Electromechanical Admittance Research Articles

Piezo-impedance transducers for residual fatigue life assessment of bolted steel joints

This article presents a new approach for fatigue life assessment of bolted steel joints using the equivalent stiffness determined by surface-bonded piezo-impedance transducers. The piezo transducers acquire electromechanical admittance signatures comprising the conductance (real part) and the susceptance (imaginary part), from which the equivalent system parameters of the joint are identified. The equivalent stiffness, one of the identified parameters, is experimentally found to be related to the residual stiffness of the joint and is correlated with the remaining life of the component in terms of the cycles of loading that can be further sustained by the joint. Through tests on three prototype steel joints, empirical equations are derived to relate the residual fatigue life to the loss of equivalent identified stiffness. The most promising feature of the proposed approach is that it employs the admittance signature of the surface-bonded piezo transducers directly, thereby circumventing the determination of the in situ stiffness of the joint.

Health Monitoring of Steel Structures Using Sub-frequency Electromechanical Impedance Technique

The electro-mechanical impedance (EMI) technique using piezoelectric lead zirconate titanate (PZT) transducers has been shown promising for health monitoring of steel structures. For damage assessment, statistical techniques such as root mean square deviation (RMSD) have been employed to compare the electro-mechanical (EM) admittance signatures acquired before and after damage. However, using the conventional RMSD approach, it is difficult to specify the damage severity and location. To overcome this limitation, a sub-frequency interval approach has been proposed by the authors for the concrete structures. In the present study, this approach is extended and applied to the steel structures. Considering low attenuation of wave and large sensing region of PZTs in steel structures, multiple PZTs are utilized to acquire the EMI signatures of an I-section steel beam. Artificial damage points are induced in the steel beam and the corresponding RMSD values for sub-frequency ranges (RMSD-S) are calculated. To qualitatively study the damage severity and location, a method combining the RMSD-S of multiple PZTs and the logarithmic attenuation of ultrasonic waves is proposed. The results demonstrate that the proposed method is robust and sensitive for damage assessment of steel structures.

Spectral element modeling based structure piezoelectric impedance computation and damage identification

This paper presents a numerical simulation study on electromechanical impedance technique for structural damage identification. The basic principle of impedance based damage detection is structural impedance will vary with the occurrence and development of structural damage, which can be measured from electromechanical admittance curves acquired from PZT patches. Therefore, structure damage can be identified from the electromechanical admittance measurements. In this study, a model based method that can identify both location and severity of structural damage through the minimization of the deviations between structural impedance curves and numerically computed response is developed. The numerical model is set up using the spectral element method, which is promised to be of high numerical efficiency and computational accuracy in the high frequency range. An optimization procedure is then formulated to estimate the property change of structural elements from the electric admittance measurement of PZT patches. A case study on a pin-pin bar is conducted to investigate the feasibility of the proposed method. The results show that the presented method can accurately identify bar damage location and severity even when the measurements are polluted by 5% noise.

Dual use of PZT patches as sensors in global dynamic and local electromechanical impedance techniques for structural health monitoring

In this article, a new approach is proposed to effectively detect the initiation and progression of structural damage by combining the global dynamic and the local electromechanical impedance (EMI) techniques, using the same set of surface-bonded piezoelectric ceramic (PZT) patches as sensors. The PZT patches are used to determine the natural frequencies and the strain mode shapes of the structure (for use in the global dynamic technique) as well as to acquire the electromechanical admittance signature (for use in the EMI technique) to facilitate an improved damage assessment. Occurrence and location of the incipient damage are determined using the EMI technique, whereas for moderate to severe damages, the location and the severity are arrived at through the global dynamic technique. Finally, damage severity is determined in terms of the original stiffness of structure using the strain mode shapes directly determined using the PZT patches. The proposed technique is illustrated using two specimens—a 4-m long steel beam and a mild steel plate 1260 mm × 630 mm × 6.5 mm in size. The integrated approach provides greater information about damage, is simple to apply, does not involve any numerical/analytical modeling a priori, and is at the same time very cost effective.

Sub-Frequency Interval Approach in Electromechanical Impedance Technique for Concrete Structure Health Monitoring

The electromechanical (EM) impedance technique using piezoelectric lead zirconate titanate (PZT) transducers for structural health monitoring (SHM) has attracted considerable attention in various engineering fields. In the conventional EM impedance technique, the EM admittance of a PZT transducer is used as a damage indicator. Statistical analysis methods such as root mean square deviation (RMSD) have been employed to associate the damage level with the changes in the EM admittance signatures, but it is difficult to determine the location of damage using such methods. This paper proposes a new approach by dividing the large frequency (30–400 kHz) range into sub-frequency intervals and calculating their respective RMSD values. The RMSD of the sub-frequency intervals (RMSD-S) will be used to study the severity and location of damage. An experiment is carried out on a real size concrete structure subjected to artificial damage. It is observed that damage close to the PZT changes the high frequency range RMSD-S significantly, while the damage far away from the PZT changes the RMSD-S in the low frequency range significantly. The relationship between the frequency range and the PZT sensing region is also presented. Finally, a damage identification scheme is proposed to estimate the location and severity of damage in concrete structures.

Parallel and Individual Interrogations of Piezo-Impedance Transducers for Damage Detection

Lead zirconate titanate (PZT)-based piezo-impedance transducers have been successfully used in structural health monitoring (SHM) of various engineering structures in the recent years. To effectively monitor structural health, identification of damage location is of great importance. Although a single PZT is sensitive enough to detect damage, it is insufficient to indicate the location of damage. Therefore, in this study, nine PZT transducers are surface bonded on an aluminum plate to investigate the feasibility of locating the damages induced in the plate. At each damage state, electromechanical admittance signatures of all PZT sensors are recorded and analyzed using the root mean square deviation (RMSD) index. Results show that the damage location can be estimated by the RMSD patterns obtained from both parallel and individual interrogations of PZTs.

Simultaneous Edge Debonding Monitoring and Repair of Dynamically Loaded Concrete Structures Strengthened with Smart Composite Materials

The present work considers the possibility of simultaneous health monitoring and active repair of the edge debonding in dynamically loaded smart concrete structures strengthened with fiber reinforced plastic (FRP) composite materials. This is achieved by using local piezoelectric (PZT) actuators/sensors, the electro-mechanical admittance concept and extreme value statistics.

Simplified Impedance Model for Adhesively Bonded Piezo-Impedance Transducers

The electromechanical impedance technique employs surface-bonded lead zirconate titanate piezoelectric ceramic patches as impedance transducers for structural health monitoring and nondestructive evaluation. The patches are bonded to the monitored structures using finitely thick adhesive bond layer, which introduces shear lag effect, thus invariably influencing the electromechanical admittance signatures. This paper presents a new simplified impedance model to incorporate shear lag effect into electromechanical admittance formulations, both one-dimensional and two-dimensional. This provides a closed-form analytical solution of the inverse problem, i.e. to derive the true structural impedance from the measured conductance and susceptance signatures, thus an improvement over the existing models. The influence of various parameters (associated with the bond layer) on admittance signatures is investigated using the proposed model and the results compared with existing models. The results show that the new mod...

Structural Parameters Identification Using PZT Sensors and Genetic Algorithms

Piezoelectric ceramic lead zirconate titanate (PZT) based electro-mechanical impedance (EMI) technique for structural health monitoring (SHM) has been successfully applied to various engineering systems [1-5]. In the traditional EMI method, statistical analysis methods such as root mean square deviation indices of the PZT electromechanical (EM) admittance are used as damage indicator, which is difficult to specify the effect of damage on structural properties. This paper proposes to use the genetic algorithms (GAs) to identify the structural parameters according to the changes in the PZT admittance signature. The basic principle is that structural damage, especially local damage, is typically related to changes in the structural physical parameters. Therefore, to recognize the changes of structural parameters is an effective way to assess the structural damage. Towards this goal, a model of driven point PZT EM admittance is established. In this model, the dynamic behavior of the structure is represented by a multiple degree of freedom (DOF) system. The EM admittance is formulated as a function of excitation frequency and the unknown structural parameters, i.e., the mass, stiffness and the damping coefficient of many single DOF elements. Using the GAs, the optimal values of structural parameters in the model can be back-calculated such that the EM admittance matches the target value. In practice, the target admittance is measured from experiments. In this paper, we use the calculated one as the target. For damage assessment, these optimal values obtained before and after the appearance of structural damage can be compared to study the effects of damage on the structural properties, which are specified to be stiffness and damping in this study. Furthermore, the identified structural parameters could be used to predict the remaining loading capacity of the structure, which serves the purpose for damage prognosis.

Monitoring Beam-Column Joint in Concrete Structures Using Piezo-Impedance Sensors

Despite that piezoelectric ceramic lead zirconate titanate (PZT) has been used for structural health monitoring (SHM) in various engineering systems, limited work has been conducted on real size concrete structures. Beam-column connections are critical regions in reinforced concrete (RC) moment-resisting frame structures. The vulnerability of RC beam-column joints has been identified from structural damage investigations over the past decades, especially in the area of earthquake engineering. In the context of a terrorist bomb attack, the beam-column joints are very vulnerable, especially when the perimeter columns lose their load carrying capacity due to damage and the beam-column joints become one of the crucial load transfer mechanism of the structural frame. To avoid catastrophic failures, it is important to monitor beam-column joints under existing gravitational loads. In this paper, an experiment is carried out on four real size concrete frame structures with different detailing subjected to gradually increased loads. A number of PZT sensors are bonded to the frame structure to acquire PZT electro-mechanical (EM) admittance signature. The structural mechanical impedance (SMI) is extracted from the PZT EM admittance signature and its sensitivity is compared with that of the EM admittance. The relations between the damage index and the loading step and tip deflection of the concrete structure are obtained. Finally the sensitivity of the PZT sensors in detection of the critical loading level is discussed. The results show that the PZT sensors are capable of monitoring the integrity and behavior of the real size concrete structures.

123 非線形圧電インピーダンス変調とき裂モニタリングヘの応用

This paper concerns a structural health monitoring (SHM) methodology that can detect and characterize local structural damages in early stage, developed by combining the concepts of two existing SHM principles, a piezoelectric impedance-based methodology and a nonlinear wave modulation spectroscopy. When the structure is subjected to a dynamic load at low-frequencies, the nonlinear vibro-acoustic interaction between the low-frequency vibration and the high-frequency wave field in the vicinity of "contact-type" damages causes the change in the driving-point mobility at the high frequency range. Therefore, if the piezoelectric element bonded on the structural surface is driven by a fixed amplitude high-frequency harmonic voltage source, the nonlinear modulation of the coupled electro-mechanical admittance can be observed as the amplitude and phase modulation of the current flowing through the piezoelectric element. A simplified modeling study of this phenomenon successfully leads to a damage evaluation index that assesses the intensity of the modulation of the modal stiffness. Experiments using a cracked beam are conducted to see how the stiffness modulation can be observed and to examine the performance of the proposed method.

Modeling the hollow cylindrical piezo-ceramics with axial polarization using equivalent electro-mechanical admittance matrix

Modeling a piezo-ceramics as an electro-mechanical element is usually done using the laws of electricity. Due to complexity of the derived circuits, this kind of modeling usually results in some simplifications. In this paper using the force–velocity boundary conditions and equalizing the mechanical elements to the electrical ones, the governing equations of a hollow cylindrical piezo-ceramics with axial polarization are solved. Then the equivalent electro-mechanical impedance is represented via matrix notation. Using the matrix algebra the resonance and anti-resonance frequencies are calculated and then compared to the experimental results. The proposed method does not need to any simplification in circuit analysis, and provides the capability of modeling the various layers of piezo-ceramics and metals together in electro-acoustical transducers.

Effect of External Vibration on PZT Impedance Signature.

Piezoelectric ceramic Lead Zirconate Titanate (PZT) transducers, working on the principle of electromechanical impedance (EMI), are increasingly applied for structural health monitoring (SHM) in aerospace, civil and mechanical engineering. The PZT transducers are usually surface bonded to or embedded in a structure and subjected to actuation so as to interrogate the structure at the desired frequency range. The interrogation results in the electromechanical admittance (inverse of EMI) signatures which can be used to estimate the structural health or integrity according to the changes of the signatures. In the existing EMI method, the monitored structure is only excited by the PZT transducers for the interrogating of EMI signature, while the vibration of the structure caused by the external excitations other than the PZT actuation is not considered. However, many structures work under vibrations in practice. To monitor such structures, issues related to the effects of vibration on the EMI signature need to be addressed because these effects may lead to misinterpretation of the structural health. This paper develops an EMI model for beam structures, which takes into account the effect of beam vibration caused by the external excitations. An experimental study is carried out to verify the theoretical model. A lab size specimen with different external excitations is tested and the effect of vibration on EMI signature is discussed.

Monitoring Vibrating Structures Using PZT Impedance Transducers

Electromechanical impedance (EMI) technique using lead zirconate titanate (PZT) transducers has been increasingly applied to structural health monitoring (SHM) of aerospace, civil and mechanical structures. The PZT transducers are usually surface bonded to or embedded in a structure and subjected to actuation so as to interrogate the structure at the desired frequency range. The interrogation results in the electromechanical admittance (inverse of EMI) signatures which can be used to estimate the structural health or integrity according to the changes of the signatures. In the existing EMI method, the monitored structure is only excited by the PZT transducers for the interrogating of EMI signature, while the vibration of the structure caused by the external excitations other than the PZT actuation is not considered. However, in real situation many structures work under vibrations. To monitor such structures, issues related to the effects of vibration on the EMI signature need to be addressed because these effects may lead to misinterpretation of the structural health. This paper develops an EMI model for beam structures, which takes into account the effect of beam vibration caused by the external excitations. An experimental study is carried out to verify the theoretical model. A Lab sized specimen with external excitation is tested and the effect of excitation on EMI signature is discussed.

Sensitivity of PZT Impedance Sensors for Damage Detection of Concrete Structures.

Piezoelectric ceramic Lead Zirconate Titanate (PZT) based electro-mechanicalimpedance (EMI) technique for structural health monitoring (SHM) has been successfullyapplied to various engineering systems. However, fundamental research work on thesensitivity of the PZT impedance sensors for damage detection is still in need. In thetraditional EMI method, the PZT electro-mechanical (EM) admittance (inverse of theimpedance) is used as damage indicator, which is difficult to specify the effect of damage onstructural properties. This paper uses the structural mechanical impedance (SMI) extractedfrom the PZT EM admittance signature as the damage indicator. A comparison study on thesensitivity of the EM admittance and the structural mechanical impedance to the damages ina concrete structure is conducted. Results show that the SMI is more sensitive to the damagethan the EM admittance thus a better indicator for damage detection. Furthermore, this paperproposes a dynamic system consisting of a number of single-degree-of-freedom elementswith mass, spring and damper components to model the SMI. A genetic algorithm isemployed to search for the optimal value of the unknown parameters in the dynamic system.An experiment is carried out on a two-storey concrete frame subjected to base vibrations thatsimulate earthquake. A number of PZT sensors are regularly arrayed and bonded to the framestructure to acquire PZT EM admittance signatures. The relationship between the damageindex and the distance of the PZT sensor from the damage is studied. Consequently, thesensitivity of the PZT sensors is discussed and their sensing region in concrete is derived.

Three-Dimensional Electromechanical Impedance Model for Multiple Piezoceramic Transducers—Structure Interaction

In the last few decades, piezoceramic (PZT) transducers have been extensively used either as actuators or as sensors in the vibration and noise control of aero, civil, and mechanical (ACM) systems. Only in the last decade, PZT transducers have been used in the electromechanical impedance (EMI) models as both sensor and actuator for the structural health monitoring of ACM systems. In the EMI models, the PZT transducers are generally surface bonded to the host structure and are then subjected to one-dimensional (1D) voltage to interrogate the structure for the desired frequency range. The interrogation results in the prediction of electromechanical admittance signatures. These signatures serve as indicators of the health/integrity of the structure. However, the existing single PZT–structure interaction models consider the PZT transducer to be negligible in mass and thus ignored. Moreover, they impose restrictions on the PZT shape, size, and isotropy. This paper presents a novel semianalytical multiple three-dimensional PZT–structure interaction model which considers the “mass” of the PZT transducers, and the transducers are subjected to parallel (1D) sinusoidal voltage. Further, the model does not impose restriction on the shape (square or rectangular), size (thin or thick), and electrical properties (isotropic or anisotropic) of PZT. The derived model is also experimentally verified using lab-sized aluminum plate. As it is generic, the model is expected to be applicable for the nondestructive evaluation of most ACM systems.

Repair of Cracked Structures under Dynamic Load Using Electromechanical Admittance Approach

In the present paper, the repair of a cracked structure under dynamic load using the electromechanical admittance (EMA) approach is investigated. Conceptually, appropriate electrical field are applied on the outer surfaces of piezoelectric (PZT) patches to effect closure of the crack. This has the effect of altering the electromechnaical (E/M) admittance signature, extracted at the electrical terminals of a specific PZT patch, considered as an admittance calculating sensor (ACS) patch, towards that of the healthy structure, which is the criterion concept used for the repair in this paper. To demonstrate the present repair methodology, a cantilever 3D beam numerical example is considered in combination with a FEM-based minimization of the difference between the healthy and cracked structure’s (E/M) admittance signature, for specific frequency ranges.

Influence of loading on the electromechanical admittance of piezoceramic transducers

Damage detection using electromechanical (EM) impedance in structural health monitoring(SHM) of engineering structures is rapidly emerging as a useful technique. In the EMimpedance method, piezoceramic (PZT) transducers are either surface bonded to orembedded inside the host structure and are subjected to electric actuation. The EMadmittance signatures of the PZT transducers, which consist of real and imaginary parts,serve as indicators to predict the health/integrity of the host structure. However, in reallife, structural components such as slabs, beams and columns are constantly subjectedto some form of external loading. The EM admittance signature obtained forsuch a constantly loaded structure is different from that obtained when damagesare present in the structure. This paper presents an experimental and statisticalinvestigation to show the influence of loading on EM admittance signatures. It is alsoobserved that the susceptance signature is a better indicator than the conductancesignature for detecting in situ stress in the host structure. This observation isfurther supported by a statistical analysis. This paper is expected to be useful forthe non-destructive evaluation of engineering structures with external loading.

An electromechanical impedance model of a piezoceramic transducer-structure in thepresence of thick adhesive bonding

In the past few decades, piezoceramic (PZT) transducers have been used extensively in thevibration and noise control of engineering structures. However, in the last decade, PZTtransducers have also been used in electromechanical impedance (EMI) based methods ofstructural health monitoring (SHM). In the EMI methods, the PZT transducers are eithersurface bonded using adhesive or wrapped with a protective cover and then bonded orembedded inside the host structure. They are then subjected to excitation in the desiredfrequency ranges to predict the electromechanical (EM) admittance signatures. These EMsignatures serve as an indicator of the health/integrity of the structure. The existingPZT-structure interaction methods consider both the PZT transducer and theadhesive layer to be negligible in mass and are thus ignored. However, for wrappedPZT, the presence of thick adhesive significantly reduces the magnitude of theEM signature. This paper presents the formulation of a three-dimensional (3D)interaction model of a PZT-structure which considers the mass of both the PZTtransducers and the adhesive. The model is generic in nature compared to the existinginteraction models. The model is verified experimentally and is expected to beapplicable to the non-destructive evaluation (NDE) of most engineering structures.

Development of an electromechanical admittance approach for application in the vibrationcontrol of intelligent structures

The present work considers the possibility of vibration control of a distributed dynamicalsystem, such as flexible plates using local piezoelectric (PZT) actuators/sensors and theelectromechanical admittance concept. When PZT actuators bonded on structures are usedin active vibration and acoustic control, the desired deformation field in the structure isobtained through the application of localized line forces and moments generated byapplying an appropriate electrical field on the outer surfaces of the PZT patches. Theelectromechanical admittance generated at the electrical terminals of a PZT-driven smartstructure is then extracted to synthesize a desired damping performance. This is achievedby a FEM-based minimization of the difference between the computed and thedesired electromechanical admittance signature for investigated frequency ranges.