Abstract Summary
Structural health monitoring (SHM) is an important approach in order to evaluate the health state and so the safety and security of structures as bridges. It also helps to maintain and to extend their lives, to detect and predict their failures. This approach regroups several techniques such as vibration based inspections, acoustic, ultrasonic or magnetic field and radiographic methods. They are based on analyzing variations of some system’s characteristics and mapping them to the state of the systems and materials. For instance, in vibration based SHM, the variations of system characteristics in linear and nonlinear dynamics, e.g., frequency and damping shifts, changes of mode shapes and backbone curves, are directly related to the current state of the system. In this study, we endow an ultrasonic technique for SHM, namely Time Reversal (TR) method. This technique is based on the time reversibility of the solutions of wave equation in a lossless medium. Several experimental and numerical studies are carried out for fault diagnosis of a beam. Experimentations are based on the iterative TR process. In general terms two configurations of transducers, i.e. piezoelectric, are considered: side by side configuration and face to face. In the first one, all transducers are positioned at one side of the damage; in the second one, transducers are positioned at both sides of the damage. For both configurations, the TR is applied in three global steps: i) an excitation wave is applied via one set of array of transducers; ii) Then, signal are recorded by other set of array of transducers; iii) they are time reversed and are reinjected to the medium. If the wave emitted in step (i) is reflected by a damage, then the re-emitted wave in step (iii) converges towards the reflecting damage. The obtained experimental results are confronted by those which are detected from the finite element modeling of the system under ultrasonic excitation. Then, further investigations/protocols are proposed for fault diagnosis of such systems.
