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Acoustics A New Technique for Acoustic Source Localization in an Anisotropic Plate without Knowing its Material Properties T. Kundu Department of Civil Engineering and Engineering Mechanics; University of Arizona 2, Tucson, Arizona, USA
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The conventional triangulation technique cannot locate the acoustic source in an anisotropic plate because this technique requires the wave speed to be independent of the propagation direction which is not the case for an anisotropic plate. All methods, proposed so far for source localization in anisotropic plates, require either the knowledge of the direction dependent velocity profile or a dense array of sensors. In this paper a technique is proposed to locate the acoustic source in large anisotropic plates with the help of only six sensors without knowing the direction dependent velocity profile in the plate. The proposed technique should work equally well for monitoring large isotropic and anisotropic plates. For an isotropic plate the number of sensors required for the acoustic source localization can be reduced to four.
| Acoustics |
Acoustics Fatigue Monitoring of High Strength Concrete Using Acoustic Emission and Ultrasonic Techniques R. Wagner1 3, M. Reiterer1 3, A. Strauss2 2, S. Urban2 1RED Bernard GmbH 4, Vienna, Austria 2University of Natural Resources and Applied Life Sciences,(BOKU) 16, Vienna, Austria Acoustic Emission (AE), Ultrasonic Testing (UT), Fatigue
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In this work we present the results of a measurement campaign performed on high strength concrete, to investigate fatigue behavior under cyclic loading in terms of a Structural Health Monitoring (SHM) system. The specimens, small concrete cylinders, were equipped with acoustic emission (AE) and ultrasonic (US) sensors which recorded signals from the onset of beginning fatigue processes in the material until complete damage of the specimen. The parameters monitored have been the acoustic emission activity and the ultrasonic signals time-of-flight respectively travel velocity. The results are in accordance to tests on different concrete material and demonstrate the capability of the proposed methods to trace the fatigue process of concrete. As roundup, results obtained with similar sensing technologies on a large scale structure are presented.
| Acoustics |
Acoustics Contribution of Acoustic Emission to Evaluate the Influence of Hygrothermal Aging on Mechanical Behavior of Hemp Reinforced Polypropylene Composites M. Salvi1 3, S. Bouzouita1, H. Daly2, A. Dogui2 1Laboratoire de Tribologie et de Dynamique des Systèmes; Ecole centrale de Lyon 3, Lyon, France 2Laboratoire de Génie Mécanique; Ecole Nationale d'Ingénieurs de Monastir, Monastir, Tunisia
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In recent years high interests of scientific and industrial worlds were concentrated on natural fibers composites. Natural fibers as hemp, flax and sisal have become suitable alternatives to glass fibers as NFs present several advantages as lightness, strength, recyclability and are relatively cheap and abundant. However, their high hygroscopic nature and their sensitivity to temperature must be taken into account. In this paper, the influence of hygrothermal aging on mechanical behaviour of Hemp/ isotactic polypropylene composites were studied using flexural tests associated to acoustic emission (AE).
| Acoustics |
Acoustics Classification of Wear by Means of Acoustic Emission and Signal Processing Techniques D. Söffker 16, D. Baccar 3 University of Duisburg-Essen 17, Duisburg, Germany
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Usually inner material effects damage the system internally before those effects can be detected visually at the material. Hence, an optical (surface) inspection cannot reveal the inner state-of-damage. Once the surface is affected e.g. by a crack, the normal reactive monitoring and maintenance procedures may not prevent the systems’ failure. Therefore a need to develop reliable and efficient condition monitoring systems able to detect damage, determine the actual state-of-damage, realize diagnostics and predict the remaining use time occurs. The goal of this paper is to introduce a system for online classification and examination of wear phenomena in metallic structure based on the application of the acoustic emission (AE) technique and time-frequency analysis. In this purpose, short-time Fourier transform (STFT) and wavelet transform (WT) were applied to AE signals indicating tribological effects occurred during the process. The results obtained from the two signal processing techniques were compared, good results with respect to advanced applications for fault detection as well as diagnostic purposes are obtained.
| Acoustics |
Acoustics Simulating the Sound Propagation of Guided Waves Using the Elastodynamic Finite Integration Technique (EFIT) J. Prager 28, M. Rahman 6 BAM Federal Institute for Materials Research and Testing 1304, Berlin, Germany Ultrasonic Testing (UT), EFIT, guided waves
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The successful design of Structural Health Monitoring Systems requires efficient simulation tools. Especially for implementing ultrasonic monitoring methods the insight into sound propagation problems inside the structure is essential when using guided waves. Although the sound propagation of guided waves in plate like structures and pipes is well understood, for more complex geometries or anisotropic materials simulations are necessary to predict the received signal depending on the type of excitation. In this contribution an innovative approach is presented for the simulation of propagation of guided waves using Elastodynamic Finite Integration Technique (EFIT). Starting with simple plate like geometries the dispersive behavior is illustrated by analyzing the propagation of different modes. Furthermore, selective excitation is introduced into the model and mode-flaw interactions are studied on different flaw types. The investigation is extended by modeling the wave propagation in structures with more complex geometries. The validity of the simulation results is verified by comparing with experimental data.
| Acoustics |
Acoustics Investigation of AE Generation from Fatigue Cracks for Structural Health Monitoring in 2014 Aluminium Alloy D. Gagar1 5, P. Foote2 6, J. McFeat3, P. Irving1 3 1Centre for IVHM; Cranfield University 35, Cranfield, United Kingdom 2BAE Systems 7, Bristol, United Kingdom 3Bae Systems Warton 5, Preston, Germany Acoustic Emission (AE), Fatigue Crack, 2014 T6 Aluminium
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Acoustic Emission (AE) generation in 2014 aluminium sheets is investigated in this study. Fatigue tests were conducted with samples under constant amplitude loading, monitoring the rates of AE signals generated during fatigue crack propagation. The load output from the test machine was correlated with recorded AE signals as a means for AE source characterisation. The results showed 3 stages in AE generation with the vast majority of AE signals recorded occurring around or below the mean cyclic load from the emergence of crack to the period just before sample failure where they appeared across the entire loading range.
| Acoustics |
Acoustics Low Power SHM via Frequency-Steerable Acoustic Transducers and Compressive Sensing L. De Marchi1 13, E. Baravelli2, M. Ruzzene2 2, N. Speciale1 2, N. Testoni1 6 1DEIS; University of Bologna 52, Bologna, Italy 2Georgia Institute of Technology (Georgia Tech) 21, Atlanta, GA, USA
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The weight penalty and maintenance concerns associated with wiring a large number of transducers have to be addressed for widespread field deployment of Structural Health Monitoring (SHM) systems. Wireless sensors can simplify such deployment. However, a major limitation of wireless ultrasound sensing technology is the incompatibility between the high frequency of the ultrasound signals and the limited data throughput of existing wireless transponders. In this work, a novel transduction concept based on shaped sensors is combined with an innovative acquisition scheme to fulfill two main objectives: 1) to reduce the number of sensing elements; 2) to lower the data throughput with compressive acquisitions.
| Acoustics |
Damage Guidelines for Using the Finite Element Method for Modeling of Guided Lamb Wave Propagation in SHM Processes M. Gresil 12, V. Giurgiutiu 6, Y. Shen, B. Poddar University of South Carolina 13, Columbia, SC, USA Ultrasonic Testing (UT), finite element modelling, Lamb Waves, Piezoelectric wafer active sensors
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The aim of the work presented in this paper is to provide guidelines for extending the modeling capacities and improve quality and reliability of 2-D guided wave propagation models using commercially available finite element method (FEM) packages. Predictive simulation of ultrasonic nondestructive evaluation (NDE) and structural health monitoring (SHM) in realistic structures is challenging. Analytical methods can perform efficiently modeling of wave propagation are limited to simple geometries. Realistic structures with complicated geometries are usually modeled with the finite element method (FEM). Commercial FEM codes offer convenient built-in resources for automated meshing, frequency analysis, as well as time integration of dynamic events. We propose to develop FEM guidelines for 2-D Lamb wave propagation with a high level of accuracy. The proposed 2-D guided wave problem will be the pitch-catch arrangement in a full 3-D geometry plate involving guided waves between a transmitter piezoelectric wafer active sensor (PWAS) and receiver PWAS. In addition, corrosion damage is added to this problem to simulate the detection of damage, and assess the detectability threshold. The general approach is to run a series of FEM models. These FEM models will be compared with the experimental data and with our 1-D analytical homemade software.
| Damage |
Damage On Quantitative Evaluation of Fatigue Cracks: An Active Way Using Nonlinear Acousto-Ultrasonic Waves C. Zhou, M. Hong 3, L. Cheng 6, Z. Su 19, Q. Wang 2 Department of Mechanical Engineering; Hong Kong Polytechnic University 32, Kowloon, Hong Kong, China Ultrasonic Testing (UT), fatigue damage, Nonlinearity, Acousto-Ultrasonics, Active Sensor network
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The majority of today’s damage detection techniques rely on linear macroscopic changes in global vibration signatures or local wave scattering phenomena. However, damage in real-world structures often initiates from fatigue cracks at microscopic levels, presenting highly nonlinear characteristics which may not be well evidenced in linear macroscopic changes. By exploring the nonlinearities of higher-order acoustoultrasonic (AU) waves, an active approach for characterizing fatigue cracks was established. Nonlinearities of higher-order AU waves, subjected to the existence and accumulation of fatigue cracks, were explored. Fundamental investigation was carried out to link the nonlinearities of AU waves to the relative distance between a sensing path and the fatigue crack. Results from simulation and experiment match well in between, which can be used to quantitatively evaluate fatigue cracks. Compared with existing detection approaches based on nonlinear AU waves, this method embodies uniqueness including utilization of a permanently attached active sensor network comprising miniaturized sensors, well accommodating the purpose of structural health monitoring.
| Damage |
Damage Critical Parameters of Impact Damage Detection in Composite Plates Using an Active Nonlinear Acousto-Ultrasonic Piezoceramic Sensor D. Saravanos 8, N. Chrysochoidis University of Patras 45, Patras, Greece
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This paper investigates the potential of an active nonlinear ultrasonics SHM methodology to reveal impact damage created in Glass/ Epoxy composite plates under cantilever support conditions. For the experimental procedure electromechanical shaker and piezoelectric devices are simultaneously used to provide the low and high frequency excitation signals respectively, while for the acquisition of the mixed signal a piezoelectric wafer is used. Nonlinearities induced at the high-frequency signal, such as sidebands at the spectral components, as well as, the modulation factor of the sensory voltage are evaluated as damage indicators. Experimental results quantify the potential of the method in detecting impact created under very low energy level impact loading. The obtained results finally show that the active nonlinear wave modulation SHM method can work in the case of realistic (clamped) supports.
| Damage |
Damage Application of the Beam-Forming Technique for Damage Detection in Plate Like Structures F. Ricci1 8, L. Lecce1 3, E. Monaco1 4, S. Tancredi1, D. Caporrino1, A. Mal2 4 1Department of Aerospace Engineering; University of Naples Federico II 38, Naples, Italy 2Mechanical and Aerospace Engineering ; University of California 17, Berkeley, CA, USA Ultrasonic Testing (UT), Phased array, crack detection, structural health monitoring
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Guided waves can travel over a long distance, they are highly sensitive to any discontinuity they might encounter along their propagation path, and they can be generated and sensed by piezo electric transducers easily bonded to the external surface of the structure under investigation. When guided waves are generated and sensed by an array of phased sensors, it’s possible to steer the wave-front in a specific direction (beamforming technique, widely used in electromagnetic radar applications). The improvements respect to the omnidirectional reception/transmission is known as receive and transmit gain, respectively. In this work a linear array of sensors is used to generate an ultrasonic wavefront steered in a specific direction, like structural radar. This effect is achieved by the combination of constructive and destructive interference of signals generated by the linear array of sensors, sequentially fired with appropriate time shifts. Numerical simulations are carried out with the LS-DYNA, an explicit Finite Element (FE) code, on an aluminum panel 6061-T6 (0.7m × 0.8m × 1mm). The damage to be identified is a 5mm diameter hole with 20mm edge cracks, located at a distance of 250 mm away from the center of the array along a direction at 60°. The array of sensors consists of 9 disk-shaped piezo patches (10mm in diameter and 0.2 mm in thickness) with a pitch of 12mm. A five-cycles sine signal with 225 kHz center frequency and in a Hanning window is used as the ex.....
| Damage |
Damage Application of Air-Coupled Ultrasonic Transducers for Damage Assessment of Composite Panels L. Ambrozinski1 8, T. Stepinski1 27 , T. Uhl1 28, B. Piwakowski2 20 1AGH- University of Science and Technology 63, Krakow, Poland 2University of Lille 27, Villeneuve d'Ascq, France
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In this paper we demonstrate how Lamb waves, excited and received by aircoupled transducers, can be used for damage assessment of composite structures. The test setup used in our experiments consisted of a pair of air-coupled transducers that operated in pitch-catch mode in the frequency band 100 to 500 kHz. The transducers were used to scan the inspected surface with the aid of a precise mechanical scanner. Incident angle of the transducers could be set to evoke and receive the desired mode of Lamb waves in the inspected panel. Results of scanning of the inspected panel using different Lamb wave modes are presented in the paper. The experimental setup was very versatile and enabled observation of various wave phenomena, e.g. reflection and mode conversion, occurring at the damage interface. The results presented in the paper illustrate the ways how the phenomena observed during the experiments can be used for damage detection.
| Damage |
Damage Assessment of Mode Shape-Based Damage Detection Methods under Real Operational Conditions T. Siebel 2, A. Friedmann 2, D. Mayer 2, M. Koch 2 Fraunhofer Institute for Structural Durability and System Reliability LBF 8, Darmstadt, Germany structural health monitoring, wind excitated vibration, operational modal analysis, modal strain energy, gapped smoothing technique
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The application of vibration-based damage detection methods to a wind turbine model is analyzed in this paper. The target is to develop a system that detects and locates damage on a structure subjected to wind excitation. With the proposed procedure vibration data is first processed by an Operational Modal Analysis. The extracted mode shapes are subsequently evaluated by two damage detection algorithms: the Modal Strain Energy method and the Gapped Smoothing Technique. Different types of damage are investigated, including tower damage and a change of foundation stiffness. First, a numerical prestudy is conducted to give information about suitable measurement quantities and density of measurement positions on the structure. Based on the numerical results an experimental setup is arranged, including the equipment of the tower with strain gauges and accelerometers. The results of the experimental work show that locating damage with the proposed approach is feasible.
| Damage |
Damage Nonlinear Ultrasound to Monitor Radiation Damage in Structural Steel K. Matlack1 2, J. Wall2 7, L. Jacobs1 2, J. Kim1 3, H. Viehrig3 2, J. Qu4 1aGeorge W. Woodruff School of Mechanical Engineering bSchool of Civil and Environmental Engineering; Georgia Institute of Technology (Georgia Tech) 21, Atlanta, GA, USA 2Electric Power Research Institute (EPRI) 94, Charlotte, NC, USA 3Department of Structural Material, Institute of Ion-Beam Physics and Materials Research; Helmholtz-Zentrum Dresden-Rossendorf 3, Dresden, Germany 4Department of Civil and Environmental Engineering; Northwestern University 19, Evanston, IL, USA Other Methods, Reactor pressure vessel materials, early damage detection, Nonlinear Ultrasound, Radiation Damage, Neutron Damage
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This work presents how the nonlinear ultrasonic technique of second harmonic generation can be used to monitor damage typical of nuclear reactor structural steel material. Second harmonic generation occurs when an ultrasonic wave interacts with microstructural features that create a nonlinear medium for the propagating ultrasonic wave. This phenomenon is measured by the acoustic nonlinearity parameter. Radiation damage causes microstructural evolution such as changes in dislocation density and the formation of precipitates, both of which have been shown to give rise to changes in the acoustic nonlinearity parameter. Previous work has shown that nonlinear ultrasonic techniques are sensitive to radiation damage, specifically that increases of radiation dose are detectable by changes in the acoustic nonlinearity parameter. For these measurements to be robust, alignment, clamping, and mounting of ultrasonic transducers to a sample must be simple, accurate, and repeatable. Nonlinear ultrasonic measurements were run on two types of nuclear reactor steel samples that were previously irradiated in the Rheinsberg power reactor to two fluence levels, up to 1020 n/cm2 (E > 1MeV), through a previous study by the IAEA. More extensive experiments were run on unirradiated standard Charpy samples to test repeatability of the measurements using the fixture and to isolate measurement variations such as surface roughness and clamping force effects.
| Damage |
Damage Design of Optimal Layout of Active Sensing Diagnostic Network for Achieving Highest Damage Detection Capability in Structures V. Janapati 2, K. Lonkar , F. Chang 5 Stanford University 12, Palo Alto, CA, USA Other Methods, structural health monitoring (SHM), spectral element method, Guided Ultrasonic Waves, Genetic Algorithm (GA), sensor network optimization
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An investigation is performed to develop a methodology for optimizing the layout of piezoelectric transducers based actuator-sensor network that will maximize the detection capability of a given SHM system for a hot spot in aerospace structures. The method utilizes a simulation tool for wave propagation as a basis to integrate preselected diagnostic algorithm with an optimization tool to maximize the probability of detection (POD) for a given damage size in a structure. The proposed method minimizes the number of actuators and sensors while maximizing POD through the selection of optimal location for each sensor and actuator. Fatigue cracks in metallic structures were studied in this investigation. This paper will highlight the method as well as some results for metallic structures.
| Damage |
Design and Analysis Laser-Vibrometric Measurement and Numerical Modeling of Local and Continuous Mode Conversion of Lamb Waves in CFRP Plates C. Willberg1 5, J. Pohl2 18, U. Gabbert1 8, G. Mook1 60 1aInstitute for Mechanics bInstitut für Werkstofftechnik und -prüfung; University of Magdeburg (OVGU) 87, Magdeburg, Germany 2Fachbereich EMW; Hochschule Anhalt 11, Köthen, Germany
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Lamb waves based methods of structural health monitoring (SHM) of CFRP structures take advantage of mode conversions and wave reflections at distinguished discontinuities, which simply can be measured with piezoelectric sensors. This well known behaviour can be used to identify structural failures, such as cracks, delaminations and other structural discontinuities. In addition to this source of mode conversion, recently we have found another type of mode conversion from S0 to A0 occurring continuously in certain CFRP laminates including twill fabric layers. This phenomenon was visualized by scanning laser vibrometry and partially clarified with help of finite element analysis. The paper describes the experimental setup and the wave mode interpretation using mode selection methods. B- and C-scans of the propagating waves clearly show the continuous conversion from the S0 to the A0 mode. This unexpected behaviour has also been found in finite element simulations taking into account the micro-structure of the composite.
| Design and Analysis |
Design and Analysis Analysis Methods of Lamb Wave Propagation in Complex Composites A. Szewieczek 20, C. Heinze 4, W. Hillger 72 , D. Schmidt 6, M. Sinapius 8 Institute of Composite Structures and Adaptive Systems (FA); Deutsches Zentrum für Luft- und Raumfahrt (DLR), German Aerospace Center 35, Braunschweig, Germany
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Structural Health Monitoring with Lamb Waves in principle allows a detection of defects in complex composite components by mounted PZT sensors. However, the wave behavior is very complex due to dispersive and anisotropic propagation respectively reflections, refractions and mode conversions on local discontinuities like defects. A clear evaluation of received signals poses a hard challenge. FEM simulations and the visualization of wave propagation under real conditions enable a better understanding of wave behavior. Therefore an ultrasonic scanning technique was adapted for Lamb Wave analysis and visualization. The combination of ultrasonic NDT and Guided Waves testing is carried out by Lamb Wave excitation with a glued PZT transducer and automated air-coupled ultrasonic scanning of the component surface. The technique delivers A-scans of each scanning point which are stored in a special 3D data file. Such a 3D file of a 1x1 m large laminate with a scanning grid of 1x1 mm includes A-scans of 10e6 measuring points with a dynamic range up to 80 dB (file size up to 50 GB). “Classic” images like B-, C-, and D-scans as well as video animations of the wave propagation can be calculated. Additional algorithms allow different methods of wave analysis, like automatic mode identification and separation, analysis of velocity and attenuation in anisotropic components or referencing of interactions with different kinds of defects. A consideration of mechanical properties of .....
| Design and Analysis |
Design and Analysis Frequency-Wavenumber Processing of Laser-Excited Guided Waves for Imaging Structural Features and Defects E. Flynn1 4, J. Lee2 14, G. Jarmer1 , G. Park1 10 1Los Alamos National Laboratory 11, Los Alamos, New Mexico, USA 2Department of Aerospace Engineering; Chonbuk National University (CBNU) 18, Jeonju, South Korea Ultrasonic Testing (UT), Other Methods, laser ultrasound, laser scanning, Frequency-Wavenumber Analysis
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Recent research efforts have demonstrated the ability to remotely and nondestructively excite broadband, multi-mode guided waves in structures through thermoelasticity using a relatively low-powered Q-switched laser. The excited waves can be sensed either locally using one or more transducers or remotely using a laser Doppler vibrometer. Incorporating high-speed mirrors, such a system has been used to effectively and rapidly scan large areas with surface normals as high as 45 degrees at a spatial resolution as small as 0.5 millimeters. The time and space sampling capability of the laser-excited guided wave system enables the processing of measured signals in the full, three-dimensional Fourier domain: horizontal and vertical in-plane wavenumber and frequency. Operating in the frequency-wavenumber domain, we describe and demonstrate an approach to identify, extract the dispersion curves of, and selectively isolate individual guided wave modes. With the ability to separate individual wave modes, the direction-, frequency-, and mode-dependent wave propagation and scattering behavior can be measured and utilized for imaging defects. We introduce two imaging algorithms for utilizing mode-separate measurements. The first, which we show to be effective for area-spanning defects, makes direct estimates of the mode- and frequency-dependent wavelength at each imaging point in the structure. The second, which is more effective for identifying small defects, images the energy o.....
| Design and Analysis |
Design and Analysis Evaluation of an Intrinsic Error Estimator for the Data Fusion of NDT Techniques Used to Identify the Material and Damage Properties of Concrete Structures D. Martini 2, V. Garnier 27, M. Ploix 12 Laboratoire de Caractérisation Non Destructive, LCND; Université de la Méditerranée 43, Aix en Provence, France NDT-wide, Other Methods, concrete, data fusion
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In this paper, we propose an intrinsic error estimator for the data fusion of NDT techniques used to identify the material and damage properties of concrete structures. This error estimator is chosen based on the global distribution of the data fusion in the space of the identified material properties. The main idea is to evaluate the accuracy of the result in estimating the gap between the most and the worst likely solutions. This error estimator is applied to synthetic data depending on the parameters of the data fusion such as the regression laws that linked the material properties to the NDT measurements. This work is part of the C2D2-ACDC project that aims at methodology transfer from five research laboratories, LMA, LMDC, IFFSTAR, GhyMaC and IEMN to industrial partners, EDF and SETRA
| Design and Analysis |
Design Principles Analytical and Experimental Investigation of Environmental Influences on Lamb Wave Propagation and Damping Measured with a Piezo-Based System K. Schubert 3, A. Stieglitz , M. Christ , A. Herrmann 5 Faserinstitut Bremen (FIBRE) 5, Bremen, Germany Ultrasonic Testing (UT), Other Methods, Structural Health Monitoring, Lamb Waves
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One of the main concerns in structural health monitoring (SHM) for composite materials is to discern between changes that are related to actual damage in the structure and changes that originate from non-damaging alterations of the material or the survey system. For both the layout of a piezo-based system (i.e. mainly the sensor/actuator area density) and the interpretation of the acquired data, the changes of the viscoelastic material properties due to normal environmental factors as temperature or moisture absorption have to be considered. Additionally, the SHM system itself and the coupling adhesive used to connect it to the material can be influenced by this factors. Without a strategy to account for those influences, a high false alarm rate has to be expected. In this presentation, experimental and analytical investigations of a SHM system based on Lamb waves measured with surface applied piezoelectric sensors are presented. The influence of temperature and humidity on the measured velocity and damping coefficients is shown as well as the high influence of both factors on the excitability of Lamb waves. Potential and limitations of analytical methods to describe the measurement system and the temperature/humidity-dependence of the piezoelectric elements properties, the adhesive layer and the material itself are investigated.
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