The concept of smart materials/structures (SMS) can be considered as a landmark in the evolution of tailored materials. There is a continuous trend from simple to complex, starting from the use of homogeneous materials supplied by nature and accepted with their natural properties followed by multi-materials (in particular, composite materials ) allowing us to create structures with properties adapted to specific users. Composite materials are replacing homogeneous and isotropic materials in more and more structures [Figure 4.3]. This is particularly true in the aerospace applications. For instance, composite parts are now currently used or envisaged for modern aircrafts. Boeing’s 7E7 Dream liner project has 50 per cent of its structures made of composites. It is worth noting that this aircraft is one of the first passenger aircraft to introduce embedded SHM systems, especially systems for impact detection .

Figure 4.3: General evolutions of materials/structures

The next step consists of making the properties of the materials and structures adapt to changing environmental conditions. This requires making them sensitive, controllable and active. The various levels of such intelligence correspond to the existence of one, two or all the three qualities.