Design & Technology
The material types used in resistant materials are woods, metals, plastics, ceramics and composites. Each of these has its own characteristic working properties, such as strength, malleability, conductivity, toughness and durability.
There are two types of timber, called hardwood and softwood. These names do not refer to the properties of the wood: some softwoods can be hard and some hardwoods can be soft.
Softwoods come from coniferous trees which are evergreen, needle-leaved, cone-bearing trees, such as cedar, fir and pine.
Hardwoods come from broad-leaved, deciduous trees. The main hardwood timbers are ash, beech, birch, cherry, elm, iroko, mahogany, meranti, oak, obeche, sapele and teak.
|Ash||Light, creamy-brown colour, open-grainedopen grain: A wood with visible large pores - eg oak., toughtough: Able to withstand blows or sudden shocks without breaking., flexibleflexible: Capable of being bent or flexed many times without breaking.||Sports equipment, wooden ladders, tool handles|
|Beech||White to pinkish-brown in colour, close-grained [close-grained: A wood with no visible large pores - eg beech. ], hardhard: Able to resist wear, scratching and indentation., tough, strongstrong: Able to withstand a force without breaking or bending., warpswarps: Bends or twists out of shape, this is common with wood as it dries. easily||Furniture, toys, tool handles|
|Elm||Light to medium brown in colour, open and sometimes interlocking graininterlocking grain: The grains have a weaved structure. For wood this makes it strong, less prone to splitting andn often suitable for bending., tough, durabledurability: The ability of a material to withstand wear, especially as a result of weathering., resists splitting, durable in water||Indoor and outdoor furniture|
|Mahogany||Pink to reddish-brown colour, fairly strong, durable, some interlocking grain||Good quality furniture|
|Oak||Light brown colour, strong, hard, tough, open-grained, corrodes steel screws and fittings||Interior woodwork, good quality furniture|
Most metals are extracted from their oresore: An ore is a rock containing enough quantities of a mineral that it is profitable to extract it. using a chemical reaction. Metals are rarely used in their pure form, and are usually mixed with other metals to improve their properties. This is called an alloyalloy: An alloy is a compound of two or more elements, at least one of which is a metal.. Most metals are good conductorsconductor: An electrical conductor is a material which allows an electrical current to pass through it easily. It has a low resistance. A thermal conductor allows thermal energy to be transferred through it easily. and can be recycled.
Ferrous metals contain iron. Examples are cast iron, mild steel, medium carbon steel, high carbon steel, stainless steel and high speed steel.
The ferrous metals listed below are all alloys.
|Name and melting point||Properties and characteristics||Principal uses|
|Cast iron 1200°C||Hardhard: Able to resist wear, scratching and indentation. skin, softer underneath, but brittlebrittle: If something is brittle it is easily broken., corrodes [corrosion: The destruction of a metal by oxidation or chemical action. ] by rusting||Parts with complex shapes which can be made by casting|
|Mild steel 1600°C||Toughtough: Able to withstand blows or sudden shocks without breaking., ductileductile: If a material is ductile it is capable of being drawn into thin sheets or wires without breaking., malleablemalleable: If a material is malleable it is capable of being hammered or pressed out of shape without being likely to break or return to the original shape., good tensile strengthtensile strength: The tension a material can withstand without breaking., poor resistance to corrosion [corrosion: The destruction of a metal by oxidation or chemical action. ]||General purpose engineering material|
|High carbon steel 1800°C||Even harder than medium carbon steel and more brittle, can be heat-treated to make it harder and tougher||Cutting tools, ball bearings|
|Stainless steel 1400°C||Hard and tough, resistant to wear and corrosion||Cutlery, kitchen equipment|
Non-ferrous metals do not contain iron. Some common non-ferrous metals are aluminium, Duralumin, copper, zinc, brass, gilding metal and tin.
|Name and melting point||Composition||Properties and characteristics||Principal uses|
|Aluminium 660°C||Pure aluminium||Good strengthstrength: The ability of a material to withstand a force without breaking or bending.-to-weight ratio, light, soft, ductile, good conductor of heat and electricity||Kitchen equipment, window frames, general cast components|
|Copper 1080°C||Pure copper||Malleable and ductile, good conductor of heat and electricity, resistant to corrosion||Water pipes, electrical wire, decorative goods|
|Brass 900-1000°C||Alloy||Resistant to corrosion, fairly hard, good conductor of heat and electricity||Ornaments, cast items such as water taps|
|Tin 230°C||Pure tin||Soft, weak, malleable, ductile and resistant to corrosion||Usually used for coating steel to form tin-plate, soft soldersolder: An alloy used to join metallic parts.|
Natural sources of plastics include:
Synthetic plastics are chemically manufactured from:
Plastics are divided into thermoplastics and thermoset plastics.
Thermoplastics can be heated and shaped many times.
|Polyamide (Nylon)||Creamy colour, toughtough: Able to withstand blows or sudden shocks without breaking., fairly hardhard: Able to resist wear, scratching and indentation., resists wear, self-lubricatinglubricating: Oiling or reducing friction. A lubricant is anything which reduces the friction between two surfaces., good resistance to chemicals and machines||Bearings, gear wheels, casings for power tools, hinges for small cupboards, curtain rail fittings and clothing|
|Polymethyl methacrylate (Acrylic)||Stiff, hard but scratches easily, durable, brittlebrittle: If something is brittle it is easily broken. in small sections, good electrical insulatorinsulator: Material that is a poor conductor of electricity or heat., machines and polishes well||Signs, covers of storage boxes, aircraft canopies and windows, covers for car lights, wash basins and baths|
|Polypropylene||Light, hard but scratches easily, tough, good resistance to chemicals, resists work fatiguework fatigue: Weakening of a material as a result of prolonged or repeated stress on it.||Medical equipment, laboratory equipment, containers with built-in hinges, 'plastic' seats, string, rope, kitchen equipment|
|Polystyrene||Light, hard, stiff, transparent, brittle, with good water resistance||Toys, especially model kits, packaging, 'plastic' boxes and containers|
|Low density polythene (LDPE)||Tough, good resistance to chemicals, flexible, fairly soft, good electrical insulator||Packaging, especially bottles, toys, packaging film and bags|
|High density polythene (HDPE)||Hard, stiff, able to be sterilised||Plastic bottles, tubing, household equipment|
Thermoset plastics can only be heated and shaped once.
|Epoxy resin||Good electrical insulator, hard, brittle unless reinforced, resists chemicals well||Casting and encapsulation, adhesives, bonding of other materials|
|Melamine formaldehyde||Stiff, hard, strong, resists some chemicals and stains||Laminates for work surfaces, electrical insulation, tableware|
|Polyester resin||Stiff, hard, brittle unless laminated, good electrical insulator, resists chemicals well||Casting and encapsulation, bonding of other materials|
|Urea formaldehyde||Stiff, hard, strong, brittle, good electrical insulator||Electrical fittings, handles and control knobs, adhesives|
Composite materials are formed by combining a reinforcing material such as wood pulp, and a bonding agent, such as glue. The wood pulp is made from the waste from cutting solid wood. MDFMDF: Medium Density Fibreboard - a type of engineered wood made of compressed wood and fibre particles held together with glue. and GRPGRP: Glass-Reinforced Plastic - a strong and versatile material made by combining a plastic (usually polyester resin) with fibres made of glass. are examples of composite materials.
Remember: Alloysalloy: An alloy is a compound of two or more elements, at least one of which is a metal. are not composite materials.
Ceramics are made from clay, sand and feldsparfeldspar: A very common group of hard, crystalline minerals containing silicon.. These materials are ground to a fine powder, mixed together and fired at high temperatures (700-2000°C).
Smart materials are reactive materials. Their properties can be changed by exposure to stimuli, such as electric and magnetic fields, stress, moisture and temperature.
Smart colours are pigments which can be incorporated into paints, dyes, inks and plastics.
Photochromatic materials are used in the manufacture of sunglasses. Exposure to sunlight causes the lens of the glasses to darken to protect the eye.
Polymorph is available in small pellets which fuse together when heated to 62˚C. It can be moulded into shape resulting in a very tough polymer. Unused pellets can be re-heated and re-used.
Polymorph is used for:
Smart grease is used to control movement, producing a dampened, slowed down feeling. For example, smart grease is used on volume control knobs and microscope slides.
Most plastics are natural insulatorsinsulator: Material that is a poor conductor of electricity or heat.. The advantages of making plastics which are conductorsconductor: An electrical conductor is a material which allows an electrical current to pass through it easily. It has a low resistance. A thermal conductor allows thermal energy to be transferred through it easily. are:
Some conductive polymers are also biocompatible [biocompatible: Can be safely used in the body. ], making them suitable for use in medical devices.
Nanoparticles improve the mechanical properties of a material, such as stiffness or elasticityelasticity: The ability of a fibre, yarn or fabric to stretch and return to its original shape.. When incorporated into polymers, they can be used as lightweight replacements for metals.
Nanomaterials are used in car manufacturing to create cars that are faster, safer and more fuel efficient. They can also be used to produce more efficient insulation and lighting systems.
Different materials exhibit different working properties. Listed below are the key properties which determine how materials behave.