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Flashcards by Clara McConnell, updated more than 1 year ago
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| Question | Answer |
| Properties of fibre reinforced composites | -Good strength to weight ratio -Resistant to corrosion -Good fatigue resistance -Low thermal expansion |
| Fibre reinforced composites: Glass reinforced plastic (GRP) | By adding strands of glass to polyester resins a very tough, rigid, lightweight material can be produced |
| Fibre reinforced composites: Carbon fibre composites | The carbon fibres are mixed with a resin, then heated in a mould to produce a composite much stronger than GRP; it's strength makes it suitable for formula one cars and racing bikes |
| Fibre reinforced composites: Kevlar | A mixture of aromatic and aramid (nylon-like) molecules. These are melted and spun into fibres, the long chain molecules are held together by strong hydrogen bonds. These fibres awe always orientated parallel to the length of the fibres giving the material it's very high strength. Weight for weight, Kevlar is five times stronger than steel and is half the density of fibre glass. |
| Fibre reinforced composites: How does Kevlar work? | Kevlar fibres are woven into a cloth which can be fashioned into protective equipment. It operates essentially as a net, absorbing the force and some of the impact, the wearer is still affected by the impact but is saved from serious injury. |
| Fibre reinforced composites: Uses of Kevlar: | -Body protection, such as bullet proof vests, where lightweight, comfort and flexibility is important -Sport equipment, such as skis, helmets and rackets, whee lightweight and strength is important -Sails for windsurfing where the material has to withstand high speeds |
| Fibre reinforced composites: Properties of Kevlar | -Flame resistant -Self extinguishing -Low electrical conductivity -High chemical resistance -High cut resistance -High toughness -High strength to weight ratio |
| Properties of particle based composites | -High strength in compression, less so in tension -Good stability -Uniform structure ensuring consistent strength -Generally free from surface defects |
| Particle based composites: Concrete | Made up of materials known as aggregates, as well as sand and cement. The final characteristics are determined by the ratio of the constituent parts. It is thoroughly mixed mixed while it is dry, water is then added. Once cast the concrete is left to harden, the temperature of the mix will rise due to the chemical reactions taking place. |
| Particle based composites: Advantages and disadvantages of Concrete | +It can be moulded into complex shapes +It has properties similar to stone, and the components are more readily extracted than stone +It can be cast in situ where as stone has to be quarried and cut to shape +It is good in compression -It is poor in tension, meaning it needs to be reinforced. |
| Particle based composites: Cements | Mixtures of metal and ceramic particles, a common type of cement is tungsten carbide, a combination of the ceramic tungsten carbide,mama the metal cobalt. It is used extensively for cutting tools as it keeps it's edge very well. |
| Particle based composites: advantages and disadvantages of cements | +Resistant to high temperatures +Tough and shock resistant -Brittle, and high melting points exclude many processes, making sintering the only suitable one |
| Sheet based composites | These are often man-made boards which we made from waste wood and wood fibres which are bonded to form a new material, for example: plywood, blackboard, chipboard, MDF and hardboard. +They have increased stability against warping +They have equal strength in all directions (unlike natural timbers) |
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