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Composite basic intro first lecturer.pdf

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Composite basic intro first lecturer.pdf

  1. 1. Composite Materials
  2. 2. More examples Composite Materials
  3. 3. A composite is any material made of more than one component. There are a lot of composites around you. Concrete is a composite. It's made of cement, gravel, and sand, and often has steel rods inside to reinforce it.
  4. 4. Balloons, not the cheaper ones that we use for water balloons which are made of natural rubber. But those fancy ones we get in the hospital. These are made of a polyester film made by DuPont called Mylar. These balloons are made of a sandwich, composed of Mylar and aluminum foil. Materials like this, made of two kinds of material, are called composites.
  5. 5. FIBER-REINFORCED COMPOSITES These are materials in which a fiber made of one material is embedded in another material.
  6. 6. NATURAL RUBBER LATEX ( POLYISOPRENE) Rubber Latex Raincoats were used which were really uncomfortable. In the middle of the nineteenth century, Charles Macintosh came up with a clever idea He took two layers of cotton fabric and embedded them in natural rubber, also known as Polyisoprene making a three-layered sandwich. This made for good raincoats because, while the rubber made it waterproof, the cotton layers made it comfortable to wear. A raincoat in Great Britain is referred to as a "mackintosh", or just a "mack“.
  7. 7. FIBER AND MATRIX • Modern composites are usually made of two components, a fiber and matrix. • The fiber is most often glass, but sometimes Kevlar, carbon fiber, or polyethylene. • • The matrix is usually a thermoset like an epoxy resin, polydicyclopentadiene, or a polyimide.
  8. 8. Role of Fibers • The fiber is embedded in the matrix in order to make the matrix stronger. • Fiber-reinforced composites have two things going for them. • They are strong and light. They're often stronger than steel, but weigh much less. • This means that composites can be used to make automobiles lighter, and thus much more fuel efficient. • This means they pollute less, too.
  9. 9. FiberglasTM Its matrix is made by reacting a polyester with carbon-carbon double bonds in its backbone, and styrene. Mixture of the styrene and polyester is poured over a mass of glass fibers. The styrene and the double bonds in the polyester react by free radical vinyl polymerization to form a cross-linked resin. The glass fibers are trapped inside, where they act as are inforcement.
  10. 10. In FiberglasTM the fibers aren't lined up in any particular direction. They're just a tangled mass, like you see in figure below.
  11. 11. Composite can be made stronger by lining up all the fibers in the same direction. Oriented fibers do some weird things to the composite. When you pull on the composite in the direction of the fibers, the composite is very strong. But if you pull on it at right angles to the fiber direction, it isn't so strong at all. Orientation of fibers & Strength
  12. 12. The woven fibers give a composite good strength in many directions
  13. 13. A loose bundle of fibers wouldn't be of much use. So the matrix holds the fibers together. Also, though fibers are strong, they can be brittle. The matrix can absorb energy by deforming under stress. This is to say, the matrix adds toughness to the composite. Moreover, while fibers have good tensile strength (that is, they're strong when you pull on them), they usually have awful compressional strength. That is, they buckle when you squash them. The matrix gives compressional strength to the composite. Role of Matrix
  14. 14. The unsaturated polyester/styrene systems. They're fine for everyday applications. Chevrolet Corvette bodies are made from composites using unsaturated polyester matrices and glass fibers. But they have some drawbacks. They shrink a good deal when they're cured, they can absorb water very easily, and their impact strength is low. They're also not very chemically resistant. Matrices and their advantages and disadvantages
  15. 15. Vinyl ester resin • Vinyl ester resin are low-cost system. The first step to making a vinyl ester resin is reacting a di-epoxide with acrylic acid, or methacrylic acid
  16. 16. After polymerization of the vinyl groups, a crosslinked resin is formed. Sometimes, bigger oligomers are used as shown below: Vinyl ester resins have some advantages over unsaturated polyesters. They don't absorb as much water, and they don't shrink nearly as much when cured. Plus, they have very good chemical resistance. Also, because of the hydroxyl groups, it bonds well to glass. This comes in handy if you're using glass as your fiber.
  17. 17. Neither vinyl ester resins nor unsaturated polyesters are very good for high temperature applications. For high temperatures, matrices like epoxy resins. To make these, a di-epoxide is used, just like making vinyl ester resins. Only this time, we don't react it with acrylic acid. Instead, we cure it with a diamine. The epoxide groups will react with the diamine, and the whole system becomes crosslinked: Because of all those hydroxyl groups, epoxy resins can bond well to glass fibers. They don't absorb water, and they don't shrink very much when they're cured. Can be used at higher temperatures, up to 160 oC. Epoxy resins as Matrices

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