GCSE Design & Technology: Smart Materials and Modern/Composite Materials Revision Guide

Smart materials

Smart materials respond reversibly to a change in their environment, such as a change in temperature, light or an applied force, and can return to their original state when the trigger is removed. A shape memory alloy, such as Nitinol (a mixture of nickel and titanium), can be bent out of shape and will return to a pre-set shape when heated above a specific temperature; this property is used in eyeglass frames, dental braces and self-adjusting valves. Thermochromic materials change colour in response to a change in temperature, and are used in novelty mugs and kettles, as well as in strip thermometers, to give a visual indication of heat. Photochromic materials change colour in response to a change in light level, and are best known for their use in self-tinting sunglasses lenses, which darken automatically in bright sunlight.

Composite materials

A composite material is made by combining two or more different materials so that the resulting material has better properties than either material would have on its own. Carbon fibre reinforced polymer combines strong carbon fibres with a polymer resin to produce a material that is extremely strong and stiff for its weight, making it popular in racing bicycles, aircraft parts and sports equipment, although it is expensive to produce. Glass-reinforced plastic (GRP) combines glass fibres with a polymer resin to produce a material that is strong, lightweight and highly resistant to corrosion, which is why it is widely used for boat hulls, car body panels and water tanks. Reinforced concrete is another common composite, combining steel rods (which resist tension well) with concrete (which resists compression well but is weak in tension) to create a material suitable for large structures such as bridges and buildings.

Technical textiles

Technical textiles are fabrics engineered for their performance properties rather than their appearance. Kevlar is an extremely strong technical textile used in bulletproof vests, cut-resistant gloves and reinforced tyres. Gore-Tex is a technical textile that is both waterproof and breathable, thanks to a membrane with pores small enough to block liquid water but large enough to let water vapour (sweat) escape, making it popular for outdoor and sports clothing.

Choosing modern and smart materials

When selecting a smart, modern or composite material, designers weigh up performance benefits, such as strength-to-weight ratio, responsiveness or durability, against factors such as cost, availability and how easily the material can be processed, joined or eventually disposed of or recycled. Many of these materials are more expensive than traditional alternatives, so they tend to be used where their special properties provide a genuine advantage that justifies the extra cost.

Common mistakes

• Mixing up thermochromic (responds to temperature) and photochromic (responds to light) materials — the names are easy to confuse but the trigger is different.
• Describing a composite as simply "a mixture of materials" without explaining that the point is to combine the useful properties of each material, such as combining tensile strength with compressive strength in reinforced concrete.
• Assuming all smart materials permanently change, when in fact a defining feature of a smart material is that the change is reversible when the trigger is removed.