A History on Composites

Composites Made by combining two or more materials (usually have very different properties) Natural, early, modern

Natural Composites Exist in both animals and plants E.g. wood (polymer held together by lignin); bone (hydroxyapatite + collagen)

History (Early composites) Wattle and daub One of the oldest man-made composite materials Over 6000 y.o. Woven lattice of wooden strips (wattle) is daubed (coated) with a sticky material (combination of soil, clay, sand, animal dung and straw) Construction material Plywood 3400 BC by Ancient Mesopotamians Made by gluing together a number of thin veneers or plies of softwood or hardwood Strength comes from its structure (odd number of veneers; each ply is at a right angle to the one below; more veneers used, stronger) Engineering material for stressed-skin applications; for marine and aviation applications (e.g. British de Havilland Mosquito bomber, primarily made using two layers of birch plywood) Often used to create curved surfaces (can easily bend with grain) Cartonnage Used in Egyptian funerary masks (First Intermediate Period of Egypt c. 2181-2055 BC) Made of layers of linen or papyrus covered with plaster Cob/Cobb/Clom Mud bricks/ mud walls Earliest man-made composite material Straw + mud (sand, clay, water) dried into a brick shape To make a building material, or for building construction First documented by Egyptian tomb paintings Good compressive strength (resists squashing), poor tensile strength (prone to bending) Fireproof, resistant to seismic activity, inexpensive Concrete Mix of aggregate (small stones/gravel), cement and sand Good compressive strength Reinforced concrete: (used in more recent times) addition of metal rods or wires to it (increase in tensile/bending strength) Papier-mch Consists of paper pieces or pulp (can be reinforced with textiles) bound with an adhesive (glue, starch, wallpaper paste) Decorative and structural role (e.g. carnival floats, effigies, theatrical use, puppetry, lamps) Bakelite First artificial fiber reinforced plastic (1907) Predated by shellac (resin from female lac bug; processed and sold as dry flakes) Thermosetting phenol formaldehyde resin Formed from elimination reaction of phenol and formaldehyde Use for its electrical nonconductivity and heat-resistant properties in electrical insulators, radio and telephone casings, and such diverse products (kitchenware, jewelry, pipe stems, firearms, childrens toys)

Making Composites Most are made of just two materials Matrix/ binder: surrounds and binds together fibers or fragment of the other material Reinforcement: fibers or fragments of a material

Modern Composites Fiberglass: first modern composite material Used for boat hulls, sports equipment, building panels and many car bodies Matrix: plastic; reinforcement: glass (made into fine threads, often woven into a sort of cloth) Carbon fibers Lighter and stronger than fiberglass; more expensive Used in aircraft structures and expensive sports equipment (e.g. golf clubs) Made by oxidizing Silicon Carbide Popular abrasive and cutting tool (due to hardness, durability and low cost) Sandpaper (particles are laminated to paper) and grip tape on skateboards Used as structural material (1980s and 1990s) For high-temperature gas turbines Intended to replace nickel superalloy turbine blades/ nozzle vanes (not successful due to low impact resistance and low fracture toughness) Composite armor (Chobham armor), ceramic plates in bulletproof vests Dragon skin (by Pinnacle Armor) For automobile parts Silicon-infiltrated carbon-carbon composite for high performance ceramic brake discs (able to withstand extreme temperatures) Silicon + graphite in C-C composite = C/SiC (carbon-fiber-reinforced silicon carbide) Used in a sintered form for diesel particulate filters Oil additive to reduce friction, emissions, harmonics LEDs Electroluminescence (1907) discovered using silicon carbide First commercial LEDs based on SiC Gallium nitride was more efficient than SiC due to SiCs indirect bandgap (unfavourable for light emission) Carbon nanotubes Even lighter and stronger than ordinary carbon fibers; extremely expensive Offer possibilities for making lighter cars and aircraft (will use less fuel than heavier vehicles)*Airbus A380 Worlds largest passenger airliner Uses modern composites in design > 20% of it is made of composite materials, mainly plastic reinforced with carbon fibers Design: first large-scale use of glass-fiber-reinforced aluminium (25% stronger than conventional airframe aluminium; 20% lighter)

Advantages of Composites Light and strong New material can be made (can exactly meet the requirements of a particular application) by choosing an appropriate combination of matrix and reinforcement material

Disadvantages Costly as a whole Raw materials are often expensive

References:http://www.rsc.org/Education/Teachers/Resources/Inspirational/resources/4.3.1.pdfhttp://www.cantab.net/users/bryanharris/Engineering%20Composites.pdfhttp://www.asminternational.org/documents/10192/3449368/05287G_Sample_Chapter.pdf/7c5b99aa-25f6-4f08-abfd-b666c88eaf67http://authors.library.caltech.edu/5456/1/hrst.mit.edu/hrs/materials/public/composites/Composites_Overview.htm