Embedded PZT Transducers Research Articles

Smart Patch for Structural Health Monitoring of Composite Repair

The bondline integrity of a repair patch to the parent composite laminate is considered the most important factor in the repair design. A smart repair patch is proposed here to allow for real-time ultrasonic guided wave monitoring of repaired composites. A diagnostic film with lead zirconate titanate (PZT) transducers and inkjet-printed wires is embedded into the repair patch using a cut-out method. The electro-mechanical impedance (EMI) method is used to verify the integrity of the embedded PZT transducers. The performance of the smart repair patch is assessed on the external panel with artificial bondline delamination and surface-mounted artificial damage. The damage index correlation coefficient and delay-and-sum (DAS) algorithm are used for damage detection and localization. The results show that the developed repair patch can successfully detect and locate damages.

Impact Localization in Composites Using Time Reversal, Embedded PZT Transducers, and Topological Algorithms

Time reversal is a powerful imaging processing technique that focuses waves at their original source using a single receiver transducer when diffusive wave field conditions are met. This has been successful proved on various engineering components and materials using elastic waves with surface bonded transducers. This paper investigates the performance of time reversal for the localisation of impact sources on fibre reinforced plastic composite structures with embedded piezoelectric sensors. A topologic approach, here named as minimum average method, is proposed to enhance the accuracy of time reversal in retrieving the impact location. Experimental tests were carried out to validate the robustness and reliability of time reversal against traditional topological approaches by altering impulsive responses contained in the baseline signals. Impact localisation results revealed that time reversal and the new topological approach provided high accuracy in identifying the impact location, particularly in the presence of double impacts and material damage, which were not accounted during the initial training process. Results indicate that time reversal with embedded transducers has potential to be effective in real operating conditions, where alterations of acoustic emission responses in the baseline signals are less predictable.

Geometry-independent attenuation and randomness of ultrasound wave propagation in concrete measured by embedded PZT transducers

Ultrasound is widely used in nondestructive testing (NDT). It is the basis of many NDT techniques, such as acoustic emission, phased array and synthetic aperture focusing technique. The attenuation of ultrasound is a key factor that ensures the feasibility of these techniques. Conventional studies of attenuation are mostly conducted in specimens that have dimensions smaller than ultrasound wavelengths. In this type of study, reflections from media boundaries interfere with the wave, resulting in a geometry-dependent attenuation that cannot be applied in another specimen with a different geometry, even if the material is identical. Another factor that impacts on the viability of ultrasound NDT techniques is the spatial uniformity of waves in the concrete sample. To serve as a reference in testing defects, the degree of randomness caused by the material’s heterogeneity should be estimated in conditions free of defects. In this study, a large concrete specimen was fabricated to suppress boundary reflections of the wave, creating an environment less dependent on geometry. Twenty-two PZT (lead zirconate-titanate ceramics) transducers were arranged in a three-by-seven array to transmit and receive ultrasound waves. This experiment sought to measure attenuation over distance and by frequency, as well as analyzing attenuation factors such as geometrical spreading and material absorption. A quadratic trend with good consistency between attenuation and frequency was found, indicating minimal local attenuation. The degree of randomness in the wave was measured by three indices: amplitude, group velocity and the frequency spectrum cross-correlation factor. Frequency dispersion was also described using group velocity. The findings of this study can serve as a reference for other NDT research, disclosing geometry-independent attenuation and the variability of wave characteristics in concrete.

Experimental Investigation on Sensitivity of Smart Aggregate Embedded in Reinforced Concrete Beam

Electromechanical impedance (EMI) based lead zirconate titanate (PZT) is an effective sensor to ensure the safety of structure. In civil engineering community, Reinforced Concrete (RC) structure is one of the most familiar engineering structures. Hence, it is very important to monitor the health of structure. In this paper, a new approach of structural health monitoring using embedded PZT in host structure is proposed. There are several issues while embedding PZT inside RC structure which are examined during study. This paper presents two experimental studies on lab sized concrete beams. First implementation was carried out with different methods of embedment of PZT and its sensitivity study when the host structure was subjected to damage. The second implementation was verified in terms of conductance sensitivity of embedded Smart Aggregate (SMAG) in varying orientation i.e. horizontal (0?) and vertical (90?) after embedding in RC beam. The electrical conductance and susceptance signatures of different embedded PZT transducers were measured and damage index was calculated by using Root Mean Square Deviation Method.

In situ Barely Visible Impact Damage detection and localization for composite structures using surface mounted and embedded PZT transducers: A comparative study

Application of guided waves excited by a network of PZT transducers integrated with a given structure is one of the promising approaches to Structural Health Monitoring (SHM). The performance of a SHM system based on PZT network is rooted in two distinct areas of the technology development, that is the hardware and the signal analysis. The first includes the type of transducers used to built a network and the way of their integration with a monitored structure. For composites, besides the possibility of the transducers attachment to a surface of an element, also embedding of PZTs into their internal structure is available. In the article Barely Visible Impact Damage (BVID) detection capabilities as well as selected physical properties of the embedded and surface mounted PZT transducers are compared in broad frequency range of the excitation. Among the compared parameters are the impedance and capacitance spectra up to 600kHz. The damage detection capabilities are compared in the range 100–350kHz. In addition to purely qualitative detection of damages a new algorithm of their localization is proposed and compared between the embedded and surface attached transducers for the frequency optimal to detect BVIDs.

An Approach to Structural Health Monitoring of Composite Structures Based on Embedded PZT Transducers

Abstract One approach to developing a system of continues automated monitoring of structural health is to use elastic waves excited in a given medium by a piezoelectric transducers network. Depending on their source and the geometry of the structure under consideration elastic waves can propagate over a significant distance. They are also sensitive to local structure discontinuities and deformations providing a tool for detecting local damage in large aerospace structures. This paper investigates the issue of Barely Visible Impact Damages (BVIDs) detection in composite materials. The model description and the results of impact tests verifying damage detection capabilities of the proposed signal characteristics are presented in the paper.

A Three-Dimensional Model of the Effective Electromechanical Impedance for an Embedded PZT Transducer

A three-dimensional model of the effective electromechanical impedance for an embedded PZT transducer is proposed by considering the interaction between a PZT patch and a host structure. By introducing an effective mechanical impedance, the coupled electromechanical admittance formulations are derived using the piezoelectric constitutive equations. Then, a modified methodology for monitoring structure changes using an electromechanical impedance (EMI) technique is proposed. In the proposed method, the changes in the host structure are monitored by using the “active” part associated with the structural mechanical impedance, which is extracted from the measured raw admittance signatures. The strength gain of a concrete beam with embedded PZT transducers during the curing age was monitored with the proposed methodology. The experimental results demonstrate that the use of the “active” part is more sensitive as opposed to the raw admittance signatures for structural health monitoring (SHM).

Effect of embedded sensors on interlaminar damage in composite structures

This research focuses on developing an embedded sensor system to monitor the health of a composite rotor component. To support this objective, simulations were developed to investigate the impact of sensor insertions on local structural micro-mechanics and sensor responses. In particular, the potential side-effects (e.g., delamination onset and growth) of imbedding lead zirconate titanate (PZT) piezoelectric sensors in composite structures were studied. A modeling approach for evaluating interlaminar damage under the influence of embedded PZT sensors is proposed. The approach uses finite element cohesive zone models to describe interlaminar damage between plies or at ply ends. In addition, an embedded multi-ply PZT model was developed and integrated with the damage models. The approach presented in this paper analyzes the propagation of interlaminar damage in the vicinity of sensors and quantifies the effect of sensor presence on damage growth. A parametric study was performed to understand how damage zones, the size and geometry of resin pockets, and the locations and properties of PZT sensors affected interfacial strength. Damage behavior, under the influence of an embedded PZT sensor, was examined in specimens having a configuration similar to that of a selected rotating rotorcraft component. Finally, optimal locations of embedded PZT transducers were determined for the specimen under consideration.

Experimental Research on Influence of Temperature on PZT-Based Health Monitoring for Smart Aggregates

Since piezoelectric materials exhibit strong temperature dependency. The change of temperature results in marked variation of the PZT transducer’s electric impedance signals, which may lead to misjudgment of the structural health condition. A experiment was implemented on smart aggregates with embedded PZT transducers under 35°C, 45°C and 55°C three working conditions, and found that the temperature had significant influence on the electric admittance signals of embedded PZT transducers. The peak magnitudes of the admittance curves changed and the curves shifted leftward. Then a temperature compensation technique was used to minimize the temperature effects.

Damage detection in composite plates with embedded PZT transducers

This paper presents a concept of a structural health monitoring system based on PZT transducers. Taking advantage of spectral element method simulations of A0 mode of the Lamb waves propagating in a multilayer composite plate have been carried out. Based on obtained signals for a clock-like configuration of sensors, a damage detection algorithm has been proposed. The results for the proposed algorithm have been presented in the form of damage maps. It can be concluded that the clock-like sensor configuration is suitable for embedding in composite plates because information about wave velocities at each angle can be included.