Characterization and control of the fiber-matrix interface in ceramic ...

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172 failure and extensive fiber pull-out. The same behavior was noted in the LAS composites. The force required to displace the fiber within the matrix is derived from the dimensions of the impression on the fiber end and the hardness of the fiber. The results are, therefore, strongly dependent on the measured hardness of the fibers. The hardness of 22.0 k 0.7 GPa was calculated from indent impressions made at 1-N loads on longitudinally oriented fibers. Ten indents were made on fibers in each sample. This value is high compared with a reported value of 13 GPa (88) for Nicalon in a glass matrix. Crystallization of Nicalon, which occurs upon heating above 1475 K, would explain the lncrease in the hardness values (130-132). The limitations of the indentation methods become apparent when high shear strengths are measured. The application of large compressive loads on the fiber ends as delivered by the indentor split or crushed the fiber. Matrix cracking and fracture at the edges of the fiber cavities made accurate measurement of impression dimensions difficult. This is reflected in the large errors in the interfacial frictional stresses. Others applying this type of test to the well-bonded, glass-epoxy and carbon-epoxy systems have avoided fiber damage by utilizing the roundedtip diamond indentor. Interfacial debonding stresses in excess of 88 MPa have been measured with no mention of splitting or crushing. The pyramidal Vickers diamond may accentuate the damage because of its shape. Unfortunately, the rounded tip does not leave an indent that can be measured easily after loading. Using a ground diamond or a flattened point requires the instrument be equipped to measure load and displacement, thus complicating the necessary instrumentation.
173 11.3.2 Tensile testinp, The usefulness of the tensile test described in this report as a semiquantitative method for determining interfacial frictional stresses was demonstrated using a Sic coating on the relatively large-diameter AVCO Sic filaments. Interfacial frictional stresses were calculated from measured critical lengths for systems with and without a modifying interlayer. The low magnitude of the values is supported by the delamination of the composites and debonding of the individual filaments from the matrix observed during four-point flexure testing of composites formed from these fibers. The tensile test is dependent on a reproducible coating with a known rupture stress. In this analysis, the strength of the coating was foi-nnd in the literature and extrapolated from mechanical-property test results. A coating-rupture strength of 500 MPa was obtained and agrees well with the values calculated from measured loads corresponding to matrix fracture during flexure testing of numerous composite specimens. The tensile method offers a number of advantages compared with the indentation test. Sample preparation is simplified and problems of fiber positioning are removed. Stress fields from neighboring fibers could influence the results of indentatlon measurements. This is not an issue in the tensile test. The greatest advantage of the tensile test is speed; however, the test is not problem-free. The sequential fragmentation of coatings on the large-diameter filaments was easily observable. Specimen preparation was relatively uncomplicated. The critical lengths of the segments were relatively long and measure frictional stresses correlated well w ith observed behavior.
Page 3:
ORNL/TM-11039 Metals and Ceramics D
Page 6 and 7:
Page 9.3 Composite Fabrication . .
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LIST OF TABLES Table Page 5,l. Prop
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Figure 8.3. 9.1.. 9.2. 9.3. 9.4. 9.
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Figure 10.18. 10.19. 10.20. 10. 21.
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ACKNOWLEDGMENTS The author wishes t
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CWCTERIZATION AND CONTROL OF THE FI
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1. INTRODUCTION During the last sev
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The development of low-density, hig
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3. FABRICATION TECHNIQUES 3.1 Intro
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11 isostatic pressing (HIP), can be
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13 utilizing the comparatively low-
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16 ORN L- DWG 85- 4 i 4 18RS HEAT1
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5. COMPOSITE DESIGN 5.1 Introductio
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21 5,2 Mechanical Considerations Th
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23 GRNL-DWG 88-74 26 Figure 5.1. Th
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25 Equation (6) shows that the stre
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27 of reinforcement. There are two
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29 in strength. Conversely, the fib
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-I_- Table 5.2. Thermally induced a
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33 1.2 ID 0.8 ;.r 1 e fi v 0.6 a4 Q
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35 will affect the interface and, t
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38 fiber-matrix bonding; thus, a fu
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40 In the analysis of the mechanica
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42 1.2 I .o .6 - E f aa '3 0.6 cn 3
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44 will result in the matrix being
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I I MATRIX MATRIX Figure 7.1. Schem
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48 F = 2a2H, where H is the hardnes
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50 OWL-PHOTO 6866-86 i d c I 20pm F
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52 where Af is the surface area of
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54 Figure 7.4. Tensile and shear st
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56 I I I / -c rc -c / . Om / / I /
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58 ORNL-OWG 87-i 8234 F Figure 7.7.
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coating and the distribution of she
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62 O m PHOTO 6676-87 i SIC FIBERS -
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the composite, therefore an interme
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methane as the reactant and is, thu
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9. EXPERIMENTAL PROCEDURES 9.1 Depo
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71 furnace. The furnace is, therefo
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73 further protection. A 6.5-cm-dia
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76 of the specimen slowly decreased
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78 The programmer is also equipped
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80 graphite holders through multipl
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82 temperature by simply switching
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84 ORNk DWG 87- 4494 3 METAL LOGR A
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86 9.5 Fracture Surface Analvsis Th
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88 treated and untreated halves wer
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90 9.8.2 Tensile testinq In an init
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92 ORNL-DUG 85-11767R.2 ? ! 2 f CEN
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94 fracture of individual Nicalon f
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96 Figure 10.1. SiC-infiltrated Nic
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99 compared with the dimensions acq
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101 Table 10.3. Strength and modulu
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100 ORNL- DWG 87-1 6292 R CVI-I73 7
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BULK FIBER SAMPLE NO. 173: FIBER SU
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107 similar samples show the film o
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Figure 10.7. SEM micrographs showin
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111 Table 10.4. Thermochemical eval
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100 ORNL-DUG 87-15969R CVI- 170 75
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115 Analysis conversion of of the m
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117 A 1 I S N 31 N I I'd I LN 3H 3
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119 n 0 W n 9 v P n w- n v
Page 139 and 140: 121 s m f c I m z - Ir 2 a 0 9 In u
Page 141 and 142: Figure 10.14. SEM micrographs of in
Page 143 and 144: J ORNL-DWC 88-6289 z cF u) w I- z O
Page 145 and 146: 127 300 I CVI-480 I I 1 0 R N L-DWG
Page 147 and 148: io0 I I I I CVI- 172 75 - - 0 z v -
Page 149 and 150: 131 RAL 033021 RAL 033023 Figure 10
Page 151: 133 include: the reaction of boron
Page 154 and 155: 136 that BN coatings react with the
Page 156 and 157: 75 7 ORNL-DWG 87-48234 50 - - c5 z
Page 158 and 159: 140 Table 10.9. Thermochemical eval
Page 160 and 161: OANL-bwo 88-9025 ORNL-DWG 66-9027 I
Page 162 and 163: 144 uncoated tows were 14 k 2 pm; t
Page 165 and 166: 11. DISCUSSION 11.1 Constituent Pro
Page 167 and 168: 149 The properties of CVD Sic have
Page 169 and 170: 151 11.2.1 Matrix cracking In the N
Page 171 and 172: 153 OWL-DWG 88-10677 CVI- (78 22 I
Page 173 and 174: 155 Table 11.3. Property comparison
Page 175 and 176: 157 a f ““f f- L c I Figure 11.
Page 177 and 178: 159
Page 179 and 180: 161 The equations demonstrate that
Page 181 and 182: 163 calculations of the matrix depo
Page 183 and 184: 165 In four of the samples, the fib
Page 185 and 186: 167 Table 11.4. Properties of glass
Page 187 and 188: 169 rare-earth magnets and coils to
Page 189: 171 stress fields along the fiber i
Page 193 and 194: 17 5 contraction have been ignored,
Page 195: 177 the system, and when the result
Page 198 and 199: 180 reduces fiber strength. The str
Page 200 and 201: 182 15. R. A. J. Sambell, D. H. Bow
Page 202 and 203: 184 41. A. J. Caputo et al., "Fiber
Page 204 and 205: 186 71, N. F. DOW, Study of Stresse
Page 206 and 207: 188 98. M. H. Rawlins et al., "Inte
Page 208 and 209: 190 125. R. Warren and C-H. Anderss
Page 210 and 211: 192 155. M. F. Doerner and W, D. Ni
Page 213 and 214: APPENDIX A. AUGER ELECTRON SPECTROS
Page 215: APPENDIX B DETAILS OF THE FIBER-SHE
Page 218 and 219: 200 Those for the fiber (primed) ar
Page 220 and 221: 202 89-92. 93. 94. 95" 96. 97. 98-9
Page 222 and 223: 204 130-133. E. I. DUPONT DE NEMOUR
Page 224 and 225: 206 173. NATIONAL ACADEMY OF SCIENC
Page 226 and 227: 208 203 - 204. 20s. 206 - 207. 208.
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