Materials, components and their properties
Materials, components and their properties is examined by asking you to classify materials and justify choices using measurable properties.
Core rules
- Woods: hardwoods (oak, beech) are generally denser and more durable; softwoods (pine, spruce) are cheaper and easier to work. Grain direction affects strength and finish.
- Metals: ferrous metals contain iron (steel, cast iron) and can rust; non-ferrous metals (aluminium, copper, brass) resist corrosion; alloys are mixtures.
- Polymers: thermoplastics (acrylic, polypropylene, PET) soften on heating and are recyclable; thermosets (epoxy, polyester resin) set permanently; elastomers (rubber) stretch and recover.
- Composites combine materials to gain properties neither has alone, for example GRP: glass fibres in polyester resin.
- Properties include density, tensile/compressive/shear strength, hardness, toughness, ductility, malleability, elasticity, conductivity, corrosion resistance and workability.
Worked example
Choose a material for a bicycle mudguard. It must be tough, low density, corrosion-resistant and formable into a curve. Aluminium is light and corrosion-resistant but needs bending and may dent. Polypropylene is tough, light, corrosion-proof and injection-mouldable, but stiffens in cold and is less UV-stable. GRP is stiff and light but labour-intensive. Polypropylene is selected because toughness, mass and mass-production cost outweigh UV weakness, which is solved with a stabiliser.
Traps
Saying "strong" when you mean tough or hard; treating "light" as a property without density; ignoring how the material will be shaped; forgetting cost, availability and recyclability.