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Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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204j 7 Mechanical Properties of <strong>Carbon</strong> <strong>Nanotube</strong>–<strong>Ceramic</strong> Nanocomposites<br />

Figure 7.15 (a) Three-point bending strength, (b) Vickers<br />

hardness <strong>and</strong> (c) indentation fracture toughness vs carbon<br />

nanofiber content for SiC/VGCF nanocomposites prepared by<br />

SPS at 1800 C under 40 MPa. Reproduced with permission from<br />

[Chap. 5, Ref. 114]. Copyright Ó (2007) Elsevier.<br />

crosss linking <strong>and</strong> pyrolysis [Chap. 5, Ref. 117]. The thermal loading technique<br />

with an edge-cracked circular disk was used to evaluate the fracture toughness of<br />

nanocomposites. Two types of MWNTs were used to reinforce the Si-C-N matrix,<br />

that is, type-A (high aspect ratio) <strong>and</strong> type-B (low aspect ratio). Figure 7.18 shows<br />

the fracture toughness vs nanotube content for nanocomposites investigated. It is<br />

apparent that the fracture toughness of the Si-C-N/MWNT nanocomposites<br />

improves significantly by adding type-A nanotubes. There is more than 60%<br />

improvement in fracture toughness of Si-C-N ceramic by adding 2 mass%<br />

MWNTs. Cracking bridging <strong>and</strong> nanotube pull-out can be readily seen in the<br />

fracture surface of the nanocomposite with 2 mass% MWNT. Little improvement

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