Modern, Smart and Composite Materials

Materials that give designers new possibilities

A material is selected because its properties suit the job a product must do. A protective garment needs strength without excessive weight; a pressure-sensitive control needs to respond when someone presses it. Developments in materials allow designers to meet these needs in ways that ordinary materials cannot.

Modern materials have been developed or adapted to offer useful properties. Smart materials change a property in response to a stimulus, such as heat, pressure or electricity. These categories can overlap: a newly developed material may also be smart. The important distinction is whether a useful response to a stimulus is part of its behaviour.

A composite material combines different materials to obtain a useful combination of properties. It need not be smart: a reinforced plastic can remain strong and lightweight without changing in response to its surroundings.

Electroluminescent wire: electricity into light

Electroluminescence means producing light in response to electrical stimulation. Electroluminescent materials can be supplied as film or wire. EL wire has a thin copper core coated with a light-emitting material called a phosphor. When supplied with the appropriate electrical power, the coating glows along the wire.

Its small diameter makes the wire flexible, so it can follow the outlines of clothing, costumes or a bicycle. This lets a designer create a glowing outline rather than use separate points of light. For runners or cyclists in low light, the benefit is increased visibility; in a costume, it is the visual effect.

The glow depends on an electrical supply. A designer therefore needs to accommodate the power source and connections as well as the wire itself. Its usefulness must be judged against these additional requirements.

LCD stands for liquid crystal display. Liquid crystals are electrically controlled to alter the passage of light and form images. LCDs provide thin, energy-efficient displays. They are not the same as EL wire: an LCD controls light to make an image, whereas an electroluminescent material emits light.

QTC: pressure changes electrical resistance

Quantum Tunnelling Composite, or QTC, responds to compression. Electrical resistance describes how strongly a material opposes the flow of current. QTC has a high resistance when it is not pressed; compression lowers its resistance, allowing current to flow more easily.

QTC contains conductive particles within a polymer. Its useful behaviour is not just a simple mechanical on/off action: the change in resistance allows a circuit to respond to pressure.

This makes QTC suitable for pressure-sensitive controls, wearable technology and speed controllers. For example, a control can use increased pressure as an input to change motor speed. QTC senses the pressure; the rest of the circuit determines what the product does with that information.

The design advantage is a material that can act as a pressure-sensitive input. The designer must still include the circuit and power supply needed to turn that input into a useful output.

Shape memory alloys: returning to a set shape

An alloy is a mixture containing a metal and one or more other elements. A shape memory alloy, or SMA, can return to a predetermined shape when heated after being deformed. Electrical heating can also provide the heat needed for this response.

For a suitable glasses frame, this means a bent part can recover its original shape when heated. In a temperature-operated switch, the change of shape can move a contact and operate the switch. Other applications include dental braces, surgical stents and fire sprinkler mechanisms.

The useful connection is heat → shape change → movement. An SMA can therefore act as an actuator: a component that creates movement. It does not remember any shape a user happens to bend it into; the recovery shape has been established beforehand.

Polymorph: mould, cool and remould

Polymorph, also called polycaprolactone or PCL, is a thermoplastic supplied as small beads or granules. A thermoplastic softens when heated and becomes rigid again when it cools. Polymorph can be softened in hot water and shaped by hand when it is safe to handle.

This is useful for prototype models, hand-shaped products and jewellery. A designer can make a trial shape, assess it and soften the material again to alter it. For example, a prototype handle can be shaped to fit a user's hand rather than being restricted to a standard profile.

When working with Polymorph, follow the manufacturer's heating instructions and use teacher supervision. Hot water and softened material can cause burns. Use a suitable tool to remove the material and let it cool enough to handle safely. It is ready to shape when it is soft and mouldable; the finished shape must cool until rigid before it is assessed or used.

Unlike an SMA, Polymorph does not automatically recover a remembered shape. Someone moulds it into a new shape. Its ease of remoulding is an advantage during development, but a product that becomes hot in use may not suit a material that softens with heat.

Composites: combining fibres and plastic

In fibre-reinforced plastics, fibres provide reinforcement and a surrounding plastic resin holds them together in the required shape. The result offers a combination of properties that neither constituent provides alone.

Glass Reinforced Plastic (GRP) combines glass fibres with plastic, commonly a thermosetting resin. A thermosetting resin sets permanently rather than softening again for remoulding. GRP is tough and can be formed into shaped shells, making it useful for boat and kayak hulls and vehicle body panels.

Carbon fibre reinforced plastic combines carbon fibres with resin. Compared with GRP, it can offer greater strength with less weight, but it is more expensive. Applications include helmets, laptop casings and sports equipment. Low weight is especially valuable where equipment must be carried, worn or moved repeatedly.

Kevlar is a strong, lightweight synthetic fibre. It can be woven into protective fabrics used in motorcycle clothing and bullet-resistant body armour. It can also reinforce composites. The distinction matters: a woven Kevlar fabric is not the same thing as Kevlar fibres embedded in resin.

Choosing for the product, not just the headline property

A useful material choice connects a property to the product's function. Carbon fibre reinforced plastic may justify its higher cost in sports equipment where reducing weight is important. GRP may be a more appropriate choice for a moulded hull where toughness, shape and cost matter more than the greatest possible weight saving.

Likewise, Kevlar's combination of strength and low weight suits wearable protection, while Polymorph's remouldability suits prototypes. A smart material is worthwhile when its response performs a needed job: QTC senses pressure, an SMA creates movement and EL wire creates light. The best choice is the one that meets the user's needs while taking account of cost, manufacture and operating conditions.

Smart responses