Piezoceramic Transducers Research Articles

Data normalisation for Lamb wave–based damage detection using cointegration: A case study with single- and multiple-temperature trends

This article presents an application of the cointegration technique for temperature effect removal (i.e. data normalisation) in Lamb wave–based damage detection. The method is based on the concept of stationarity of time series. Analysis of cointegrating residuals and stationary statistical characteristics – before and after the cointegration process – are used for damage detection. The method is validated using Lamb wave data from undamaged and damaged aluminium plates instrumented with low-profile, surface-bonded piezoceramic transducers. Two temperature variation cases (single- and multiple-temperature trends) are investigated. The experimental results show that the cointegration process can remove undesired temperature effects and accurately detect damage.

Impact damage detection in laminated composites by non-linear vibro-acoustic wave modulations

The paper presents an application of nonlinear acoustics for impact damage detection in composite laminates. Two composite plates were analysed. A low-velocity impact was used to damage one of the plates. Ultrasonic C-scan was applied to reveal the extent of barely visible impact damage. Finite element modelling was used to find vibration mode shapes of the plates and to estimate the local defect resonance frequency in the damaged plate. A delamination divergence study was performed to establish excitation parameters for nonlinear acoustics tests used for damage detection. Both composite plates were instrumented with surface-bonded, low-profile piezoceramic transducers that were used for the high-frequency ultrasonic excitation. Both an arbitrary frequency and a frequency corresponding to the local defect resonance were investigated. The low-frequency modal excitation was applied using an electromagnetic shaker. Scanning laser vibrometry was applied to acquire the vibro-acoustic responses from the plates. The study not only demonstrates that nonlinear vibro-acoustic modulations can successfully reveal the barely visible impact damage in composite plates, but also that the entire procedure can be enhanced when the ultrasonic excitation frequency corresponds to the resonant frequency of damage.

Active Sensing Based Bolted Structure Health Monitoring Using Piezoceramic Transducers

Bolted structures are commonly used in civil infrastructure. It is important to perform bolt inspection regularly to ensure the safety of structures. Traditional bolt inspection methods are time-consuming; moreover, bulky instruments are needed in these methods. In this paper, a piezoceramic based active sensing approach is developed to perform the health monitoring of bolted structures. Surface-bonded piezoceramic patches are used as health monitoring transducers. Wavelet packet analysis is used to analyze the sensor data to extract the features that indicate bolt looseness. Based on wavelet packet analysis results, a damage index is developed to quantitatively evaluate the damage status. To verify the effectiveness of the proposed method, a bolted connection experiment with piezoceramic transducers was performed. In the experiment, the looseness of the bolt is adjusted by a torque wrench. Experimental results show that the proposed approach is effective to detect and evaluate bolt looseness.

Feasibility Study on Crack Detection of Pipelines Using Piezoceramic Transducers

Damage detection of pipelines is of great significance in terms of safety in the oil and gas industry. Currently, lead zirconate titanates (PZTs) are the most popular piezoceramic materials and show great potential in the applications of structural health monitoring. In this paper, the authors present a feasibility study on the crack detection and severity monitoring of pipelines using PZT transducers. Due to their electromechanical properties, the piezoceramic transducers can be either as an actuator or a sensor to generate or detect the stress wave. The active sensing approach was applied to monitor the crack severity of pipelines. The crack in the stress wave propagation path can be regarded as a stress relief, which reduces the received energy by the sensors. In the test, eight different operating conditions were tested in which one artificial crack was created ranging from 0 mm to 10.5 mm. A wavelet packet-based crack severity index was also built to quantitatively identify the pipeline damage condition at various crack depths.

Compensation of piezoceramic bonding layer degradation for structural health monitoring

The compensation of the degradation of the bonding layer of piezoceramics used in structural health monitoring is addressed in this article. A simple admittance model is first used to measure and extract the variation of admittance parameters using the same acquisition chain which is used by the structural health monitoring system for damage monitoring. More precisely, the method uses measurable changes in physical transducer modal damping at frequencies around piezoceramic resonance to estimate the extent of degradation. Then, a finite element model is used to obtain calibration curves linking the variations in transducer modal damping to amplitude and phase of the ultrasonic signals generated or measured by the piezoceramics. Such calibration curves are obtained by simulating with the FEM the effect of varying the bonding layer coverage area and Young’s modulus on (a) admittance and (b) amplitude and phase of the ultrasonic signals. From this, a signal correction factor is developed for the dominant bonding layer coverage area degradation failure mode to compensate for the changes in amplitude and phase of guided waves generated and measured by degraded piezoceramic transducers. The measured modal damping determines the amount of bonding layer degradation from the simulated modal damping calibration curves and then the quantified bonding layer degradation amount selects the amplitude and phase correction to be applied to measured signals from the calibration curves. The benefits of the signal correction factor are demonstrated below piezoceramic resonance to improve damage imaging and localization using the Embedded Ultrasonic Structural Radar algorithm (delay and sum method) when a single transducer in a sparse array of transducers fixed to an aluminum plate is damaged due to the close proximity of drop-weight impacts. Up to a certain damage extent, the signal correction factor could allow an extension of the service life of the structural health monitoring system.

Using piezoelectric oscillating system for welding synthetic fabrics

The high-efficiency oscillating system for welding synthetic fabrics is discussed. It is shown that to increase the productivity of the welding process and reduce the electrical power, it is necessary to use ultrasonic generators self-adjusting with respect to the required oscillation amplitude. The productivity of the processes of ultrasonic welding using piezoceramic and nickel transducers is analysed and the currently available methods of seam welding of synthetic fabrics produced from polymer materials are discussed.

Modelling of a novel high-impedance matching layer for high frequency (>30 MHz) ultrasonic transducers

This work describes a new approach to impedance matching for ultrasonic transducers. A single matching layer with high acoustic impedance of 16MRayls is demonstrated to show a bandwidth of around 70%, compared with conventional single matching layer designs of around 50%. Although as a consequence of this improvement in bandwidth, there is a loss in sensitivity, this is found to be similar to an equivalent double matching layer design. Designs are calculated by using the KLM model and are then verified by FEA simulation, with very good agreement Considering the fabrication difficulties encountered in creating a high-frequency double matched design due to the requirement for materials with specific acoustic impedances, the need to accurately control the thickness of layers, and the relatively narrow bandwidths available for conventional single matched designs, the new approach shows advantages in that alternative (and perhaps more practical) materials become available, and offers a bandwidth close to that of a double layer design with the simplicity of a single layer design. The disadvantage is a trade-off in sensitivity. A typical example of a piezoceramic transducer matched to water can give a 70% fractional bandwidth (comparable to an ideal double matched design of 72%) with a 3dB penalty in insertion loss.

Fatigue lifetime study of piezoceramic patch transducers

This study investigates the loading limits and fatigue behavior of laminar piezoceramic patch transducers, based on monolithic lead zirconate titanate (PZT) plates encapsulated in epoxy resin matrix. Testing includes tensile and compressive mechanical loading, at different temperatures, as well as electric actuation. The objective is the identification of typical failure mechanisms and suitable models for failure and lifetime analysis. In tensile loading, which is observed to have the strongest influence on the patch lifetime, the relevant failure mechanism in quasi-static and cyclic loading is found to be cracking of the PZT plate, causing degradation of the patch performance. Based on the micro-structural investigations and FE simulation, the fracture toughness of the PZT plate is analyzed and a micro-crack-propagation-based fatigue lifetime model is derived. The effect of the fragmentation of the piezoceramic plate on the patch performance is analyzed by the presented functional length concept, based on the shear lag model, yielding very good quantitative agreement.

Multi-scale mechanics of smart material systems and structures

During the last few decades, active composites have been in the focus of intense technological and fundamental researches from industry and academia, respectively. Besides, the wide use of passive composites in transport vehicles and infrastructures led to their functionalisation for their monitoring and control. Good candidates for related sensing, actuation or transduction functions are the so-called smart materials, such as piezoelectric materials, shape memory alloys or polymers, electroor magneto-strictive materials, electroor magnetorheological fluids and electro-active polymers. With the help of integrated control algorithms and processing devices, passive material systems and structures become smart; therefore, due to their multi-physical and multi-disciplinary nature, their multi-scale modelling and simulation are still not yet fully mastered. Hence, in order to reach robust designs of these advanced smart material systems and structures, special fundamental and applied research efforts are still required in order to reach: (i) materials multi-physical effective properties complete and reliable data sets; (ii) efficient multi-scale models and local/global solutions; (iii) mastering integrity and reliability critical issues for wider and safer applications. This focused issue of Acta Mechanica presents six revised, from ten peer-reviewed, manuscripts that were extended after their selection from the twelve contributions presented in two sessions at the Mini-Symposium MS27 on Multi-scale Mechanics of Smart Material Systems and Structures, co-organised by the present guest editors during the 8th European Solid Mechanics Conference held at Graz (Austria) on 9–13 July 2012. These six papers focused on one or more of the above mentioned research issues of Multi-scale Mechanics of Smart Material Systems and Structures; in particular, Micro-mechanics-based numerical homogenisations of magneto-electro-rheological particle and piezoelectric fibre reinforced polymer composite material systems, local (section)-global (structural) analytical models and solutions for the piezoelectric d15 shear-induced torsion actuation and sensing problems, multi-scale fatigue life analyses of polymer encapsulated piezoceramic transducers, and behaviour and response nonlinearities analyses for healthy and cracked piezoelectric transducers at room or cryogenic temperatures. It is hoped that this focused issue contributes to the progress of this topic state-of-the-art and serves the research needs of the Acta Mechanica readers. As a closure, we would like to thank the authors, for their high quality contributions; the reviewers, for their constructive expertises; and the Editor-in-Chief, Professor Hans Irschik, for letting us the entire freedom of this issue management and his editorial administration team for the great help in managing anonymously the managing guest editor’s co-authored contributions.

Disk shaped piezo-ceramic transducer for P and S wave measurement in a laboratory soil specimen

Piezo-ceramic elements are customized as transducers for the measurement of mechanical properties of materials in the engineering field. This was made possible with the industrial production of piezo-ceramic elements in various shapes and sizes. This paper describes the development of a single flat disk shaped piezo-ceramic transducer for measuring both compression and shear wave on an identical soil specimen. Procedures for interpreting results, initial verifications of its performance and applications are also presented. Two types of piezo-ceramic elements, one for measuring P waves and the other for S waves, were placed together in a metal housing, which worked as a wave measuring transducer installed in a triaxial apparatus. Three kinds of granular geo-materials, fine, medium-coarse and coarse sands, were tested. Small strain shear stiffness, Gmax, of the tested sands was evaluated by various techniques, including proposed disk transducer method, trigger and accelerometer method and traxial small strain cyclic loading. Shear moduli obtained from all the techniques fell in a similar range within allowable scatters and it was confirmed that the disk transducer was one of applicable wave measurement technique for laboratory soil specimens.

Cointegration approach for temperature effect compensation in Lamb-wave-based damage detection

Lamb waves are often used in smart structures with integrated, low-profile piezoceramic transducers for damage detection. However, it is well known that the method is prone to contamination from a variety of interference sources including environmental and operational conditions. The paper demonstrates how to remove the undesired temperature effect from Lamb wave data. The method is based on the concept of cointegration that is partially built on the analysis of the non-stationary behaviour of time series. Instead of directly using Lamb wave responses for damage detection, two approaches are proposed: (i) analysis of cointegrating residuals obtained from the cointegration process of Lamb wave responses, (ii) analysis of stationary characteristics of Lamb wave responses before and after cointegration. The method is tested on undamaged and damaged aluminium plates exposed to temperature variations. The experimental results show that the method can: isolate damage-sensitive features from temperature variations, detect the existence of damage and classify its severity.

Impact damage detection in composite chiral sandwich panels using nonlinear vibro-acoustic modulations

This paper reports an application of nonlinear acoustics to impact damage detection in a composite chiral sandwich panel. The panel is built from a chiral honeycomb and two composite skins. High-frequency ultrasonic excitation and low-frequency modal excitation were used to observe nonlinear modulations in ultrasonic waves due to structural damage. Low-profile, surface-bonded piezoceramic transducers were used for ultrasonic excitation. Non-contact laser vibrometry was applied for ultrasonic sensing. The work presented focuses on the analysis of the modulation intensities and damage-related nonlinearities. The paper demonstrates that the method can be used for impact damage detection in composite chiral sandwich panels.

Cellular automata for Lamb wave propagation modelling in smart structures

Lamb waves are widely used for damage detection applications in smart structures instrumented with low-profile, surface-bonded piezoceramic transducers. A great deal of research has demonstrated that numerical simulations of Lamb wave propagation are important for practical implementations of the method. A cellular automata algorithm—with a triangular discretization scheme—is proposed for Lamb wave propagation modelling. The method is illustrated using two-dimensional models of damage detection.

Efficiency of electromechanical impedance for load and damage assessment along the thickness of lead zirconate titanate transducers in structural monitoring

In the recent years, electromechanical impedance–based structural health monitoring has emerged as an alternate to conventional monitoring techniques, especially for aerospace structures where the surface areas are more predominant than the thickness. In the impedance–technique, piezoceramic (lead zirconate titanate) transducers are bonded on the structure to be monitored such that surface area (length × width) of the transducer is in contact with the structure. In the presence of electric field, these transducers interrogate the structure which results in a unique health signal known as admittance signatures. Any deviation in the signature during the period of monitoring indicates disintegrity in the structure. The existing impedance technique has focused on disintegrity on the surface of the structure along the length and width directions of a transducer. This article monitors the increment of load and damage severity along the thickness direction. At first, a load and the increments of load were monitored on a carbon steel gear specimen, where the load was applied parallel to the thickness of transducer such that the load was axial on the specimen. The signatures were obtained for each load increment. Later, an aluminium plate was used to study damage increment along the length and thickness directions separately. The signatures were recorded for each damage increment stage. The signatures were carefully studied and validated using three-dimensional predictive impedance model along the length and thickness directions. This study is expected to be useful for monitoring gears and shafts in mechanical systems where the thickness is predominant.

Impedance-Based Temperature Sensing With Piezoceramic Devices

This paper deals with the temperature dependence of the electrical impedance of piezoceramic transducers. The behavior under thermal loads is investigated for bulk ceramics and composite structures where the piezoceramics are integrated into passive materials. According to these identified dependencies, temperature sensing through the piezoceramics impedance is realized using a polynomial fitting method. A creep operator and a lead filter are introduced to consider the time-dependent behavior of the electrical impedance. The presented approach is applied to a commercially available air ultrasound transducer. The accuracy of the measurement method is investigated for an arbitrary temperature profile yielding ${\pm}{\rm 4.5}^{\circ}{\rm C}$ . The presented method can be utilized for additionally sensing temperature in devices with integrated piezoceramic transducers, especially ultrasound transducers or in structural health-monitoring applications.

An Enhanced Experimental Facility for Durability and Performance Characterisation of Piezoelectric Transducers for Structural Health Monitoring

With any structural health monitoring (SHM) system, verification of the health of the sensing elements is essential in ensuring confidence in the measurements furnished by the system. In particular, SHM systems utilised for structural hot spot monitoring applications will conceivably require transducers to operate reliably after sustained exposure to severe mechanical loading. Consequently, a good understanding of the long term mechanical durability performance of structurally integrated piezoelectric transducers is vital when designing and implementing robust SHM systems. An experimental facility has been developed at the Australian Defence Science and Technology Organisation (DSTO) capable of performing an autonomous long-term mechanical durability test on piezoceramic transducers. The Autonomous Mechanical Durability Experimentation and Analysis System (AMeDEAS) incorporates a general purpose data acquisition program controlling up to three 8-channel relay multiplexers and two instruments. AMeDEAS is highly flexible, allowing user-specified channel configurations and automatic interrogation of selected instruments. The system also interfaces with the uni-axial mechanical testing machine to provide control of the load sequence allowing transducer elements to be interrogated under stable load-free conditions after being subject to a predefined loading regime. AMeDEAS was used to investigate the fatigue characteristics of a low-profile layered piezoceramic transducer package developed by DSTO. A total of 16 transducers were tested under tension-dominated cyclic loading with peak-to-peak strain amplitude increasing from 400 με to a maximum of 3000 με, with periodic acoustic transduction efficiency and electromechanical impedance measurements taken throughout the test. This paper details the AMeDEAS and includes preliminary results which confirm the efficacy of the new facility.

Single Transducer Pair Lamb Wave Time Reversal for Damage Detection in Composite Laminates

This paper investigates the potential of single transducer pair guided waves time reversal to detect damage in composite laminates. According to dynamic reciprocity of Lamb waves propagation in linear media, the time reversal process should reconstruct the original signal. The similarity of original and reconstructed time signals is calculated for different damage types using numerical and experimental studies with the aim to investigate, if the interaction of the wave pulse with inhomogeneities introduces any nonlinearity that time reversibility breaks down and single transducer pair time reversal could be used as damage diagnostics tool. 3D explicit finite element analysis is used for the numerical simulation and laser Doppler vibrometry is used to capture out-of-plane displacement time histories excited by an adhesively bonded piezoceramic transducer disc in the experimental time reversal process. In the case of an undamaged composite laminate the similarity index used to quantify the similarity of the original and reconstructed wave pulses is better than 95%. The similarity index is smaller for laminates with artificial damages including embedded fluoro polymer films to simulate delamination damage, through holes and bonded mass inhomogeneities. Although numerical and experimental similarity indices are smaller at higher frequencies, there is no clear evidence that single transducer pair time reversibility breaks down and represents a reliable damage diagnostics tool.

Piezoelectric Properties of Fine-Grained Pb(Mg1/3Nb2/3)O3–Pb(Zr,Ti)O3–Bi(Zn1/2Ti1/2)O3 Quaternary Solid Solution Ceramics

On the basis of solid state reaction eutectic behavior between Pb(Mg1/3Nb2/3)O3–Pb(Zr,Ti)O3 (PMN–PZT) and metastable perovskite-type Bi(Zn1/2Ti1/2)O3 (BZT), perovskite-structured PMN–PZT–BZT quaternary solid solution piezoceramics with various compositions were experimentally demonstrated with an intrinsic low sintering temperature in the windows of 950–1050 °C. These fine-grained densified PMN–PZT–BZT ceramics were able to be poled sufficiently at room temperature through polarization–electric field hysteresis loop measurement, different from normal poling treatment with DC bias field at high temperature, which will simplify future device processing of monolithic multilayer piezoceramic transducers. A typical piezoelectric property of dielectric constant ε33T/ε0 = 3471, piezoelectric constant d33 = 480 pC/N, planar coupling coefficient kp = 0.41, thickness coupling coefficient kt = 0.50, mechanical quality factor Qm = 68 and relaxor ferroelectric phase transition temperature Tm = 167 °C at 1 MHz was obtained for the fine-grained densified Pb0.96Sr0.04(Mg1/3Nb2/3)0.37Zr0.24Ti0.39O3+3%Bi(Zn0.5Ti0.5)O3+2%NiO ceramics sintered at 1020 °C, which is much promising to manufacture monolithic multilayer piezoelectric transducers with Ag95/Pd5 as inner electrode material.

The analysis of electromechanical characteristics of radiating cylindrical piezoceramic transducer with surface coated by solid elec-trodes located in the closed ring layer

In this article is estimated the influence of closed ring layer parameters on the electromechanical characteristics of radiating electroacoustical cylindrical piezoceramic radially polarized transducer. To solve the problem there are used method of partial regions, the Fourier method and the property of completeness and orthogonality of cylindrical wave functions.

Proof-of-concept experimental study of damage detection of concrete piles using embedded piezoceramic transducers

This paper presents a proof-of-concept experimental study of an innovative active-sensing approach for damage detection of concrete piles by using embedded piezoceramic transducers. In the proposed active-sensing approach, one piezoceramic transducer is used as an actuator to generate a stress wave to propagate through the concrete pile and the other distributed piezoceramic transducers are used as sensors to detect the wave response. Cracks or damage inside the concrete structure act as stress relief in the wave propagation path. The amplitude of the wave and the transmission energy will decrease due to the existence of cracks or damage. Experiments were performed on two bored piles instrumented with embedded piezoceramic transducers. The experimental results demonstrate the effectiveness of the proposed approach for pile damage detection.