Active fiber composites for the generation of Lamb waves (original) (raw)
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The Abstracts of ATEM : International Conference on Advanced Technology in Experimental Mechanics : Asian Conference on Experimental Mechanics
Active Fiber Composites (AFC) consist of one layer of piezoelectric ceramic fibers embedded in an epoxy matrix and sandwiched between two sets of interdigitated electrodes. They show orthotropic mechanical properties due to their design and manufacturing. The small thickness and the conformability to curved surfaces make them suitable for applications in structural health monitoring (SHM) with acoustic nondestructive testing methods. The piezoelectric properties of the AFC allow for both actuation and sensing capabilities with the same element which enables emitting and receiving of structural waves (e.g., Lamb waves) for monitoring of critical structural elements. Before realizing specific applications for AFC in SHM systems, it is necessary to characterize the transfer behavior of AFC bonded on a structure for excitation and sensing of transient waves which propagate in the structure. To characterize this behavior experimentally, the acoustic wave field in a thin, planar structure excited from surface bonded AFC is explored with a laser interferometer. Surface velocities at different positions around an AFC bonded on an aluminum plate during transient excitation are recorded. The transfer function is calculated for different angles from the fiber direction of the AFC for both the first symmetric and the first antisymmetric Lamb wave mode. The sensing process is also investigated: structural waves generated by surface bonded piezoelectric ceramic discs are measured likewise with laser interferometry in the vicinity of the AFC and with the AFC itself. Results show, that the emitting and receiving capabilities of the AFC decrease with increasing angle from the fiber direction of the AFC. Typical maxima and minima in the transfer function depend on the length of the AFC.
Lamb wave transducers made of piezoelectric macro-fiber composite
Structural Control and Health Monitoring, 2012
During recent years, an intensive research activity concerning the application of Lamb waves (LWs) for SHM has been observed. LWs may be generated and sensed using different types of transducers, and their selection is essential for the SHM system's performance. Results of the investigation of three types of transducers based on macro-fiber composite (MFC) are presented in this paper; two types of commercially available MFC actuators are compared with a novel type of custom-designed interdigital transducer also based on the MFC substrate. After a short presentation of the piezoelectric transducer designed for SHM applications, details concerning the proposed interdigital transducer design are provided. Beampatterns of the investigated transducers are first compared using numerical FEM simulations, and next, the numerically obtained beampatterns are verified experimentally using laser vibrometry. In the final part of this paper, advantages and disadvantages of the investigated transducers are discussed.
Lamb Wave Ultrasonic System for Active Mode Damage Detection in Composite Materials
2013
The work describes a new approach for the development of a SHM system based on flexible piezopolymer transducers which have some advantages over the piezoceramic thin disk transducers in space applications. The flexible piezopolymer transducers made with thin 100 μm PVDF film were proposed by the authors in previous works (Capineri et al., 2002) (Bellan et al., 2005a) (Bellan et al., 2005b). The proposed technology is based on a network of transducers arranged in array configuration, designed to excite particular types of ultrasonic Lamb waves in laminate materials (metallic or composite). This type of transducers are called interdigital transducers because the comb geometry of the electrodes. The finger to finger distance of interdigital electrode patterns determine the central wavelength of the transducer and then the corresponding Lamb wave’s mode. The interest for this technology comes from the characteristics of this piezoelectric polymer film that can operate in a broader rang...
Composite Structures, 2002
The paper presents a set of numerical results on the use of surface mounted piezoelectric transducers to analyse the effects of impact damage and delamination of plate-like structures on the Lamb wave mode. The effects of the size, properties and orientation of the damage upon a propagating Lamb wave is qualitatively determined. In this paper, impact damage was simulated by a local change in the stiffness of the material in the structure and a delamination. The effects on the transmission of the incident Lamb wave when it propagates through a region of change in density are analysed. This paper will also demonstrate how the properties of a propagating Lamb wave can be affected by the existence of a delamination in a plate.
2022
The most common researched area of damage in a composite material such as carbon fibre reinforced plastics (CFRP) used currently in aircraft construction is barely visible impact damage (BVID), significantly reducing mechanical properties. Early detection and qualification would improve safety and reduce the cost of repair. In this context, structural health monitoring (SHM) techniques have been developed that could monitor a structure at any time by using a network of sensors. Widely used discrete ceramic transducers can generate and sense Lamb waves travelling in the structure. Wave propagation must then be analysed for effective damage identification. An effective SHM system is desired to meet several demands, such as minimised weight penalty, non-intrusive system not interfering with the structure performance, costeffectiveness for implementation with targeted sensitivity and area coverage, capability of monitoring non-accessible and critical hot spot regions, robustness, and reliability. This review starts with an introduction on Lamb waves fundamentals and their use in SHM, and then particularly focuses on methods using piezoelectric transducers and mode selection. Some relevant applications on different structural configurations are discussed. Finally, recent developments on piezoelectric coating and direct-write sensor technology for tailored transducers are highlighted with some thoughts for near future research work.
Piezo-composite transducer for mode and direction selectivity of Lamb waves
2018
Ultrasonic-based SHM (Structural Health Monitoring) applications commonly rely on the use of piezo-electric patches to emit and receive ultrasonic waves. The objective is to study the propagation of the waves through a structure to assess its structural integrity. Because of the elevated number of echoes and possible modes of propagation of the waves within the structure, those applications suffer from a burden of signal processing. This paper presents a composite piezo-electric patch that was designed and successfully tested for reducing the complexity of the SHM detection schemes by selecting the mode and direction of the Lamb waves received. The piezo-composite is composed of a row of eight independent ceramic pillars separated with polymer, so it is a 1-D matrix of independent piezo-patches. Used with adequate electronics and signal processing, it was shown that it allowed selecting the direction and the mode of the Lamb waves.
Ultrasonic waves for health monitoring of composite structures
Ultrasonic waves offer a great potential for structural health monitoring (SHM) in many industrial applications. The application of ultrasonic waves takes advantage of mode conversions and wave reflections at distinguished discontinuities, which can be used to identify structural failures and damages. The high sensitivity of Lamb waves with respect to small structural changes and the low costs to build a network of surface attached piezoelectric transducers to excite and to receive the waves makes such a system very attractive for industrial applications. The numerical modeling of waves in complex structures with commercial finite element software tools, applying standard finite elements with linear or quadratic shape functions, requires an enormous computational power, which exceeds today´s computer resources. Therefore, we proposed to use higher order finite element schemes, which may result in much lower computational costs for ultrasonic wave propagation analysis in complex fiber reinforced composites. In the paper the advantage of higher order finite elements is demonstrated with help of a benchmark example. Finally it is shown that the numerical results can also be experimentally verified by applying a laser-scanning vibrometer.
Structural health monitoring in composite materials using Lamb wave methods
2002
Cost-effective and reliable damage detection is critical for the utilization of composite materials. This paper presents part of an experimental and analytical survey of candidate m ethods for in-situ damage detection of composite materials. Experimental results are presented for the application of Lamb wave techniques to quasi-isotropic graphite/epoxy thin coupons and sandwich beams containing representative damage modes, including delamination, transverse ply cracks and through-holes. Optimization experiments provided a procedure capable of easily and accurately determining the presence of damage by monitoring the transmitted waves with piezoceramic sensors (PZT). Lamb wave techniques have been proven to provide more information about damage type, severity and location than previously tested methods, and may prove suitable for structural health monitoring applications since they travel long distances and can be applied with conformable piezoelectric actuators and sensors that require little power.
Structural Health Monitoring of Lightweight Structures by Use of Lamb Waves
In the experimental part of this work, the excitation and propagation of Lamb waves in carbon fiber reinforced composite plates is presented by visualized experimental data. Lamb waves are easily excited by thin piezoelectric patches adhered to the surface of the structure. Their propagation is observed experimentally by Scanning Laser Vibrometry. Results from Lamb wave reflection and mode conversion at damage locations are shown indicating the potential and the restrictions of the inspection method. In the numerical part of this work, honeycomb sandwich panels are considered which are also frequently used as lightweight structures due to their high stiffness. Because of their complex build-up the understanding of Lamb wave generation and propagation is much more difficult than in the case of conventional composite plates. Therefore, finite element simulations have been performed to study guided waves at different frequency ranges and in sandwich panels with different build-ups. The...