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ADVANCED MECHANICS OF COMPOSITE MATERIALS Episode 2

Tham khảo tài liệu 'advanced mechanics of composite materials episode 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 22 Advanced mechanics of composite materials the mechanical properties of metal matrix composites are controlled by the matrix to a considerably larger extent though the fibers still provide the major contribution to the strength and stiffness of the material. The next step in the development of composite materials that can be treated as matrix materials reinforced with fibers rather than fibers bonded with matrix which is the case for polymeric composites is associated with ceramic matrix composites possessing very high thermal resistance. The stiffnesses of the fibers which are usually metal steel tungsten molybdenum niobium carbon boron or ceramic SiC Al2O3 and ceramic matrices oxides carbides nitrides borides and silicides are not very different and the fibers do not carry the main fraction of the load in ceramic composites. The function of the fibers is to provide strength and mainly toughness resistance to cracks of the composite because non-reinforced ceramic materials are very brittle. Ceramic composites can operate under very high temperatures depending on the melting temperature of the matrix that varies from 1200 to 3500 C. Naturally the higher the temperature the more complicated is the manufacturing process. The main shortcoming of ceramic composites is associated with a low ultimate tensile elongation of the ceramic matrix resulting in cracks appearing in the matrix under relatively low tensile stress applied to the material. An outstanding combination of high mechanical characteristics and temperature resistance is demonstrated by carbon-carbon composites in which both components - fibers and matrix are made from one and the same material but with different structure. A carbon matrix is formed as a result of carbonization of an organic resin phenolic and furfural resin or pitch with which carbon fibers are impregnated or of chemical vapor deposition of pyrolitic carbon from a hydrocarbon gas. In an inert atmosphere or in a vacuum carboncarbon .