ABSTRACT
Smart materials are materials that respond to multiple inputs. Traditional materials like aluminum or steel deform under the application of loads. On the other hand, smart material has two-way action. To explain the two-way action, let us consider a piezoelectric material such as lead zirconate titanate, in short called PZT, which is a ceramic form of material. This material, when subjected to a load, deforms and generates voltage. If the same material is subjected to voltage, it not only generates charge displacement but also mechanically deforms to generate strains. Hence the constitutive law for a typical smart material has two relations, one called the sensing relation, and the second called the actuation relation. There are a number of different smart materials available commercially. The commonly used smart materials are the piezoelectric materials and magnetrostrictive materials. Piezoelectric material responds to both loads and electric fields, while the magnetostrictive material responds to both loads and magnetic fields. In other words, smart materials help convert one form of energy into another form of energy. That is, in
piezoelectric material, energy conversion takes place from mechanical energy to electrical energy during loading, while the opposite happens when the same structure is subjected to voltage. It is this conversion of one form of energy to another that makes this material useful as sensors or actuators to perform a host of functions such as vibration control, noise control, damage detection, etc. Figure 14.1 shows typically how one can embed a smart PZT patch in a laminated composite. A good account of these materials is given in [363].
