AQA A-Level Design and Technology: Product Design

## Choosing a material A designer names a material for a product and then defends the choice by weighing several things against each other: the physical and mechanical properties (the working characteristics), what the product has to do, how it should look and feel, what the material and its processing cost, and what happens to it when the product is made and when it is thrown away. A material that is ideal on one of these is often poor on another. Carbon fibre reinforced plastic is stiff and light but expensive and hard to recycle, so it suits a racing bicycle and not a school ruler. Pine is cheap and easy to work but decays outdoors unless it is treated, so it suits a shed frame once it has been preservative treated and not a boat hull. Combinations matter as much as single materials. A kettle uses a polymer body, a metal element, a rubber or elastomer grip and a thermostat, and each part is chosen for its own job. A good justification therefore names the property, says why the product needs it, and says what is given up. Typical physical and working characteristics that come up are malleability, toughness, hardness, resistance to corrosion and degradation, thermal conductivity and electrical conductivity. ## The material families ### Metals Metals are ductile and malleable to varying degrees, strong, good conductors of heat and electricity, and can be joined by heat processes and alloyed. They are split into three groups. * **Ferrous metals** contain iron as the main…