Developments in Ceramic Materials Research

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192 M. A. Sheik 3.4.2. Thermal Analysis of DLR-XT – Strategy and Results The morphology and the geometric structure of the material has been translated into a three-dimensional macro unit cell model, as shown in Figure 13. Following that, microscopic sub-models of porosity types A, B, C, as shown in Figure 14, have been created for steadystate finite element analyses similar to that performed for the macro unit cell model. Class D porosity is then introduced in the main unit cell model, where a denuded portion of the central section, as shown in Figure 11, is created. The results of these analyses in the form of the degraded fibre tow and matrix thermal properties are listed in Table 5. Material properties for the fibre tow and the matrix in the macro unit cell are the prescribed values tabulated in Table 5. Assignment of degraded thermal properties hence addresses the influence of initial porosities on the thermal behaviour of the material. From Table 6 an obvious degradation of the overall composite thermal conductivity is noted during the sequential introduction of each type of porosity. In addition, it is also evident that Class B porosity (trans-tow cracks) has a dominant effect on the transverse thermal conductivity, ‘k’ value for the composite whereas Class C porosity (matrix cracks) mainly affects the longitudinal ‘k’ value. To a certain extent, the latter value is also influenced by shrinkage de-bonding or Class A2 porosity. These results conclude that Class C porosity is the primary form of defect that causes the most appreciable reduction of overall spatial thermal conductivity profile of the CMC when these values are used at the macro unit cell level. Finally, the analysis of 3D thermal transport carried at the composite macro Unit Cell level, in combination with the fourth class of porosity, the Denuded Matrix Regions, produced the final k values are presented in Table 7. Table 5. Degradation of thermal conductivity with sequential introduction of each class of porosity
Modeling of Thermal Transport in Ceramics Matrix Composites 193 Table 6. Tabulation of degraded thermal conductivity values of through-thickness and in-plane flow direction along with its overall sequential degradation in the unit cell. Values in parenthesis show the percentage reduction with respect to virgin material Thermal Conductivity (W m -1 K -1 ) C Tow SiC Matrix Macro Unit Cell || ⊥ || ⊥ In Plane Through Thickness Values for Virgin Material 32.407 5.086 70 70 34.89 16.29 Values for Material with Class A Porosity Values for Material with Class A and B Porosity Values for Material with Class A, B and C Porosity Values for Material with Class A, B, and C Porosity used in Class D Porosity affected unit cell 32.344 5.036 70 70 34.85 16.23 32.24 4.441 70 70 34.55 15.52 29.68 4.441 29.683 70 26.94 15.09 29.683 4.441 29.683 70 25.06 13.64 Table 7. Comparison of 1D experimental results vs. FE analyses results for thermal conductivity, k (W m -1 K -1 ) Direction Experimental FE Modelling Steady-State Transient Through Thickness 14.39 13.639 11.55 In-Plane 22.45 25.06 25.16 A further correlation can be established between the mechanical damage on a CMC causing degradation of its thermal diffusivity through the same modelling strategy. A range of property values are given to the class-C sub-model and the eventual overall effects plotted in Figure 18. It represents the resulting degradation in thermal diffusivity from a successive increase in matrix crack density. Although this does not account for the total reduction of the
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DEVELOPMENTS IN CERAMIC MATERIALS R
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Copyright © 2007 by Nova Science P
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PREFACE Ceramics are refractory, in
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Preface ix crystals is discussed. A
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Preface xi spectra and the directio
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2 Leslie G. Cecil comprehensive dat
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4 Leslie G. Cecil Ringle et al. (19
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6 Leslie G. Cecil The main architec
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8 Leslie G. Cecil can study “the
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10 Leslie G. Cecil Middleton et al.
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12 Leslie G. Cecil The laser ablate
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14 Leslie G. Cecil There are two ge
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16 Leslie G. Cecil distinct recipes
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18 Leslie G. Cecil second group (Fi
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20 Leslie G. Cecil The Vitzil-Orang
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22 Leslie G. Cecil Table 3. Mahalan
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24 Leslie G. Cecil Ixlú and Ch’i
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26 Leslie G. Cecil structures (D. R
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28 Leslie G. Cecil paste and Macanc
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30 Leslie G. Cecil Bieber, A. M. Jr
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32 Leslie G. Cecil Kepecs, S. M., a
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34 Leslie G. Cecil Schele, L., Grub
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36 Z. C. Li, Z. J. Pei and C. Tread
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54 T. T. Basiev, V. A. Demidenko, K
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62 I, % 100 80 60 40 20 0 T. T. Bas
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68 Fluorescence, a.u. 1 T. T. Basie
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70 Fluorescence, a.u. 1 0.1 0.01 0.
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78 k, cm -1 20 18 16 14 12 10 8 6 4
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82 Photon counts 300 250 200 150 10
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84 Fluorescence, a.u. I transfer ,
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86 ln(I transfer (t)) -4.2 -4.4 -4.
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88 Fluorescence, a.u. I transfer ,
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In: Developments in Ceramic Materia
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Synthesis, Spectroscopic and Magnet
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a c Synthesis, Spectroscopic and Ma
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Transmission Transmission Transmiss
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Sm (J/Kmol) Sm (J/Kmol) 15 10 5 Syn
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Intensity (a.u.) Intensity (a.u.) 8
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242 Development of Display Technolo
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244 Li Chen technology moved to the
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246 Li Chen The continuing evolutio
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248 Li Chen the back contact cathod
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250 Li Chen Figure 3. Vertical side
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252 Li Chen Figure 6. Molybdenum mi
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254 Li Chen Figure 8(a). I-V curve
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256 Li Chen Figure 9. Life time tes
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258 Figure 11(a). Plasma generated
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260 Li Chen [13] C.A. Spindt, K.R.
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262 S. Ardizzone, C. L. Bianchi, G.
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A absorption spectra, 66, 67, 77, 7
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correlation function, 156 corrosion
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group membership, 13, 20, 21, 22, 2
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microstructure(s), x, xi, 73, 74, 2
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efraction index, 61 refractive inde
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time, vii, ix, 1, 3, 7, 8, 11, 26,
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Developments in Ceramic Materials Research

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