Fatigue damage reduction for flexible structure through active control

In recent years, the large development of light and flexible structures led to a wide interest about techniques for active vibration suppression. Indeed, these structures are typically characterized by low damping and, consequently, by a significant amplification of vibrations, especially when the structure is forced close to its natural frequencies. System vibrations result in high stresses of the material, which may strongly reduce the structure lifetime. For this reason, all the techniques able to reduce vibrations and stresses are of great interest. Most of the researches focused on the vibration suppression, assuming that the fatigue reduction would be a direct consequence. Anyway, even if in many applications it can be regarded as true, there are some cases in which vibration reduction does not automatically imply an improvement in terms of fatigue life. For this reason, this paper proposes a new approach, able to take into account the fatigue phenomemon directly in the definition of the control algorithm. The proposed approach is firstly introduced from a theoretical point of view, describing the control algorithm and how it deals with the fatigue damaging. Then, the control logic is tested both numerically and experimentally on a plate instrumented with accelerometers, strain gauges and piezoelectric actuators. A comparison between the proposed solution and state of the art control techniques is proposed and critically analyzed to demonstrate how the fatigue life of the structure can be improved.