Depolarization diagnosis of PWAS used for EMI based structural health monitoring system for composite plates

Abstract

Implementation of Electromechanical Impedance (EMI) as a technique to carry out Structural Health Monitoring (SHM) has been proved to be such effective tool in the last two decades, especially for structures made of composite material. EMI technique is the revolutionary evolution of the conventional Vibrational Based Damage Identification (VBDI) techniques. Unlike VBDI techniques, EMI technique has the privilege of employment tinny permanent piece of equipment which is known as Piezoelectric Wafer Active Sensor (PWAS). Although it has such advantage, it brings the necessity of continuous and robust diagnosis process of the PWAS used in the SHM system to ensure that output signals are caused by real variation of the modal parameters for the host structure rather than being occurred due to degradation and-or physical damage of the PWAS system itself. The study presented in this paper is focused on the self-diagnosis of PWAS used to carry out SHM via implementation of EMI technique. The main concern of this research is to study the ability of EMI technique to determine depolarization of PWAS and its influence on the performance of EMI based SHM system employed for structures made of composite plates. The used specimen (s) is / are underwent controlled excitation over desired frequency range, the imaginary part of admittance is plotted over desired frequency range. The whole process is then repeated for different levels of depolarization for the same specimen (s). The modeling process is carried out using a finite element commercial package, ANSYS v.15.0 in which multi-physics-based modeling can be used for such coupling field of piezoelectricity. MATLAB code is written to process the output data received from numerical simulations into counterpart spectrum and to calculate the statistical damage index Root Mean Square deviation (RMSD) that is used in damage detection. The calculated RMSD found to be non-zero values, which means false prediction. These results shows how important to have self-diagnosis for PAWS used in SHM system for further reliable measurements and data interrogation using EMI technique.

An integrated algorithm for structural health monitoring of composite plate using electromechanical impedance

“…PWAS malfunction can be caused either by the degradation of PWAS coupling properties (depolarization) that may happen due to life time or operational conditions or due to partial loss of mass of the PWAS due to hard impact. The simulation results carried out by Amin and Salem [28] for simulated PAWS malfunction for mass loss and depolarization show downward shift in the imaginary part of the admittance Y(ω) as shown in Figure (10) and Figure (11), respectively. These results coincide with the conclusions reached by Park et al [27] .…”

“…The simulations carried out using the EMI technique as it considered the possible malfunction of the PWASs due to desponding of the adhesive layer and / or due to the PWAS depolarization. A parametric study is carried out Amin and Salem [28] to investigate the impact of propagation of desponding between PWAS and the monitored composite plate on the imaginary part of admittance spectrum. The simulation studies considered different levels of area desponding between PWAS and host structure (0%, 36%, 64%, 84% and 100%).…”

“…Fig. 9: Relation between frequency and imaginary part of admittance in case of desponding propagation by Amin and Salem [28] . Fig.…”