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論文
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秋山, 繁 ; 天田, 重庚 ; 千田, 哲也 ; 島田, 道男 ; 古谷, 典〓 ; 矢野, 不二夫
概要:
application/pdf<br />Journal Article<br />Nuclear power plants have the greatest potential for use in space ships, under
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water vehicles, and so on. Because the space and the weight for those plants have limitation, it is very important to develop new radiation shielding materials which have excellent mechanical strength and heat-resistant characteristics. Chromium carbide ceramics (Cr_3C_2) is the neutron absorber which is more excellent than titanium boride ceramics and has been investigated as a radiation shielding material. This report presents an evaluation of thermal shock strength by the laser irradiation technique for chromium carbide ceramics. Their temperature and thermal stress distributions are analyzed by the finite element method (FEM), and critical fracture curves, which can specify a critical power density for a given laser beam spot diameter, are obtained from the relationships between the spot diameter of the laser beam and the maximum tensile thermal stress. And furthermore, size effects to the fracture criterion of chromium carbide ceramics are examined, and the laser irradiation experiments are performed on chromium carbide ceramics using a CO_2 laser. Finally, theoretical results are compared with experimental ones, and the thermal shock strength P_L of Cr_3C_2 ceramics with laser irradiation is ～3.4 W/mm^2 for tension by the FEM analyses
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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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天田, 重庚 ; 白井, 直樹
概要:
application/pdf<br />Journal Article<br />A thin plate is heated locally by a laser beam and simultaneously, a large thermal elastic plastic stress-strain state is generated in the heated, thin surface layer. This state can lead to
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plate bending upon cooling. The bending configuration depends mostly on the plate geometry, and heating and cooling process. We presents some experimental results of bending the plate in V-, U- and concave shapes. A model of this process is constructed and the theoretical predictions are carried out based on FEM analysis using eleastic-plastic theory. Bending angles obtained experimentally and theoretically are in good agreement.
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| 4.
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Akiyama, Shigeru ; Amada, Shigeyasu ; Yoshii, Tokuharu
概要:
application/pdf<br />Journal Article<br />Various structural ceramics have been developed as heat-resistant materials. In some applications it is anticipated that they will be exposed to very-high-temperature environments of the order of
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thousands of degrees. Moreover, these ceramics are subjected to thermal loadings which change rapidly with time. Therefore, it is very important to investigate their thermal shock characteristics. In this report, the distributions of temperatures and thermal stresses of cylindrical-shaped Al_2O_3 ceramics under irradiation by laser beams are analyzed using the finite element method. Critical fracture curves are obtained from the relationships between spot diameters of laser beams and maximum values of thermal stresses for various power densities of laser beams. The irradiation experiments yield these critical fracture curves, and theoretical and experimental curves are in good agreement.
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| 5.
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論文
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秋山, 繁 ; 天田, 重庚 ; 島田, 道男 ; 千田, 哲也 ; 吉井, 徳治
概要:
application/pdf<br />Journal Article<br />Nuclear power plants have the greatest potential for use in space ships, underwater vehicles, and so on. It is very important to develop new radiation shielding materials which have excellent
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mechanical strength and heat-resistant characteristics. Titanium boride ceramic (TiB_2) is an excellent neutron absorber and has been investigated as a radiation shielding material. This report presents an evaluation of thermal shock resistance by the laser irradiation technique for three kinds of titanium boride ceramics with 3, 8, and 15% porosity. Their temperature and thermal stress distributions are analyzed by the finite-element method, and the relationship between the spot diameter of the laser beam and the maximum tensile thermal stress is derived for various power densities of the laser beams. Critical fracture curves are obtained from these relationships, which can specify a critical power density for a given laser beam spot diameter. The irradiation experiments are performed on titanium boride ceramics using a C0_2 laser. Finally, theoretical results are compared with experimental ones.
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| 6.
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論文
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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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| 7.
論文 |
論文
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秋山, 繁 ; 天田, 重庚 ; 島田, 道男 ; 吉井, 徳治
概要:
application/pdf<br />Journal Article<br />Various structural ceramics have been developed as heat-resistant materials. However, in some applications it is anticipated that they will be exposed to very-high-temperature environments of
…
the order of thousands of degrees. Moreover, those ceramics are subjected to thermal loadings which change rapidly with time. Therefore, it is very important to investigate their thermal shock characteristics. In this report, the distributions of temperatures and thermal stresses of cylindrical-shaped Al_2O_3 ceramics under irradiation by laser beams are analyzed using the finite-element method. Critical fracture curves are obtained from the relationships between spot diameters of laser beams and maximum values of thermal stresses for various power densities of laser beams. The irradiation experiments lead to these critical fracture curves, and both theoretical and experimental curves are in good agreement.
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| 8.
論文 |
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
…
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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