Showing papers in "Ndt & E International in 2013"
TL;DR: In this article, the authors describe a method to effectively image structural features and defects using local estimates of the wavenumber of propagating guided Lamb waves at a fine grid of spatial sampling points.
Abstract: This paper describes a method to effectively image structural features and defects using local estimates of the wavenumber of propagating guided Lamb waves at a fine grid of spatial sampling points. The guided waves are rapidly excited at each grid point using a scanning Q-switched laser system and sensed by a single fixed ultrasonic transducer. Through reciprocity, this produces a full-wave-field time history of a virtual wave being excited from the transducer. Using frequency–wavenumber processing, localized wavelength estimates are obtained by isolating each wave mode, narrowband filtering to one or more high-energy frequency bands, and identifying the center-wavelength of a sliding wavenumber band-pass filter that maximizes the energy at each grid point. The approach was capable of producing detailed images of hidden wall-thinning in an aluminum plate and a steel pipe section and local impact delamination in a complicated composite component.
161 citations
TL;DR: In this article, the possibility for using thermography for detecting surface cracks in welded metal plate was discussed, and it was shown that thermography can be used within non-destructive testing for detecting several different types of defects.
Abstract: Thermography is today used within non-destructive testing for detecting several different types of defects. The possibility for using thermography for detecting surface cracks in welded metal plate ...
114 citations
TL;DR: In this article, a non-contact measurement method is proposed to estimate the tension in hanger cables by using digital image processing, which is convenient and cost-efficient because it can be used to remotely measure the dynamic responses of the hanger cable.
Abstract: In this study, a non-contact measurement method is proposed to estimate the tension in hanger cables by using digital image processing. Digital images were acquired through a vision-based system using a portable digital video camera (camcorder), which was used to remotely measure the dynamic responses and was chosen because it is convenient and cost-efficient. Digital image correlation technique, as one of digital image processing algorithms, was applied to develop an image processing algorithm. An image transform function was used to correct the geometric distortion between the deformed and undeformed images and to calculate the subpixels. The motion of the vision-based system caused by external wind or vibration at camera location was corrected considering a fixed object in the image without any additional sensors. Using this algorithm, the dynamic response of the hanger cable and the resolution of the modal frequencies were improved. It was also confirmed that the dynamic characteristics of the hanger cables can be estimated with only the cable shape not attaching any target.
113 citations
TL;DR: In this article, the TFM was modified to include the directional dependence of ultrasonic velocity in an anisotropic composite laminate, and practical procedures for measuring the direction-dependent velocity profile were described.
Abstract: As carbon fibre composite becomes more widely used for primary structural components in aerospace and other applications, the reliable detection of small defects in thick-sections is increasingly important. This article describes an experimental procedure for improving the detectability of such defects based on modifications to the Total Focusing Method (TFM) of processing ultrasonic array data to form an image. First the TFM is modified to include the directional dependence of ultrasonic velocity in an anisotropic composite laminate, and practical procedures for measuring the direction-dependent velocity profile are described. The performance of the TFM is then optimised in terms of the signal to noise ratio for Side-Drilled Holes (SDHs) by tuning both the frequency-domain filtering of data and the maximum aperture angle used in processing. Finally an attenuation correction is applied to the image so that the background structural noise level is uniform at all depths. The result is an image where the sensitivity (i.e. the signal to noise ratio) to a particular feature is independent of depth. Signals from 1.5 mm diameter SDHs in the final image at depths of 4, 10 and 16 mm are around 15 dB above the root-mean-square level of the surrounding structural noise. In a standard TFM image, the signals from the same SDHs are not visible above the structural noise.
101 citations
TL;DR: In this article, the authors describe the application of two non-destructive testing techniques: ground-penetrating radar and seismic tomography, in the analysis of some structural elements' inner geometries and physical properties.
Abstract: Geophysical prospecting surveys are being increasingly used in non-destructive evaluations of structures, and several methods can be applied in the evaluation of cultural heritage buildings. However, accurate studies of cultural heritage structures usually need the application of combined techniques, historic and structural knowledge also being necessary. The present paper describes the application of two non-destructive testing techniques: ground-penetrating radar and seismic tomography, in the analysis of some structural elements' inner geometries and physical properties. This job is part of a more complete project developed to define the Mallorca Cathedral structural behaviour. Both geophysical methods are used in a complementary way. GPR allows the detection of small anomalies (changes of about centimetres), and the results are used to select the most appropriate seismic tomography initial model. The aim of the study is to define the internal structural configuration as well as the stone quality. Results reveal the internal structure of columns, walls and buttresses, showing different structural elements. Even when the visual inspection points to external damages, the detailed NDT evaluation indicates that the inner structure is in good condition and the ashlars are of good quality.
82 citations
TL;DR: In this article, a new approach for weld defect identification from radiographic images is presented based on the generation of a database of defect features using Mel-frequency Cepstral Coefficients (MFCCs) and polynomial coefficients extracted from the Power Density Spectra (PDSs) of the weld segmented areas after performing pre-processing and segmentation stages.
Abstract: This paper presents a new approach for weld defect identification from radiographic images. This approach is based on the generation of a database of defect features using Mel-Frequency Cepstral Coefficients (MFCCs) and polynomial coefficients extracted from the Power Density Spectra (PDSs) of the weld segmented areas after performing pre-processing and segmentation stages. Artificial Neural Networks (ANNs) are used for the feature matching process in order to automatically identify defects in radiographic images. The performance of the proposed approach is evaluated using 150 radiographic images in the presence of various types of noise and blurring. The experimental results show that the proposed approach can be used in a reliable way for automatic weld defect identification from radiographic images in noisy environments, and can achieve high recognition rates.
80 citations
TL;DR: In this article, the effect of plastic deformation on magnetic behavior has been investigated in low carbon steel specimens under applied tension after unloading in the elastic-plastic region for different strain levels.
Abstract: Metal magnetic memory (MMM) technique can be potentially used to evaluate early damage of ferromagnetic materials nondestructively due to its high sensitivity to stress and stress–strain state. An experimental investigation of the effect of plastic deformation on magnetic behavior has been undertaken in low carbon steel specimens. The measurements were made under applied tension after unloading in the elastic–plastic region for different strain levels. Magnetic memory signals show apparently different variation characteristics in the elastic and plastic ranges, and the magnetic signals are sharply changed by a rather small plastic deformation, which is in agreement with the predictions of the modified magnetomechanical effect model correlating magnetic memory signal with plastic strain. The results of the present work indicate that the MMM method can detect macroyielding and early stage of plastic deformation effectively.
79 citations
TL;DR: In this article, the authors used the anisotropic properties of the small angle scattering signal to image the fiber bundles running in different directions independently with excellent contrast and found that SDFI allows for the visualisation of the weave pattern structure and analysis of the size of the carbon fiber bundle in three dimensions, even if individual fibres cannot be separated or the absorption contrast between the carbon fibres and the epoxy matrix is very low.
Abstract: X-ray scatter dark field imaging (SDFI) using a Talbot-Lau grating interferometer has recently attracted growing interest for the non-destructive testing and evaluation of light materials. In this work, we developed the method further for the characterisation of the laminate structure of carbon fibre reinforced polymers. In particular, we used the anisotropic properties of the small angle scattering signal to image the fibre bundles running in different directions independently with excellent contrast. The results obtained for four different woven carbon fibre reinforced polymer samples were compared to high resolution X-ray computed tomography results. We found that SDFI allows for the visualisation of the weave pattern structure and analysis of the size of the carbon fibre bundle in three dimensions, even if the individual fibres cannot be separated or the absorption contrast between the carbon fibres and the epoxy matrix is very low.
76 citations
TL;DR: In this article, the nonlinear ultrasonic measurements are performed and their results are compared with those from ultrasonic velocity and attenuation measurements for early detection of thermal degradation of mechanical properties in 2205 duplex stainless steel.
Abstract: Early thermal damage in 2205 duplex stainless steel which is caused by the precipitation of second phases during a short term exposure to high temperature (700 °C) is investigated. Nonlinear ultrasonic measurements are performed and their results are compared with those from ultrasonic velocity and attenuation measurements. Experimental results show that the measured acoustic nonlinearity parameter is more sensitive than the ultrasonic longitudinal velocity and attenuation to the precipitation of chi and sigma phases early in the aging treatments. The results from the nonlinear ultrasonic measurements are also supported with those from the scanning electron microscopy (SEM), Rockwell C hardness and Charpy impact test. Especially notable is the close correlation between the hardness and the nonlinearity parameter. This research therefore proposes the nonlinear ultrasonic method as a nondestructive assessment means for early detection of thermal degradation of mechanical properties in 2205 duplex stainless steel.
71 citations
TL;DR: In this article, a ray-based approach is provided as a fast computational tool to determine average material properties and a novel full-waveform inversion based on a multilayered forward model is presented.
Abstract: The spreading of deicing salt on roads during winter and the consequent migration of chloride ions within concrete exposes structures reinforcement to corrosion. Reinforcement corrosion is problematic because it reduces the structure's load carrying capacity and a long-term consequence can be structural failure. The use of Ground Penetrating Radar (GPR) technology is commonly applied to reinforced concrete structural mapping. This paper provides methodologies for the calculation of the electromagnetic parameters from GPR data accounting for chloride content and its distribution within concrete. The previous work showed that they are linked with water and chloride content. A GPR dataset was carried out with bi-static off-ground GPR antennas during an experiment recreating chloride contamination processes in concrete specimens. Two novel solutions are presented in this paper, their use on the dataset returned the electromagnetic parameters of the concrete specimens with knowledge of their thickness. Firstly, a ray-based approach is provided as a fast computational tool to determine average material properties. Thereafter, a novel full-waveform inversion based on a multilayered forward model is presented. It allows the identification of conductivity gradients present inside the concrete. Finally, the results are compared with additional destructive testing; they present a good correspondence. (C) 2013 Elsevier Ltd. All rights reserved.
68 citations
TL;DR: In this paper, the transmission process of a surface wave EMAT is studied, based on a previously established 3D model, with the aim of enhancing the amplitude of ultrasonic waves generated by the EMAT.
Abstract: The amplitude of an ultrasonic signal generated by electromagnetic acoustic transducers (EMATs) is typically low when compared to those generated by contacting transducers, which restricts the application of EMATs in the fields of nondestructive testing and nondestructive evaluation. The transmission process of a surface wave EMAT is studied, based on a previously established 3-D model, with the aim of enhancing the amplitude of ultrasonic waves generated by the EMAT. The effect of changing various EMAT parameters on the surface wave is investigated, by utilizing the orthogonal test method. Results indicate that after optimization, the signal amplitude of the EMAT has increased by 25.2%.
TL;DR: In this article, an efficient image-based damage detection system that can automatically identify damages to the cable surface through image processing techniques and pattern recognition was introduced, which combines image enhancement techniques with principal component analysis (PCA) algorithm.
Abstract: Since cable members are the major structural components of cable bridges, they should be properly inspected for surface damage and inside defects such as corrosion and/or breakage of wires. This study introduces an efficient image-based damage detection system that can automatically identify damages to the cable surface through image processing techniques and pattern recognition. The damage detection algorithm combines image enhancement techniques with principal component analysis (PCA) algorithm. Images from three cameras attached to a cable climbing robot are wirelessly transmitted to a server computer located on a stationary cable support. To improve the overall quality of the images, this study utilizes an image enhancement method together with a noise removal technique. Next the input images are projected into PCA sub-space, the Mahalanobis square distance is used to determine the distances between the input images and sample patterns. The smallest distance is found to be a match for an input image. The proposed damage detection algorithm was verified through laboratory tests on three types of cables. Results of the tests showed that the proposed system could be used to detect damage to bridge cables.
TL;DR: In this paper, a multi-ring electrical resistivity cell for the evaluation of concrete is presented, which is capable of assessing the homogeneity of the investigated specimen and is used for obtaining representative bulk resistivity results.
Abstract: Direct Current (DC) electrical resistivity is a material property well known to be sensitive to various aspects of concrete condition related to corrosion risk. This paper describes the development of a multi-ring electrical resistivity cell for the evaluation of concrete. A multi-electrode surface resistivity probe for on-site applications is also presented. The multi-ring resistivity cell is capable of assessing the homogeneity of the investigated specimen, which is an important requirement for obtaining representative bulk resistivity results. The multi-electrode surface probe is used for depth investigation of cover concrete to identify moisture and chloride gradients by means of electrical resistivity tomography (ERT). The paper focuses on the development of these two resistivity devices, and the numerical modelisation, calibration, validation and cross-correlation thereof. The development of the resistivity cell will enable future work to establish master curves relating DC-resistivity to parameters indicative of concrete condition (particularly water content, chloride content and porosity). The final aim is then to estimate these state parameters for in situ concrete by means of the combination of electromagnetic non-destructive evaluation (NDE) techniques such as Electrical Resistivity Tomography (ERT), capacitive method and Ground Penetrating Radar (GPR).
TL;DR: In this paper, a new method for stress testing based on the theory of Barkhausen noise has been introduced using changing feature values for monitoring stress and temperature, and the results showed that the network had a high degree of accuracy and generalization ability, to get the values of stress.
Abstract: A new method for stress testing based on the theory of Barkhausen noise has been introduced using changing feature values for monitoring stress and temperature. However, changes in temperature not only have an effect on the stress but also the MBN signal itself. In order to get the accurate stress value and eliminate the temperature effect, we proposed a data processing method for stress testing based on MBN. The study found that within the steel elastic range, the Barkhausen noise feature values, including mean value, RMS value, ring numbers, peak value and the ratio of envelope peak and full peak width at half of maximum amplitude decrease with increasing temperature, there is a fixed monotonic relationship which provides a theoretical basis for building the back propagation (BP) neural network model, with stress as the output value and temperature, mean value, RMS value, ring numbers, peak value and the ratio of peak and full width of half maximum as the input values. The MATLAB 7.8.0 neural network toolbox was used to model and simulate the neural network and samples used to validate the trained BP neural network. The results showed that the network had a high degree of accuracy and generalization ability, to get the values of stress.
TL;DR: In this paper, an image compounding technique that uses the information obtained from different propagation modes of Lamb waves for non-destructive testing of plate-like structures is proposed, where a linear array consisting of 16 piezoelectric elements is attached to a 1-mm thickness aluminum plate, coupling the fundamental A0 and S0 modes at the frequencies of 100 kHz and 360 kHz, respectively.
Abstract: Several Lamb wave modes can be coupled to a particular structure, depending on its geometry and transducer used to generate the guided waves. Each Lamb mode interacts in a particular form with different types of defects, like notches, delamination, surface defects, resulting in different information which can be used to improve damage detection and characterization. An image compounding technique that uses the information obtained from different propagation modes of Lamb waves for non-destructive testing of plate-like structures is proposed. A linear array consisting of 16 piezoelectric elements is attached to a 1 mm thickness aluminum plate, coupling the fundamental A0 and S0 modes at the frequencies of 100 kHz and 360 kHz, respectively. For each mode two images are obtained from amplitude and phase information: one image using the Total Focusing Method (TFM) and one phase image obtained from the Sign Coherence Factor (SCF). Each TFM image is multiplied by the SCF image of the respective mode to improve contrast and reduce side and grating lobes effects. The high dispersive characteristic of the A0 mode is compensated for adequate defect detection. The information in the SCF images is used to select one of the TFM mode images, at each pixel, to obtain the compounded image. As a result, dead zone is reduced, resolution and contrast are improved, enhancing damage detection when compared to the use of only one mode.
TL;DR: In this article, PEC signal response due to variability in magnetic coupling to the fastener was analyzed using Modified Principal Component Analysis (PCA) to detect the presence of cracks.
Abstract: Stress corrosion cracks may develop between fasteners in the aluminum inner wing spars of F/A-18 Hornet aircraft. These fasteners secure carbon-fibre/epoxy composite wing skin, of nominal 13 mm thickness, to the spar. Inspection of the spar through the wing skin is required in order to avoid wing disassembly. Pulsed eddy currents, generated by a probe design that utilizes the ferrous fastener as a flux conduit, are demonstrated as having the capability of detecting simulated cracks within the spar with the wing skin present. Differentially connected pickup coils are used to sense differences in response due to asymmetries in induced eddy current fields arising in the presence of cracks. To overcome variability in PEC signal response due to variability in magnetic coupling to the fastener, a large measurement set was analyzed using Modified Principal Component Analysis (PCA). The modified PCA minimizes residual sum of squares to extract eigenfunction scores, which are used to detect the presence of cracks ending on one side of the fastener hole. The ability of the method to sense simulated cracks independent of confounding measurement parameters was demonstrated.
TL;DR: In this article, a case study of the Damaoshan Tunnel located in Fujian province, China is executed to perform a condition assessment combining ground-penetrating radar (GPR) and finite-difference time-domain (FDTD) techniques based on prior information regarding the designed tunnel structure.
Abstract: Ground-penetrating radar (GPR) is widely used in the field of civil engineering; it can locate anomalies and record detailed information on the possible presence of damage within a tunnel. However, because of the complexity of tunnel structures and a long data interpretation period, the analysis and interpretation of field data is a relatively difficult and time-consuming task. In this paper, a case study of the Damaoshan Tunnel located in Fujian province, China is executed to perform a condition assessment combining GPR and finite-difference time-domain (FDTD) techniques based on prior information regarding the designed tunnel structure. This combination is used to assist and improve the interpretation of field data. The aims of this survey are to locate the rebar, estimate the thickness of the second lining, and determine the presence and distribution of any damage for an annual inspection. Additionally, a symmetry-based algorithm and a hyperbola match method are combined to achieve these goals and determine the wave velocity inversion. The interpreted results, based on both measured and simulated data, reveal that the combination of FDTD and GPR techniques is a quick and efficient survey methodology for tunnel evaluation. The survey shows that the rebar number is 367 (which is less than the standard 492), the average qualified rate of lining thickness is 79.87% of the design parameters, and there are 81 damages spanning the entire tunnel.
TL;DR: In this paper, acoustic emission (AE) monitoring has been applied to a series of small-scale laboratory specimens under compression and shear to develop deeper understanding of the stages of fracture development process and signal characteristics under quasistatic and long-term fatigue loading.
Abstract: Acoustic emission (AE) monitoring has the unique ability to record crack propagation and the response of structures to live loading; however, its use for masonry is currently very limited. AE technique was applied to a series of small-scale laboratory specimens under compression and shear to develop deeper understanding of the stages of fracture development process and signal characteristics under quasi-static and long-term fatigue loading. Field monitoring was subsequently carried out on a brick masonry arch bridge to identify its response to traffic loading, structural condition and efficacy of strengthening works with the help of laboratory test results.
TL;DR: In this article, the Tower of the Nations, located in the Mostra D'Oltremare urban park in Naples, Italy, has been used for non-invasive structural assessment of historical structures.
Abstract: Seismic risk mitigation in urban areas is a very relevant issue in European regions, such as Italy and Greece, characterized by the presence of a large stock of heritage structures. Enhancing the knowledge about the dynamics of structures is definitely useful in view of seismic assessment and design of risk mitigation interventions. However, this task can be difficult in the case of heritage structures, since several uncertainties affect material properties and structural patterns. In this paper, the opportunities provided by dynamic identification techniques for the non-destructive evaluation of heritage structures are discussed with focus on an interesting case study. This refers to the characterization of a modern heritage reinforced concrete building as a preliminary step towards seismic assessment. The structure under investigation is the Tower of the Nations, located in the Mostra D'Oltremare urban park in Naples, Italy. The paper shows how the combination of ambient vibration tests and model refinement can represent a valuable tool for an indirect non-invasive structural assessment of historical structures. Their proper analysis and modeling, in fact, is usually very challenging from the scientific and technical viewpoint due to their unique structural configurations, the several modeling uncertainties and the need to keep destructive investigations very limited. In this framework the present paper shows how a rational choice of the updating parameters and of the objective function can support the model optimization taking into account the ultimate objectives of the analysis, namely the setting of a reliable model for the assessment of the seismic performance of the structure in the linear regime. As a result, the paper describes the refinement of the model of the Tower of the Nations, in a way able to minimize the scatter with the experimental data and, at the same time, enhance the accuracy of response spectrum and seismic time-history linear analyses.
TL;DR: In this article, the impact damage was artificially produced by impact energies of 3.63, 8.89 and 13.21, respectively, by carbon fiber reinforced polymers (CFRP).
Abstract: Carbon fiber reinforced polymers (CFRPs) are widely used for various structural materials because of their high stiffness and strength. Detecting damages in CFRP composites is important for structural safety. This study was conducted to detect impact damage in CFRP specimens using the millimeter-wave of 65–67 GHz. The impact damage was artificially produced by impact energies of 3.63 J, 8.89 J and 13.21 J, respectively. Since the CFRP composites are electrically anisotropic materials, reflection coefficients are affected by the angle between the electrical field vector direction of the electromagnetic wave and the carbon fiber direction in the CFRP surface. When this angle was 0°, reflection coefficients on the surface with and without damage were easily distinguished. Accordingly, imaging the CFRP specimens including the impact damage was conducted using changes of the reflection coefficient. In addition, in order to obtain better image, the edge detection image processing technique was applied to the original image, and a more natural image was obtained. The magnitude of impact energy producing damage could also be distinguished through the image.
TL;DR: In this paper, feature-guided wave modes dominated by shearing motion were identified to be well suited, with energy concentrated at the stiffener and bond line, limiting energy radiation into the plate and thus maximising inspection length.
Abstract: Adhesively bonded stiffeners are employed in aerospace applications to increase structural stiffness The potential of feature-guided wave modes for the verification of adhesion and curing state in difficult-to-access regions has been investigated The properties of guided wave modes propagating along a T-shaped stiffener bonded to an aluminium plate were calculated using the Semi-Analytical Finite Element (SAFE) method Feature-guided modes dominated by shearing motion were identified to be well suited, with energy concentrated at the stiffener and bond line, limiting energy radiation into the plate and thus maximising inspection length The influences of the bond line stiffness and thickness on the guided wave behaviour were investigated using SAFE and 3D Finite Element calculations, and found to be significant Experiments were conducted to measure the properties of the guided waves during the curing of an epoxy joint attaching a stiffener to a plate The feature-guided mode was excited using a piezo-electric shear transducer and measured using a laser interferometer The measured phase speed changed significantly during curing The frequency dependency was found to match well with the SAFE calculations for a variation of the shear (Coulomb) modulus of the adhesive The potential of the feature-guided shear wave mode for bond line inspection and monitoring has been shown and the choice of guided wave mode and frequency range for good sensitivity to the bond line state discussed
TL;DR: In this article, the phase of induced voltage in the bobbin coil is interpreted in terms of the circumferential location of the defect and the properties of the probe are investigated using a three dimensional finite element model, and validated experimentally using measurements.
Abstract: Eddy current probes are used extensively to evaluate the integrity of steam generator tubes in nuclear power plants and to detect cracks in tube walls. The probe design has evolved from simple bobbin probes to mechanically rotating multi-coil probes providing high resolution images of tube integrity. This paper presents a novel rotating field eddy current probe with bobbin pickup coil that generates a rotating magnetic field, thereby avoiding mechanical rotation of probe. Three balanced identical rectangular windings carrying excitation currents with 120° phase difference generate an electrically rotating magnetic field that is sensitive to defects of all orientations. A bobbin coil located in the center is used as a pick up sensor. The phase of induced voltage in the bobbin coil is interpreted in terms of the circumferential location of the defect. The properties of the probe are investigated using a three dimensional finite element model, and validated experimentally using measurements.
TL;DR: In this article, a time-frequency signal processing procedure aimed at extending pulse-echo defect detection methods based on guided waves to irregular waveguides is proposed, which returns the distance traveled by a guided wave that has propagated along a waveguide composed by segments with different dispersive properties by processing the detected echo signal.
Abstract: A time–frequency signal processing procedure aimed at extending pulse-echo defect detection methods based on guided waves to irregular waveguides is proposed. In particular, the procedure returns the distance traveled by a guided wave that has propagated along a waveguide composed by segments with different dispersive properties by processing the detected echo signal. To such aim, the acquired signal is processed by means of a two-step procedure. First, a warped frequency transform (WFT) is used to compensate the dispersion of the guided wave due to the traveled distance in a portion of the waveguide that is assumed as reference. Next, a further compensation is applied to remove from the warped signal the group delay introduced by the remaining irregular portion of the waveguide. Thanks to this processing strategy, the actual distance traveled by the wave in the regular portion of the irregular waveguide is revealed. Thus, the proposed procedure is suitable for automatically locate defect-induced reflections in irregular waveguides and can be easily implemented in real applications for structural health monitoring purposes. The potential of the procedure is demonstrated and validated numerically by simulating and processing Lamb waves propagating in waveguides made up of different uniform, tapered and curved segments.
TL;DR: In this paper, an experimental study to evaluate shapes and sizes of defect under thick coating by microwaves NDT is demonstrated using an X-band (8.2-12.4 GHz) open-ended rectangular waveguide.
Abstract: An experimental study to evaluate shapes and sizes of defect under thick coating by microwaves NDT is demonstrated. Specially fabricated thick fire protect coated steel panels with embedded defects are inspected using an X-band (8.2–12.4 GHz) open-ended rectangular waveguide. The fundamental idea behind using this probe is presented along with several experimental results to validate this method for defect detection under coating. The reflected signal related to the phase and magnitude of the reflection coefficient at the waveguide aperture is used to create images of these coated samples under test. These images indicate the ability of microwaves for identifying and sizing defects under thick coating layer. Linear sweep technique is used here to obtain multiple frequency spectrum variances. Principle Component Analysis (PCA) algorithms have been employed to enhance the resolution of our proposed method. A series of performance comparison with PCA algorithms are also provided to extract the defect features from thick coating layer influence. To evaluate the proposed technique, steel with known defect and five coated steel plates with unknown defect under different coating thickness are measured. Results indicate that the defect detection capability has been enhanced with the suitable use of signal processing methods.
TL;DR: An optimized dictionary of matching pursuit (MP) is designed and combined with the ultrasonic guided wave for characterizing pipeline defect, which consequently achieves good performance in estimating the axial length of a defect as mentioned in this paper.
Abstract: An optimized dictionary of matching pursuit (MP) is designed and combined with the ultrasonic guided wave for characterizing pipeline defect, which consequently achieves good performance in estimating the axial length of a defect. In the research field of guided wave based pipeline defect inspection, quantitative characterization on the detected defect remains as an unsolved research task and is seldom reported in the related publications. This paper reports a new method of MP equipped with an optimized dictionary through analyzing the interference between the reflection components embedded in a defect reflection signal in order to enable efficient extraction of defect information. The proposed method not only enhances signal-to-noise ratio of reflection signal, but also characterizes the axial length of pipeline defect directly and accurately. The method has been verified by simulated data, artificial defects in real pipes as well as real corrosion in a servicing pipe.
TL;DR: In this article, the authors proposed using synthetic aperture focusing with the virtual source method to extend the effective range of the focused transducer for internal imaging of pipelines, and applied it to point-like scatterers and a corroded pipe surface, and the results demonstrate that a high lateral resolution can be obtained even when the pipe wall is several focal lengths away from the transducers.
Abstract: Focused ultrasonic monolithic transducers are often used for internal imaging of pipelines. The transducers yield a high lateral resolution as long as the distance between the pipe wall and the transducer corresponds to the transducer focal length. If the distance to the wall changes, for example due to increasing pipe diameter or de-centering of the inspection robot, the lateral resolution is decreased. We propose using synthetic aperture focusing with the virtual source method to extend the effective range of the focused transducer. It is assumed that the measurements are performed over a cylindrical surface, and we employ the Cylindrical Phase Shift Migration algorithm to perform the synthetic aperture focusing. The imaging algorithm is applied to scans of both pointlike scatterers and a corroded pipe surface, and the results demonstrate that a high lateral resolution can be obtained even when the pipe wall is several focal lengths away from the transducer.
TL;DR: In this paper, the impact of the component geometry on quantitative relationships between residual stress and the residual magnetic field (RMF) component gradients is studied. And the authors present an analysis of the algorithm for the evaluation of residual stress of the first order using the gradients of the RMF components.
Abstract: The paper presents an analysis of the universality of the algorithm for the evaluation of residual stress of the first order using the gradients of the residual magnetic field (RMF) components. The impact of the component geometry on quantitative relationships between residual stress and the RMF component gradients are studied. Two kinds of flat samples with a different geometries (type A and B) are analysed. For different degrees of plastic strain, on the surface of the samples, the distributions of the RMF components are measured. The finite element method is used to model residual stress in the samples. The quantitative relationships between the RMF component gradients and equivalent residual (von Mises) stress are developed based on the measurements of samples with type A notch geometry. These relationships are verified by using them to evaluate residual stress in type B samples with a different geometry. It is found that the quantitative evaluation of residual stress in components which is based on the RMF gradients requires at every instance the development of a transition function for the specific geometry, material and orientation of the component in the magnetic field of the Earth.
TL;DR: In this article, a method to automatically characterize impact damage in carbon fiber composites using active thermography is proposed, where shape and amplitude features are extracted from the defects detected using image processing.
Abstract: The use of composite materials in the industry has increased in the past few decades due to their high strength and stiffness to weight ratios. However, composite materials have a serious weakness: their sensitivity to impact damage. This work proposes a method to automatically characterize impact damage in carbon fiber composites using active thermography. Shape and amplitude features are extracted from the defects detected using image processing. The analysis of these features provides relevant conclusions about their relation to the impact energy, and the influence of number of plies and the type of core of the composite. Finally, a classifier based on neural networks is proposed to automatically characterize the detected defects caused by impact damage according to impact energy. Tests carried out over several specimens that contain impact damage of different energies show excellent performance for the classifier.
TL;DR: In this article, the progression of self-healing of cracked concrete is monitored in situ by diffuse ultrasound, in a novel application of this technique, in which the diffuse ultrasonic measurements are conducted on uncracked, tensile through-thickness cracked, and flexure partial thicknessed concrete specimens, and microscopic measurements of crack width on the specimen surface are taken over a 4 month exposure time period.
Abstract: The progression of self-healing of cracked concrete is monitored in situ by diffuse ultrasound, in a novel application of this technique. The diffuse ultrasonic measurements are conducted on uncracked, tensile through-thickness cracked, and flexure partial-thickness cracked concrete specimens. Specimens made from three different mix designs are unbonded post-tensioned with a precompression force of 6.2 MPa that allows for the generation of cracks with widths less than 200 μm that should exhibit self-healing and are then exposed to a simulated marine environment. To estimate the extent of crack healing over time, two diffuse ultrasonic parameters are measured: an effective diffusivity and an arrival time of maximum energy (ATME). In addition, microscopic measurements of crack width on the specimen surface are taken over a 4 month exposure time period. Initial cracking causes an increase in the ATME and a significant decrease in diffusivity as compared to those of the reference, uncracked control specimens. With the progress of self-healing, the ATME of both tensile and flexure cracked specimens decreases, while the diffusivity increases and recovers the initial values found in the uncracked control specimens. These changes in the ATME and diffusivity suggest autogenous healing of the cracks. Comparisons of experimental results for these two parameters show that the diffusivity predicts self-healing trends in a more effective way than the ATME. A simple model is used to evaluate healing rates in different concrete mixes. The healing rates determined for the three mix designs are consistent with the results of independent observations. Finally, it is concluded that the present diffuse ultrasonic method is capable of monitoring and evaluating the self-healing of concrete.
TL;DR: In this article, a method for probabilistic fatigue life prediction using nondestructive testing data considering uncertainties from NDE data and fatigue model parameters is presented. But the method utilizes uncertainty quantification models for detection, sizing, and inputs.
Abstract: A method for probabilistic fatigue life prediction using nondestructive testing data considering uncertainties from nondestructive examination (NDE) data and fatigue model parameters. The method utilizes uncertainty quantification models for detection, sizing, fatigue model parameters and inputs. A probability of detection model is developed based on a log-linear model coupling an actual flaw size with a nondestructive examination (NDE) reported size. A distribution of the actual flaw size is derived for both NDE data without flaw indications and NDE data with flaw indications by using probabilistic modeling and Bayes theorem. A turbine rotor example with real world NDE inspection data is presented to demonstrate the overall methodology.