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 Journal of Nondestructive Evaluation   [SJR: 0.863]   [H-I: 27]   [9 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1573-4862 - ISSN (Online) 0195-9298    Published by Springer-Verlag  [2349 journals]
• Eddy Current Thermography with Adaptive Carrier Algorithm for
Non-destructive Testing of Debonding Defects in Thermal Barrier Coatings
• Authors: Wenying Zhu; Zhanwei Liu; Dacheng Jiao; Huimin Xie
Abstract: Interfacial defects can cause the premature failure of thermal barrier coatings (TBCs). An Eddy current thermography (ECT) method under the transmission mode in the heating phase is developed in this study to detect the artificial debonding defects in TBCs samples. When ECT is used, the temperature distribution of specimen surface is uneven on account of geometric heating effect, skin effect, edge effect and abnormal emissivity. Among them, the influence of the surface emissivity is the smallest, because the background noise is subtracted before the thermal images are processed. The uneven temperature distribution shields the weak thermal response characteristics of the defects and interferes with the identification of the defects. Adaptive carrier algorithms are established as post-processing algorithms to resolve this problem. The feasibility and validity of the developed methods are verified by simulation and validation tests using TBCs samples with a 2 mm artificial debonding defect and a 0.5 mm blind-hole defect.
PubDate: 2018-04-09
DOI: 10.1007/s10921-018-0483-3
Issue No: Vol. 37, No. 2 (2018)

• Laser Multi-mode Scanning Thermography Method for Fast Inspection of
Micro-cracks in TBCs Surface
• Authors: Dacheng Jiao; Wenxiong Shi; Zhanwei Liu; Huimin Xie
Abstract: Conventional non-destructive testing methods are difficult to be applied in defect detection of thermal barrier coating (TBCs) because of some of its characteristics, such as porosity and thin thickness, etc. For detecting surface cracks in TBCs, a laser multi-modes scanning thermography (SMLT) method has been developed in this paper, combining fast scan mode using linear laser with fine scan mode using point laser on the tested specimen surface. Linear scanning has a large detection range and detection speed, and point scanning has a higher sensitivity. Through the theoretical analysis, numerical simulation and experimental verification, five unique thermal response features of the cracks stimulated by two scanning modes were discovered and summarized. These features in the thermal images include temperature sharply rising in local region, distinct increase of the area of high temperature zone, obvious ‘tailing’, ‘dislocation’ and thermal obstruction phenomenon, respectively. Therefore, with the corresponding post-processing algorithm developed here, the location and shape of surface cracks in TBCs can be efficiently detected by analyzing the information of these thermal response features. Validation tests showed that the surface cracks with the width of more than $$20\,\upmu \hbox {m}$$ can be quickly detected in line-scan stage, while in point-scan stage, the $$9.5\,\upmu \hbox {m}$$ wide surface cracks can be accurately detected.
PubDate: 2018-04-06
DOI: 10.1007/s10921-018-0485-1
Issue No: Vol. 37, No. 2 (2018)

• Infrared Thermographic Testing of Steel Structures by Using the Phenomenon
of Heat Release Caused by Deformation
• Authors: E. A. Moyseychik; V. P. Vavilov; M. V. Kuimova
Abstract: Deformation of steel parts is accompanied by either heating or cooling of particular zones depending on deformation mechanism. The use of infrared thermographic equipment allows analyzing spatial/temporal temperature distributions on the surface of steel parts thus allowing the evaluation of heat release caused by deformation in bulk material. Determination of stressed state in critical parts by analyzing infrared thermograms can be most simply conducted for components subjected to uniaxial tension–compression. The paper describes some potentials and problems of nondestructive testing of steel parts and constructions based on the analysis of heat release caused by deformation. By analyzing this methodology, it is possible to better evaluate the life expectancy of critical parts in steel structures (components of offshore oil platforms, seismic-resistant buildings, frames of large mining trucks, etc.).
PubDate: 2018-04-03
DOI: 10.1007/s10921-018-0482-4
Issue No: Vol. 37, No. 2 (2018)

• Multi-Helical Path Exploitation in Sparsity-Based Guided-Wave Imaging of
Defects in Pipes
• Authors: A. Golato; F. Ahmad; S. Santhanam; M. G. Amin
Abstract: In this paper, a defect localization scheme for cylindrical pipes is presented which relies on guided-wave scattering by defects. The proposed scheme is predicated on the use of a sparse array of ultrasonic transducers and the sparse nature of defects on the pipe surface. Two circular rings of transducers, functioning as transmitters and receivers, are used to encompass the region to be inspected. Multiple helical paths exist for waves to travel from the transmitters to the receivers, after being scattered by the defects. Model based dictionary matrices are constructed for each path, relating the signals arriving at the receivers to the locations of potential defects. The resulting linear signal model is inverted by group sparse reconstruction to localize defects present in the pipe. Experimental validations of the proposed multi-helical path exploitation approach are provided for defects on an aluminum pipe.
PubDate: 2018-03-29
DOI: 10.1007/s10921-018-0481-5
Issue No: Vol. 37, No. 2 (2018)

• Non-destructive Flaw Mapping of Steel Surfaces by the Continuous Magnetic
Barkhausen Noise Method: Detection of Plastic Deformation
• Authors: Freddy Armando Franco Grijalba; Linilson Rodrigues Padovese
Abstract: This paper reports the use of a non-destructive scanning technique to identify plastic deformation defects generated in steel. The technique is based on measurement of continuous magnetic Barkhausen noise (CMBN). In the experiments described here, surfaces with plastic deformations produced by crushing stresses in a 1070 steel are scanned, and the influence of probe configuration, coil type, scanner speed, applied magnetic field and the frequency band used for the analysis on the effectiveness of the technique is studied. A moving smoothing window based on a second order statistical moment is used to analyze the time signal. The results show that the method can detect the position of plastic deformation defects and distinguish between their amplitudes.
PubDate: 2018-03-19
DOI: 10.1007/s10921-018-0480-6
Issue No: Vol. 37, No. 2 (2018)

• More than Fifty Shades of Grey: Quantitative Characterization of Defects
and Interpretation Using SNR and CNR
• Authors: R. Usamentiaga; C. Ibarra-Castanedo; X. Maldague
Abstract: The quantitative characterization of defects in images is commonly performed using the signal-to-noise ratio (SNR). However, there is a strong debate about this measure. First, because there is no single accepted definition of SNR. Second, because the SNR measurements are highly affected by the regions used to estimate the power of the signal and noise in the image. This work provides an overview of some of the most commonly used SNR measures. Images with different sources of noise, and defects with different contrasts, are used to evaluate and compare the ability of these measures to quantitatively characterize defects. The measures are also evaluated when the images are transformed using common image processing operations, including filtering and gamma correction. This work also proposes a methodology to define the regions used to estimate the power of the signal and noise in the images. Two alternative procedures are proposed weather prior information is available about the inspected specimen or not. The proposed methodology is applied on real data from infrared testing, where the considered SNR measures are evaluated.
PubDate: 2018-03-19
DOI: 10.1007/s10921-018-0479-z
Issue No: Vol. 37, No. 2 (2018)

• A Novel Nonlinear Acoustic Health Monitoring Approach for Detecting Loose
Bolts
• Authors: Amin Baghalian; Volkan Y. Senyurek; Shervin Tashakori; Dwayne McDaniel; Ibrahim N. Tansel
Abstract: To date, sensors have been the inevitable component of structural health monitoring (SHM) systems. Typically, sensory signals are digitized, processed by computers, and then the information is presented to the operator with plots or warnings depending on the sophistication of the system. This study proposes a novel nonlinear acoustic health monitoring (NAHM) approach for detection of loose bolts, which can work with and without any sensors. The structure is excited with bitonal excitations, which their difference is in the audible range. When the bolts are well tightened, the structure remains silent. But, the structure creates audible sound or verbal warnings in the presence of one or more loose bolts. There is no need for sensor(s), A/D converters or computers between the operator and the structure. However, it is also possible to attach a piezoelectric sensor or to use a microphone/sound level meter for further analysis of the structure’s response. The feasibility of the concept was demonstrated by detecting the loose bolt in a bolted plate system. For demonstrating the industrial potential of the proposed NAHM system, the concept was implemented for two simple washers held with nuts and bolts. Additionally, the intensities of the audible alarms were studied at different torque levels. The proposed NAHM may be used as a low-cost sensor-free SHM or as a backup for conventional nonlinear SHM systems.
PubDate: 2018-03-14
DOI: 10.1007/s10921-018-0478-0
Issue No: Vol. 37, No. 2 (2018)

• Hybrid Ultrasonic TOFD Imaging of Weld Flaws Using Wavelet Transforms and
Image Registration
• Authors: Jia-xu Duan; Lin Luo; Xiao-rong Gao; Jian-ping Peng; Jin-long Li
Abstract: Ultrasonic time of flight diffraction (TOFD) is an effective weld crack inspection technique. Due to the intensity of diffraction wave is rather weak compared with the lateral wave and the bottom echo wave, thus the signal-to-ratio (SNR) of TOFD image is low. A new dichotomous method is comprised of two steps that contains wavelet shrinkage and image registration is proposed in this paper to reduce the noise and improve the resolution of TOFD images as well. In order to evaluate the reliability of our proposed method in this paper, we have established the experiment system, and sampled a number of TOFD data with random distribution of noise characteristics. We adopted one-dimension wavelet transform and two-dimension wavelet transform in the very beginning of the first step of the proposed algorithm respectively. The SNR of the result obtained in this step is improved significantly compared with the classic algorithms. Next, the image registration is applied. After the registered images have been added to form a new one, then it comes to the final result that shows not only the SNR but also the definition of the image is enhanced effectively.
PubDate: 2018-03-01
DOI: 10.1007/s10921-018-0476-2
Issue No: Vol. 37, No. 2 (2018)

• A Novel RFID-Based Strain Sensor for Wireless Structural Health Monitoring
• Authors: Matheus F. Kuhn; Guilherme P. Breier; Allan R. P. Dias; Thomas G. R. Clarke
Abstract: Conventional tools for deformation measurement are widely used for structural health monitoring—i.e. strain gauges and fiber optic sensors—due to their relative low cost and efficiency. However, these techniques still present some drawbacks particularly in limited access locations, since their usage requires some sort of cabling or battery-driven electronics. Thus, in a few situations there may be room for new technologies for deformation monitoring of structures. One of the options are passive radio frequency identification (RFID)-based sensors. In synthesis, like conventional methods, these sensors are attached to the surface a test-piece, but are then remotely interrogated and powered by a transmitter. The solidarity of the sensor to the underlying material means that the detected signal is modified in a way that can be correlated to sample strain in a given direction. This paper encompasses the project of a wireless deformation sensor based on an inverted-F antenna focusing on its miniaturization and performance optimization. For this purpose, such an antenna was designed with the help of finite element modelling tools for operation on a 2.0 mm-thick aluminium sheet, and then experimentally validated through static loading tests. Finally, even though sensors of this kind are still in early developments, results show that RFID sensors represents a promising method for remote deformation assessment in components.
PubDate: 2018-02-26
DOI: 10.1007/s10921-018-0475-3
Issue No: Vol. 37, No. 2 (2018)

• Mapping of Deformation-Induced Magnetic Fields in Carbon Steels Using a
GMR Sensor Based Metal Magnetic Memory Technique
• Authors: W. Sharatchandra Singh; R. Stegemann; M. Kreutzbruck; C. K. Mukhopadhyay; B. Purnachandra Rao
Abstract: Giant magneto-resistive (GMR) sensor based metal magnetic memory (MMM) technique is proposed for mapping of deformation-induced self-magnetic leakage fields (SMLFs) in carbon steel. The specimens were subjected to different amounts of tensile deformation and the deformation-induced SMLFs were measured using a GMR sensor after unloading the specimens. 3D-nonlinear finite element modeling was performed to predict stress–strain state in a steel specimen under tensile load. The experimentally obtained SMLF images were correlated with the finite element model predicted stress–strain states. Studies reveal that the MMM technique can detect the plastic deformation with signal-to-noise ratio better than 20 dB. The technique enables the mapping of plastic deformation in carbon steels for the evaluation of the severity of deformation. The study also reveals that deformation-induced SMLF is influenced by the presence of initial surface residual stress, introduced by shot peening. The intensity of SMLF signal is found to increase with increase in tensile load and decrease with shot peening.
PubDate: 2018-02-21
DOI: 10.1007/s10921-018-0470-8
Issue No: Vol. 37, No. 2 (2018)

• Influence of Composite Ply Layup on Active Thermographic Non-destructive
Inspection of Carbon Fiber-Reinforced Plastic Laminates
• Authors: Masashi Ishikawa; Masashi Koyama
Abstract: This paper examines the effect of the composite ply layup on defect detection using non-destructive active thermographic inspection of carbon fiber-reinforced plastic (CFRP) laminates. Numerical calculations using simplified models were performed and verified experimentally. The results indicated that the local temperature contrast ( $$\Delta T$$ ) observed on the surface of the laminates, generally caused by existing internal defects, depended on two characteristics of the laminates: the difference between the orientation angles of neighboring layers $$(\theta _{\mathrm{d}})$$ and the number of different orientation angles in the layers $$(N_{\mathrm{a}})$$ . The $$\Delta T$$ was higher when $$\theta _{\mathrm{d}}$$ and $$N_{\mathrm{a}}$$ were small. These effects were more clearly observed when inspecting CFRPs reinforced with carbon fibers with higher thermal conductivity (such as pitch-based fibers), and when the number of layers is larger.
PubDate: 2018-02-20
DOI: 10.1007/s10921-018-0472-6
Issue No: Vol. 37, No. 2 (2018)

• Probability of Detection (PoD) Curves Based on Weibull Statistics
• Authors: Mohamed Subair Syed Akbar Ali; Prabhu Rajagopal
Abstract: Probability of detection (PoD) curves are a popular metric for the reliability assessment of Nondestructive Testing (NDT) procedures. However, the classical Berens method for signal response PoD analysis strongly relies on the hypothesis of Gaussian residuals which can be violated in practical conditions. In particular, data from sparse field trials can be scattered and or skewed. Hence, this paper studies the feasibility of assuming a Weibull distribution, which is known for versatility in representing several fundamental statistical states, for regression residuals without modifying the overall Berens framework for PoD curve determination. The proposed ‘Weibull-Berens’ PoD statistics is first shown to compare well with the classical Berens method for an ideal case of Gaussian residuals. The advantages of the method are further demonstrated using a synthesised dataset, as well as a practical case of non-Gaussian residuals arising from reduced number of experimental trials.
PubDate: 2018-02-20
DOI: 10.1007/s10921-018-0468-2
Issue No: Vol. 37, No. 2 (2018)

• An Effective Method to Inspect Adhesive Quality of Wind Turbine Blades
Using Transmission Thermography
• Authors: Xiao-li Li; Jiangang Sun; Ning Tao; Lichun Feng; Jing-ling Shen; Yi He; Cunlin Zhang; Yue-jin Zhao
Abstract: The wind turbine blade is one of the most important parts in a wind turbine system. The blade consists of a massive outer shell that is supported by an internal shear web with a thick layer of adhesive between them. Therefore the adhesive quality is a critical factor to guarantee it works properly for a designed service life of up to two decades. At present, it has been very challenging to evaluate the quality of this adhesive layer. In this study, a step-heating transmission thermography method was developed to measure the thickness variation of a blade shell, which was used for a quantitative evaluation of the adhesive quality. This method was verified first in a laboratory using three simulated blade specimens with wall thicknesses ranging from 13 to 31 mm. It was then used to inspect a 45.3 m wind blade. Based on the measured thickness distributions, an automated searching algorithm was developed to locate the adhesive edges which in turn determined the adhesive width and the adhesive-deficient area. The results obtained in this research demonstrated that the transmission thermography thickness measurement method is an effective way to evaluate the adhesive quality for wind turbine blades.
PubDate: 2018-02-20
DOI: 10.1007/s10921-018-0473-5
Issue No: Vol. 37, No. 2 (2018)

• An Experimentally Accessible Probability of Detection Model for Acoustic
Emission Measurements
• Authors: Markus G. R. Sause; Florian F. Linscheid; Markus Wiehler
Abstract: In testing of structural components by the acoustic emission method, the requirement arises for quantitative prediction of the probability of detection (PoD) of an acoustic emission signal. Motivated similar as for other nondestructive testing methods, the suitability of given experimental settings to reach a certain likelihood of not missing relevant signals should be predicted. In contrast to other nondestructive testing methods, two of the key factors are not only the equipment and the inspector, but also the variability of the acoustic emission sources and the attenuation effects. As the strength of crack-based acoustic emission sources cannot be changed arbitrarily in the experiment, their characteristic amplitude distribution is accounted for by generation of reference datasets in small laboratory scale specimens. This assumes datasets with 100% PoD for those signals at a particular propagation distance. The prediction of the resulting PoD at another distance in a structure is achieved by means of amplitude reduction based on the measured attenuation values. For the latter, approaches using constant attenuation factors and attenuation mapping approaches are evaluated and compared to an experimental assessment of the PoD values using artificial test sources. Based on the agreement of calculated and measured PoD values, the presented approach appears promising to predict PoD values in geometrically and acoustically complex structures.
PubDate: 2018-02-20
DOI: 10.1007/s10921-018-0474-4
Issue No: Vol. 37, No. 2 (2018)

• Acoustic Modal Testing of Bicycle Rims
• Authors: Matthew Ford; Patrick Peng; Oluwaseyi Balogun
Abstract: The stiffness, strength, and safety of a bicycle wheel depend critically on the stiffness of its rim. However, the complicated cross-sections of modern bicycle rims make estimation of the stiffness by geometric methods very difficult. We have measured the radial bending stiffness and lateral-torsional stiffness of bicycle rims by experimental modal analysis using a smartphone microphone. Our acoustic method is fast, cheap, and non-destructive, and estimates the radial bending stiffness, $$EI_{11}$$ , to within 8% and the torsional stiffness, GJ, to within 11% as compared with a direct mechanical test. The acoustic method also provides a direct measurement of the coupled lateral-torsional effective stiffness, which is necessary for calculating many useful properties of bicycle wheels such as stiffness, buckling tension, and the influence of spoke tensioning. For a complete bicycle wheel, the lateral stiffness can be determined by a superposition of equivalent springs for each mode in series, where each mode stiffness contains a rim stiffness and spoke stiffness combined in parallel. We give example calculations on two realistic bicycle wheels using our experimentally derived rim properties to show how stiff spokes can compensate for a flexible rim, while a very stiff rim doesn’t necessarily result in a stiff wheel.
PubDate: 2018-02-12
DOI: 10.1007/s10921-018-0471-7
Issue No: Vol. 37, No. 1 (2018)

• Alternating Current Electric Flux Leakage Testing for Defect Detection and
Characterization
• Authors: Yanhua Sun; Shiwei Liu; Zhijian Ye; Min Gu; Changde Liu; Yihua Kang; Lingsong He
Abstract: This paper analyzes the inspection characteristics of the alternating current electric flux leakage (AC-EFL) testing method. Three specimens with different conductivity are prepared, and a series of experiments is carried out to explore the advantages and disadvantages of the AC-EFL method. For metal materials that carry an alternating current (AC), defect detection can be realized using both AC-EFL and electric current perturbation (ECP). However, the signal noise ratio (SNR) from using the AC-EFL method is lower than that obtained using the ECP method according to the experimental results obtained from an aluminum plate. For both the Ni–Zn ferrite specimens with very low conductivity and the carbon fiber reinforced polymer (CFRP) specimens with low anisotropic conductivity, the ECP method failed to detect defects because of the weak disturbed magnetic field that was caused by the defects, whereas the AC-EFL method was able to realize the defect detection. These proof-of-concept experimental results indicate that compared to magnetic field testing method, the AC-EFL is more suitable for inspecting low-conductivity materials.
PubDate: 2018-02-09
DOI: 10.1007/s10921-018-0469-1
Issue No: Vol. 37, No. 1 (2018)

• Three Dimensional Characterization of Defects by Ultrasonic Time-of-Flight
Diffraction (ToFD) Technique
• Authors: Ali Habibpour-Ledari; Farhang Honarvar
Abstract: Ultrasonic time-of-flight diffraction (ToFD) technique has high accuracy in locating and sizing discontinuities. The primary reason for this accuracy is the use of time instead of amplitude for measurement of the depth and size of discontinuities. Despite the many advantages of ToFD, it suffers from a number of shortcomings, the most notable one being its two-dimensional character. The goal of this paper is to develop an algorithm, as a prerequisite, to extend ToFD measurements to a three-dimensional space. For this purpose, a combination of multiple transmitting and receiving probes is proposed instead of just one pair commonly used in ToFD measurements. The approach for locating and sizing defects in a 3D space follows the methods used in radar and acoustic positioning systems. Non-iterative techniques are used for positioning a single source (defect) based on signals collected by several transducers. The estimation formula, in the form of a closed-form solution, is derived by linear least-squares minimization. In addition to existing conventional passive algorithms, a new active algorithm is also proposed for the general arrangement of transducers. This algorithm is tested on a steel specimen having an artificially implanted discontinuity and the three-dimensional location of the defect is estimated.
PubDate: 2018-02-07
DOI: 10.1007/s10921-018-0465-5
Issue No: Vol. 37, No. 1 (2018)

• Microfocus Bremsstrahlung Source Based on a Narrow Internal Target of a
Betatron
• Authors: M. M. Rychkov; V. V. Kaplin; E. L. Malikov; V. A. Smolyanskii; V. Gentsel’man; I. K. Vas’kovskii
Abstract: The paper addresses the research into the properties of bremsstrahlung generated by interaction of the internal electron beam of the 18 MeV betatron with narrow targets, 50 and $$8 \,\upmu \hbox {m}$$ thick Si crystals and $$13 \,\upmu \hbox {m}$$ thick Ta foil with a length of 4 mm along the electron beam, mounted in the goniometer inside the betatron chamber. The radiation beams generated in the targets were used to obtain the images of a microstructure of thin wire pairs and an object that consisted of four steel bars with $$10\, \upmu \hbox {m}$$ gaps between them. The images indicate high absorption contrast of their components due to a small horizontal size of the radiation source the width of which in the cases of Si crystals and Ta foil was 30-, 187- and 115-fold smaller than the diameter of the electron beam, respectively. The edge phase-contrast was also observed due to high spatial coherency of the radiation with the linear microfocus generated in the source based on the B-18 betatron with a narrow target inside.
PubDate: 2018-02-05
DOI: 10.1007/s10921-018-0464-6
Issue No: Vol. 37, No. 1 (2018)

• Damage Evaluation in Woven Glass Reinforced Polyamide 6.6/6 Composites
Using Ultrasound Phase-Shift Analysis and X-ray Tomography
• Authors: Pascal Pomarède; Fodil Meraghni; Laurent Peltier; Stéphane Delalande; Nico F. Declercq
Abstract: The paper proposes a new experimental methodology, based on ultrasonic measurements, that aims at evaluating the anisotropic damage in woven semi-crystalline polymer composites through new damage indicators. Due to their microstructure, woven composite materials are characterized by an anisotropic evolution of damage induced by different damage mechanisms occurring at the micro or mesoscopic scales. In this work, these damage modes in polyamide 6.6/6-woven glass fiber reinforced composites have been investigated qualitatively and quantitatively by X-ray micro-computed tomography (mCT) analysis on composite samples cut according to two orientations with respect to the mold flow direction. Composite samples are initially damaged at different levels during preliminary interrupted tensile tests. Ultrasonic investigations using C-scan imaging have been carried out without yielding significant results. Consequently, an ultrasonic method for stiffness constants estimation based on the bulk and guided wave velocity measurements is applied. Two damage indicators are then proposed. The first consists in calculating the Frobenius norm of the obtained stiffness matrix. The second is computed using the phase shift between two ultrasonic signals respectively measured on the tested samples and an undamaged reference sample. Both X-ray mCT and ultrasonic investigations show a higher damage evolution with respect to the applied stress for the samples oriented at $$45^{\circ }$$ from the warp direction compared to the samples in the $$0^{\circ }$$ configuration. The evolution of the second ultrasonic damage indicator exhibits a good correlation with the void volume fraction evolution estimated by mCT as well as with the damage calculated using the measured elastic modulus reduction. The merit of this research is of importance for the automotive industry.
PubDate: 2018-02-05
DOI: 10.1007/s10921-018-0467-3
Issue No: Vol. 37, No. 1 (2018)

• The Capability Assessment of the Spectrum Decomposition Technique for
Measurements of the Group Velocity of Lamb Waves
• Abstract: The ultrasonic guided waves are dispersive waves characterized by the phase and group velocities dispersion curves. In order to use guided waves in various industrial applications, their parameters must be known. Since these guided wave velocities depend on the frequency and thickness of the material, they propagate differently comparing to bulk ultrasonic waves. Therefore, to analyze the parameters of such waves, new measurement techniques should be proposed and possibilities of their application have to be investigated. In this paper possibilities to measure the group velocity based on the spectrum decomposition approach are presented. The investigations are carried out using the simulated and experimental signals of Lamb wave propagating in a 2 mm thickness aluminium plate. The two fundamental modes $$\hbox {A}_{0}$$ and $$\hbox {S}_{0}$$ are selected. Using the proposed technique, segments of the group velocity dispersion curves have been reconstructed and compared with the dispersion curves calculated by the SAFE method to estimate errors. Accordingly to the obtained lower absolute and relative errors, an optimal set of narrowband filters with bandwidth from 20 kHz up to 100 kHz for the $$\hbox {A}_{0}$$ mode and from 80 kHz up to 160 kHz for the $$\hbox {S}_{0}$$ mode are proposed. Applying the proposed optimal frequency sets of narrowband filters for the experimental signals, segments of the group velocity dispersion curves for both modes are reconstructed. The average relative error for the $$\hbox {A}_{0}$$ mode is 1.7–2.2% (expanded relative uncertainty ± (2.2–2.8)%) and 0.78–1.2% (expanded relative uncertainty ± (0.5–0.8)%) for the $$\hbox {S}_{0}$$ mode.
PubDate: 2018-04-04
DOI: 10.1007/s10921-018-0484-2

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