scispace - formally typeset
Search or ask a question

Showing papers in "Journal of Nondestructive Evaluation in 2004"


Journal ArticleDOI
TL;DR: In this paper, an experimental study is presented to gain information about limits in detection of defects in composites by infrared-thermography, and the results are presented in terms of difference of temperature (pulse), or difference of phase angle (lockin), between damaged zones and sound material.
Abstract: The aim of the present experimental study is to gain information about limits in detection of defects in composites by infraredthermography. Specimens are manufactured of either carbon/epoxy, or glass/epoxy, and withinclusions of foreign materials to simulate defects of different size and positioned at different depths. Tests are carried out by using both pulse and lockin techniques. Results are presented in terms of difference of temperature (pulse), or difference of phase angle (lockin), between damaged zones and sound material. It seems that, apart from diameter and depth, thethickness is very crucial for defects visibility.

76 citations


Journal ArticleDOI
TL;DR: In this article, shot-peened nickel-base superalloys exhibit an apparent increase in eddy current conductivity at increasing inspection frequencies, which can be exploited for nondestructive residual stress assessment of subsurface residual stresses.
Abstract: It is shown in this paper that, in contrast with most other materials, shot-peened nickel-base superalloys exhibit an apparent increase in eddy current conductivity at increasing inspection frequencies, which can be exploited for nondestructive residual stress assessment of subsurface residual stresses. It has been found that the primary reason why nickel-base superalloys, which are often used in the most critical gas-turbine engine components, lend themselves easily for eddy current residual stress assessment lies in their favorable electro-elastic behavior, namely that the parallel stress coefficient of the eddy current conductivity has a large negative value while the normal coefficient is smaller but also negative. As a result, the average stress coefficient is also large and negative, therefore the essentially isotropic compressive plane state of stress produced by most surface treatments causes a significant increase in conductivity parallel to the surface. The exact reason for this unusual behavior is presently unknown, but the role of paramagnetic contributions cannot be excluded, therefore the measured quantity will be referred to as “apparent” eddy current conductivity. Experimental results are presented to demonstrate that the magnitude of the increase in apparent eddy current conductivity correlates well with the initial peening intensity as well as with the remnant residual stress after thermal relaxation.

74 citations


Journal ArticleDOI
TL;DR: In this paper, three kinds of defects, namely lack of fusion (LF), lack of penetration (LP) and porosity (PO), were inserted into the specimens durin the welding process, generating pattern defects.
Abstract: The TOFD (“Time of Flight Diffraction”) technique is being widely used for automatic weld inspection, especially in the petrochemical industry, where welding quality is essential to avoid productivity losses. Although it provides high speed inspection, high sizing reliability and low rate of false defect indications, the classification of defects using ultrasound signals generated by the TOFD technique is still frequently questioned, because it depends heavily on the knowledge and experience of the operator. However, the use of computational tools for signal preprocessing and pattern recognition, such as the artificial neural networks, improves the classification reliability of defects detected by this technique. In this present work, three kinds of defects: lack of fusion (LF), lack of penetration (LP) and porosity (PO) were inserted into the specimens durin the welding process, generating pattern defects. The position, type and dimension of each inserted defect were recorded using conventional ultrasonic and radiographic techniques. The Fourier Transform and Wavelet Transform were used for preprocessing A-scan signals acquired during weld inspection by TOFD technique. This study was able to show the versatility of Wavelet Transform to preprocess these kinds of signals, since the correct scale in Continuous Wavelet Transform had been selected to supply a neural network. Hierarchical linear classifiers were implemented into the neural network in order to distinguish the main defects in welded joints detected by the TOFD technique. The results show the good success rate of welding defect recognition in preprocessed TOFD signals, mainly using Wavelet Transform. On the whole, the results obtained were very promising and could give relevant contributions to the development of an automatic system of detection and classification of welding defects inspected by the TOFD technique.

31 citations


Journal ArticleDOI
TL;DR: In this article, the acoustic emission (AE) fatigue crack monitoring technique was used to detect cracks in the splice doubler angle, splice plate, and bottom chord of the armored vehicle launch bridge.
Abstract: The Armored Vehicle Launch Bridge (AVLB) is subjected to cyclic loading during launching as well as during tank crossings. The cyclic loading causes cracks to initiate in critical bridge components, and then to propagate. Unless these cracks are detected and repaired before they rapidly grow to reach their critical stage of propagation, the failure of bridge components can occur. Three AVLB components, the splice doubler angle, the splice plate, and the bottom chord, are susceptible to fatigue damage. In the present study, laboratory fatigue tests on the materials used for the components, aluminum 2014-T6, aluminum 7050-T765, and ASTM A36 steel, were conducted using the acoustic emission (AE) fatigue crack monitoring technique. A total of fourteen compact-tension specimens were prepared in this study: six aluminum 2014-T6, four aluminum 7050-T76511, and four ASTM A36 steel specimens. The characteristics of AE signals associated with the stress intensity factor, K, were obtained to understand AE behavior corresponding to the fatigue crack growth in the materials. Several AE parameters, such as AE counts, energy, and hits, have been shown to be useful tools for detecting cracks, providing early warnings, and preventing failure of the AVLB structures. A major jump in AEcount rate as well as AE hit rate occurred when Kmax reached a value of about 30~MPa√m (27 ksi√in.) for aluminum 2014-T6 specimens and about 50 MPa√m (46 ksi√in.) for aluminum 7050-T76511 specimens. Also, AE source location techniques were able to successfully locate the path ofcrack propagation.

27 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed an ultrasonic measurement model that can predict the pulse-echo signals from a flat-bottom hole in an isotropic, homogeneous solid specimen immersed in water in a computationally efficient manner.
Abstract: This paper proposes an ultrasonic measurement model that can predict the pulse-echo signals from a flat-bottom hole in an isotropic, homogeneous solid specimen immersed in water in a computationally efficient manner. To develop such a model, a measurement model approach is adopted based on two important assumptions: the paraxial approximation for the transducer beam and the small flaw assumption for the flat-bottom hole. The modular model that results from these two assumptions contains three terms: a diffraction correction term, a far-field scattering amplitude term and a system efficiency factor term. The diffraction correction is defined based on a multi-Gaussian beam model which allows the rapid evaluation of the wave field incident on the hole. The far-field scattering amplitude of the flat-bottom hole is obtained using the Kirchhoff approximation together with the small flaw assumption. The system efficiency factor is determined by deconvolution of an experimental front surface reflection signal by a reference reflector model. Here, the contribution of each of these three terms to the overall measurement model are described in detail and the accuracy of the proposed model is verified by the comparison of the model-based predictions to experiments.

27 citations


Journal ArticleDOI
TL;DR: In this article, a low-amplitude filtering technique was developed for the identification of fiber breakage in fiber reinforced plastics from acoustic emission data, where the acoustic emission hits associated with fiber breakages were separated from the hits related with other failure mechanisms by filtering out the low amplitude hits from the measured data.
Abstract: A new low-amplitude filtering technique has been developed for the identification of fiber breakage in fiber reinforced plastics from acoustic emission data. In this approach, the acoustic emission hits associated with fiber breakage are separated from the hits associated with other failure mechanisms by filtering out the low amplitude hits from the measured data. The lowest remaining amplitude upon the cumulative plot of the remaining hits vs. load coinciding with the cumulative signal strength vs. load plot is taken as the borderline between fiber breakage hits and non-fiber breakage hits. Experiments were conducted on unidirectional-fiber specimens and complex-fiber specimens to examine the efficacy of the proposed technique. Evaluation of the experimental results by visual inspection and extensive scanning electron microscope studies verifies the low-amplitude filtering technique as a reliable tool for identifying fiber breakage in fiber reinforced plastics.

24 citations


Journal ArticleDOI
TL;DR: In this article, a new methodology for evaluating the crack depth and the crack opening stress intensity factor of small closed cracks using an ultrasonic technique has been described, and the accuracy and reliability of this new non-destructive evaluation (NDE) method is verified by comparing the evaluated crack depth with the actual one.
Abstract: This paper describes a new methodology for evaluating the crack depth and the crack opening stress intensity factor of small closed cracks using an ultrasonic technique. Surface connected back-wall cracks of depth ranging from 0.4 to 4.0 mm in steel specimens are considered. The crack corner echo amplitude of an ultrasonic shear wave, SW, beam of 50° incidence in material is used. First, the ultrasonic echo response of an open crack is determined as a function of crack depth. Next, based on changing the crack closure stress, an empirical relation between the crack closure stress and the crack-echo response is formulated. The crack depth and the crack closure stress of an unknown closed crack based on these relations are determined by inverse analysis of the ultrasonic response of the crack. From the evaluated crack depth and crack closure stress, the crack opening stress intensity factor is determined. The accuracy and reliability of this new nondestructive evaluation (NDE) method is verified by comparing the evaluated crack depth with the actual one. The latter is measured on the fractured surface obtained after carrying out ultrasonic testing. The ultrasonic method developed is proved to be a powerful tool for quantitative and nondestructive evaluation of the crack depth as well as the crack closure stress.

23 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a new approach to modeling angle beam ultrasonic testing that can predict pulse-echo signals, in an absolute and computationally efficient manner, from various reflectors in steel welded joints.
Abstract: This paper proposes a new approach to modeling angle beam ultrasonic testing that can predict pulse-echo signals, in an absolute and computationally efficient manner, from various reflectors in steel welded joints. This approach relies on a model of the entire ultrasonic measurement process, a model which requires one to solve three subsidiary problems; 1) determination of a system efficiency factor, 2) evaluation of the ultrasonic beam field around the flaw, and 3) calculation of the scattering from the reflector. Here, solutions are offered for each of those three subsidiary problems. To solve the first problem we employ the specular reflection from the cylindrical part of a STB-A1 (Standard Test Block in compliance with Japanese Industrial Standards Z 2347) (equivalently IIW (International Institute of Welding) type 1) standard block to determine the system efficiency factor. To solve the second problem, we calculate the ultrasonic wave field at the flaw with a highly efficient multi-Gaussian beam model. For the third problem, we treat the scattering from a reflector by high frequency approximations. We explicitly give the solutions to all three of these subsidiary problems for counter bore, crack, and side-drilled hole reflectors. Experimental results that validate this approach are also given.

19 citations


Journal ArticleDOI
TL;DR: In this paper, a new methodology for analyzing the closure stress of small fatigue cracks using ultrasonics is described, which can be used to overcome the difficulties encountered by crack closure in recent nondestructive ultrasonic techniques and may lead the way in quantitative evaluation of crack depth and exact closure stress.
Abstract: This paper describes a new methodology for analyzing the closure stress of small fatigue cracks using ultrasonics. Surface connected back-wall cracks in steel specimens are considered. The crack-corner echo of ultrasonic shear wave beam of 50° incidence in the material is used. In order to account for the exact effect of closure stress on ultrasonic response, the echo amplitude is analyzed based on artificially applying additional closure stress. The initial closure stress at no load condition is determined by the standard compliance technique. A relationship between the closure stress and the crack-echo response is established which provides the facility of getting a true model of crack closure stress. The relationship is found to be independent of crack depth. The present approach can be used to overcome the difficulties encountered by crack closure in recent nondestructive ultrasonic techniques and may lead the way in quantitative evaluation of crack depth as well as exact closure stress.

17 citations


Journal ArticleDOI
TL;DR: In this article, the authors used EIS sensors to inspect carbon fiber reinforced polymer (CFRP)-reinforced concrete structures exposed to a variety of test conditions and found that the capacitance and constant phase element magnitude correlated very well with both bonded area/delamination and moisture.
Abstract: Electrochemical impedance spectroscopy (EIS) sensors have been used to inspect carbon fiber reinforced polymer (CFRP) -reinforced concrete structures exposed to a variety of test conditions. Similar specimens were also used to investigate the detection of delamination between the CFRP and the concrete using a modified wedge test configuration. The use of external electrodes attached to the CFRP surface, coupled with the embedded rebar, provided the best results. Equivalent circuit modeling was used to analyze the impedance spectra. Several circuit parameters, especially the capacitance and constant phase element (CPE) magnitude, correlated very well with both bonded area/delamination and moisture. Both parameters exhibit a linear relationship with delamination area. The capacitance also showed a linear relationship with moisture content while the CPE was more strongly dependent on moisture. Differences in the response of the specimens subjected to the different exposure conditions were seen and explained based on the moisture uptake of the various specimens.

17 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured the thermoelectric power (TEP) of cast duplex stainless steel and found that TEP increased with aging time, and good correlations were found between TEP and toughness.
Abstract: In order to non-destructively evaluate changes in toughness of cast duplex stainless steel, which is frequently used in main coolant pipes of PWR type nuclear power plants, due to thermal aging, we tried to apply thermoelectric power (TEP) measurement. because TEP is sensitive to microstructural material changes, and to clarify the mechanism behind TEP changes due to thermal aging. As a result, TEP of cast duplex stainless steel increased with aging time, and good correlations were found between TEP and toughness. Concerning the mechanism, TEP of high and low Cr content alloys was higher than that of intermediate Cr content alloys. Because high and low Cr areas are created in the ferrite phase due to thermal aging. TEP of the entire material increased. Furthermore, when each Cr fluctuating area acted in parallel, the increase in TEP became larger. According to the Mott-Jones theory, TEP is largely related to the electron density of states at the Fermi level. The electron density of states of Fe–Cr–Ni alloys in the valence band was measured with X-ray photoelectron spectroscopy (XPS). As a result, there was a high correlation between the TEP calculated from the XPS spectrum and the measured TEP. Therefore, we showed experimentally that the electron density of states changed due to variations in Cr concentration, which also affect TEP.

Journal ArticleDOI
TL;DR: In this article, micro X-ray fluorescence (MXRF) imaging is evaluated as a potential NDE method to inspect the chromium disilicide coating of the Space Shuttle orbiter thrusters.
Abstract: Space Shuttle orbiter thrusters fabricated from C-103 niobium alloy rely on a fused chromium disilicide coating as protection from high-temperature oxidation. Coating voids caused by high-temperature spalling, micrometeorite damage, or other impact damage must first be detected, and then characterized to measure the amount of remaining coating materials, since service life is directly proportional to coating thickness. Existing techniques to estimate the thickness of this diffusion layer are labor intensive, prone to error, and require contact with the coating. Alternative non-contact methods are sought that can automate the detection and characterization of coating defects. Micro X-ray fluorescence (MXRF) imaging is evaluated in this study as a potential NDE method to inspect the chromium disilicide coating. MXRF imaging, a relatively new technique to map the elemental composition of a surface, creates a high spatial resolution multispectral image that can be analyzed to detect coating voids and to quantify the remaining coating materials diffused in the alloy. Analysis of image data collected from sectioned thruster samples confirms that MXRF imaging is a viable detection and characterization method for the thruster coating inspection problem.

Journal ArticleDOI
TL;DR: In this paper, a methodology to characterize the fretting fatigue damage by analyzing the surface topography and to detect cracks under fretting fatigued surface by imaging heat generation due to high amplitude acoustic excitation was presented.
Abstract: Fretting fatigue has been the cause of many premature failures in aerospace components. There is a growing need of nondestructive evaluation techniques to characterize damage and detect cracks due to fretting fatigue. This paper presents a methodology to characterize the fretting fatigue damage by analyzing the surface topography and to detect cracks under fretting fatigued surface by imaging heat generation due to high amplitude acoustic excitation. The White Light Interference Microscopy (WLIM) was used to obtain three-dimensional surface profilometry data of fretted and non-fretted regions of titanium alloy (Ti-6A1-4V) specimens subjected to different number of fretting fatigue cycles. Surface topography measurements were analyzed in terms of the Power Spectral Density (PSD) and Fretting Fatigue Damage Parameter (FFDP). The FFDP showed an increasing trend in magnitude with increasing numbers of fretting fatigue cycles, when the fretting fatigue damage occurred through stick-slip condition. When the fretting fatigue damage occurred due to gross sliding, the FFDP did not show enough change. Thus, it appears that FFDP may be used as an indicator of the degradation of fretted surface under stick-slip condition. Cracks in presence of fretting fatigue damage were imaged using Sonic infrared technique. This technique appears to have a capability to detect cracks with a resolution of at least 200 μm. The benefits and limitations of thes two NDE techniques for fretting fatigue damage evaluation and crack detection are discussed.