Smart materials

Smart – or shape memory – materials are an invention that has changed the world of engineering. There are two types: metal alloys and plastic polymers. The metal alloys were made first and they are usually an expensive mixture of titanium and nickel.

Shape memory materials are called ‘smart’ because they react to changes in their environment, for example:

- plastics that return to their original shape when the temperature changes. One use is in surgery where plastic threads ‘remember’ the shape of a knot, react to the patient’s body temperature and make themselves into stitches.

- metal alloys that have a ‘memory’ and can return to their original shape. They are used in medical implant s that are compressed so they can be put inside the patient’s body through a small cut. The implant then expand s back to its original shape. More everyday uses are for flexible spectacle frames and teeth braces.

- solids that darken in sunlight, like the lenses in some sunglasses.

- Liquid crystals that change shape and colour. These have been used in climbing ropes that change colour if there is too much strain and weight on them.

The future of these materials and their possible uses is limited only by human imagination. One clever idea is that if car were made of smart metal, a minor accident could be repaired by leaving the car in the sun!

3. Complete the definitions (1-8) below with the highlighted words in the text.

1 An___________is something medical put inside the body, e.g. a heart valve.

2 You need a good____________to think of new and interesting ideas.

3 _______________are materials made from mixing two metals.

4 To_________means to become bigger.

5 To__________is to change because something else happens.

6 The___________is everything around a person or thing.

7 To be __________means to be made smaller.

Speaking

Work with a partner. Choose one of the smart materials in the text. Think of five interesting ways it could be used. Compare your ideas with other students.

Think of examples from nature that are like smart materials, for example, things that can change shape or colour, or repair themselves.

Read the text and do the tasks below

Vocabulary

Change in a controlled fashion

External stimuli

Moisture

In the reverse manner

Swell

Collapse

Undergo changes

Acidity

Dramatically

Steadily

The force of an impact

To deploy the airbag

Tiny iron particle

Clutch

Valve

The text is taken from http://www.cs.ualberta.ca/~database/MEMS/sma_mems/smrt.html

Smart materials are materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as stress, temperature, moisture, pH, electric or magnetic fields. There are a number of types of smart material, some of which are already common. Some examples are as following:

· Piezoelectric materials are materials that produce a voltage when stress is applied. Since this effect also applies in the reverse manner, a voltage across the sample will produce stress within the sample. Suitably designed structures made from these materials can therefore be made that bend, expand or contract when a voltage is applied.

· Shape memory alloys and shape memory polymers are Thermoresponsive materials where deformation can be induced and recovered through temperature changes.

· Magnetic shape memory alloys are materials that change their shape in response to a significant change in the magnetic field.

· pH-sensitive polymers are materials which swell/collapse when the pH of the surrounding media changes.

· Temperature-responsive polymers are materials which undergo changes upon temperature.

· Halochromic materials are commonly materials that change their colour as a result of changing acidity. One suggested application is for paints that can change colour to indicate corrosion in the metal underneath them. Chromogenic systems change colour in response to electrical, optical or thermal changes. These include electrochromic materials, which change their colour or opacity on the application of a voltage (e.g. liquid crystal displays), thermochromic materials change in color depending on their temperature, and photochromic materials, which change colour in response to light - for example, light sensitive sunglasses that darken when exposed to bright sunlight. Non-Newtonian fluid is a liquid which changes its viscosity in response to an applied shear rate. In other words the liquid will change its viscosity in response to some sort of force or pressure. One good example of this is Oobleck, a fluid that seems to temporarily turn into a solid when a force is applied quickly.^[1] Another good example is Custard, as long as it is starch based.

Science and technology have made amazing developments in the design of electronics and machinery using standard materials, which do not have particularly special properties (i.e. steel, aluminum, gold). Imagine the range of possibilities, which exist for special materials that have properties scientists can manipulate. Some such materials have the ability to change shape or size simply by adding a little bit of heat, or to change from a liquid to a solid almost instantly when near a magnet; these materials are called smart materials.

Smart materials have one or more properties that can be dramatically altered. Most everyday materials have physical properties, which cannot be significantly altered; for example if oil is heated it will become a little thinner, whereas a smart material with variable viscosity may turn from a fluid which flows easily to a solid. A variety of smart materials already exist, and are being researched extensively. These include piezoelectric materials, magneto-rheostatic materials, electro-rheostatic materials, and shape memory alloys. Some everyday items are already incorporating smart materials (coffeepots, cars, the International Space Station, eyeglasses) and the number of applications for them is growing steadily. Each individual type of smart material has a different property which can be significantly altered, such as viscosity, volume, and conductivity. The property that can be altered influences what types of applications the smart material can be used for.

Дата добавления: 2015-11-16