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Showing papers in "Journal of Nondestructive Evaluation in 2018"


Journal ArticleDOI
TL;DR: To correct for scatter in real-time, the deep scatter estimation (DSE) is developed which uses a deep convolutional neural network which is trained to reproduce the output of MC simulations using only the acquired projection data as input.
Abstract: X-ray scatter is a major cause of image quality degradation in dimensional CT. Especially, in case of highly attenuating components scatter-to-primary ratios may easily be higher than 1. The corresponding artifacts which appear as cupping or dark streaks in the CT reconstruction may impair a metrological assessment. Therefore, an appropriate scatter correction is crucial. Thereby, the gold standard is to predict the scatter distribution using a Monte Carlo (MC) code and subtract the corresponding scatter estimate from the measured raw data. MC, however, is too slow to be used routinely. To correct for scatter in real-time, we developed the deep scatter estimation (DSE). It uses a deep convolutional neural network which is trained to reproduce the output of MC simulations using only the acquired projection data as input. Once trained, DSE can be applied in real-time. The present study demonstrates the potential of the proposed approach using simulations and measurements. In both cases the DSE yields highly accurate scatter estimates that differ by< 3% from our MC scatter predictions. Further, DSE clearly outperforms kernel-based scatter estimation techniques and hybrid approaches, as they are in use today.

80 citations


Journal ArticleDOI
TL;DR: This work provides an overview of some of the most commonly used SNR measures and proposes a methodology to define the regions used to estimate the power of the signal and noise in the images.
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.

44 citations


Journal ArticleDOI
TL;DR: In this paper, the imaging capabilities of PAUT (5MHz) as well as near-field microwave imaging system (33.5 GHz) are discussed and evaluated for a number of specimens with man-made surface defects.
Abstract: Detecting and imaging near-surface defects is of significant importance in many applications. Detecting corrosion/defects under thin paint layer applied on metallic substrates, evaluating debond under a Teflon coat, as well as evaluating the integrity of the dielectric coats remains a challenge in many industries settings. Periodic testing is imperative for a wide range of industries to isolate material defects that could lead to catastrophic failures, expensive repairs, or a complete shutdown. Out of the many non-destructive testing (NDT) techniques available, phased array ultrasonic testing (PAUT) is widely used in various industries for material inspection. It has shown exceptional capability in detection of defects, including material loss and corrosion in metals. On the other hand, near-field microwave NDT is emerging as a powerful inspection modality for similar applications. In this paper, imaging capabilities of PAUT (5 MHz) as well as near-field microwave imaging system (33.5 GHz) are discussed and evaluated for a number of specimens with man-made surface defects. The evaluated defects include flat bottom slots, holes and corrosion-under-paint. Images produced by both techniques are presented. The images produced by the microwave imaging system are benchmarked with PAUT system.

35 citations


Journal ArticleDOI
TL;DR: In this article, a micro magnetic bridge probe (MMBP) of higher spatial resolution is designed and developed with an arbitrary width between the two sides of this MMBP in the testing magnetic bridge.
Abstract: Magnetic flux leakage (MFL) testing has been widely used as an efficient non-destructive testing method to detect damage in ferromagnetic materials. It’s of great importance to improve the testing capability of MFL sensors. In this paper, a micro magnetic bridge method in MFL of high sensitivity is proposed to detect micro-cracks. This method consists of a micro magnetic bridge core and an induction coil. Furthermore, a novel micro magnetic bridge probe (MMBP) of higher spatial resolution is designed and developed with $$10~\upmu \hbox {m}$$ width between the two sides of this MMBP in the testing magnetic bridge. The lift-off effect of this new MMBP is studied via finite element method and experimental verification. The results show this MMBP can achieve high sensitivity only when working with a micro-lift-off value. To examine the detecting capability of this MMBP, micro-cracks in magnetic particle inspection sensitivity testing pieces are all inspected, and the lowest depth value is only $$7~\upmu \hbox {m}$$ . The MMBP in this paper improves the testing capability of MFL to the micrometre scale and can be widely used to detect grinding micro-cracks in bearing rings.

32 citations


Journal ArticleDOI
TL;DR: In this article, a multivariable regression analysis was applied for the task of shot peening and some remarkable correlations were found between the shot-peening parameters, residual stress profile and Barkhausen noise features.
Abstract: The production of gear components includes numerous manufacturing operations which are carried out to ensure proper surface characteristics of components to deal with wear and fatigue. Surface shot peening is one way to increase the compressive residual stresses on the surface and thus ensure better wear and fatigue resistance. An experimental plan for shot peening was conducted to produce samples with varying surface characteristics. Residual stress profile and Barkhausen noise measurements were carried out for the samples. The objective of the study was to evaluate the interactions between the shot peening parameters studied, the residual stress profiles and the Barkhausen noise measurements. A multivariable regression analysis was applied for the task. Some remarkable correlations were found between the shot peening parameters, residual stress profile and Barkhausen noise features. The most important finding was that when the shot peening intensity was high enough, over 0.5 mmA, it dominated the shot peening coverage density parameter and thus no correlations could be gained. On the other hand, if the intensity parameter was lower than the limit of 0.5 mmA, the correlation between residual stress and Barkhausen noise measurements was remarkable. This means that the surface Barkhausen noise measurements could be used for the evaluation of the stress gradient in the shot peening process.

32 citations


Journal ArticleDOI
TL;DR: In this paper, a non-collinear shear wave mixing technique is proposed for evaluation of fatigue crack orientation, and numerical analysis of the nonlinear interaction of two shear waves with crack is performed using two-dimensional finite-element simulations.
Abstract: In this paper, a non-collinear shear wave mixing technique is proposed for evaluation of fatigue crack orientation. Numerical analysis of the nonlinear interaction of two shear waves with crack is performed using two-dimensional finite-element simulations. The simulation results show that the nonlinear interaction of the two shears waves with cracks leads to the generation of transmitted and reflected sum-frequency longitudinal waves (SFLW), moreover the propagation direction of reflected SFLW is correlated with the orientation of crack, which can be used for crack orientation evaluation. Non-collinear wave-mixing experiments were conducted on specimens with fatigue crack. The experimental results show that the directivity of the generated SFLW agrees well with the simulation results, and non-collinear shear wave mixing has potential use in fatigue crack orientation evaluation.

26 citations


Journal ArticleDOI
TL;DR: Results show that RFID sensors represents a promising method for remote deformation assessment in components.
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.

25 citations


Journal ArticleDOI
TL;DR: In this article, the authors used pulsed thermography (PT) and pulsed phase thermography to detect delaminations with a width-to-depth ratio (w2d) ranging from 1.0 to 7.9.
Abstract: The active thermography technique is one of the most effective nondestructive tests for evaluating subsurface delaminations in concrete structures. The limitation of this method, which has been studied for some time, is that the width of the smallest detectable defect should be at least two times larger than its depth. However, controversy on this matter remains for concrete material with largely uncertain homogeneity, although the development of the infrared (IR) detector technology improved the above-mentioned limitation. In this study, the pulsed thermography (PT) technique is therefore conducted in the laboratory to investigate the detectability of delaminations with the width-to-depth ratio (w2d) ranging from 1.0 to 7.9 by using a long IR wavelength detector with a focal plane array of 640 $$\times $$ 480 pixels. The study focuses on the w2d ratio lower than 2.0. A concrete specimen was made with 12 embedded simulated delaminations having different sizes and depths. The results showed that a combination of PT and pulsed phase thermography can be used to detect delaminations with a w2d ratio equal or greater than 1.25. In addition, the absolute contrast above the delamination increases with the higher w2d ratio, indicating that even for a relatively deep delamination, it is still detectable if a delamination is provided by appropriate heat energy and its size is sufficiently large. Finally, the study also indicates that as the amount of heating energy provided is increased, the greater accuracy in predicting the depth can be obtained.

25 citations


Journal ArticleDOI
TL;DR: In this paper, the applicability of acoustic emission (AE) technique to evaluate delamination crack in glass/epoxy composite laminates under quasi-static and fatigue loading was investigated.
Abstract: The aim of this study was to investigate the applicability of acoustic emission (AE) technique to evaluate delamination crack in glass/epoxy composite laminates under quasi-static and fatigue loading. To this aim, double cantilever beam specimens were subjected to mode I quasi-static and fatigue loading conditions and the generated AE signals were recorded during the tests. By analyzing the mechanical and AE results, an analytical correlation between the AE energy with the released strain energy and the crack growth was established. It was found that there is a 3rd degree polynomial correlation between the crack growth and the cumulative AE energy. Using this correlation the delamination crack growth was predicted under both the static and fatigue loading conditions. The predicted crack growth values was were in a good agreement with the visually recorded data during the tests. The results indicated that the proposed AE-based method has good applicability to evaluate the delamination crack growth under quasi-static and fatigue loading conditions, especially when the crack is embedded within the structure and could not be seen visually.

24 citations


Journal ArticleDOI
TL;DR: In this article, an ultrasonic monitoring approach that uses a coda wave comparison (CWC) technique was presented, which makes use of the highly sensitive diffuse (or coda) portion of a recorded ultrasonic waveform.
Abstract: Condition or health monitoring of concrete structures has experienced increasing interest over the last decade. While conventional sensors such as strain gauges are accurate and reliable, they only allow for surface observations. In contrast, ultrasonic waves propagate through the thickness of a member and can thus detect internal changes. In this paper we present an ultrasonic monitoring approach that uses a coda wave comparison (CWC) technique, which makes use of the highly sensitive diffuse (or coda) portion of a recorded ultrasonic waveform. In this study, the changes in the applied stress were correlated to the changes observed in the ultrasonic waveforms, which were estimated using magnitude-squared coherence (MSC). The CWC technique was evaluated by investigating key influence parameters that affect the relationship between MSC and the applied stress. First, two concrete cylinders were cast and tested to study the effect of maximum aggregate size. Second, two concrete prisms were used to study the effect of the frequency of the transmitted pulse. Finally, we discuss a field test involving a prestressed concrete bridge girder and a column. The results show that MSC is capable of discriminating minute stress changes in a laboratory as well as a field setting.

24 citations


Journal ArticleDOI
TL;DR: In this paper, the relationship between the surface hardness of 12CrMoV steel plate and the measured MBN and TMF signals is investigated with multivariable linear regression (MLR) model and BP neural network technique.
Abstract: Both magnetic Barkhausen noise (MBN) and tangential magnetic field (TMF) strength can be applied in the quantitative prediction of surface hardness of ferromagnetic specimens. The prediction accuracy depends on the selected model and the input parameters of the model. In this study, the relationship between the surface hardness of 12CrMoV steel plate and the measured MBN and TMF signals is investigated with multivariable linear regression (MLR) model and BP neural network technique. A comparative study between the MLR and BP model is conducted. The external validation results show that the BP model utilizing four MBN features as the input nodes has a smaller average prediction error (3.7%) than that of the MLR model (13.2%). Features extracted from the MBN and TMF signals are combined together as the input parameters of the BP model in order to achieve high accuracy. After adding two more TMF features into the input nodes of the BP network, the external validation results suggest that the average prediction error is decreased from 3.7 to 3.5%.

Journal ArticleDOI
TL;DR: In this article, a laser multi-modes scanning thermography (SMLT) method has been developed for defect detection of thermal barrier coating (TBCs) because of some of its characteristics, such as porosity and thin thickness, etc.
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.

Journal ArticleDOI
TL;DR: In this article, a new non-destructive permittivity measurement method is presented, where the material under test is placed in the near-field region of a microwave open-ended waveguide.
Abstract: A new convenient and non-destructive permittivity measurement method is presented. No physical cut of specimens is needed here for material characterisation. In the setup, the material under test is placed in the near-field region of a microwave open-ended waveguide. An electromagnetic model of the setup is built in the Computer Simulation Technology simulation software. Employing optimisation, the permittivity is obtained from the measured reflection coefficients $$\hbox {S}_{11}$$ . Using the same technique, the effect of the model size is investigated that could reduce the modelling effort for large structures. The efficiency of a traditional method (i.e., Newton) and an intelligent algorithm (i.e. particle swarm optimisation) for permittivity calculation is thoroughly studied and compared. The proposed methodology is validated by experimental data. It is demonstrated that the proposed method can provide more accurate permittivity results than the intrusive in-waveguide measurement. The proposed methodology can contribute to electromagnetic analysis, thickness measurement and non-destructive evaluation.

Journal ArticleDOI
TL;DR: In this paper, a calibration method for acoustic emission and ultrasonic sensors that is effective from 1 kHz to 1 MHz is described, which combines generalized ray theory and finite element analysis to model wave propagation at higher and lower frequencies, respectively.
Abstract: This paper describes a calibration method for acoustic emission and ultrasonic sensors that is effective from 1 kHz to 1 MHz. The method combines generalized ray theory and finite element analysis to model wave propagation at higher and lower frequencies, respectively. A ball impact is used as a calibration source, a thick aluminum plate is used as the test block, and hot glue is used as the couplant. We demonstrate this method on five commercial piezoelectric sensors: Physical Acoustics (PAC) R15a, PAC WSa, Panametrics V101, Panametrics V103, and Valpey-Fisher Pinducer. Our calibration results show that reflections and other wave phases can be more clearly identified with the less-resonant Panametrics sensors. The PAC sensors have the greatest sensitivity and are able to detect surface normal displacements at least down to 1 pm amplitude in the 100s of kHz frequency band. Aperture effect is minimized by the small size of the Pinducer. Our method focuses on the amplitude response of the sensors (phase is ignored) and extends the calibration to a frequency band that is lower than typical analyses. Low frequency information is useful for determining the seismic moment of a seismic source (analogous to the magnitude of an earthquake) and can increase the amount of information acquired in a single recording.

Journal ArticleDOI
TL;DR: In this article, the effects of the presence of an adhesive layer on acoustic emission (AE) wave propagation were investigated using a pencil lead break (PLB) as a simulated AE source at varying propagation distances and orientations.
Abstract: Acoustic emission (AE) monitoring shows promise as one of the most effective methods for condition monitoring of adhesively-bonded joints. Previous research has demonstrated its ability to detect, locate and classify adhesive joint failure, though in these studies little attention appears to have been paid to the differences in AE wave propagation through the bonded and un-bonded sections of the specimens tested, or to the effects of the wave modes excited or the propagation distances. This paper details an experimental study conducted on large aluminium sheet specimens to identify the effects of the presence of an adhesive layer on AE wave propagation. Three specimens are considered; a single aluminium sheet, two aluminium sheets placed together without adhesive, and an adhesively-bonded specimen. A pencil lead break (PLB) is used as a simulated AE source, and is applied to the three specimens at varying propagation distances and orientations. The acquired signals are processed using wavelet-transforms to explore time-frequency features, and compared with modified group-velocity curves based on the Rayleigh–Lamb equations to allow identification of wave-modes and edge-reflections. The effects of propagation distance and source orientation are investigated while comparison is made between the three specimens. It is concluded that while the wave propagation modes can be approximated as being constant throughout all three specimens, there is a significant change in the received waveforms due to the attenuation of high-frequency components exhibited by the bonded specimen. These findings may be utilised to provide a deeper understanding of acquired AE data, improving the current abilities to identify, locate and characterise damage mechanisms occurring within adhesive joints, ultimately improving safety in the use of adhesive bonding for critical applications.

Journal ArticleDOI
TL;DR: In this paper, samples of high-density homogeneous particleboards (PBs) of sugarcane bagasse and castor oil polyurethane resin were manufactured and subjected to low velocity impacts using an instrumented drop weight impact tower and four different energy levels.
Abstract: With a view to gaining an in-depth assessment of the response of particleboards (PBs) to different in-service loading conditions, samples of high-density homogeneous PBs of sugarcane bagasse and castor oil polyurethane resin were manufactured and subjected to low velocity impacts using an instrumented drop weight impact tower and four different energy levels, namely 5, 10, 20 and 30 J. The prediction of the damage modes was assessed using Comsol Multiphysics $$^\circledR .$$ In particular, the random distribution of the fibres and their lengths were reproduced through a robust model. The experimentally obtained dent depths due to the impactor were compared with the ones numerically simulated showing good agreement. The post-impact damage was evaluated by a simultaneous system of image acquisitions coming from two different sensors. In particular, thermograms were recorded during the heating up and cooling down phases, while the specklegrams were gathered one at room temperature (as reference) and the remaining during the cooling down phase. On one hand, the specklegrams were processed via a new software package named Ncorr v.1.2, which is an open-source subset-based 2D digital image correlation (DIC) package that combines modern DIC algorithms proposed in the literature with additional enhancements. On the other hand, the thermographic results linked to a square pulse were compared with those coming from the laser line thermography technique that heats a line-region on the surface of the sample instead of a spot. Surprisingly, both the vibrothermography and the line scanning thermography methods coupled with a robotized system show substantial advantages in the defect detection around the impacted zone.

Journal ArticleDOI
TL;DR: In this article, acoustic emission was applied for detection of micro-crack initiation in carbon fiber reinforced polymer composites subjected to shear stresses, and the acoustic emission historic index was the most effective AE parameter in damage initiation control.
Abstract: Acoustic emission (AE) was applied for detection of microcrack initiation in carbon fiber reinforced polymer composites subjected to shear stresses. Experimental materials were prepared from polyester bonded unidirectional (1D) non-crimp fabric and 2D plain-weave carbon fiber fabrics, using the resin transfer moulding technology. Control of epoxy resin/carbon textile proportions enabled variation of fiber volume content from small (34/35% for 2D/1D), through medium (51%) to high (68%). Rectangular samples ( $$45 \times 4 \times 2$$ mm) were cut from 1D plates along [0] and across [90] fibers. Similar size samples from 2D plates were cut along warp/weft axes as well as in two orthogonal bias directions. Selected side surfaces were polished for microscopic (SEM) observations. Short-beam-strength tests were performed in 3-point bending (l/h $$=$$ 4), with two AE sensors attached for damage monitoring, which allowed to interrupt loading sequence before final failure. The acoustic emission historic index was the most effective AE parameter in damage initiation control. Microcracks developing on polished composite side-surfaces were observed under the SEM and direct microscopic evidence confirmed fiber debonding to be the principal mechanism of crack initiation in these materials and testing conditions before any further damage.

Journal ArticleDOI
TL;DR: This study proposes a novel nonlinear acoustic health monitoring approach for detection of loose bolts, which can work with and without any sensors, and may be used as a low-cost sensor-free SHM or as a backup for conventional nonlinear SHM systems.
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.

Journal ArticleDOI
TL;DR: Simulation of ultrasound propagation in two-dimensional media containing, each one, different kinds of modeled discontinuities which mimic defects in welded joints were performed, and clustering and classification algorithms were employed to associate each simulated ultrasound signal with its corresponding modeled defects.
Abstract: Nondestructive testing is widely used to detect and to size up discontinuities embedded in a material. Among the several ultrasonic techniques, time of flight diffraction (TOFD) combines high speed inspection, high sizing reliability and low rate of incorrect results. However, the classification of defects through ultrasound signals acquired by the TOFD technique depends heavily on the knowledge and experience of the operator and thus, this classification is still frequently questioned. Besides, this task requires long processing time due to the large amount of data to be analyzed. Nevertheless, computational tools for pattern recognition can be employed to analyze a high amount of data with large efficiency. In the present work, simulation of ultrasound propagation in two-dimensional media containing, each one, different kinds of modeled discontinuities which mimic defects in welded joints were performed. Clustering (k-means) and classification (principal component analysis and k-nearest neighbors) algorithms were employed to associate each simulated ultrasound signal with its corresponding modeled defects. The results for each method were analyzed, discussed and compared. The results are very promising.

Journal ArticleDOI
TL;DR: In this article, 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.
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.

Journal ArticleDOI
TL;DR: 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 To FD measurements.
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

Journal ArticleDOI
TL;DR: In this paper, the authors evaluate a procedure designed to create reproducible and controlled cracks in concrete, based on using expanding mortar in a series of blind holes to guide the direction of the crack development.
Abstract: The non-destructive assessment of cracks in concrete is a common task for which non-destructive evaluation solutions have been published. Primarily, these tests have been carried out on artificial cracks that have been created by using notches instead of natural cracks. This study evaluates a procedure designed to create reproducible and controlled cracks in concrete. The procedure is based on using expanding mortar in a series of blind holes. This is done in combination with carefully aligned reinforcement to guide the direction of the crack development. The depth of the crack is also controlled by reinforcement. Crack depth varies statistically in the range of the maximum aggregate size (16 mm) used for concrete.

Journal ArticleDOI
Jiaxu Duan1, Lin Luo1, Xiaorong Gao1, Jianping Peng1, Jinlong Li1 
TL;DR: A new dichotomous method 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.
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.

Journal ArticleDOI
TL;DR: In this article, the volume fraction of pores and its distribution in CMC samples containing different amounts of porosity were quantified using optical microscopy and X-ray computed tomography scans.
Abstract: Thermography is one of the Non-Destructive Evaluation methods used to qualitatively estimate the amount of porosity in as-manufactured ceramic matrix composite (CMC) parts. Through-transmission (TT) thermography allows for comparison of thermal diffusivity caused by differences in material density and porosity at different locations in the part. In this study, volume fraction of pores and its distribution in CMC samples containing different amounts of porosity was quantified using optical microscopy and X-ray computed tomography scans. TT thermography was done on the same specimens and images were analyzed to determine the distribution of thermal diffusivity. Comparison of porosity measurements and thermal diffusivity images shows an inverse correlation. A simple two-phase analytical model describing this relationship is derived for composites and its solution is shown to compare favorably with experimental data. In the absence of porosity data, the model can be used to estimate porosity directly from thermal diffusivity data.

Journal ArticleDOI
TL;DR: The adaptive cross approximation (ACA) algorithm to accelerate boundary element method (BEM) for eddy current nondestructive evaluation (NDE) problem and modified ACA (MACA) for more memory saving while keeping almost same accuracy compared with original ACA is presented.
Abstract: This paper presents the adaptive cross approximation (ACA) algorithm to accelerate boundary element method (BEM) for eddy current nondestructive evaluation (NDE) problem. The eddy current problem is formulated by boundary integral equation and discretized into matrix equations by BEM. Stratton–Chu formulation is selected and implemented for the conductive medium which does not has low frequency breakdown issue. The ACA algorithm has the advantage of purely algebraic and kernel independent. It starts with hierarchically partitioning the object to get diagonal blocks, near blocks and far blocks. The far-block interactions which are rank deficient can be compressed by ACA algorithm meanwhile the elements for diagonal-block interactions and near-block interactions are stored and computed by BEM. We apply modified ACA (MACA) for more memory saving while keeping almost same accuracy compared with original ACA. For numerical testing, several practical NDE examples such as coil above a half space conductor, tube in a fast reactor and Testing Electromagnetic Analysis Methods (TEAM) workshop benchmark problem are presented to show the robust and efficiency of our method. With the aid of ACA, for electrically small problems, the complexity of both the memory requirement and CPU time for BEM are reduced to $$ O\left( {N\log N} \right). $$

Journal ArticleDOI
TL;DR: In this article, an experimental methodology, based on ultrasonic measurements, that aims at evaluating the anisotropic damage in woven semi-crystalline polymer composites through new damage indicators is proposed.
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.

Journal ArticleDOI
TL;DR: In this paper, a wire rope tester based on magnetic flux leakage is constructed, where two rings of NdFeB are cut in axial direction into 32 equal arc segments such that each arc segment subtends an angle of 22.5° at the centre.
Abstract: A new wire rope tester based on principle of magnetic flux leakage is constructed. Two rings of NdFeB are cut in axial direction into 32 equal arc segments such that each arc segment subtends an angle of 22.5° at the centre. These arc segments are then parallely magnetized in magnetizer. A ferromagnetic cylinderical yoke is constructed by hinging two ferromagnetic half cylinders along one axial edge. A fixture consisting of a wooden square base, wooden mandrel, stepped and slotted Aluminium cylinder and Aluminium fillers is made to assemble the NdFeB magnets in a ring on both the ends of the ferromagnetic yoke. A Hall effect sensor is instrumented inside the yoke in the middle at radial distance of 34 mm from the axis of the yoke. A ferromagnetic wire rope with a defect is inserted in the novel wire rope tester. It has been successfully shown by performing Non-destructive testing that whenever a defect in a wire rope passes below the Hall-effect sensor instrumented in the wire rope tester developed in this work, a signal is generated indicating the defect.

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TL;DR: In this article, a non-destructive evaluation of interlayer disbond defects in aerospace grade Fibre Metal Laminate sheets (FMLs) is presented, where a continuous laser is moved over the material surface, while the thermal footprint of the moving heat source is acquired by an infrared thermal camera.
Abstract: This work describes a numerical study on non-destructive evaluation of interlayer disbond defects in aerospace grade Fibre Metal Laminate sheets (FMLs). A recently proposed infrared non-destructive testing setup is considered, where a continuous laser is moved over the material surface, while the thermal footprint of the moving heat source is acquired, e.g. by an infrared thermal camera. Interlayer disbonds are then detected by analysing the features of the acquired thermograms. The experimental feasibility of this approach has been recently proved. The present work proposes a numerical simulation of the NDT approach, where the material thermal response is analysed and correlated to defects signatures. The numerical study has in particular investigated the influence of a number of different features on the defect detectability, and on the accuracy of defect edges and position identification. Such features comprise different FML materials (GLARE, CARAL, Ti-Gr), laser heat deposition and regions of data analyses.

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TL;DR: In this paper, the amplitude reduction based on measured attenuation values is used to predict the probability of detection (PoD) of an acoustic emission signal at a given propagation distance.
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.

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TL;DR: Impact tests with an impulse hammer combined with experimental modal analysis are conducted to determine the clamping force by interpreting the change in the local mode frequency of a bolt head in the high frequency region as a function of the clamped force.
Abstract: It is important to determine and control the clamping force of a bolted joint. Due to its simple setup, the torque control method is typically used to control the clamping force when tightening bolts. After tightening, hammer tests, ultrasonic techniques and methods employing sheet materials as sensors are often used. Many methods have been proposed, but using them to determine and control the clamping force during or after tightening bolts is labor intensive or expensive. Here we conduct impact tests with an impulse hammer combined with experimental modal analysis to determine the clamping force by interpreting the change in the local mode frequency of a bolt head in the high frequency region as a function of the clamping force. To demonstrate the applicability of our method, we also investigate its limits with regard to bolt sizes.