Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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materials [17]. This is because VIF result cannot be reproduced, hence does not yield a reliable KICvalue. He compared the KICvalues of silicon nitride specimens obtained from standardized fracture toughness test and VIF technique. He found that Antis equation underestimates the fracture toughness whilst Niihara s equation overestimates the toughness. Although Miyoshi equation yields a result close to that of standardized fracture toughness test, a calibration constant is needed to fit the data. Therefore, the fracture toughness of brittle ceramics should be determined from the standardized fracture toughness test. The standard fracture test produces reliable fracture toughness values because the specimen with a well-defined single crack is subjected to a well-defined mechanical loading condition. On the contrary, VIF test has a complex three-dimensional cracks and ill-defined crack arrest condition. For new ceramic materials with unknown fracture toughness value, VIF test should not be used to determine the toughness. This is because VIF toughness can deviate up to 48% from the true fracture toughness value [18]. Despite these deficiencies, the VIF test is used extensively to determine the fracture toughness of ceramic-CNT nanocomposites. 7.2 Toughening and Strengthening Mechanisms 7.2 Toughening and Strengthening Mechanismsj187 The mechanisms responsible for toughening of CNT-reinforced ceramics include crack deflection, crack bridging and nanotube pull-out. The toughening behavior can be explored from the Vickers indentation of ceramic-CNT nanocomposites synthesized from AAO membranes. Such nanocomposite coatings contain a highly ordered array of parallel nanotubes in an alumina matrix. Xia et al. prepared highly aligned alumina-MWNT nanocomposites using AAO coatings of different thicknesses (20 and 90 mm) through template synthesis [Chap. 5, Ref. 81]. After multi-step anodizing, Co or Ni catalyst particles were deposited into the bottom of nanopores of amorphous alumina coatings. CVD treatment at 645 C was employed to grow MWNTs up the pore walls. Controlling the composition of reactant gases and deposition time produces MWNTs with different wall thickness. The nanotubes formed inside the AAO coating with 90 mm thickness have a larger diameter and a thinner wall thickness than those formed with 20 mm. The nanocomposites were then subjected to nanoindentation using a Berkovitch indenter. Interestingly, alumina-MWNT nanocomposites exhibit all the toughening features similar to those observed in conventional fiber-reinforced composites, that is, crack deflection, crack bridging and crack pull-out (Figure 7.1(a)–(c)). Consequently, interface debonding and sliding can occur in composite materials with nanostructures. Furthermore, the nanocomposite having nanotubes with thinner wall thickness and larger diameter is more resistant to indentation damage. This is demonstrated by the collapse of CNTs into shear bands, leading to the absorption of large energy during indentation. No racking is observed during deformation of the nanocomposite coating (Figure 7.2). The shear band formation is somewhat similar to shear yielding observed in polymers. For polymeric materials, shear banding often initiates from
188j 7 Mechanical Properties of Carbon Nanotube–Ceramic Nanocomposites Figure 7.1 SEM micrographs showing (a) crack intersection with the successive alumina/MWNT interfaces and defection around the MWNTs along the interface; (b) CNT bridging the gap between the crack surfaces; (c) nanotube pull-out. Reproduced with permission from [Chap. 5, Ref. 81]. Copyright Ó (2004) Elsevier. cavitation of second-phase elastomer particles followed by the shear yielding of the polymer matrix. Consequently, much energy can be dissipated during mechanical deformation, thereby improving the fracture toughness of polymers considerably. For highly disordered ceramic-CNT nanocomposites, crack deflection, crack bridging and crack pull-out mechanisms are often observed [Chap. 5, Ref. 44, Figure 7.2 SEM micrograph showing collapse of the nanotubes into a shear band (indicated by the arrows) for the nanocomposite coating of 90 mm thickness. Reproduced with permission from [Chap. 5, Ref. 81]. Copyright Ó (2004) Elsevier.
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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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134j 5 Carbon Nanotube-Ceramic Nano
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Page 231 and 232: Table 8.1 Patent processes for maki
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Page 243: 228j Index l laser ablation 7 load
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