Smart material

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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 stressSmart Materials in Civil Engineering Applications

However, ‘sensual structures’ need not be restricted to hi-tech applications such as aircraft. They could be used in the monitoring of civil engineering structures to assess durability. Monitoring of the current and long term behaviour of a bridge would lead to enhanced safety during its life since it would provide early warning of structural problems at a stage where minor repairs would enhance durability, and when used in conjunction with structural rehabilitation could be used to safety monitor the structure beyond its original design life. This would influence the life costs of such structures by reducing upfront construction costs (since smart structures would allow reduced safety factors in initial design), and by extending the safe life of the structure. ‘Sensual’ materials and structures also have a wide range of potential domestic applications, as in food packaging for monitoring safe storage and cooking.

The above examples address only ‘sensual’ structures. However, smart materials and structures offer the possibility of structures which not only sense but also adapt to their environment. Such adaptive materials and structures benefit from the sensual aspects highlighted earlier, but in addition have the capability to move, vibrate, and exhibit a multitude of other real time responses.

Potential applications of such adaptive materials and structures range from the ability to control the aeroelastic form of an aircraft wing, thus minimising drag and improving operational efficiency, to vibration control of lightweight structures such as satellites, and power pick-up pantographs on trains. The domestic environment is also a potential market for such materials and structures, with the possibility of touch sensitive materials for seating, domestic appliances, and other products. These concepts may seem ‘blue sky’, but some may be nearing commercial readiness as you read this.

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.