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Composite Materials. - Krishan K. Chawla. < Fibers>. 1. introduction. • Reinforcement 로써 여러가지 형태가 존재하지만 가장우수한 형태는 fiber form 이다. matrix. R einforcement. ▶ The use of fibers form is based on three important characteristic.
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Composite Materials - Krishan K. Chawla < Fibers>
1. introduction • Reinforcement 로써 여러가지 형태가 존재하지만 가장우수한 형태는 fiber form 이다. matrix Reinforcement ▶ The use of fibers form is based on three important characteristic • A smaller diameter with respect to its grain size or other microstructural unit → Size effect 즉 작은단면적일수록 재료가 가질수있는 결함의 확률은 작아진다. • A high aspect ratio ( length / diameter, l/d) → large fraction 은 매트릭스 걸리는 하중을 fiber 로 이동시킬수 있음. • A very high degree of flexibility → elastic modulus 는 재료자체의 물성에 의존하지만 fiber 의 지름은 flexibility 에 민감함. ▶ fiber 종류- Glass fiber, Boron fiber, Carbon fiber, Organic fiber, ceramic fiber Metallic fiber…
2. Glass Fibers ▶ Common glass fibers are silica based (~50%-60%) • E Glass- electrical insulator and good strength, reasonable Young’s modulus • C Glass- stands for corrossion • S Glass- stand for the higher silica content and glass is able to withstand higher temperatures than other glasses. 3. Boron Fibers • fabrication Reaction zone 1. Thermal decomposition of a CVD on substrate w 2. Reduction of boron halide. B Sic 4. Carbon Fibers • carbon fiber 는 graphite 의 a 축의 장점을 이용하기 위해 유기전구체를 고온에서 graphitization 하여 만듬.
• Schematic of carbon fiber production Precursor fiber Oxidation Up to 250℃ Carbonization 250~1500℃ Graphitization 1500~2500℃ 4. Organic Fibers • kevlar- meant mainly for use as rubber reinforcement fot tires • kevlar 29 – meant for ropes, cables, coated fabrics for inflatables, architectural… • kevlar 49 – meant for reinforcement of epoxy, polyester, and other resins for use in aerospace, marine…… ▶ organic fiber 는 이방성을 가지는 재료로써 압축응력 과 인장응력의 큰 차이를 보임. • Tensile direction- covalent bonding • compressive direction- hydrogen , van der Waals H H H H
5. Ceramic Fibers ▶ ceramic fiber is high strength and elastic modulus with high-temperature capability and a general freedom from environmental attack • fabrication- CVD, polymer Pyrolysis , sol-gel • silicon carbide fibers- CVD deposited on a W (sometimes carbon) substrate heated to 1300℃ CARBON MONOFILAMENT Sic 1 Si % Depth of surface 2 3 Zone 1 : carbon rich: to promote bonding with the matrix This fiber gives a buffer layer at the surface that allow fiber strength to be maintainted Even during the high-temperature incorporation into a metal matrix.
Tensile strength Young’s modulus 7. Comparison of fibers •진보된 우수한 fiber의 특징은 density 가 낮다. Sic B •몇몇 fiber 들은 이방성을 지니므로 응력방향을 선택받게 된다.. • fiber의 brittle 함을 matrix 와의 조합으로 극복한다..
