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Showing papers in "Journal of Nondestructive Evaluation in 2011"


Journal ArticleDOI
TL;DR: In this article, an Artificial Neural Network and signal processing technique is proposed to improve the sensibility of flaw detection and to classify defects in ultrasonic testing. And the results of the algorithms developed and applied to ultrasonic signals are highly reliable and precise for online quality monitoring.
Abstract: A methodology is developed to detect defects in NDT of materials using an Artificial Neural Network and signal processing technique. This technique is proposed to improve the sensibility of flaw detection and to classify defects in Ultrasonic testing. Wavelet transform is used to derive a feature vector which contains two-dimensional information on various types of defects. These vectors are then classified using an ANN trained with the back propagation algorithm. The inputs of the ANN are the features extracted from each ultrasonic oscillogram. Four different types of defect are considered namely porosity, lack of fusion, and tungsten inclusion and non defect. The training of the ANN uses supervised learning mechanism and therefore each input has the respective desired output. The available dataset is randomly split into a training subset (to update the weight values) and a validation subset. With the wavelet features and ANN, good classification at the rate of 94% is obtained. According to the results, the algorithms developed and applied to ultrasonic signals are highly reliable and precise for online quality monitoring.

130 citations


Journal ArticleDOI
TL;DR: In this article, a Teflon tape of width 45 mm is kept in the mid plane of the laminate which serves as an initiator for delamination during loading, and a tensile test in the transverse direction along with acoustic emission monitoring is performed.
Abstract: In order to design structural components using composite materials a deep understanding of the material behaviour and its failure mechanisms is necessary. To create a better understanding of the initiation, growth and interaction of the different types of damage, damage monitoring during mechanical loading is very important. To this direction, AE is a powerful non destructive technique for real time monitoring of damage development in materials and structures which has been used successfully for the identification of damage mechanisms in composite structures under quasi static and dynamic-cycle loading. In this present work, pure resin plate and GFRP composite laminates with stacking sequence of [00]6, are fabricated using Hand lay-up method. During the layup a Teflon tape of width 45 mm is kept in the mid plane of the laminate which serves as an initiator for delamination during loading. As per ASTM STD D5528 01 DCB (Double Cantilever Beam) specimens are cut out from the laminates and are subjected to tensile test in the transverse direction along with acoustic emission monitoring. While loading, Markings are made on the sides of the specimen to track the crack front using a magnifying lens. Parametric analysis is performed on the AE data obtained during crack propagation to discriminate the failure modes. Fast Fourier Transform (FFT) enabled the calculation of frequency content of each damage mechanism. Further STFFT analysis is performed on a portion of the waveforms representing the dominant frequency content pertaining to each damage mechanism.

49 citations


Journal ArticleDOI
TL;DR: Close-range photogrammetry algorithms were designed to extract spatial information from photographic image data, and geometrically measure the horizontal drift (also called interstory drift) sustained at key floors along the edge of a damaged building as discussed by the authors.
Abstract: Timely and accurate evaluation of damage sustained by buildings after seismic events such as earthquakes or blasts is critical to determine the buildings’ safety and suitability for their future occupancy. Time used in conducting the evaluations substantially affects the duration for which the potentially damaged buildings remain unusable. The elapsed time may lead to direct economic losses to both public and private owners, and society at large. The presented research investigates the application of close-range photogrammetry surveying techniques and Augmented Reality (AR) visualization to design a semi-automated method for rapidly measuring structural damage induced in tall buildings by seismic events such as earthquakes or explosions. Close-range photogrammetry algorithms were designed to extract spatial information from photographic image data, and geometrically measure the horizontal drift (also called interstory drift) sustained at key floors along the edge of a damaged building. The measured drift can then be used to compute damage indices that correlate the drift to the building’s structural integrity and safety. In this research, the measurement accuracy of the calculated drift using photogrammetry principles is particularly studied. The experimental results achieved an acceptable and usable accuracy level of 5 mm using a consumer grade digital SLR camera, demonstrating the potential of photogrammetry assisted rapid measurement of earthquake-induced building damage. It is expected that in the future, as advances in optical-sensing and positioning technologies continue to make high-end cameras and measurement systems (GPS, compass) more affordable, higher accuracy will be practically achievable for further improvement in measurements using the proposed method.

42 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated whether the sample dimensions measured in laboratory have effect on P-wave velocity or not, and the results were statistically analyzed using the method of least squares regression, exponential, and polynomial relationship with high correlation coefficient.
Abstract: P-wave velocity is one of the non-destructive geophysical methods directly or indirectly used by engineering working by various filed. Thus the accuracy of the recorded P-wave velocity affects these parameters. In this survey whether the sample dimensions measured in laboratory have effect on P-wave velocity or not was investigated. Nine different rock groups were used in this study. Six different diameter core samples were prepared from each of the groups. Ultrasonic tests were carried out on the core samples having different diameter to investigate how the sound velocity varies with sample dimension. The test results were statistically analyzed using the method of least squares regression, exponential, and polynomial relationship with high correlation coefficient were found between the sample diameters and P-wave velocities. In four sample groups a decrease in ultrasonic velocity depending on an increase in diameter was observed. In five other sample groups in the samples up to 78.68 mm diameter, a decrease in P-wave velocity value was observed but a significant increase in the P-wave velocity was observed for the biggest diameter samples. This observed decrease connected with sample dimension varies dependently on physical characteristic properties of the sample.

38 citations


Journal ArticleDOI
TL;DR: In this article, a simple procedure is proposed for confirming and demonstrating the representativeness of used flaws, and the available information on es- sential flaw parameters for various NDE techniques is re- viewed.
Abstract: The reliability of non-destructive evaluation de- pends on multitude of different factors. Consequently, it is difficult to assess the performance of the system. The only practical way to overcome this complexity and asses inspec- tion reliability is using practical trials. In practical trials the inspection is performed on a known, flawed sample and reli- ability is judged by comparing the acquired inspection result with known state of the sample. However, confirming (and demonstrating), that the practical trials and, in particular, the usedflaws are representative to postulatedinspectioncase is, at present, challenging. In this paper, the open literature is reviewed and compiled to the extent necessary for providing a starting point for confirming and demonstrating representativeness of flaws used in the practical trials. The available information on es- sential flaw parameters for various NDE techniques is re- viewed. The used measurement methods for each parameter is discussed and the available in-service data summarized. Finally, a simple procedure is proposed for confirming and demonstrating the representativeness of used flaws.

37 citations


Journal ArticleDOI
TL;DR: In this paper, an impact-based acoustic NDE method where the traffic noise was filtered by employing a noise cancelling algorithm and where subjectivity was eliminated by introducing feature extraction and pattern recognition algorithms was presented.
Abstract: Delamination is a commonly observed distress in concrete bridge decks. Among all the delamination detection methods, acoustic methods have the advantages of being fast and inexpensive. In traditional acoustic inspection methods, the inspector drags a chain alone or hammers on the bridge deck and detects delamination from the “hollowness” of the sound. The signals are often contaminated by ambient traffic noise and the detection of delamination is highly subjective. This paper describes the performance of an impact-based acoustic NDE method where the traffic noise was filtered by employing a noise cancelling algorithm and where subjectivity was eliminated by introducing feature extraction and pattern recognition algorithms. Different algorithms were compared and the best one was selected in each category. The comparison showed that the modified independent component analysis (ICA) algorithm was most effective in cancelling the traffic noise and features consisting of mel-frequency cepstral coefficients (MFCCs) had the best performance in terms of repeatability and separability. The condition of the bridge deck was then detected by a radial basis function (RBF) neural network. The performance of the system was evaluated using both experimental and field data. The results show that the selected algorithms increase the noise robustness of acoustic methods and perform satisfactorily if the training data is representative.

32 citations


Journal ArticleDOI
TL;DR: In this paper, the authors explore near field effects for both laser generation and laser detection points near a defect, and compare the enhancements for defects which are angled relative to the surface.
Abstract: Enhancement of the Rayleigh wave signal amplitude at a surface defect, due to interference of incident, reflected and mode converted waves, has been reported by several authors, and it has been suggested that this could be used as a fingerprint of the presence of such cracking. The scanning laser line source technique in particular, where signal amplitude is enhanced as the laser generating the Rayleigh waves is in the region of a surface defect, has been reported as a suitable detection tool. However, the previous work has looked primarily at defects propagating normal to the surface, which may not always be a suitable approximation, and the enhancement measured when a detection laser rather than a generation laser is near a crack may, in some cases, be more significant. This work explores near field effects for both laser generation and laser detection points near a defect, and compares the enhancements for defects which are angled relative to the surface. We use a combination of finite element method models and experimental results, and probe enhancements of both the amplitude and frequency signals, and show that scanning the detection point may be a better method for locating surface defects if they are inclined at an angle to the surface.

31 citations


Journal ArticleDOI
TL;DR: In this article, the phase of the signal from an interface is also affected by the anisotropic microtexture of Ti-6Al-4V, and good separation between well-bonded and partially bonded samples was achieved using a symmetric inspection, where the magnitude and phase of reflection coefficient were calculated for normal incidence from opposite sides of the diffusion bond.
Abstract: Diffusion bonds offer several advantages over alternative welding methods, including the ability to produce near-net shapes and achieve almost parent metal strength. However, voids remnant from the joining process can be tens of microns in their lateral dimension, making them difficult to detect with conventional pulse-echo immersion inspection at any significant metal depth. In titanium the inspection is particularly challenging; the anisotropic microstructure is highly scattering and the diffusion bond itself forms an interface between regions of preferred crystallographic orientation (macrozones), which can act as a weak spatially coherent reflector. A simple interfacial spring model predicts that, for partial bonds (sub-wavelength voids distributed on the bond line) and at certain frequencies, the phase of the signal can be used to separate the component of the signal due to the change in texture at the interface and the component due to the flaw. Here it is shown that the phase of the signal from an interface is also affected by the anisotropic microtexture of Ti–6Al–4V. Good separation between well-bonded and partially bonded samples was achieved using a symmetric inspection, where the magnitude and phase of the reflection coefficient were calculated for normal incidence from opposite sides of the diffusion bond.

28 citations


Journal ArticleDOI
TL;DR: In this paper, an experimental study was carried out to evaluate the potential of the ultrasonic technique with ultrasonic velocity and attenuation measurements, to assess the heat aging effects on duplex stainless steel SAF 2205, at temperatures of 425°C and 475°C for time periods of 12 h, 24 h, 50 h, 100 h and 200 h, as well as in the as received state of the material.
Abstract: In this work, an experimental study was carried out to evaluate the potential of the ultrasonic technique, with ultrasonic velocity and attenuation measurements, to assess the heat aging effects on duplex stainless steel SAF 2205, at temperatures of 425°C and 475°C for time periods of 12 h, 24 h, 50 h, 100 h and 200 h, as well as in the as received state of the material. Velocity measurements were calculated for both longitudinal and transversal waves. The elastic constants, Young’s modulus and shear modulus, of the material were computed from the relationship between longitudinal and transversal velocities. For the ultrasonic attenuation, only longitudinal waves were considered. Despite the large scatter measurements, both ultrasonic velocity and attenuation increased with the heat aging time, particularly at 475°C. Thus, it may be concluded that the technique used is promising and provides relevant contributions to an accurate characterization of materials and evaluation of their mechanical properties in a non-destructive manner.

24 citations


Journal ArticleDOI
TL;DR: In this article, the estimation of probability of detection (POD) for a vibrothermography inspection procedure is described based on a large scale experiment on specimens with two different kinds of metal containing fatigue cracks.
Abstract: This paper describes the estimation of probability of detection (POD) for a vibrothermography inspection procedure. The results are based on a large scale experiment on specimens with two different kinds of metal containing fatigue cracks. The specimens were tested independently at three inspection sites: Iowa State University (ISU), Pratt and Whitney (PW) and General Electric (GE). Despite the substantially different vibrothermography configurations and experimental measurement responses, the estimated PODs as function of crack length and dynamic stress were similar for all three inspection sites, which make quantitative POD comparisons possible across different inspection sites.

20 citations


Journal ArticleDOI
TL;DR: In this paper, an optical fiber sensor based on the moisture dependency of absorption of laser light was developed to measure humidity and AE from active corrosion under insulation (CUI) by connecting coating of polyvinyl alcohol and CoCl2 coating and pullulan coating as a cladding layer.
Abstract: We simultaneously monitored humidity and AE from active corrosion under insulation (CUI). For humidity monitoring, we developed an optical fiber sensor based on the moisture dependency of absorption of laser light by connecting coating of polyvinyl alcohol and CoCl2 coating and pullulan coating in series on the fiber as a cladding layer. The sensor could be used to measure humidity of 65–95% RH at 80°C. The temperature dependence of the sensor was as small as 2.5% RH/10°C. We monitored active CUI by the acoustic emission technique and humidity sensing under wetting and drying cycles. Most AE signals were produced during the drying process in each wetting and drying cycle, and the AE rate increased with the time of wetness (period of humidification).

Journal ArticleDOI
TL;DR: In this paper, a new methodology based on a simple and novel combination of TOFD and the immersion technique has been proposed by the authors that successfully extends the application of ToFD to thinner sections down to 3 mm.
Abstract: Time of flight diffraction (TOFD) is a well-developed ultrasonic non-destructive testing (NDT) technique which has been applied successfully for accurate sizing of defects in thick sections. Codes of practice such as ASME now permit TOFD for routine examination as an alternative to radiography for thick weldments. However, examination of thinner sections by TOFD has its limitations. The main limitation is that as the thickness of the specimen reduces, the lateral wave, diffracted wave and the back wall echo merge together and it is very difficult to identify and size the discontinuity. Also, the size of conventional transducers limits the required probe separation. Limited success has been obtained internationally through the application of miniature probes and software for extending TOFD to lower thicknesses. In these cases, the minimum thickness that has been examined is 7 mm. A new methodology based on a simple and novel combination of TOFD and the immersion technique has been proposed by the authors that successfully extends the application of TOFD to thinner sections down to 3 mm. Immersion coupling provides a delay line, the necessary angles and probe separation making it possible to examine the thin components successfully. This paper highlights the results of detailed experimental investigations on immersion TOFD and its successful application for the evaluation of welds in hexcan used for encapsulating nuclear fuel pins.

Journal ArticleDOI
TL;DR: In this paper, a new ODS Frequency Response Function (ODS FRF) for investigations using SLDV is formulated and a new form of scale factor for the ODS FRF is also introduced to normalize the effects from variable excitation force.
Abstract: Operating Deflection Shapes (ODS) has emerged as one of the powerful techniques in vibration analysis to understand and to evaluate the absolute dynamic behaviour of a machine, component or an entire structure. Traditionally, accelerometers have been used to get the ODS of a structure. However, recent development shows that certain situation may not allow direct contact with the structure under investigation. Therefore, Scanning Laser Doppler Vibrometer (SLDV) has become popular in the investigation. In this paper, a new ODS Frequency Response Function (ODS FRF) for investigations using SLDV is formulated. The ODS FRF is used to construct the ODS of the structure. A new form of scale factor for the ODS FRF is also introduced to normalize the effects from variable excitation force. The importance of this scale factor is demonstrated on a beam and plate under the excitation of varying forces. It is found that the suggested ODS FRF and the scale factor give the desired result in comparison with theory.

Journal ArticleDOI
TL;DR: In this article, signal analysis and POD of laboratory grown fatigue cracks in the corners of bolt holes of 7075-T6 aluminum is examined, and a number of parameters that enhance crack detection are identified, including the use of intimate contact probes versus steel sheath (non-contact), higher frequencies and use of C-Scan display.
Abstract: Fatigue cracks are prone to develop around fasteners found in multi-layer aluminum structures on ageing aircraft such as the CC-130 Hercules and CP-140 Aurora (P-3 Orion). Probability of Detection (POD) studies using eddy current techniques within the bolt holes contribute to risk assessments used in evaluating the serviceability of these aircraft. Improving POD by optimizing the inspection system can reduce the required frequency of inspections, since assurance of detection of smaller crack sizes extends the interval for which growth of cracks to a critical size may occur. In this work signal analysis and POD of laboratory grown fatigue cracks in the corners of bolt holes of 7075-T6 aluminum is examined. A number of parameters that enhance crack detection are identified, including the use of intimate contact probes versus steel sheath (non-contact), higher frequencies and the use of C-Scan display. Results demonstrate better detectability at 1600 kHz, than at the normally used 400 kHz, and enhanced recognition and assurance of identification of peak crack signal for data recorded and displayed in a C-Scan format. Results are compared with a previous POD study, which used current field techniques for detection.

Journal ArticleDOI
TL;DR: In this article, a standard protocol for quantitative X-ray computed tomography (μCT) analysis of porous bioceramics was proposed. But the authors did not specify the optimal values for more detailed parameters (e.g., threshold determination).
Abstract: Microfocus X-ray computed tomography (μCT) has now become widely available for the nondestructive evaluation of porous bioceramics suitable for use as a bone substitute in orthopedic surgery. As part of an official Japanese working committee, we recently participated in the preparation of a proposed standard protocol for the quantitative μCT analysis of porous bioceramics sent to the International Organization for Standardization (ISO). In this protocol, the recommended basic conditions for analysis were [field of view (XY plane): 3.0 mm, spatial resolution: 6 μm/pixel (or the closest minimal values available for both parameters on a particular μCT system), matrix size: 512 pixels], and we have now further determined the optimal values for more detailed parameters (e.g., threshold determination). To validate the utility of the complete protocol, three different types of ceramic sample [a ceramic of β-tricalcium phosphate (β-TCP) and two types of hydroxyapatite (HAp) with different porosities] were evaluated with three different types of cone-beam μCT scanner (the Shimadzu SMX-100CT, Shimadzu inspeXio-90CT, and Skyscan-1174 scanners). Acquired images were quantified using 3D-reconstruction software, VGStudio MAX (version 1.2). After comparing data obtained from these three μCT scanners, we have found that determinations of both porosity and pore-interconnectivity were very similar from one system to the other although the total number of measured pores did vary between scanners. The present data indicate that our protocol for μCT analysis is reliable enough to quantify the porosity and interconnectivity of porous bioceramics and would therefore facilitate both large-scale screening and quality control of porous bioceramic samples.

Journal ArticleDOI
TL;DR: In this paper, the 1-D stress wave theory is applied to assess pile integrity in a nondestructive way, and a method for uncoupling the soil resistance and the pile impedance effects is presented.
Abstract: The pulse-echo method is commonly used to assess pile integrity in a nondestructive way. One of the strategies for detecting relative variation in pile impedance is to analyze the wave reflections from the anomalies based on the 1-D stress wave theory. In current practice, however, several difficulties remain to be resolved in interpreting the wave patterns. Firstly, due to possible three-dimensional (3-D) behavior near the source and dispersion behavior far from the source, 1-D stress wave theory is not always applicable in analyzing the reflections from the anomalies. Secondly, reflections can be produced continuously along the shaft due to the pile-soil interaction, so that the reflection patterns are highly correlated to those from the pile body in complex layered soil profiles, and thus it is generally difficult to distinguish whether the reflections are produced by pile anomalies or by the changes in the soil profiles. In this paper, actual wave characteristics are analyzed based on numerical simulations and guided wave theory, the conditions for 1-D approximation are suggested, and the a method for uncoupling the soil resistance and the pile impedance effects is presented. The evaluation of pile integrity can be improved with help of the 1-D based signal matching technique. The technique is applied to experiments conducted on model piles, test piles for accreditation of pile inspectors, and routine in-situ piles. The results show that 1-D stress wave theory is approximately applicable in analyzing the reflections from deep anomalies under certain limited conditions, and the soil resistance and the pile impedance effects can be effectively uncoupled by relating the pile-soil interaction to the pile radius and the properties of the surrounding soils.

Journal ArticleDOI
TL;DR: In this article, the authors have shown that degradation of pipelines is the result of the continuous attack by the environment of these conduits like climate change (temperature, rate moisture in the ground, etc.…) that may lead to a corrosive environment.
Abstract: Degradation of pipelines is the result of the continuous attack by the environment of these conduits like climate change (temperature, rate moisture in the ground, etc.…) that may lead to a corrosive environment. The design and the maintenance of these conduits and pipelines is a challenge for oil industry seen the serious consequences which can occur because of several reasons, example: defects of the cracks types, rust…, etc. Which can cause escapes of the transported matter or ruptures of these conduits with all that involves like economic loss and pollution of the environment.

Journal ArticleDOI
TL;DR: In this article, the authors proposed a method to detect notch-like damages in plates using piezoelectric transducers, which does not use prior baseline data for damage detection.
Abstract: This paper describes a method to detect notch like damages in plates using piezoelectric transducers. The method does not use prior baseline data for damage detection. A single pair of piezoelectric wafer transducers made of Lead Zirconate Titanate (PZT) is attached back to back on the opposite sides of a plate and are used for simultaneous actuation and sensing. A notch, which is a sudden change in thickness of the plate, leads to mode conversion of Lamb waves. The mode converted wave component in the measured signal is then separated from the other Lamb wave mode components using polarization characteristics of the piezoelectric wafer transducers. The damage index is a function of the amplitude of this mode converted component of the signal. In real world situations, the damage index will not be exactly zero due to inaccuracy in transducer collocation and non-uniformity in their bonding conditions. Therefore, a (non-zero) threshold for the damage index needs to be established to avoid false alarms. True to the spirit of baseline-free damage detection, this threshold is computed from the signals acquired only from the current state of the structure. This is achieved by using redundancy in signal measurements. Since the method detects damages without having to rely on baseline data, environmental variations like temperature change do not affect its performance. Results from numerical simulations as well as experiments on aluminum specimens are provided to demonstrate the effectiveness of the method described above.

Journal ArticleDOI
TL;DR: In this paper, thin piezoelectric films have been deposited directly on top of steel and aluminum substrates as integrated ultrasonic transducer (IUT) receivers to detect laser generated ultrasound.
Abstract: Thick (>50 μm) piezoelectric films have been deposited directly on top of steel and aluminum substrates as integrated ultrasonic transducer (IUT) receivers to detect laser generated ultrasound. The film fabrication is based on a sol-gel spray technique. In this study IUTs intrinsically acting as bulk longitudinal wave receivers use various mode conversion approaches and serve as longitudinal, shear, symmetric, anti-symmetric and shear horizontal plate wave receivers. Different laser generation conditions such as point and line sources of different sizes are also applied to investigate the capabilities of IUT receivers. Ultrasonic measurements on metal substrates with planar and curved surfaces at temperature up to 400°C using laser generated and IUT ultrasound receiver are demonstrated.

Journal ArticleDOI
TL;DR: In this paper, a two-stage damage detection method based on energy balance equation and evidence fusion is presented to solve structural multi-damage identification problem, and an Energy Balance Equation (EBE) index was presented to identify structural damage extent.
Abstract: In order to solve structural multi-damage identification problem, a two-stage damage detection method based on energy balance equation and evidence fusion is presented. First, a Frequency Change Identification (FCI) method and Modal Strain Energy Dissipation Ratio (MSEDR) method are utilized to preliminarily identify structural damage locations, and then a Fusion Damage Localization (FDL) method based on evidence theory is proposed to precisely detect damage locations. The FDL method mainly utilizes evidence theory to combine both the FCI localization information and the MSEDR localization information. Thus, more precise damage localization information can be acquired. After the damaged locations are determined, an Energy Balance Equation (EBE) index is presented to identify structural damage extent. Considering that strain energy dissipation should be equal to the change of modal strain energy, a quartic EBE equation is deduced, and structural damage extent can be obtained through the solution of the equation. An average quantification index is also proposed to improve identification precision. The simulation results demonstrate that the FDL method can perfectly detect structural damage locations, and the EBE index and average index can identify structural damage extent.

Journal ArticleDOI
TL;DR: In this article, a dual-energy computer tomograph for oceanographic research vessel with a diameter up to 12 cm and a height up to 1m was built and tested on-board of the R/V Mare Nigrum.
Abstract: A dedicated on-board dual energy computer tomograph able to generate both tomographic and digital radiographic images of unconsolidated sediments cores with a diameter up to 12 cm and a height up to 1 m was built and tested on-board of the R/V Mare Nigrum. This instrument, designed to be used on-board of any oceanographic research vessel with minimum adaptations, can work very well on stationary laboratory too, provided that there is adequate protection against hard X-rays. The tomograph has a single 160 kV X-ray tube and two set of 240 in-line X-ray detectors separated by a copper attenuator (dual-energy arrangement) allowing one to obtain tomographic as well as digital radiographic images depicting the distribution of both density and effective atomic number of the objects. In tomographic and radiographic mode, the spatial resolution of reconstructed images of the linear attenuation coefficient is about 0.5 mm while in dual-energy mode, when reconstructed images depict the distribution of densities and effective atomic numbers that requires an additional smoothing filtering, the spatial resolution is about 1 mm. By using a set of standard samples with known values of densities and effective atomic numbers we have estimated the precision in calculating the local values of these parameters to a maximum of 8%. By its performance and by its ability to work on-board, the tomograph could be useful not only for oceanographic researches but also for any exploratory tests performed on open sea.

Journal ArticleDOI
TL;DR: In this article, the feasibility of using transmitted wave energy for joint rigidity assessment was investigated on a joint between two aluminum plates consisting of a dry aluminum-toaluminum connection, similar to possible panel-to-panel connections that could be used as part of a modular satellite design.
Abstract: A modular satellite design has been proposed in order to enable rapid deployment of satellites. The design would allow panels with common functions to be manufactured and tested long before a new satellite is needed. Once the satellite is assembled, a quality assessment of the connections between panels would need to be performed before the craft is deemed flight worthy. This paper reports on an investigation on the feasibility of using transmitted wave energy for joint rigidity assessment. The experimental setup and methods will be presented. Experiments were conducted on a joint between two aluminum plates consisting of a dry aluminum-to-aluminum connection, similar to possible panel-to-panel connections that could be used as part of a modular satellite design. Comparisons were made between wave energy transmission and a mechanical assessment of the joint rigidity. Results show excellent correlation between joint rigidity and energy transmission, demonstrating the feasibility of the using wave energy transmission amplitudes to inspect metal-to-metal dry connections.

Journal ArticleDOI
TL;DR: In this article, a self-developed air-coupled Lamb wave NDT system has been used in three different metallic plates, such as stainless steel, copper and brass.
Abstract: This paper experimentally demonstrates the viability of Lamb waves generation and detection in metallic plates using ultrasonic air-coupled concave array transducers. For this purpose, a self-developed air-coupled Lamb wave NDT system has been used in three different metallic plates, such as stainless steel, copper and brass. First, pure copper plates were used to calibrate the measuring system and then other tests were performed in 304 stainless steel and CW508L brass. The obtained Lamb waves confirm the theoretical values, both in the phase velocity and in the group velocity measurements. In addition, a complete study of the errors in the measurements is also provided.

Journal ArticleDOI
Kin Ho Lo1
TL;DR: In this article, it has been found that the room-temperature a.c. magnetic susceptibility also has a good temperature-dependence when spinodal decomposition occurs.
Abstract: Duplex stainless steels are embrittled on exposure to elevated temperatures because of spinodal decomposition (<550°C) and sigma phase formation (between 600°C and 900°C). The sigma phase has been discovered to undergo a paramagnetic-to-ferromagnetic transition at cryogenic temperatures and its Curie temperature has a good dependence on prior annealing temperature. Additionally, it has been found that the room-temperature a.c. magnetic susceptibility also has a good temperature-dependence when spinodal decomposition occurs. It is viable to use room-temperature a.c. magnetic susceptibility and the cryogenic magnetic transition of the sigma phase for 1. temperature measurement and 2. discrimination between spinodal decomposition and sigma phase formation in duplex stainless steels.

Journal ArticleDOI
TL;DR: In this paper, a study aimed at evaluating the effectiveness of fiberglass wrapping in controlling and reducing the rate of corrosion in bridge concrete columns was presented, where a fiberglass wrap is placed as a barrier between the concrete surface and the surrounding environment and is expected to reduce the detrimental effect of traffic splashing of deicing solutions.
Abstract: Many in-service concrete bridge decks and columns built before the advent of epoxy coated bars show cracking and spalling of the concrete due to corrosion of the steel reinforcement. In cold regions, the corrosion rate of concrete bridge decks and columns is accelerated by the use of deicing solutions in winter. The corrosion of the steel rebars causes cracking, delamination, and spalling of reinforced concrete structures and increases the cost of rehabilitation and maintenance operations. In Wisconsin (USA), fiberglass wrapping has been used for corrosion protection of reinforced concrete columns. In this methodology, a fiberglass wrap is placed as a barrier between the concrete surface and the surrounding environment and is expected to reduce the detrimental effect of traffic splashing of deicing solutions. This paper describes a study aimed at evaluating the effectiveness of fiberglass wrapping in controlling and reducing the rate of corrosion in bridge concrete columns. Field tests included nondestructive wave propagation and half-cell potential methods. Nondestructive evaluation results were examined and compared to chloride ion (Cl−) intrusion measurements. The data show that fiberglass wrapping helps in arresting the chloride ion ingress to the columns, however, it does not help reduce corrosion rates in chloride contaminated concrete columns.

Journal ArticleDOI
TL;DR: In this paper, a rapid nondestructive evaluation (NDE) technique based on surface wave acoustic microscopy (SWAM) has been developed for inspection of surface/subsurface defects in silicon nitride (Si3N4) balls.
Abstract: A rapid nondestructive evaluation (NDE) technique based on surface wave acoustic microscopy (SWAM) has been developed for inspection of surface/subsurface defects in silicon nitride (Si3N4) balls. This technique exploits advantages of convergent surface acoustic waves generated by a sharply focused ultrasonic transducer by placing the transducer’s focal point below the ball surface, or defocusing. The use of surface waves to interrogate an area, rather than a point as in conventional acoustic microscopy, at a time on the ball surface can greatly improve the efficiency of defect detection. To ensure the inspection of surface defects with SWAM, we first simulated surface wave generation and propagation on a Si3N4 ball using finite element method (FEM). Then we tested different ultrasonic transducers for effective surface wave generation and detection. Transducers with varying frequency, f-number, defocusing distance, etc. for surface defect detection were experimentally compared. C-shape surface cracks on Si3N4 balls of different sizes were successfully detected. As a result, a SWAM prototype for rapid detection of surface defects in silicon nitride balls was successfully demonstrated.

Journal ArticleDOI
TL;DR: In this article, the surface of an annealed 316L stainless steel coupon was laser-shank peened and Vickers hardness measurements were subsequently taken of its surface, which was compared with measurements taken using the technique of positron annihilation Doppler broadening spectroscopy.
Abstract: The surface of an annealed 316L stainless steel coupon was laser shock peened and Vickers hardness measurements were subsequently taken of its surface. This Vickers hardness data was compared with measurements taken using the technique of positron annihilation Doppler broadening spectroscopy. When compared, a correlation was found between the Vickers hardness data measurements and those made using Doppler broadening spectroscopy. Although materials with a high defect density can cause the S-parameter measurements to saturate, variations in the S-parameter measurements suggest that through further research the Doppler broadening technique could be used as a viable alternative to measuring a material’s hardness. In turn, this technique, could be useful in industrial settings where surface hardness and surface defects are used to predict lifetime of components.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a model to predict the feasibility of E-NDE evaluation by inducing eddy currents in the structure to be examined, if this is conducting, and applied it to the case of a defect with a standard shape.
Abstract: Electromagnetic Non Destructive Evaluation (E-NDE) is often conducted by inducing eddy currents in the structure to be examined, if this is conducting. Existence of flaws is detected by difference between the response of defect-free structures and damaged ones. In the present paper, we model such processes in order to predict the feasibility of this evaluation and to facilitate the interpretation of the observation. An original method is to represent a crack by a current source producing a magnetic signal. We have applied it to the case of a defect with a standard shape. The experimental evidences for the validity of this method are given.

Journal ArticleDOI
TL;DR: In this paper, a non-contact capacitance probe has been used to explore the possibility of capacitance sensing for compositional control, and the feasibility of monitoring changes in the slurry composition during infiltration of the fiber mat is also discussed.
Abstract: Continuous fiber reinforced ceramic matrix composites (CMC’s) made from aluminum oxide fibers and matrices are usually fabricated using a tape casting process. In this process, ceramic slurry consisting of the oxide powder, a polymeric binder and a solvent is infiltrated into a woven ceramic fiber mat. After evaporation of some of the solvent, the resulting flexible tapes can be stacked and sintered to create a composite component. Because the fraction of ceramic powder in the slurry can vary during processing, in-situ compositional sensors are required for on-line feedback control to limit property variations in the composite material. Since the dielectric properties of the slurry components are distinctly different, the effective permittivity of the slurry depends upon its composition. Here, a non-contact capacitance probe has been used to explore the possibility of capacitance sensing for compositional control. Results indicate that the removal of solvent during a precision drying step may be monitored by this approach. The feasibility of monitoring changes in the slurry’s composition during infiltration of the fiber mat is also discussed.

Journal ArticleDOI
TL;DR: A novel method called FLIT-LBP is presented, which utilizes finite line integral transform (FLIT) to extract direction information, based on which appropriate weight arrangement can be chosen, to enhance blurry defect images with different directions.
Abstract: The blurring of DR image often affects defect inspection. In this paper, a novel method called FLIT-LBP for the enhancement of blurry DR image is presented. The proposed method utilizes finite line integral transform (FLIT) to extract direction information, based on which appropriate weight arrangement can be chosen. Weight arrangement is a sorting order of weights that converts binary codes to decimal codes in local binary patterns (LBP). And the central pixel information is extracted by computing the mean value in LBP. By combining the direction extraction of FLIT and the local comparison of LBP, FLIT-LBP is able to enhance blurry defect images with different directions. Experimental results show that FLIT-LBP performs better than LBP and FLIT respectively. In addition, in the case of defects with different contrast ratios lying in the same image, our method achieves better enhancement than grayscale stretch does.