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Volume 148
Issue 4
IEE Proceedings - Science, Measurement and Technology
Volume 148, Issue 4, July 2001
Volumes & issues:
Volume 148, Issue 4
July 2001
Editorial: Non-destructive testing and evaluation
- Author(s): N. Saffari
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 148, Issue 4, p. 137 –138
- DOI: 10.1049/ip-smt:20010603
- Type: Article
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- Author(s): C. Edwards ; T. Stratoudaki ; S. Dixon ; S. Palmer
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 148, Issue 4, p. 139 –142
- DOI: 10.1049/ip-smt:20010465
- Type: Article
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Laser techniques are beginning to be used for non-contact ultrasonic inspection of carbon fibre reinforced composites in industry. The ultrasound is normally generated with a high-power pulsed laser and is detected with a laser interferometer. Other non-contact detection methods can also be used, such as simpler laser beam deflection techniques and air coupled transducers. The authors compare the generation efficiency and damage thresholds of a fundamental Nd:YAG laser (1.06 µm), and a TEA CO2 laser (10.6 µm) which is normally preferred for carbon-fibre reinforced composites). A Nd:YAG laser with an optical parametric oscillator (OPO) tunable up to 4 µm is also examined. The laser energy is absorbed within the optical absorption depth; the temperature rise is affected by the wavelength and laser pulse duration. It is essential to remain in the thermoelastic regime in order not to damage the material. A modified Michelson interferometer is used to detect the absolute displacement of the ultrasound. Optical beam deflection techniques and air-coupled transducers are also evaluated as detectors. - Author(s): H.-J. Salzburger ; G. Dobmann ; H. Mohrbacher
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 148, Issue 4, p. 143 –148
- DOI: 10.1049/ip-smt:20010534
- Type: Article
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In modern design of automobile bodies reduction in weight and maximisation of the structural stiffness and passive safety are the main challenge. The ‘tailored blank’ has contributed to achieving a significant weight reduction in recent years. Single flat sheets are joined by laser welding into the desired configuration without filler wire. Usually the quality of the welds is assured by precise preparation of the plate edges and measurement of two of the process parameters. However, due to process deviations, defects occur, which make non-destructive testing (NDT) necessary. These defects include incomplete welding, lack of fusion, misalignment of the weld, holes and porosity. The paper presents a versatile ultrasonic (UT) inspection technique designed for in-line inspection of laser welds of tailored blanks. Conventional ultrasonic tetsing is ruled out because of the necessary liquid coupling medium. Therefore, the proposed inspection approach is based on the application of guided ultrasonic (plate) waves with shear horizontal polarisation excited and detected by couplant-free electromagnetic acoustic transducers (EMATs). - Author(s): A. McNab ; D. Reilly ; A. Potts ; M. Toft
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 148, Issue 4, p. 149 –158
- DOI: 10.1049/ip-smt:20010470
- Type: Article
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Visualisation in 3-D can significantly improve the interpretation and understanding of imaged NDT data sets. The advantages of using 3-D graphics to assist in the interpretation of ultrasonic data are discussed in the context of an advanced software environment for the reconstruction, visualisation and analysis of 3-D images within a component CAD model. The software combines the analysis features of established 2-D packages with facilities for real-time data rotation, interactive orthogonal/oblique slicing and ‘true’ image reconstruction, where scanning-surface shape and reflection from component boundaries are accounted for through interaction with the full 3-D model of the component. A number of novel facilities exploit the graphics capability of the system. These include the overlay of 3-D images with individual control of image transparency; a floating tooltip window for interrogation of data point co-ordinates and amplitude; image annotation tools, including 3-D distance measurement; and automated defect sizing based on ‘6 dB drop’ and ‘maximum amplitude’ methods. A graphical user interface has also been designed for a well established flaw response model, which allows the user to easily specify the flaw size, shape, orientation and location; probe parameters and scan pattern on the component. The output is presented as a simulated ultrasound image. - Author(s): D. Atkinson and G. Hayward
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 148, Issue 4, p. 160 –168
- DOI: 10.1049/ip-smt:20010460
- Type: Article
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Work aimed towards the realisation of an embedded ultrasonic system for structural condition monitoring is described. Alien fibres embedded within carbon fibre reinforced composite plates could be utilised to guide ultrasound to strategic release points for the interrogation of the test sample, with minimal structural degradation. In particular, an array of fibre waveguides could be utilised to deliver periodic stresses to a plate-type structure to excite Lamb wave propagation. With such a system several problems need to be addressed. Ideally, single mode propagation in the fibre waveguide is required to provide increased control of the coupling of ultrasound from the waveguide to the desired Lamb wave mode. The choice of a suitable waveguide material and geometry is also crucial to ensure the guided ultrasound does not leak into the structure at undesirable locations and that the structural integrity of the test sample is maintained. Consequently, various waveguide configurations are investigated to establish an arrangement capable of meeting the system requirements. Finally, S0 Lamb wave generation and detection in a hard-setting polymer plate and a carbon fibre reinforced composite plate is demonstrated utilising embedded active acoustic waveguides sensors. - Author(s): R.P. Dalton ; P. Cawley ; M.J. Lowe
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 148, Issue 4, p. 169 –177
- DOI: 10.1049/ip-smt:20010467
- Type: Article
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A study of the propagation of acoustic emission (AE) signals through metallic aircraft fuselage structure is presented. It was found that only the fundamental modes: A0 and S0 in a low frequency band, centred at about 70 kHz, exhibit long-range propagation. In this low-frequency band the fundamental modes exhibit low attenuation in all the waveguide systems that are likely to be encountered in metallic aircraft. Metallic fuselage structure features a high density of joints between the skin and support structure and numerical modelling indicated that these modes have an energy transmission efficiency of about 70% across a typical joint. This is supported by experimental data. Such efficient transmission over a succession of joints contrasts with that found at higher frequencies, where previous work found that the interference of modes with similar phase velocity inhibits long-range propagation. Such ‘mode twinning’ does not occur in the frequency range around 70 kHz, and so efficient propagation of AE signals is possible. - Author(s): K.J. Bois ; A.D. Benally ; R. Zoughi
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 148, Issue 4, p. 178 –182
- DOI: 10.1049/ip-smt:20010482
- Type: Article
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In recent years near-field microwave nondestructive testing and evaluation techniques have shown great promise for evaluating different properties of cement-based structures. An important issue regarding the inspection of these structures is the ability to determine the presence and evaluate the content of chloride in them. Chlorides can be introduced in these structures in many different ways including when salts are present in their mixing water. Consequently, for this investigation, two sets of 8" × 8" × 8" (203 mm) cubic mortar specimens were prepared each with a water-to-cement (w/c) ratio of 0.5 and 0.6, respectively, and both sets with sand-to-cement ratios of (s/c) of 1.5. Four specimens were produced for each set with different salt (NaCl) contents added to the mixing water, producing salt-to-cement (NaCl/c) ratios of 0.0, 1, 2 and 3%, respectively. For the purpose of compressive strength measurement, cylindrical specimens of these mortar specimens were also prepared and tested for their compressive strength. Microwave reflection properties of these specimens were measured at S-band (2.6–3.95 GHz) and X-band (8.2–12.4 GHz), employing open-ended rectangular waveguide probes. It is shown that the magnitude of reflection coefficient is a useful parameter for detecting different chloride levels in these specimens. Moreover, the influence of chloride on the curing properties (i.e. setting time) and the compressive strength of these specimens are subsequently shown to be well correlated to the measured magnitude of reflection coefficient of these specimens at S-band. It is also shown that this correlation is unambiguous as a function of w/c which possesses significant practical ramifications. - Author(s): D.J. Harrison
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 148, Issue 4, p. 183 –186
- DOI: 10.1049/ip-smt:20010461
- Type: Article
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The change in impedance of a cylindrical eddy-current coil, when placed on a layered conducting structure, is determined by the material properties and geometry of the structure and the spatial frequency spectrum of the coil. It is shown how the spatial frequency spectrum can be derived from the impedance spectrum of a coil for a characterised specimen. Once this is known, the performance of the coil can be predicted for any specimen. This process is illustrated using impedance measurements of both a large air-cored coil and a small ferrite-cored coil. - Author(s): S.H.H. Sadeghi and A.H. Salemi
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 148, Issue 4, p. 187 –192
- DOI: 10.1049/ip-smt:20010483
- Type: Article
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The theoretical prediction of eddy-current probe output signals for various nondestructive testing (NDT) applications usually involves solution of the electromagnetic field due to a current-carrying excitation loop in the vicinity of a flawless conductor. The paper presents a general theory for the time-harmonic magnetic field distribution produced by an arbitrary shape current-carrying excitation loop around a linear, isotropic, homogeneous conducting slab. In this theory the authors develop a Fourier-integral-based model for computing the magnetic field distributions, which greatly simplifies the computation procedure. The main feature of the model is its ability to analyse two- and three-dimensional excitation geometry, with a similar degree of computation burden. This feature stems from the fact that in this model, knowledge of the field distribution at the place of the conductor surface in free space suffices to compute the field in the presence of the conductor. To demonstrate the accuracy of the model, the authors consider two special cases of an infinite straight wire and an elliptical loop exciter. The comparison of the results with those obtained using the conventional algorithms in the literature validates the model introduced in the paper. To show the generality of the model, the authors also present results associated with a solenoid exciter with a three-dimensional geometry for which no analytical solution is available in the literature. - Author(s): D. Mirshekar-Syahkal and R.F. Mostafavi
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 148, Issue 4, p. 193 –196
- DOI: 10.1049/ip-smt:20010517
- Type: Article
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As in the eddy-current technique, a major problem in separating and sizing deep surface cracks in the AC field measurement (ACFM) technique is the saturation of the crack signal. It is essential that the operator ensures the crack signal does not reach saturation for the deepest possible crack. The paper explains how the parameters of the probe and inducer in the high-sensitivity ACFM technique with a rhombic inducer control the sensitivity and saturation level. Theoretical results are presented on the effects of the inducer size, probe position and probe length on the crack signal. It is shown that for an inspection task where there is an indication of the maximum crack depth, the saturation problem can be avoided by choosing the right size inducer, the right position for the probe and the correct probe length.
Laser generated ultrasound: efficiency and damage thresholds in carbon fibre reinforced composites
Quality control of laser welds of tailored blanks using guided waves and EMATs
Role of 3-D graphics in NDT data processing
Active fibre waveguide sensor for embedded structural condition monitoring
Propagation of acoustic emission signals in metallic fuselage structure
Near-field microwave non-invasive determination of NaCl in mortar
Characterisation of cylindrical eddy-current probes in terms of their spatial frequency spectra
Electromagnetic field distributions around conducting slabs, produced by eddy-current probes with arbitrary shape current-carrying excitation loops
Effects of probe and inducer on saturation of crack signal in high-sensitivity AC field measurement technique
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