to 1200℃. The coefficient of friction decreased with increasing temperature and this temperature dependency became more pronounced as higher contact pressures were applied. Wear loss at room temperature could be interpreted as being caused by one of either two different behavior modes. These have a rate difference of a factor of ten. At temperatures higher than 800℃, the wear loss was far less than that at lower temperatures and a smooth, flat friction face, which should be responsible for the low friction coefficient and small wear loss, was observed.
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| 8.
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論文
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秋山, 繁 ; 天田, 重庚
概要:
application/pdf<br />Journal Article<br />Structural ceramics are attracting attention in the development of space ships, aircraft and nuclear fusion reactors because they have excellent wear-resistant and heat-resistant
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characteristics. However, in some applications it is anticipated that they will be exposed to very high temperatures of the order of thousands of degrees. Therefore, it is very important to investigate their thermal shock characteristics. In this report, the distributions of temperatures and thermal stresses of cylindrically shaped ceramics under laser beams are discussed using the finite element computer code (MARC) with arbitrary quadrilateral axisymmetric ring elements. The relationships between spot diameters of laser beams and maximum values of compressive thermal stresses are derived for various power densities. From these relationships, a critial fracture curve is obtained, and it is compared with the experimental result.
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久門, 輝正 ; 加瀬, 博文
概要:
application/pdf<br />Journal Article<br />Assuming that the micro-asperities on semicylindrical hard asperities with spherical ends ploughing through a softer surface, analyses ware carried out on the effects of the surface topographical
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parameters, such as the mean heights of the micro-asperities, radius of curvature of the tips of the semicylindrical asperities etc., on the wear rate of a soft surface. The theoretical trends of the wear rates varying with a normal load and the topography of the worn surface agreed with the experimental trends of those of Si_3N_4 pins rubbed on four kinds of ceramic disks. The wear rates of the Si_3N_4 pins and disks increased with an increase in the mean depths of grooves and r. m. s. roughness on worn ceramic surfaces. Their trends, which varied with a normal load, also agreed with those of the truncated effects on a probability density of surface heights.
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