Building Materials, Third Edition

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The term smart materials, intelligent materials, active materials or adaptive materials, describe
a group of material system with unique properties. Generally these materials respond with a
change in shape upon application of externally applied driving forces. In addition some
material system do not exhibit a shape change but rather have other significant properties. The
examples are electro and magneto rheological fluids. These fluids can change viscosity over
many orders of magnitude on application of an external magnetic or electrical field.
Consequently, the term smart materials is not very well defined and frequently used to describe
different systems and their behaviours.
To add to the confusion the term smart devises, smart
systems or smart structures are often carelessly used. Here
one should note that in general the system complexity
increases from the unit “materials” to “device” to “system”
to “structures”.

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The most common way of structuring is by looking at the Input and the out put of a material
system as shown in Fig.21.8. The input or stimulus can be for example a change in temperature
or in magnetic field. The material then intrinsically responds with an output, which in turn can
be for example a change in length of the material, change in viscosity or change in electrical
conductivity.
Smart materials can be divided into two groups. One group comprises the “classical” active
materials as viewed by the academic community and is characterized by the type of response
these materials generates. Upon application of stimulus the materials respond with a change in
shape and/or in length of the material. The input is always transformed into strain, which can
be used to introduce motion or dynamics into a system. These materials are the most widely
used group for design of smart structures, where active materials are integrated into a mechanical
host structure (for example a building or a helicopter rotor blade) with the goal to change the

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