3.1 Introduction

All structures vibrate to some extent. Usually in aerospace, robotics and automotive structures this vibration is not wanted and can lead to catastrophic failure. This failure may arise in the long term due to fatigue causing cracks, or it may occur quickly due to the material not being able to cope with the material stresses from the large amplitude displacements. Even if failure docs not occur the resulting noise and vibration is often unpleasant, and certainly not a desirable feature in a consumer product. In many applications the structure may be stiffened so that the response is less, and the resonances of the structure are moved above the forcing frequencies. Alternatively discrete dampers similar to automotive engine mounts or shock absorbers may be used. However these are large and heavy devices, and only a limited number of them may be used. The trend in aerospace and automotive applications is to produce lighter structures that are more energy efficient and responsive. This not only makes the structure less stiff, and therefore more susceptible to vibration, but also makes controlling the vibration more difficult. This chapter highlights some of the techniques that may be used to reduce the vibration of a lightweight structure, and introduces the concept of a smart structure.

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