Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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7 Mechanical Properties of Carbon Nanotube–Ceramic Nanocomposites 7.1 Fracture Toughness Mechanical strength, hardness and fracture toughness are key parameters in the materials selection process for ceramic materials. Ceramics are attractive structural materials for engineering applications because of their high mechanical strength. However, ceramics are brittle as a result of their high resistance to dislocation slip. Designing to prevent catastrophic failure of ceramic materials under the application of external stresses requires a fundamental knowledge of their fracture mechanisms. Fracture toughness is fundamental design property of materials containing cracks that undergo fracture as a result of unstable crack propagation. A fracture mechanics approach is developed to assess the materials resistance to fracture in the presence of a crack. Linear elastic fracture mechanics (LEFM) is used to evaluate the toughness of brittle materials that fracture in elastic deformation regime. In this approach, stress intensity factor (K) is used to characterize the magnitude of stress field at a crack tip during mechanical loading. The critical value of the stress intensity factor resulting from unstable crack propagation and final failure of the materials under tensile mode is termed as fracture toughness or K IC. Most ceramic materials suffer fracture before the onset of plastic deformation. The fracture toughness of ceramics can be determined experimentally using different specimen configurations, such as single edge precracked beam (SEPB), single edge notched (SENB), single edge V-notched beam (SEVNB) and chevron notched beam (CNB). Such specimens are mechanically loaded under three-point or four-point flexural conditions [1–6]. These measurements can give bending strength and true fracture toughness values that can be accurately reproduced. Further, SEPB, SEVNB and CNB measurements have been accepted as standard test methods by the American Society for Testing and Materials (ASTM). Generally, a pre-existing sharp crack must be made in specimens prior to the fracture toughness measurements. For instance, SEPB specimens are pre-cracked in a specially designed bridge–anvil tool under a compressive load. This yields quite a large crack tip radius over the entire width. Thus, the geometry of the crack is difficult to control. For SENB specimens, the pre-crack can be simply made by using a diamond j185
186j 7 Mechanical Properties of Carbon Nanotube–Ceramic Nanocomposites saw or machining. The notch-root radius must be smaller than 10 mm in order to obtain reliable fracture toughness results [7]. With the SEVNB it is relatively easy to sharpen the V-notch with a razor blade. In general, ceramic materials are rather sensitive to the sharpness of the crack tip. A large notch-root tends to overestimate the real fracture toughness of ceramics. For instance, the SEVNB fracture toughness of alumina with a notch-root radius of 300 mm is quite large, that is, 7.6 MPa m 1/2 . This toughness can be reduced to an acceptable value of 3.8 MPa m 1/2 by using a notch-root radius of
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Sie Chin Tjong Carbon Nanotube Rein
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Sie Chin Tjong Carbon Nanotube Rein
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Contents Preface IX List of Abbrevi
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5 Carbon Nanotube-Ceramic Nanocompo
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Preface Carbon nanotubes are nanost
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XII List of Abbreviations HIP hot i
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1 Introduction 1.1 Background Compo
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Figure 1.2 Transmission electron mi
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1.3 Synthesis of Carbon Nanotubes 1
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MWNTs can be as high as 70% of the
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Figure 1.7 In situ TEM images recor
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1.3 Synthesis of Carbon Nanotubesj1
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show TEM images of MWNTs synthesize
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Since then, large efforts have been
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1.3.4 Patent Processes Carbon nanot
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1.4 Purification of Carbon Nanotube
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Table 1.3 Patent processes for the
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Figure 1.13 Schematic illustration
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1.5 Mechanical Properties of Carbon
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Figure 1.14 Carbon nanotubes in hig
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Figure 1.15 In situ tensile deforma
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Table 1.7 Theoretical and experimen
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Nomenclature ~a 1 , ~a 2 Unit vecto
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carbon nanotubes. Physical Review L
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70 Jang, I., Uh, H.S., Cho, H.J., L
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108 Shelimov, K.B., Esenaliev, R.O.
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Bonnamy, S., Beguin, F., Burnham, N
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2 Carbon Nanotube-Metal Nanocomposi
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isostatic pressing. In certain case
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This implies the absence of effecti
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coating material, the plasma gun an
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Table 2.4 Changes in the size and v
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Figure 2.6 (a) Low and (b) high mag
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Figure 2.8 SEM micrographs showing
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Figure 2.11 Bright field TEM microg
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Figure 2.13 TEM image of bulk Al/5
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2.5 Magnesium-Based Nanocomposites
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limited improvement in ultimate ten
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Figure 2.18 SEM micrographs of the
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Figure 2.19 (a) Low and (b) high ma
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Figure 2.22 SEM micrographs of (a)
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Figure 2.25 (a) TEM micrograph show
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2.8 Transition Metal-Based Nanocomp
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Figure 2.27 TEM image of electrodep
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Figure 2.29 SEM micrographs of (a)
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Figure 2.31 Schematic representatio
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einforcement content SiCp/Al compos
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Materials Science Forum, 534-536 (P
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composite. Materials Science and En
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111 Cha, S.I., Kim, K.T., Arshad, S
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90j 3 Physical Properties of Carbon
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100j 3 Physical Properties of Carbo
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102j 3 Physical Properties of Carbo
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104j 4 Mechanical Characteristics o
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132j 5 Carbon Nanotube-Ceramic Nano
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