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Showing papers in "Ndt & E International in 2005"


Journal ArticleDOI
TL;DR: This paper describes an alternative approach in which the full matrix of time domain signals from every transmitter–receiver pair is captured and post-processed and shown to offer significant performance advantages for NDE.
Abstract: Processing of ultrasonic array data is traditionally based on having parallel transmission circuits that enable staggered firing of transmitter elements to produce the desired wavefront. This paper describes an alternative approach in which the full matrix of time domain signals from every transmitter–receiver pair is captured and post-processed. Various post-processing approaches are modelled and assessed in terms of their ability to image a point-like reflector. Experimental results are then presented which show good quantitative agreement with the modelled results. An advanced processing algorithm is also implemented which allows the array to be focused at every point in the target region in both transmission and reception. This approach is shown to offer significant performance advantages for NDE.

747 citations


Journal ArticleDOI
TL;DR: In this paper, the results from dynamic live load tests using the non-contact laser Doppler vibrometer (LDV) system with those from two types of contact sensors are compared.
Abstract: This paper compares results from dynamic live load tests using the non-contact laser Doppler vibrometer (LDV) system with those from two types of contact sensors. Bridge girder deflections and vibrations are simultaneously measured using a linear variable differential transducer (LVDT)-cable system (deflection) and geophone sensors (velocity), both attached to the girders, and the LDV, equipped with displacement and velocity signal decoders. Live load tests are performed on a 3-span continuous unit of the 9-span Doremus Avenue Bridge Replacement Project using 5-axle trucks of known weight and configuration. The Doremus Avenue Bridge is a composite steel slab-on-girder construction. Bridge response is compared for two of the 10 girders. Overall, the LDV measurements of deflection and velocity compare very well with those recorded by the contact sensors and may be used as an alternative to the two systems. Other advantages and disadvantages are also highlighted.

397 citations


Journal ArticleDOI
TL;DR: In this paper, a new method for detecting localized bearing defects based on wavelet transform was proposed, which can be used for detecting single and multiple faults in ball bearing race faults.
Abstract: Due to the importance of rolling bearings as the most widely used machine elements, it is necessary to establish a suitable condition monitoring procedure to prevent malfunctions and breakages during operation. This paper presents a new method for detecting localized bearing defects based on wavelet transform. Bearing race faults have been detected by using discrete wavelet transform (DWT). Vibration signals from ball bearings having single and multiple point defects on inner race, outer race, ball fault and combination of these faults have been considered for analysis. Wavelet transform provides a variable resolution time–frequency distribution from which periodic structural ringing due to repetitive force impulses, generated upon the passing of each rolling element over the defect, are detected. It is found that the impulses appear periodically with a time period corresponding to characteristic defect frequencies. In this study, the diagnoses of ball bearing race faults have been investigated using wavelet transform. These results are compared with feature extraction data and results from spectrum analysis. It has been clearly shown that DWT can be used as an effective tool for detecting single and multiple faults in ball bearings. This paper also presents a new method of pattern recognition for bearing fault monitoring using hidden Markov Models (HMMs). Experimental results show that successful bearing fault detection rates as high as 99% can be achieved by this approach.

269 citations


Journal ArticleDOI
TL;DR: In this paper, the authors applied Kohonen's map as an unsupervised clustering method for the acoustic emission (AE) signals generated in cross-ply composite specimens during tensile tests.
Abstract: The acoustic emission (AE) technique is a useful way for the investigation of local damage in materials. This study deals with the ability of a Kohonen's map to classify recorded AE signals collected during tensile tests on cross-ply glass/epoxy composites in order to monitor the chronology of the damaging process. An unsupervised clustering analysis shows that AE signals are distributed into three clusters. The proposed two-stage procedure is a combination of the Self-Organising Map (SOM) and the k-means methods. In the present work, Kohonen's map is applied as an unsupervised clustering method for the AE signals generated in cross-ply composite specimens during tensile tests. The input vectors of the signal descriptors used in the clustering procedure are calculated from the signal waveforms. The k-means method is then applied on the neurones of the map in order to delimit the clusters and to visualise the topology of the map.

199 citations


Journal ArticleDOI
TL;DR: In this paper, a new feature, termed as the rising point, related to the propagation time of electromagnetic waves in metallic targets is proposed for defect classification, which can be detected and quantified robustly and lift-off can also be derived from the rising time.
Abstract: The objective of this study is to identify defects such as surface cracks, subsurface defects and metal losses using feature based pulsed eddy current sensors. A new feature, termed as the rising point, related to the propagation time of electromagnetic waves in metallic targets is proposed for defect classification. Experimental studies of the validation, robustness of the new feature of rising time are reported. In addition to other features, defects can be detected and quantified robustly and lift-off can also be derived from the rising time. Conclusion and further work are derived on the basis of the findings.

184 citations


Journal ArticleDOI
TL;DR: In this article, an approach using normalization and two reference signals to reduce the lift-off problem with pulsed eddy current NDT testing is proposed, which can be applied for measurement of metal thickness beneath nonconductive coatings, microstructure, strain/stress measurement, where the output is sensitive to the liftoff effect.
Abstract: The lift-off effect is commonly known to be one of the main obstacles for effective eddy current NDT testing as it can easily mask defect signals. Pulsed eddy current techniques, which are believed to be potentially rich of information, are also sensitive to the effect. An approach using normalisation and two reference signals to reduce the lift-off problem with pulsed eddy current techniques is proposed. Experimental testing on the proposed technique and results are presented in this report. Results show that significant reduction in the effect has been achieved mainly in metal loss and sub-surface slot inspection. The technique can also be applied for measurement of metal thickness beneath non-conductive coatings, microstructure, strain/stress measurement, where the output is sensitive to the lift-off effect.

163 citations


Journal ArticleDOI
TL;DR: In this article, the authors demonstrate the use of a commercial finite element package, ABAQUS EXPLICIT, to model ultrasonic guided waves in structural components for high-speed defect detection in railroad tracks.
Abstract: The aim of this work is to demonstrate the use of a commercial finite element package, ABAQUS EXPLICIT, to model ultrasonic guided waves in structural components. The particular application of interest is modeling the interaction of a broadband vertical bending mode with transverse-type defects in railroad tracks. This topic is part of a broader project on high-speed defect detection in rails by long-range ultrasonic inspections. Reflection coefficient spectra in the 20–45 kHz range are obtained for four different sizes and three different orientations of transverse head flaws. A preliminary study of Lamb waves in a free plate helps drawing modeling guidelines for the rail.

153 citations


Journal ArticleDOI
TL;DR: In this article, an experimental investigation that examines the effectiveness of acoustic emission (AE) for gear defect identification is presented, concluding that application of the AE technique to seeded gear defect detection is fraught with difficulties.
Abstract: Acoustic emission (AE) is gaining ground as a non-destructive technique for health diagnosis on rotating machinery. There are vast opportunities for development of the AE technique on various forms of rotating machinery, including gearboxes. This paper reviews some recent developments in application of AE to gear defect diagnosis. Furthermore, an experimental investigation that examines the effectiveness of AE for gear defect identification is presented. It is concluded that application of the AE technique to seeded gear defect detection is fraught with difficulties. In addition, the viability of the AE technique for gear defect detection from non-rotating components of a machine is called into question.

145 citations


Journal ArticleDOI
TL;DR: In this paper, a single-degree-of-freedom lumped system is employed to simulate the dynamic behavior of a cantilever beam with a breathing crack and the time varying stiffness is modelled using a simple periodic function.
Abstract: In this paper the dynamic behaviour of a cantilever beam with a breathing crack is investigated both theoretically and experimentally. The primary aim is to reveal the nonlinear behaviour of the system by using time frequency methods as an alternative to Fourier analysis methodology. A simple single-degree-of freedom lumped system is employed to simulate the dynamic behaviour of the beam. The time varying stiffness is modelled using a simple periodic function. Both simulated and experimental response data are analysed by applying empirical mode decomposition and Hilbert transform and the instantaneous frequency (IF) is obtained. It is shown that the IF oscillates between the frequencies corresponding to open and closed states revealing the physical process of crack breathing. The variation of the IF follows definite trends and therefore can be used as an indicator of the crack size. It allows an efficient and accurate description of the nonlinearities caused by the presence of a breathing crack. Consequently, it can be used to improve vibration based crack detection techniques.

138 citations


Journal ArticleDOI
TL;DR: The results showed that the use of a MLP neural network approach could be quite effective in automating the identification and location of embedded steel reinforcing bars from a radar investigation.
Abstract: Ground-penetrating radar is becoming increasingly popular for use as a non-destructive assessment method for investigating reinforced concrete structures. The amount of data collected however can be very large and take a significant level of subjective experience to interpret. This study focuses upon the use of a neural network approach to automate and facilitate the post-processing of ground penetrating radar results. The radar data is reduced to a simplified data set by using an edge detection routine. Signal reflections from reinforcing bars displaying a hyperbolic image format are detected using a multi-layer perceptron (MLP) network with a single hidden layer containing 8 nodes to recognise a simplified hyperbolic shape. Training and testing of the network was carried out making use of an emulsion analogue tank, simulating the properties of concrete, and using real concrete specimens. The results showed that the use of a MLP neural network approach could be quite effective in automating the identification and location of embedded steel reinforcing bars from a radar investigation. Accurate estimation of depth, or cover, requires a reliable knowledge of the dielectric properties of the concrete, and recent work using a specially-developed wideband horn antenna for direct determination of in situ properties is also outlined.

127 citations


Journal ArticleDOI
TL;DR: In this article, a new method for crack detection in beams based on instantaneous frequency and empirical mode decomposition is proposed, which can be used to improve the effectiveness of vibration-based crack detection techniques.
Abstract: In this paper, a new method for crack detection in beams based on instantaneous frequency and empirical mode decomposition is proposed. The dynamic behaviour of a cantilever beam with a breathing crack under harmonic excitation is investigated both theoretically and experimentally. A simple single-degree-of-freedom system with varying stiffness is employed to simulate the dynamic behaviour of the beam. The time-varying stiffness is modelled using a simple periodic function. Both simulated and experimental response data are analysed by applying empirical mode decomposition and Hilbert transform and the instantaneous frequency of each oscillatory mode is obtained. It is shown that the instantaneous frequency oscillates between frequencies corresponding to the open and closed states revealing the breathing of the crack. The variation of the instantaneous frequency increases with increasing crack depth following a polynomial law and consequently can be used for estimation of crack size. Using the intrinsic modes of the system, the harmonic distortion of the distorted sinusoidal response is calculated. It follows that the harmonic distortion increases with crack depth following definite trends and can be also used as an effective indicator for crack size. The proposed time–frequency approach is superior compared to Fourier analysis and can be used to improve the effectiveness of vibration-based crack detection techniques.

Journal ArticleDOI
TL;DR: A new method called wavelet-ICA filter is proposed in this paper that attempts to extract the independent feature by only using one transducer to ensure enough information for separation of all sources.
Abstract: Independent component analysis (ICA) is a new effective technique for separation of statistically independent sources. Generally, ICA requires that the number of sensors must be no less than the number of independent sources to ensure enough information for separation of all sources. In some practical applications, this requirement of ICA is not met and we are interested in separation of only one source. A new method called wavelet-ICA filter is proposed in this paper that attempts to extract the independent feature by only using one transducer. The method employs ICA to regularize the wavelet decompositions of a signal to find the independent feature. Morlet wavelet is employed in this application for its nonorthogonality. The analysis of the feasibility of the method is shown in this paper. The effectiveness of this method is demonstrated by applying it to both simulated signals and vibration signals collected from a gearbox for periodic impulse detection. PCA is also used for the same purpose as comparisons. The results show that the proposed method using ICA is much better than PCA for separation of an independent feature.

Journal ArticleDOI
L. Alfayez1, G. Dyson2
TL;DR: The AE technique was shown to offer early detection of incipient cavitation and the technique has demonstrated the ability to determine the best efficiency point (BEP) of a pump.
Abstract: Pumps play a significant role in industrial plants and need continuous monitoring to minimise loss of production. To date, there is limited published information on the application of acoustic emission (AE) to incipient pump cavitation. This paper presents a case study where AE has been applied for detecting incipient cavitation and determining the best efficiency point (BEP) of a 60 kW centrifugal pump. Results presented are based on net positive suction head (NPSH) and performance tests. In conclusion, the AE technique was shown to offer early detection of incipient cavitation, furthermore, the technique has demonstrated the ability to determine the BEP of a pump.

Journal ArticleDOI
TL;DR: In this paper, a numerical method for calculating guided wave propagation in an infinite cylinder composed of Functionally Graded Materials (FGM) is presented, which is essentially an inhomogeneous material composite, made up of two or more materials chosen to obtain desirable properties for specific applications.
Abstract: A numerical method for calculating guided wave propagation in an infinite cylinder composed of Functionally Graded Materials (FGM) is presented in this article. An FGM is essentially an inhomogeneous material composite, made up of two or more materials chosen to obtain desirable properties for specific applications. In this study, properties of the material like Young's modulus, Poisson's ratio and mass density, are assumed to vary in the direction of the thickness according to a known radial variation law. The proposed solution makes use of Legendre polynomials and harmonic functions to expand each mechanical displacement component. It also incorporates the stress-free boundary conditions directly into the equations of motion. Normalized frequencies of the guided acoustic modes are calculated as a function of normalized thickness. Mechanical displacements, normal stresses and power flow distributions are presented for certain specific modes. The developed software is capable of dealing efficiently and accurately with a variety of homogeneous and inhomogeneous cylinders. Advantages of the proposed method and potential applications are described.

Journal ArticleDOI
TL;DR: In this article, the application of georadar to the detection of three main structural problems for the Bell Tower (Torrazzo) of Cremona is presented, together with the difficulties in acquisition and data elaboration and the description of auxiliary investigations used to validate interpretation of the results.
Abstract: Frequently, the application of NDT (non-destructive testing) to historic buildings is needed in order to search for hidden parts of the structure or for structural faults. The designer who requires the investigation is always facing the difficult situation of accepting the interpretation of the results given by the NDT experts, who in turn are usually only exceptionally expert in material and structures. Only a strict collaboration between the designer and the experts and the use of different investigation techniques, from the simplest to the more sophisticated can help in the interpretation of the results. The application of georadar to the detection of three main structural problems for the Bell Tower (Torrazzo) of Cremona is presented, together with the description of the difficulties in acquisition and data elaboration and the description of auxiliary investigations used to validate interpretation of the results.

Journal ArticleDOI
TL;DR: In this article, the authors present the operating methodologies and the results achieved by the application in the field of radar methodologies to map utilities, and for applications to civil building with special regard to the determination of the intern morphology, to the lack of homogeneity research and defectiveness and to the location of the steel reinforcements.
Abstract: The radar technology, used to perform investigations on the civil buildings, derives from that used for investigations of the ground known with the name of Georadar. This is diffusing rapidly among the investigation methodology not destructive in the field of the structural engineering. It is based on the sending of electromagnetic waves of very short length and the recording of the time of arrival and of the breadth of any signals reflected on the interface between materials with a different dielectric constant. The aim of this paper is to present the operating methodologies and the results achieved by the application in the field of radar methodologies to map utilities, and for applications to civil building with special regard to the determination of the intern morphology, to the lack of homogeneity research and defectiveness and to the determination of the location of the steel reinforcements. Specifically, the system used, made up of one apparatus of field acquisition and another of delayed processing, seems to be able to provide good planimetric and three-dimensional restitution with regard to location and placement. In this paper, special attention has been paid to the processing of the acquired data and on the interpretation of experimental tests conducted on a civil building.

Journal ArticleDOI
TL;DR: In this paper, the authors describe the use of non-destructive testing to examine the efficiency of tunnel lining grouting programs, with particular emphasis on results obtained by the impulse response and impulse radar methods.
Abstract: Concrete tunnel linings, whether pre-cast or cast in place, are designed to distribute external soil pressures as uniformly as possible through the tunnel shell. To this effect, the contact between the lining and the surrounding soil is usually assured by grouting the annular space between. Any voiding in the grout at this interface negates the purpose of the grout. This paper describes the use of non-destructive testing to examine the efficiency of tunnel lining grouting programmes, with particular emphasis on results obtained by the impulse response and impulse radar methods. The rail, water supply and sewer tunnels discussed in this article vary in diameter between 1 and 5 m, and emphasis is placed on the rapid results obtained by these methods.

Journal ArticleDOI
TL;DR: In this article, a real-time imaging and detecting system is setup to detect weld defects in steel tube, based on spatial characteristics near defects, and defects such as slags, blowholes and incomplete penetration are automatically detected using the method of fuzzy pattern recognition, and the system will automatically alarm if the defect exceeds the national standard.
Abstract: In order to detect weld defects in steel tube, a real-time imaging and detecting system is setup. In the extracted weld seam, based on spatial characteristics near defects—variance and contrast, defects such as slags, blowholes and incomplete penetration are automatically detected using the method of fuzzy pattern recognition, and the system will automatically alarm if the defect exceeds the national standard. Compared with other methods, it is simple and fast, and has fewer misinterpretations. It can detect weld defects in real-time.

Journal ArticleDOI
TL;DR: In this article, a new technique of nondestructively assessing the compression strength of concrete, which employs artificial neural networks, is presented, and a data set based on results of testing concretes (with a 28-day strength of 24-105 MPa) by different non-destructive methods was used to train and test an artificial neural network.
Abstract: A new technique of nondestructively assessing the compression strength of concrete, which employs artificial neural networks, is presented. A data set based on results of testing concretes (with a 28-day strength of 24–105 MPa) by different nondestructive methods was used to train and test an artificial neural network. The methodology of neural identification of the strength is described. The obtained results, including those of the practical verification of the technique, are reported.

Journal ArticleDOI
TL;DR: In this article, a simple and efficient mark tracking method for local strain measurement is presented. But the method is insensitive to illumination variation and to in-plane rotation of the specimen.
Abstract: The mark tracking method is a simple and efficient technique for a local strain measurement. We show the possibilities of the mark tracking for field measurement. We present a procedure which allows us to experimentally characterise this technique depending on the sensor and the marks' dimensions. The method presented is insensitive to illumination variation and to in-plane rotation of the specimen. The strain values are obtained by analysis of four marks. In order to obtain a displacement field, we analyse a series of small groups of spots. With the help of an average of the parameters (using a series of initial images), we suppress the systematic error that we can observe when we use a method comparing an initial state to a deformed one. So the strain uncertainty becomes less that 0.0002 for a local study and 0.002 for a whole field study (measurement base 20×20 pixel2).

Journal ArticleDOI
TL;DR: In this paper, a visual dot pattern technique is proposed to identify the acoustic emission and vibration signals for fault diagnosis in an internal combustion engine and drive axle shaft, and experiments are carried out to evaluate the proposed system under various fault conditions.
Abstract: An investigation of the fault diagnosis technique in internal combustion engines based on the visual dot pattern of acoustic and vibration signals is presented in this paper. Acoustic emissions and vibration signals are well known as being able to be used for monitoring the conditions of rotating machineries. Most of the conventional methods for fault diagnosis using acoustic and vibration signals are primarily based on observing the amplitude differences in the time or frequency domain. Unfortunately, the signals caused by damaged elements, such as those buried in broadband background noise or from smearing problems arising in practical applications, particularly at low revolution, are not always available. In the present study, a visual dot pattern technique is proposed to identify the acoustic emission and vibration signals for fault diagnosis in an internal combustion engine and drive axle shaft. Experiments are carried out to evaluate the proposed system for fault diagnosis under various fault conditions. The experimental results indicate that the proposed technique is effective in the fault diagnosis of an internal combustion engine and drive axle shaft.

Journal ArticleDOI
TL;DR: In this article, the eddy current response signals from FCD 450-600 grades of cast iron were measured and a good correlation with their hardness and tensile properties was found.
Abstract: Eddy current method was applied for evaluation of material properties of ductile cast iron. Measurements of eddy current response signals from FCD 450–600 grades of cast iron demonstrated good correlation with their hardness and tensile properties. Alternative ultrasonic method was explored for assessment of hardness of the studied samples and showed its inadequacy for specimens with similar graphite nodularity.

Journal ArticleDOI
TL;DR: In this paper, nonlinear pattern classifiers were developed, using neural networks, and the largest number of radiographic patterns as possible was used as well as statistical inference techniques of random selection of data with bootstrap and without repositioning in order to estimate the accuracy of the classification.
Abstract: Over the last two decades, there has been a considerably increase in the number of publications of research projects for the detection and classification of welding defects in radiographs using image processing and pattern recognition tools. All these research projects aim to set up an automatic or semi-automatic classification system for weld joint defects detected by the radiographic method. A classification system as such would allow a reduction in some inherent inexactnesses that occur in the conventional method, consequently increasing the precision of the report. This work is a study to estimate the accuracy of classification of the main classes of weld defects, such as: undercut, lack of penetration, porosity, slag inclusion, crack or lack of fusion. To carry out this work nonlinear pattern classifiers were developed, using neural networks. Also the largest number of radiographic patterns as possible was used as well as statistical inference techniques of random selection of data with (Bootstrap) and without repositioning in order to estimate the accuracy of the classification. The results pointed to an estimated accuracy of around 80% for the classes of defects analyzed.

Journal ArticleDOI
TL;DR: In this article, the effect of chloride ions on passivity breakdown of steel, respectively, in simulated concrete pore solution (SCP) and in concrete reinforcement, was investigated in a heating-cooling cycle.
Abstract: The tenacious oxide passive film, which is formed on the surface of embedded reinforcing steel under high alkaline condition of concrete, protects the steel against corrosion However, the condition of passivity may be destroyed, due to processes such as leaking out of fluids from concrete, atmospheric carbonation or through the uptake of chloride ions Passive steel reinforcing corrosion induced by chloride is a well-known problem, especially where chloride-containing admixtures or chloride contaminated aggregate are incorporated into the concrete The objective of this work is on one hand to study the effect of chloride ions on passivity breakdown of steel, respectively, in simulated concrete pore solution (SCP) and in concrete reinforcement, and on the other hand to reproduce the carbonation phenomena by applying to the concrete samples a heating-cooling cycles In this context, the acoustic emission coupled to the electrochemical techniques (potentiodynamic and electrochemical impedance spectroscopy (EIS)) are used The results show clearly that [Cl-]/[OH-] ratio of 06 is the critical threshold where the depassivation set-up can be initiated In addition, the carbonation process is very aggressive with chloride ions and shows a perfect correlation with acoustic emission evolution A physical model of the reinforcement/electrolyte interface is proposed to describe the behavior of the reinforcement against corrosion in chloride solution (A) "Reprinted with permission from Elsevier"

Journal ArticleDOI
TL;DR: In this paper, the results of a theoretical and experimental study of planar rectangular coils in eddy-current NDE are presented, and closed-form expressions for the coil impedance are presented for these three cases and the theoretical predictions are validated against experiment using a series of coils with different aspect ratios and both non-magnetic and magnetic plates.
Abstract: The results of a theoretical and experimental study of planar rectangular coils in eddy-current NDE are presented. Three fundamental cases are examined: a planar coil (i) in free space, (ii) above a defect-free conductive half-space and (iii) centered above a long, uniform crack. Closed-form expressions for the coil impedance are presented for these three cases and the theoretical predictions are validated against experiment using a series of coils with different aspect ratios and both non-magnetic and magnetic plates. While the change in normalized coil impedance due to the half-space depends only weakly on the coil aspect ratio, the change in normalized impedance due to the crack depends strongly on coil aspect ratio with the maximum normalized response observed for an aspect ratio of 1:1, i.e. for square coils. In contrast to planar circular coils, the response of planar rectangular coils depends on their orientation with respect to the crack. This orientation dependence is investigated in detail.

Journal ArticleDOI
TL;DR: In this article, a neural network was trained to extract the information that characterises a range of internal defects in different types of composite materials and applied to all the points of a sequence of thermographic images.
Abstract: Safety in aeronautics could be improved if continuous checks were guaranteed during the in-service inspection of aircraft. However, until now, the maintenance costs of so doing have proved prohibitive. For this reason there is a great interest for the development of low cost non-destructive inspection techniques that can be applied during normal routine tests. The analysis of the internal defects (not detectable by a visual inspection) of the aircraft composite materials is a difficult task unless invasive techniques are applied. In this paper, we have addressed the problem of inspecting composite materials by using automatic analysis of thermographic techniques. The analysis of the time/space variations in a sequence of thermographic images allows the identification of internal defects in composite materials that otherwise could not be detected. A neural network was trained to extract the information that characterises a range of internal defects in different types of composite materials. After the training phase the same neural network was applied to all the points of a sequence of thermographic images. The experimental results demonstrate the ability of the method to recognize regions containing defects but also to identify the contour regions that cannot be associated either with a defective or with a sound region.

Journal ArticleDOI
TL;DR: In this paper, the wavelet transform was applied to acoustic emission (AE) signals from scratch tests on stainless steel samples with Cr or Ti nitride coatings obtained by physical vapor deposition, in order to characterize the coating adherence failure mechanisms.
Abstract: Wavelet Transform (WT) was applied to Acoustic Emission (AE) signals from scratch tests on stainless steel samples with Cr or Ti nitride coatings obtained by physical vapor deposition, in order to characterize the coating adherence failure mechanisms. The WT, employed to analize the essentially non-stationary AE signals, was adequate to identify different stages of failure (transversal coating microfractures and coating/matrix debonding microfractures), which could be precisely delimited by a unique parameter.

Journal ArticleDOI
TL;DR: Simulation and practical application of the proposed time–energy density analysis approach based on wavelet transform to roller bearing with faults show that the method can extract the fault characteristics from vibration signal efficiently.
Abstract: Energy is an important physical variable in signal analysis. The distribution of energy with the change of time and frequency can show the characteristics of a signal. A time–energy density analysis approach based on wavelet transform is proposed in this paper. This method can analyze the energy distribution of signal with the change of time in different frequency bands. Simulation and practical application of the proposed method to roller bearing with faults show that the time–energy density analysis approach can extract the fault characteristics from vibration signal efficiently.

Journal ArticleDOI
TL;DR: In this article, a wave propagation-based technique to detect and localize incipient damages in structures and machines is presented, which utilizes arrays of surface-bonded piezoceramic (PZT) patches, which serve as transmitters and receivers of elastic waves through the monitored component.
Abstract: This paper presents a wave propagation-based technique to detect and localize incipient damages in structures and machines. The technique utilizes arrays of surface-bonded piezoceramic (PZT) patches, which serve as transmitters and receivers of elastic waves through the monitored component. The operating frequency is maintained in the order of 100–150 kHz to enable high sensitivity in damage detection. The resulting frequency transfer functions facilitate the identification of the damaged region in the structure. The presented technique, which utilizes simple, economical and commercially available hardware and sensors, can be easily employed for real-time and online monitoring of critical structures, such as machine parts and aircraft components.

Journal ArticleDOI
TL;DR: In this article, the authors used three-dimensional (3D) magnetic finite element analysis (FEA) to simulate the MFL signal from a circular dent geometry with associated residual stresses.
Abstract: We have used three-dimensional (3D) magnetic finite element analysis (FEA) to simulate the MFL signal from a circular dent geometry with associated residual stresses. Strain distribution information around the dent was obtained from an earlier work using finite element structural modeling. In the magnetic FEA dent model, the localized residual stresses were simulated by assigning appropriate values of magnetic anisotropy to the relevant magnetic regions. The simulated flux leakage patterns were found to be in good agreement with the experimentally observed MFL patterns associated with dent shape as well as with the stress effects from the dent.