Showing papers in "Journal of Nondestructive Evaluation in 2000"
TL;DR: In this article, the set-up of an experiment is presented, based upon theoretical considerations and experimental data, the parameters of the setup and the possibilities as well as limits of residual stress analysis by white high-energy synchrotron radiation.
Abstract: White high-energy synchrotron radiation has recently been introduced as a new tool for the analysis of the triaxial residual stress state in the bulk of metals, ceramics, and composite materials First, the set-up of an experiment is presented Then, based upon theoretical considerations and experimental data, the parameters of the setup and the possibilities as well as limits of residual stress analysis by white high-energy synchrotron radiation are discussed The resolution in energy as well as the spatial resolution achievable are shown and the implications of the material investigated such as coarse grains and texture are studied Examples for simultaneous texture and residual stress analyses are presented
47 citations
TL;DR: In this article, the thermographic principle of debonded building-finish system is proposed based on laboratory calibrations, and an effective approach is developed to eliminate the disturbance of reflection.
Abstract: Infrared thermography is a well-established technique for evaluating material properties through thermal measurement. In this paper, the thermographic principle of debonded building-finish system is proposed based on laboratory calibrations. An effective approach is developed to eliminate the disturbance of reflection. The survey results prove that this method is reliable in detecting the debonded ceramic tiles on a building finish. With defective areas appearing differently from well-bonded regions, as a result of their differential transmittance of infrared (IR) radiation, the large surfaces can be rapidly scanned. The proposed approach makes it possible to perform interpretation and analysis with a high degree of accuracy.
41 citations
TL;DR: In this article, the frequency-wavenumber (F-K) migration was applied to the ultrasonic data processing and can improve the quality of ultrasonic image in both size and location of the flaws.
Abstract: In ultrasonic nondestructive evaluation (NDE), the depth of the image is usually calculated by multiplying the traveling time of the echoes with the velocity of the medium. If the flaw is not a horizontal plane, the flaw images may be distorted and mislocated. Although the lateral resolution and sizing accuracy of the flaw image can be improved using the digital signal processing methods, e.g., the utilization of the blocking filter or deconvolution filter, these methods do a little favor about the distortion and mislocation problems. The migration, an image-processing method used widely in reflection seismology, is introduced to process the ultrasonic data in this study. Since the signals are coherent and the noises are random, the flaw image can be transformed from its apparent position to the true position using the migration method and the resolution of the image may be improved. Not only the real positions of the oblique cracks can be found upon applying the frequency-wavenumber (F-K) migration to process ultrasonic data, but, in addition, the dimensions of the flaws can be estimated more accurately. Results presented in this study show that the migration method can be applied successfully to the ultrasonic data processing and can improve the quality of ultrasonic image in both size and location of the flaws.
20 citations
TL;DR: In this paper, boundary element modeling is used for defect classification and sizing analysis, and a theoretical presentation illustrates some trends and features that might be useful in sizing analysis and a few basic flaw shapes of different size are studied in an attempt to shed some light onto the difficult classification and size process.
Abstract: Guided waves have demonstrated their value in flaw detection in a variety of different and unusual circumstances, including inspection over long distances with just 1 or 2 probes and inspection under coatings, fluids, and insulation. Via mode control and phase velocity and frequency tuning, defect detection sensitivity can be superb. The problem of going beyond detection to defect classification and sizing, however, is extremely difficult. By way of boundary element modeling, some new approaches to classification and sizing are introduced. A theoretical presentation illustrates some trends and features that might be useful in sizing analysis. Parametric studies and analysis showing amplitude versus frequency profiles for various mode input and mode conversion output via through transmission are presented. A few basic flaw shapes of different size are studied in an attempt to shed some light onto the difficult classification and sizing process.
17 citations
TL;DR: In this paper, the authors describe results on the ultrasonic analysis of adhesively bonded aluminium plates using normal incidence radially polarised shear wave ElectroMagnetic Acoustic Transducers (EMATs).
Abstract: This paper describes some results on the ultrasonic analysis of adhesively bonded aluminium plates using normal incidence radially polarised shear wave ElectroMagnetic Acoustic Transducers (EMATs). The EMAT system presented here has undergone significant development work and improvements compared to previously published examples.(9,19) The electronic ‘deadtime’ of the system has been reduced to approximately 1 microsecond and the frequency range over which measurements can be taken has been extended. The capability of the technique to detect gross and subtle defects is demonstrated.
11 citations
TL;DR: In this paper, a laser-excited eddy current (EC) imaging technique, or so-called photoinductive imaging, was applied to characterize corner cracks at the edge of a bolt hole, which revealed the geometrical shape of the electrical-discharge-machined (EDM) notches that were either triangular or rectangular.
Abstract: We applied a laser-excited eddy current (EC) imaging technique, or so-called photoinductive (PI) imaging, to characterize corner cracks at the edge of a bolt hole. Crack images with excellent signal-to-noise-ratios were obtained. The PI signals revealed the geometrical shape of the electrical-discharge-machined (EDM) notches that were either triangular or rectangular. The results show that this technique is promising to characterize the length, as well as possibly the depth and shape, of corner cracks. In this paper we present measurement results of 0.25-mm, 0.50-mm, and 0.75-mm rectangular and triangular EDM notches. We also show measurement results of a very small notch (<0.25 mm) which would be difficult to detect with conventional eddy current techniques. The dependencies of PI signals on laser chopping frequencies and eddy current frequencies are also examined. To demonstrate the photoinductive imaging capabilities to image actual cracks, we display images of fatigue cracks grown in a Ti-6Al-4V hole specimen. Finally, we present comparisons of the photoinductive imaging results with usual eddy current images obtained from a 0.75-mm triangular EDM notch using a rotating bolt-hole scanner. This article intends to verify experimentally that the photoinductive imaging technique has a potential to become a useful nondestructive testing method.
8 citations
TL;DR: In this paper, a nondestructive optimal determination of elastic properties from ultrasonic bulk wave velocity measurements on a monolithic ceramic plate immersed in water is presented, which can be described by twenty-one dependent stiffness constants and its intrinsic elastic material symmetry was hexagonal (or transversely isotropic).
Abstract: A nondestructive optimal determination of elastic properties from ultrasonic bulk wave velocity measurements on a monolithic ceramic plate immersed in water is presented. This procedure, that is applicable to flat plates with unknown material properties, is based on already established methods and includes discussions, using experimental data, on the reliability of the elastic property identification, such as the stiffness tensor and the material symmetry. By solving inverse propagation problems deduced from the Christoffel equation and depending on wave speed measurements, we show that the studied sample can be described by twenty-one dependent stiffness constants and that its intrinsic elastic material symmetry was hexagonal (or transversely isotropic).
8 citations
TL;DR: In this article, a two-dimensional acoustic surface waveguide system was developed to enhance the transmission of Acoustic Emission (AE) signals in high attenuation concrete materials, where steel wires were selected as a waveguide material and were attached on the surface area of reinforced concrete structures.
Abstract: This paper describes the development of a two-dimensional acoustic surface waveguide system to enhance the transmission of Acoustic Emission (AE) signals in high attenuation concrete materials. The design of the surface waveguide system and the AE source location results are described. In this study, steel wires were selected as a waveguide material and were attached on the surface area of reinforced concrete structures. AE sensors were mounted at the end of the waveguides. The waveguides were connected to a concrete slab at joints with small contact areas using epoxy. This minimizes the amount of AE energy that could dissipate back to concrete. Thus, AE signals can be transmitted a longer distance. Experiments using standard pencil-lead breaks were conducted at 49 locations on a surface of a reinforced concrete floor slab to provide artificial AE signals. High transmission efficiencies were experimentally determined for the epoxy joints developed to attach the waveguides on the concrete surface. Results confirm that the use of the two-dimensional surface waveguides can significantly increase the AE monitoring range. A multi-layer Neural Network (NN) system was employed to predict locations of the AE sources. Four data sets of AE parameters and their corresponding 49 source locations in each data set were used to train the NN system. A testing data set was then used to demonstrate the ability of the NN in identifying the locations of the AE sources. Satisfactory prediction results from the NN were obtained.
6 citations
TL;DR: In this article, the authors proposed a method for using a pair of identical fiber Bragg gratings to measure the unbalanced strain factor in an isothermal-mechanical system.
Abstract: This paper proposes a method for using a pair of identical fiber Bragg gratings to measure the unbalanced strain factor in an isothermal-mechanical system. Cascading two identical fiber Bragg gratings, the unbalanced strain factor caused by the disturbance can be interrogated from the peak difference of the two reflecting Bragg wavelengths. If the mechanical system is in an isothermal environment, the thermal variations in the Bragg grating detection system can be automatically compensated. To verify the feasibility of the unbalanced strain detection using a pair of fiber Bragg gratings, the wall-thinning monitor in a pressure vessel system was investigated. The proposed technique is easy to install, immune to electro-magnetic and thermal interference, and highly sensitive in-time to remote monitoring for fiber optic smart structures. A finite element model (FEM) is used to simulate the wall thinning in a pressure vessel system. The minimum detectable unbalanced strain and cross-talk between two reflecting Bragg wavelengths were investigated.
6 citations
TL;DR: In this article, the effect of surface coating on the response of a metallic substrate to pulsed thermal excitation is examined with the view to assessing its impact on the efficacy of quantitative thermographic evaluation as applied to the problem of material loss evaluation.
Abstract: The effect of a surface coating on the response of a metallic substrate to pulsed thermal excitation is examined with the view to assessing its impact on the efficacy of quantitative thermographic evaluation as applied to the problem of material loss evaluation. An analytical model describing the response of a layered structure to a surface thermal excitation has been developed and its predictions are shown to be in excellent qualitative agreement with experimental observations. The results indicate that for materials with high thermal diffusivity, a surface paint layer bears important influence on the development of the surface thermal response and should be taken into account when undertaking quantitative assessments of thermographic data.
4 citations
TL;DR: In this paper, a 2D neural network classifier based on the probabilistic neural network was used to detect nonconducting inclusions in conducting media, and a reasonable recognition error of less than 20 % was obtained if the signal-to-noise ratio is larger than or equal to 1/10.
Abstract: A theoretical study was conducted using a multiple-voltage probe sensor for detecting nonconducting inclusions in conducting media. Results show that the multiple-voltage probe sensor is capable of providing precise quantitative measurements of submerged nonconducting objects if the surface voltage response has a standard two-peak form. The standard response is observed for well-localized non-slender single inclusions below the sensor surface. In this case, the peak separation distance is associated with the inclusion depth whereas the peak magnitude is associated with the inclusion volume. Linear dependencies of the inclusion depth and the inclusion volume are observed for a wide variety of inclusion shapes. The predefined form of the surface voltage response makes it feasible to identify useful signal responses at very high noise levels. This is accomplished by using a 2D neural network classifier, based on the probabilistic neural network. A reasonable recognition error of less than 20 % is obtained if the signal-to-noise ratio is larger than or equal to 1/10. A metal casting example shows that the multiple-voltage probe sensor can measure inclusion concentrations in hot conducting melts (gas bubbles and sludge) with inclusion radii in the range from 100 to 1000 μm. In contrast to existing particle counter technology, this sensor construction is simple to construct and does not require special aperture and vacuum treatment.
TL;DR: In this article, the radiation characteristics of ultrasonic transducers for this wave type were determined by point source superposition, making use of an analytical relationship for the wave propagation direction as a function of the spatial coordinates.
Abstract: Based on the description of shear horizontal (SH) wave propagation in arbitrarily oriented transversely isotropic media, radiation characteristics of ultrasonic transducers for this wave type are determined. The radiated wavefields are obtained by point source superposition, making use of an analytical relationship for the wave propagation direction as a function of the spatial coordinates. Approximate formulae are given for the radiation characteristics of circular and rectangular transducers in the far-field, which are in a form similar to the isotropic material case. Focusing on transversely isotropic weld metal specimens and unidirectional composites, numerical evaluation is performed for normal-incidence probes as well as for electromagnetic acoustic transducers.
TL;DR: In this paper, an adaptive time-delay self-focusing technique has been used to focus ultrasound on the edge (tip) of a surface-breaking crack emanating from the opposite side of a plate.
Abstract: An adaptive time-delay self-focusing technique has been used to focus ultrasound on the edge (tip) of a surface-breaking crack emanating from the opposite side of a plate. The diffraction of the focused signal has been measured with the array. Simulation of the self-focusing process and the diffraction by the crack edge has been carried out to obtain numerical results for the edge diffraction. Ray tracing has been used to determine the incident wave field in the plate. Comparisons between the numerical results and the measured data show good agreement. The results have been used to determine the depth of the crack.
TL;DR: In this article, a signal deconvolution technique was proposed to improve the prediction of tube burst pressure from bobbin-coil eddy current measurements of steam generator tubing. But this technique is limited in the sense that it cannot distinguish crack signals from those arising from artifacts.
Abstract: Eddy current techniques are extremely sensitive to the presence of axial cracks in nuclear power plant steam generator tube walls, but they are equally sensitive to the presence of dents, fretting, support structures, corrosion products, and other artifacts. Eddy current signal interpretation is further complicated by cracking geometries more complex than a single axial crack. Although there has been limited success in classifying and sizing defects through artificial neural networks, the ability to predict tubing integrity has, so far, eluded modelers. In large part, this lack of success stems from an inability to distinguish crack signals from those arising from artifacts. We present here a new signal processing technique that deconvolves raw eddy current voltage signals into separate signal contributions from different sources, which allows signals associated with a dominant crack to be identified. The signal deconvolution technique, combined with artificial neural network modeling, significantly improves the prediction of tube burst pressure from bobbin-coil eddy current measurements of steam generator tubing.