Macro Fiber Composite Transducers Research Articles

Post-tensioning tendon force estimation of in-service prestressed concrete structure using cylindrical lamb waves

This paper proposes an ultrasonic-based force estimation technique for the post-tensioning (PT) tendon of an in-service prestressed concrete structure. First, three macro fiber composite transducers are installed on the surface of an in-service PT tendon subjected to an unknown tensile force for the generation and measurement of cylindrical Lamb waves. Then, the velocities of the longitudinal and shear waves are calculated using the measured cylindrical Lamb waves at two ultrasonic input frequencies. Subsequently, the Poisson’s ratio, elastic modulus, and strain induced by the PT tendon force are estimated from the longitudinal and shear wave velocities. Finally, the PT tendon force is obtained from the estimated mechanical property values. The experimental validation was performed using a mono-strand PT tendon under various temperature conditions, and the developed technique estimated the unknown PT tendon force in the range of 10–100 kN with a 6.22 kN maximum error and a 2.99 kN root-mean-square error. The uniqueness of this paper includes (1) no requirement for temperature compensation for field deployment, (2) PT tendon force estimation without calibration of the PT tendon force and cylindrical Lamb wave relationship, and (3) easy sensor installation and no interference with the PT construction process.

Baseline-free absolute strain estimation for cylindrical structures

The total strain induced by forces in a structure, known as absolute strain, provides crucial information about structural integrity. The unexpected variations in absolute strain can compromise the overall safety of the structural system. In this paper, a baseline-free absolute strain estimation technique is developed based on the acoustoelastic effect of ultrasonic guided wave for in-service cylindrical structures. To generate and sense ultrasonic guided waves, two macro-fiber composite (MFC) transducers were installed on the surfaces of cylindrical structures subjected to tensile force. Additionally, a strain gauge was used to measure the relative strain generated after installing the MFC transducers and the strain gauge. The absolute strain was estimated using the velocity of the ultrasonic guided waves and the relative strain, without the need for calibration tests and baseline data obtained from known absolute strain levels. The effectiveness of the developed technique was experimentally examined using blind data obtained from a hollow steel cylinder and an aluminum mooring cable from a submerged floating tunnel model.

Excitation of torsional guided waves with flexible PZT transducers in water-filled pipes

Estimation of structural damage to predict the service lifetime of liquid-filled pipelines is important to reduce waste or to avoid accidents. In this work, experimental and numerical simulations were carried out to characterize the acoustic wave propagation of the lowest cylindrical torsional mode in a pipe with discontinuities. Wave mode was generated and received using flexible macro-fiber composite transducers (MFC). An analysis of beam energy directionality of shear horizontal (SH) and Lamb modes was carried out prior to the tests on the cylindrical structure. A method to control the generation and detection of torsional waves in the pipe considering the directionality of the SH-plate waves was proposed. Tests were carried out in a water-filled pipe to study the leakage effect in the detection of discontinuities. The results showed that although torsional as well as flexural modes can be simultaneously excited by the MFC patch actuator, the orientation of the patch can also allow mode selection. Finally, it was found that flexible patches generate torsional waves efficiently and could be used to detect circumferential discontinuities in water-filled pipes.

A Damage Detection Method Based on Flexible Macro-Fiber Composite

Macro-fiber composite (MFC) transducers exhibit superior directionality and flexibility, as well as a high response to Lamb waves, which endows them an intrinsic advantage in damage detection. This article applies MFC transducers to “active–passive” damage detection, a technique which is not well-documented, on a curved structure. By rationally laying out the actuators and rosette receivers on a curved structure of interest, we are able to detect the baseline-free location of infinitesimal damage in the structure. This study combines computational simulations, theoretical analyses, and experimental validations to investigate directional excitation and reception characteristics, in which the incoming wave direction estimation algorithm of MFC delta rosette structure is obtained and damage is characterized by the intensity image synthesized from error estimation curves of two MFC rosette receivers. Experimental results show that the location errors in pinpointing the damage positions on the curved aluminum plate are all within 10 mm, and this system can effectively detect damage in the structure with up to 5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{-1}$ </tex-math></inline-formula> curvature. Our preliminary results demonstrate that MFC has the potential to precisely locate damage on complex curved structures and provides a novel testing technique to monitor the health state of complex structures.

Development of a miniature dynamic stiffness measurement prototype toward structural health monitoring of space inflatable structures

Inflatable structures are increasingly used in aerospace engineering. However, the space survivability and durability of such structures are of particular concern due to material aging in space environment and unexpected external impact threats. Thus, it is very urgent to in-situ monitor and assess structural health condition for space inflatable structures. Since inflatable structures are often lightweight, large-sized and flexible, their low-frequency vibration response contains much information about structural health condition. To facilitate in-situ structural health monitoring of space inflatable structures, this paper developed a miniature low-frequency dynamic stiffness measurement prototype. The prototype is capable of generating two channels of swept-sine excitation signals, and concurrently acquiring six channels of response signals. Recorded data is communicated and downlinked from the host spacecraft to the ground, and then the dynamic stiffness is derived to determine structural health condition. To validate the developed prototype, two simulated inflatable space structures are fabricated and tested, including an inflatable boom and an inflatable torus, and then Macro-Fiber Composite transducers are attached on two specimens as actuators and sensors in tests. Experimental studies show that the prototype functions well and the outputted results are consistent with that measured by large-bulked commercial ground devices. Additionally, the multi-channel functionality of the prototype is verified by carrying out the multi-input multi-output test. In summary, the prototype features small size, light weight, and low power consumption, which has the potential for future space applications.

Detection of torsional guided wave generation using macro-fiber composite transducers and basis pursuit denoising

In engineering structures, such as large fluid-filled pipelines, continuous monitoring for damage detection is needed. To address this issue, we study the generation of guided waves in pipes by using a circumferential strip of macro fiber composite transducer to generate and detect torsional and flexural lower modes. The propagated elastic waves and their resulting reflected and mode-converted signals at the interaction wave discontinuity are post-processed with basis pursuit denoising using a Gabor dictionary to improve signal identification. Numerical results are obtained and experimentally tested on a stainless-steel pipe A-36 (43.6 and 48.2 mm in inner and outer diameter). It was found that the proposed method makes it possible to identify an artificial discontinuity by detecting the scattered wave and converted modes of a propagated torsional wave.

Experimental Study of Macro Fiber Composite-Magnet Energy Harvester for Self-Powered Active Magnetic Bearing Rotor Vibration Sensor

The paper presents the design, fabrication, and characterization of an energy harvester for an active magnetic bearing (AMB) rotor vibration using a macro fiber composite (MFC) with magnetic coupling. The MFC cantilevers configuration, together with neodymium magnets, is used for the contact-free rotor radial vibration self-powered sensor. The permanent magnets attached to the rotor and to the four MFC element beams ensure the mechanical energy transfer and the MFC cantilever vibration excitation. In the proposed prototype, the MFC transducer output voltage depends on the air-gap between two magnets. This paper investigates the optimum conditions to harvest as much as possible electric energy at different clearances and rotational speeds. Furthermore, to assess the rotor vibration sensitivity, the experimental results of the MFC-magnet self-powered sensor are compared with measurements obtained using a fiber optic sensor. The maximal obtained harvesting power equals 673.47 µW for the rotor speed of 3150 rpm. Moreover, the MFC cantilever was proposed as the rotor vibration sensor. The MFC-magnet self-powered vibration sensor output was compared with the fiber optic laser sensor. The mismatched vibration amplitude for both sensors does not exceed 1 µm.

Application of Ultrasonic Guided Waves for Inspection of High Density Polyethylene Pipe Systems

The structural integrity assessment of thermoplastic pipes has become an interesting area of research due to its elevated usage in the liquid/gas transportation industry. Ultrasonic guided wave testing has gained higher attention from industry for the inspection of elongated structures due to the reduced inspection time and cost associated with conventional non-destructive testing techniques, e.g., ultrasonic testing, radiography, and visual inspection. Current research addresses the inspection of thermoplastic pipes using ultrasonic guided waves as a low cost and permanently installed structural health-monitoring tool. Laboratory and numerical investigations were conducted to study the potential of using ultrasonic guided waves to assess the structural health of thermoplastic pipe structures in order to define optimum frequency range for inspection, array design, and length of inspection. In order to achieve a better surface contact, flexible Macro-Fiber Composite transducers were used in this investigation, and the Teletest® Focus+ system was used as the pulser/receiver. Optimum frequency range of inspection was at 15−25 kHz due to the level of attenuation at higher frequencies and the larger dead zone at lower frequencies due to the pulse length. A minimum of 14 transducers around the circumference of a 3 inch pipe were required to suppress higher order flexural modes at 16 kHz. According to the studied condition, 1.84 m of inspection coverage could be achieved at a single direction for pulse-echo, which could be improved by using a higher number of transducers for excitation and using pitch-catch configuration.

Analysis of Wave Patterns Under the Region of Macro-Fiber Composite Transducer to Improve the Analytical Modelling for Directivity Calculation in Isotropic Medium

Analytical modelling is an efficient approach to estimate the directivity of a transducer generating guided waves in the research field of ultrasonic non-destructive testing of the large and complex structures due to its short processing time as compared to the numerical modelling and experimental techniques. The wave patterns or the amplitude variations along the region of ultrasonic transducer itself depend on its behavior, excitation frequency, and the type of propagating wave mode. Depending on the wave-pattern of a propagating wave mode, the appropriate value of the amplitude correction factor must be multiplied to the amplitudes of the excitation signal for the accurate evaluation of directivity pattern of the ultrasonic transducers generating guided waves in analytical modelling. The objective of this work is to analyse the wave patterns under the region of macro-fiber composite (MFC) transducer to improve the accuracy of a previously developed analytical model for the prediction of directivity patterns. Firstly, the amplitude correction factor based on the wave patterns under the region of P1-type MFC (MFC-2814) transducer at two different frequencies (80 kHz, 3 periods and 220 kHz, 3 period) glued on 2 mm Al alloy plate has been estimated analytically in the case of an asymmetric (A0) guided Lamb wave. The validation of analytically estimated amplitude correction factor is performed by a proposed experimental method that allows analyzing the behaviour of MFC transducer under its region by gluing MFC on bottom surface and scanning the receiver on the top surface of the sample. Later on, the estimated amplitude correction factor is included in the previously developed 2D analytical model for the improvement in the directivity patterns of the A0 mode. The modified analytical model shows a significant improvement in the directivity pattern of the A0 wave mode in comparison to the results obtained by the previous model without considering the proper wave patterns. The results reveal that errors between the directivity estimated by the present modified 2D analytical model and experimental investigation are reduced by more than 58% in comparison to the previously developed analytical model.

Applications of piezoelectric MFC type transducers in mechatronic measurement systems - the impact of a mechanical subsystem damage on a system operation

The work include a report of research works concerning applications of non-classical piezoelectric transducers in mechatronic measuring systems. Composite piezoelectric transducers called Macro Fiber Composite (MFC) are considered. Characteristics of considered transducers were made, indicating their advantages and disadvantages, as well as the results of carried out laboratory tests are presented, in which MFC transducers were used as sensors for mechatronic measurement systems. A series of laboratory tests was carried out on the created laboratory stand to determine the impact on the measured values of damage of the mechanical subsystem on which the MFC-type piezoelectric transducer was glued. Results of measurements are presented and analysed in relation to different applications of the piezoelectric MFC sensors.

Ultrasonic Lamb Waves for Wireless Power Transfer.

Ultrasonic guided plate waves (Lamb waves) can be used to transfer power along the length of metal plates, achieving longer distance wireless power transfer (WPT), while not being impeded by electromagnetic shielding from the metal plate. In this article, a fundamental study on the performance of Lamb wave WPT is presented, including modeling, simulations, and experimental verification. By using Macro-Fiber Composite (MFC), d33 -mode, piezoelectric transducers bonded to a [Formula: see text] mm aluminum plate using an epoxy, power transfer of 0.47 W with 56% overall power transfer efficiency was achieved at a 204-mm distance. The measured frequency response of the power transfer efficiency matches well with the simulated results, and the effects of complex load impedance matching and transducer sizing were investigated. It is shown that the location where the efficiency is maximized roughly corresponds to the zero-order symmetrical mode (S0) standing wave patterns due to reflections from the plate edges. For practical implementation, the effect of using different methods to temporarily or permanently bond the MFC transducers to the metal plate was also investigated, as well as the effect of electrically grounding the metal plate.

Structure-preserving low-order modeling approach of laminated composite plates integrated with macro-fiber composite transducers for dynamic applications

An Equivalent Substructure Modeling (ESM) approach of laminated composite plates with integrated macro-fiber composite (MFC) transducers is described. The proposed approach generates structure-preserving low-order system models for dynamic applications such as vibration suppression and energy harvesting. The direct piezoelectric effect of MFC transducers is derived from the electrical boundary conditions and it has the same coupling patterns as equivalent forces which describe the inverse piezoelectric effect. Hence, the reversibility of the piezoelectric effect is ensured and the electrical dynamics of the system can be simulated. The dual electromechanical couplings are assigned to a low-order structural model generated by an equivalent substructure concept. A laminated composite plate with integrated MFC transducers is used for validations and the simulated results agree well with experimental data. Two given study cases demonstrated that the ESM approach not only can generate accurate low-order system models but also provides a flexible fashion to design piezoelectric composite systems.

Identification and Characterization of Defects in Glass Fiber Reinforced Plastic by Refining the Guided Lamb Waves.

In this paper, the disbond-type defect presented on glass fiber reinforced plastic material is analyzed by refining the guided Lamb wave signals. A segment of wind turbine blade is considered as a test sample. The low-frequency ultrasonic measurement system is used for the non-destructive testing of the test sample using guided waves. The P-1 type macro-fiber composite transducer as a transmitter and contact-type piezoceramic transducer as a receiver are used for the testing of a sample. The disbond type defect having a diameter of 81 mm is detected from the experimental results. To improve the accuracy in locating and sizing the defects and estimation of the time of flight and phase velocity of ultrasonic guided waves in defective region, signal processing algorithm is developed by utilizing the promising properties of various ultrasonic signal processing techniques such as wavelet transform, amplitude detection, two-dimensional Fast-Fourier transform, Hilbert transform and variational mode decomposition. The discrete wavelet transform is used to denoise the guided wave signals and then, the size and location of defects are estimated by amplitude detection. The reflected wave signals from the opposite edge of the sample are removed by applying the two-dimensional Fast-Fourier transform to the experimental B-scan signal. Afterwards, variational mode decomposition and Hilbert transform are used for the phase velocity and time-delay estimation by comparing the instantaneous amplitudes of the defective and defect-free signal. The validation and the demonstration of reproducibility of the algorithm is performed by extracting the features of a 51 mm defect from another experimental B-scan.

Flexible Shear Mode Transducer for Structural Health Monitoring Using Ultrasonic Guided Waves

The application of the fundamental shear-horizontal wave mode for guided wave structural health monitoring is undoubtedly beneficial due to its nondispersive characteristics. Existing guided wave shear mode transducers are rigid and brittle, because of these characteristics, bonding them to irregular surfaces (i.e., curved surfaces) is challenging. There is a huge market interest in the development of a flexible shear mode transducer, which eases the transducer bonding process onto irregular surfaces and improves the surface contact between the transducer and the structure. This study presents a flexible shear mode transducer for structural health monitoring using low-frequency guided waves (20–120 kHz). The proposed transducer is manufactured using piezoceramic, and based on the results of this study, it exhibits the directional excitation of fundamental shear-horizontal mode at 20–120 kHz. Finite element analysis and laboratory experiments were conducted to study the behavior of the proposed transducer. Field trials were conducted on a liquid storage tank with an undulated surface (due to corrosion). The performance of the proposed transducer is also compared to the commercially available macro fiber composite transducers. The proposed transducer was driven by the industrialized ultrasonic guided wave inspection system; Teletest Focus+ in line with the application of tank floor inspection using ultrasonic guided waves.

2D Analytical Model for the Directivity Prediction of Ultrasonic Contact Type Transducers in the Generation of Guided Waves.

In this paper, a novel 2D analytical model based on the Huygens’s principle of wave propagation is proposed in order to predict the directivity patterns of contact type ultrasonic transducers in the generation of guided waves (GWs). The developed model is able to estimate the directivity patterns at any distance, at any excitation frequency and for any configuration and shape of the transducers with prior information of phase dispersive characteristics of the guided wave modes and the behavior of transducer. This, in turn, facilitates to choose the appropriate transducer or arrays of transducers, suitable guided wave modes and excitation frequency for the nondestructive testing (NDT) and structural health monitoring (SHM) applications. The model is demonstrated for P1-type macro-fiber composite (MFC) transducer glued on a 2 mm thick aluminum (Al) alloy plate. The directivity patterns of MFC transducer in the generation of fundamental guided Lamb modes (the S0 and A0) and shear horizontal mode (the SH0) are successfully obtained at 80 kHz, 5-period excitation signal. The results are verified using 3D finite element (FE) modelling and experimental investigation. The results obtained using the proposed model shows the good agreement with those obtained using numerical simulations and experimental analysis. The calculation time using the analytical model was significantly shorter as compared to the time spent in experimental analysis and FE numerical modelling.

Raziskava 3D karakteristik odmika pretvornika iz kompozita z makrovlakni (MFC-P1)

Raziskava 3D karakteristik odmika pretvornika iz kompozita z makrovlakni (MFC-P1)

Refinement of defect detection in the contact and non-contact ultrasonic non-destructive testing of wind turbine blade using guided waves

The guided waves are widely used for the inspection of many composite structures as they can travel up to long distance along the thickness of the structure. Most of the times, the experimental investigations standalone is not able to locate and size the damages or defects due to dispersive, superimposed and scattered guided wave modes. Hence signal refinement of ultrasonic guided wave signals is required for identifying and characterizing the defects. In this work, disbond type defects presented on different locations of the segment of the wind turbine blade are estimated by applying the signal refinement techniques after experimental analysis. The experiment was carried out on a 1005 x 870 mm segment of wind turbine blade manufactured using a composite glass fiber reinforced plastic material. Two defects on the trailing edge (with diameter 15 and 25 mm) and three defects on the main spar (with diameters 25, 51 and 81 mm) of the WTB segment were investigated. The combination of macro fiber composite transducer, contact type and air-coupled transducers were used to transmit and receive the ultrasonic guided waves. The signal processing techniques are applied to the experimental signals for the estimation and characterization of defects.

Development of a 2D analytical model for the prediction of directivity pattern of transducers in the generation of guided wave modes

The guided waves (GW) are extensively used in the nondestructive testing (NDT) and structure health monitoring (SHM) of the large and complex structures. It enables to detect the defects up to few meters away from the transducers. However, the defects could occur at longer distances. In order to cover the test area of interest for the estimation of defects and to find the exact position of the transducers to be glued/ embedded, the directivity pattern of the transducers must be known. The aim of the presented work is to develop the 2D analytical model for the estimation of directivity patterns of the transducers at various frequencies and distances. The model was developed using the Huygens's principle of wave propagation distances with considering the known phase dispersive characteristics of the guided wave modes in the medium. The principle of modelling will work to plot the directivity pattern at any distance, at any excitation frequency and with any configuration and shape of the transducers. In order to demonstrate the model, the directivity patterns of P1-type macro-fiber composite (MFC) transducer in the generation of fundamental Lamb modes and shear horizontal mode at 300 mm from the center of MFC were obtained. The input signal used was 80 kHz, 3 period signal and propagation medium was Al plate of 2 mm thickness. The prediction about the position of where MFC transducer should be placed or glued on the object and selection of proper wave modes in order to estimate the defects in various materials is also discussed. The results were validated using finite element analysis (FEA) performed in ANSYS and further verified by the experimental analysis using low-frequency (LF) ultrasonic measurement system ULTRALAB, developed by Ultrasound Research Institute, Kaunas University of Technology. The proposed analytical model will not only facilitate to decide the position and number of transducers but also leads to choosing the configuration of transducer and wave modes suitable to be used for the inspection of defects.

Long-term fatigue behavior of a cantilever piezoelectric energy harvester

Piezoelectric energy harvesting has attracted extensive research in the advancement of new designs and techniques over the last decade. The cantilever shaped piezoelectric energy harvesting beam is one of the most employed designs, due to its simplicity and flexibility for further performance enhancement. The strain distribution along the cantilever piezoelectric energy harvesting beam is nonuniform, which would induce fatigue damage at the root of the cantilever on the long run. This particular issue has seldom been addressed in the literature. This article presents an experimental investigation on the fatigue behavior of a cantilever piezoelectric energy harvesting beam at different base excitation levels. The experimental study is augmented with analytical formulation to examine the strain levels and with finite element analysis formulation to model the piezoelectric energy harvesting beam with a macro fiber composite piezoelectric transducer. A two-dimensional model is developed based on the three-dimensional model to investigate crack propagation in the piezoelectric energy harvesting beam. Furthermore, the electromechanical impedance technique is employed to monitor the progression of damage in the experimental specimens. The root mean square deviation and relative root mean square deviation of the impedance values and voltage obtained from the macro fiber composite transducer provide a profound introspection into the damage propagation in the piezoelectric energy harvesting beam. This study provides an insight into the behavior of the piezoelectric energy harvesting beam undergoing fatigue loading due to a uniform sinusoidal base excitation by analyzing the output voltage, resonant frequency, tip displacement, tip velocity, and impedance variations. It will pave the way for future studies on the fatigue-based design guides for piezoelectric energy harvesting beams.

An analysis of the possibility of Macro Fiber Composite transducers application in modernized freight wagon

Paper presents an analysis of the possibility of application of piezoelectric foils - Macro Fiber Composite (MFC) in modernized freight wagons. It was verified if they can be successfully applied as sensors in developed system for structural health monitoring and in energy harvesting system. It is a part of a research project that aim is to develop a technology of freight wagons modernization. The goal of the project is to elongate the period between periodic repairs (by better corrosion protection) and improve conditions of exploitation of modernized wagons (easier unloading during winter conditions - no freezes of the charge to the freight wagon body shell). The additional aim is to develop system for structural health monitoring of the modernized body of the freight wagon as well as the system supporting management of a fleet of wagons using GPS system with power supply based on the energy recovered by MFC's from the wagon's vibrations during its exploitation. Results of laboratory tests as well as results of measurements on the real freight wagon during observed driving of the wagon are presented. At the same time measurements of the electric voltage generated by the MFC transducers excited by low frequencies harmonic excitation were verified.