Damage Detection of L-Shaped Beam Structure with a Crack by Electromechanical Impedance Response: Analytical Approach and Experimental Validation

Damage detection and structural health monitoring using the electromechanical impedance method has been accepted as an effective technique between various approaches of nondestructive evaluation. Many efforts have been made on experimental methods for obtaining the impedance of structures. However, expensive experimental methods encourage researchers to develop theoretical models. In this paper, a new theoretical model is developed for damage detection of L-shaped beams, which are basic components in frame structures, with an embedded piezoelectric wafer active sensor. For this purpose, a chirp signal of voltage is used to activate a piezoelectric patch for inducing local strains that lead to lateral forces and bending moments on the structure, emerging resonance and anti-resonance vibration behavior of the structure in a wide frequency range. Considering these induced loads, the impedance at each point of the structure is determined by calculating the dynamic stiffness of structures. The model results verified by experiments. The estimated impedance spectrum for both pristine and damaged structure has shown an acceptable agreement, particularly, around the structural resonances. The results show that electromechanical impedance responses of the structure depend on excitation and natural frequencies of the structure which emerge as resonance frequencies in the impedance spectrum. Finally, damage detection is performed using statistical algorithms including root-mean-square deviation and cross-correlation by comparing pristine and damaged L-shaped beams and accordance between experiment and model results demonstrates the efficacy of predicted spectra.