Study on pre-damage diagnosis and analysis of adhesively bonded smart PZT sensors using EMI technique

Abstract

The electro-mechanical impedance technique (EMI) is one of the best methods for continuous structural health monitoring (SHM) by embedding a smart piezoelectric ceramic Lead Zirconate Titanate (PZT) sensor or pasting it over the surface of the structure. The smart PZT transducer is intensely affected by the adhesive bonding condition between the PZT patch and the host structure. The current paper studies the damage-diagnosis process of the coupled electro-mechanical behavior of an adhesively bonded smart PZT transducer. The inverse of impedance signatures is used for investigating pre-damage diagnosis and analysis of surface-mounted PZT transducer. A parametric study on the variation of adhesive property is carried out to overcome the shear lag effect. The novel contribution of this paper discusses a methodology for an early diagnosis of damage in the PZT transducer and adhesive bond layer during the SHM process. Firstly, the damage is introduced to the PZT patch and bonding layer, and the corresponding EMI signatures are obtained using numerical modeling and simulations. The damage detection using susceptance is discussed for lower frequencies from 0 to 20 kHz. It is observed that the change in susceptance signature is not large enough to detect adhesive debonding. Subsequently, the conductance signatures are utilized for the investigation. It is observed that damage in the adhesive layer and PZT patch cause upward or downward shift with no alteration along the horizontal direction. It helps to detect sensor breakage and adhesive debonding effectively. Secondly, the simulation results are verified using the theoretical analysis for the single piezo configuration by improved continuum-based impedance equations. A modified dual piezo configuration is investigated to validate the proposed method. Experimental investigation on PZT-bonded aluminum plate involving perfectly bonded, adhesive debonding, and sensor breakage conditions are conducted to verify the process. It is found that the real part of the admittance signature is reliable and critical in sensor diagnosis, and sensor faults of debonding and breakage can be identified and differentiated. It also validates the semi-analytical work results. Therefore, the proposed methodology for pre-diagnosing damage present in the smart PZT sensor and adhesive layer using the EMI technique can be utilized for effective SHM.