A novel structural health monitoring (SHM) methodology, based on nonlinear wave modulation spectroscopy, is presented for the detection of delamination cracks in composites. The basic element is a novel active nonlinear acousto-ultrasonic piezoelectric sensor enabling low-cost and wide-frequency operational bandwidth. The active sensor configuration involves two piezoceramic wafer actuators, each one excited with a low- and high-frequency signal respectively, and a piezoceramic sensor, all permanently bonded on the tested structure. Experiments are conducted on two sets of composite strips containing delamination cracks of different sizes. Measured results illustrate first the efficiency of the nonlinear ultrasonics methodology to detect delamination cracks, as well as, the potential and benefits of the new active sensor. The sensitivity of the active sensor response to the crack size and the applied high-frequency carrier signals at the actuators, vary at various frequency and voltage levels indicating the appropriate testing setup. Additionally repeatability of proposed SHM methodology is studied.

Tuned mass dampers are well-known devices for efficient reduction of structural vibrations; however, they can only control the vibration of a single mode in a narrow frequency range and are not easily retunable. This article presents a semi-active tuned mass damper, consisting of a piezoelectric device connected to an external resistive–inductive electric circuit, which enables multi-modal vibration control, is highly tunable, and introduces high damping. The dynamics of the coupled electromechanical system, which includes the primary and auxiliary masses, the piezoelectric device, and the shunt circuit, are analyzed and the effect of the resistance and inductance is investigated. An experimental prototype using a specialty piezoelectric device is fabricated and tested. The experimental measurements greatly agree with the analytical results, validating the strong electromechanical coupling and the enhanced vibration suppression capabilities of the proposed damper. Moreover, the variation of inductive impedance demonstrates substantial semi-active broadband multi-modal vibration control potential, by introducing an additional highly tunable electromechanical resonant oscillator in the system dynamics, and also by enabling the enhancement of coupling and energy dissipation on targeted modal frequencies.

A structural health monitoring methodology, based on nonlinear wave modulation spectroscopy, is presented and aims to detect matrix cracks in composites. Experiments were conducted on cross-ply carbon/epoxy strips containing matrix cracks, induced via three-point bending. Damage in all tested specimens was categorized according to the acoustic emission hits recorded during loading. The nonlinear ultrasonics methodology is applied via an active nonlinear acousto-ultrasonic piezoelectric sensor, enabling low-cost and wide-frequency operational bandwidth. This active sensor configuration involves two piezoceramic wafer actuators, one excited with a low- and the other with a high-frequency signal, and a piezoceramic sensor, all permanently bonded on the tested structure. The sensitivity of the nonlinear active sensor response at specific high carrier frequencies is depicted and damage indices are proposed. The experimental results illustrate the effectiveness of the nonlinear ultrasonic wave mixing method in matrix crack detection, as well as the potential of the new active sensor for permanent structural health monitoring.