Akshay Surendra Kumar Naidu

Non-parametric damage detection and characterization using smart piezoceramic material

The detection of damages by modal analysis and similar vibration techniques depends upon the knowledge and estimation of various modal parameters. In addition to the associated difficulties, such low-frequency dynamic response based techniques fail to detect incipient damages. Smart piezoelectric ceramic (PZT) transducers, which act both as actuators and sensors in a self-analyzing manner, are emerging to be effective in non-parametric health monitoring of structural systems. In this paper we present the results of an experimental study for the detection and characterization of damages using PZT transducers on aluminum specimens. The method of extracting the impedance characteristics of the PZT transducer, which is electromechanically coupled to the host structure, is adopted for damage detection. Three types of damage are simulated and assessed by the bonded PZT transducers for characterization. We present the effectiveness of PZT transducers in the detection and characterization of incipient damages without the need to know the modal parameters. The PZT transducers are found to have a significantly large sensing area for detecting even small incipient damages. The possibility of replicating the pristine state signatures of different transducers under similar conditions of bonding and geometrical location is also explored. For appropriate characterization of damages, a few statistical signature pattern recognition techniques are evaluated.

Damage severity and propagation characterization with admittance signatures of piezo transducers

The electromechanical (EM) impedance method is emerging as an effective tool for structural damage detection. Damage is detected by changes in the EM impedance signatures of the smart piezoelectric transducer bonded on the structure. The damage quantification has so far been restricted to using non-parametric statistical indices to measure changes in the signatures. Such measures, although simplistic, fail to correlate the changes in the signatures to physical parameters of the structures. Thus, although effective in detecting the presence of damage, the method fails to give further information about the location and severity of the damage. In this paper, the EM impedance method integrated with a finite element (FE) model is presented as a means for characterizing damage growth. Damage growth is characterized by quantifying the changes in the natural frequency shifts of the structure extracted from the EM admittance signatures. A new damage characterization index is derived, which is experimentally validated to be capable of distinguishing a localized increase in severity from damage propagation through the structure.

Identifying damage location with admittance signatures of smart piezo-transducers

Modal analysis-based damage detection techniques that use only the first few modes are not sensitive to incipient damages. The alternative of using the conventional methods to extract natural frequencies and mode shapes for higher modes is also a difficult task. In this paper, the electromechanical (E/M) impedance method integrated with a finite element (FE) model is presented as a means for damage location identification using the higher modes. Damage location is identified by correlating the changes in natural frequencies at the higher modes with the corresponding mode shapes of the undamaged structure. The natural frequency shifts of the structure are obtained from the shifts in the peaks of the E/M admittance signatures of smart piezo-transducers bonded on to the host structure. The mode shapes are obtained from the equivalent FE model of the undamaged structure. Numerical and experimental investigations of the proposed method are presented.

Damage detection in concrete structures with smart piezoceramic transducers

Detection of damages and progressive deterioration in structures is a critical issue. Visual inspections are tedious and unreliable. Incipient damages are often not discernible by low frequency dynamic response and other NDE techniques. Smart piezoelectric ceramic (PZT) transducers are emerging as an effective alternative in health monitoring of structures. The electro-mechanical impedance method employs the self-actuating and sensing characteristics of the PZT, without having to use actuators and sensors separately. When excited by an ac source, the PZT transducers bonded to the host structure activates the higher modes of vibration locally. Changes in the admittance response of the transducer serves as an indicator of damage around the transducer. In this paper, the effectiveness of PZT transducers for characterizing damages in concrete, in terms of the damage extent and location, is experimentally examined. The root mean square deviation (RMSD) index, adopted to quantify the changes in the admittance signatures, correlates with the damage extent. The damages on the surface that is not mounted by the PZT are also discernible. An array of transducers proves effective in detecting the damaged zone. The progressive incipient crack can be detected much before it actually becomes visible to the naked eye.

Application of the electro-mechanical impedance method for the identification of in-situ stress in structures

In the beginning, the electro-mechanical (EM) impedance method for structural health monitoring was recognized as a means of structural in-situ stress monitoring and measurement. Consequently, theoretical analysis based on the EM impedance method as a tool for in-situ stress identification in structural members was presented. A dynamic impedance model derived from the Euler-Bernoulli beam theory was developed to investigate the influence of in-situ stress on the dynamic and electro-mechanical response of a smart beam interrogated by a pair of symmetrically bounded, surface-bonded piezoceramic (PZT) transducers. Numerical simulation was performed for a laboratory sized smart beam subjected to a multitude of axial loads at the ends. It was found that natural frequency shifts takes place in the presence of in-situ stress. Furthermore, these shifts, which are linearly related to the magnitude of applied load, is directly reflected in the point-wise dynamic stiffness response. However, in terms of the electro-mechanical response, which can be measured directly, the shift of peaks of the EM admittance signature is not directly indicative of the natural frequency shifts. This arises as an inverse problem in engineering, which cannot be deciphered using direct approach. Back calculation of the in-situ stress using genetic algorithm (GA) was proposed.

Incipient damage localization with smart piezoelectric transducers using high-frequency actuation

Modal analysis based damage detection techniques using only first few modes are not sensitive for damage identification. The sensitivity of the modal parameters to damage is greater at the higher modes of vibration. Yet, actuation of structures at high frequencies is very difficult with the conventional modal testing methods. In this paper, a new technique that uses smart piezoelectric (PZT) material to extract the modal frequencies for higher modes of vibration is presented. A PZT transducer possesses simultaneous actuating and sensing capabilities. The electromechanical (e/m) impedance method exploits this feature of the PZT transducer to measure its drive-point impedance characteristics when bonded to a structure. Damage location is identified using the natural frequency shifts obtained from the structural impedance signatures and the corresponding undamaged state modes shapes. This technique is superior to other methods, which rely only on statistical quantification of changes in the measured structural signatures. The damage locations were successfully identified by this method for a finite element simulated beam model. The natural frequencies obtained experimentally for longitudinal and bending modes were fairly consistent with the analytical predictions. However, the modeling of damage as merely a source of stiffness reduction proves insufficient to accurately estimate its location, experimentally.

An impedance-based piezoelectric-structure interaction model for smart structure applications

Publisher Summary This chapter presents the theoretical development and the experimental verification of a new simplified approach to model the multiphysics dynamic interaction between the PZT patches and their host structures in the smart systems. The mechanical coupling between the patch and the structure is modeled in two dimensions to accurately consider the planar vibrations. The derived equations are simple enough to be directly utilized for extracting the mechanical impedance of an unknown structure from the experimental signatures of a PZT patch surface bonded to it. This is an improvement over the existing models whose complexity prohibits direct application in similar practical scenarios. The presented formulations are experimentally verified by means of test on a smart system comprising an aluminum block instrumented with a PZT patch.