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Subject of study. Carbon composite laminates are one of the major aviation structural materials. Owing to its merits of being non-contact, self-coherent, non-destructive, and full field, digital shearing speckle pattern interferom...
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Subject of study. Carbon composite laminates are one of the major aviation structural materials. Owing to its merits of being non-contact, self-coherent, non-destructive, and full field, digital shearing speckle pattern interferometry (DSSPI) has the potential to be effective in the detection of defects on carbon composites with various surface shapes, especially the close-type defect on composite laminates. Method. In this paper, a DSSPI system containing both simulation and experiment, used for the measurement of carbon composite laminates with different curvature radii, is established. Main results. Based on our proposed criterion to evaluate whether the defects can be judged or not, the experiment loading parameters are applied, and the detection abilities under variable loading parameters are predicted. The effectiveness of the experiment system is verified through comparison with the X-ray and the ultrasound techniques. The simulation results are consistent with the experiments, showing its effectiveness. Practical significance. The work in this paper can provide reliable guidance to the loading parameters and predict the detection performance in a real DSSPI experiment system. (C) 2022 Optica Publishing Group.
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An attempt was made to evaluate nondestructively thermally degraded 2.25Cr-1Mo steel by. magnetic Barkhausen noise (MBN) technique. Microstructural analysis (mean size of carbides), measurement of mechanical property (hardness) an...
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An attempt was made to evaluate nondestructively thermally degraded 2.25Cr-1Mo steel by. magnetic Barkhausen noise (MBN) technique. Microstructural analysis (mean size of carbides), measurement of mechanical property (hardness) and magnetic Barkhausen noise parameters (rms voltage, count) for a wide range of specimens isothermally degraded at 630 C were carried out to obtain the correlations between them. Both the rms voltage (MBNrms) and the count (MBNcount) of MBN signal were observed to increase rapidly in the initial 1000 hours of aging time and then slowly thereafter, which was attributed to decreased number of carbides as a result of carbides coarsening during thermal aging. Linear correlations of MBNcount with both the mean size of carbides and the hardness were found. MBNcount was suggested as a promising nondestructive evaluation parameter for assessing the thermally degraded microstructure and mechanical property of the 2.25Cr-1Mo steel. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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Even though extensive research has attempted to establish nondestructive evaluation (NDE) techniques for lumber, little effort has focused on NDE of log quality. If an NDE procedure is established for grading and sorting logs, a s...
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Even though extensive research has attempted to establish nondestructive evaluation (NDE) techniques for lumber, little effort has focused on NDE of log quality. If an NDE procedure is established for grading and sorting logs, a significant savings of time and money can be realized and potentially valuable wood waste can be reduced. In this study, a stress wave technique was applied to 20 larch logs with diameters of 25 cm to 30 cm to compare the dynamic modulus of elasticity (MOE) of logs to structural properties of 2 by 4 lumber produced from the same logs. Following stress wave tests, the logs were sawn to 2 by 4 lumber and dried to a moisture content of 15 percent. The lumber was tested by various nondestructive testing (NDT) methods to obtain dynamic MOE; next, static MOE and MOR were obtained by static bending tests. Dynamic MOE of a log was calculated from stress wave velocity for the log and compared with dynamic and static MOE and MOR measured for lumber produced from the same log. Stress waves, ultrasonics, and transverse vibration techniques were employed as NDT methods applied to lumber. As a result of comparing the dynamic MOE of logs with the static and dynamic MOE and MOR of lumber, a reasonable relationship was found between the nondestructive parameter of logs and the nondestructive and destructive parameters of lumber.
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We have carried out experimental investigation of eddy current non-destructive evaluation using a high-T-c SQUID magnetometer. By mapping out field distributions with the SQUID magnetometer, flaws 10 mm below the surface in conduc...
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We have carried out experimental investigation of eddy current non-destructive evaluation using a high-T-c SQUID magnetometer. By mapping out field distributions with the SQUID magnetometer, flaws 10 mm below the surface in conducting aluminum structures can be clearly identified. We have also designed and fabricated a first-order planar gradiometer on a large area LaAlO3 substrate with a baseline of 16 mm. [References: 3]
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The nondestructive evaluation (NDE) for the crack inside a graphite slab was investigated by using the high-T-c SQUID NDE system in unshielded environment. The crack-depth dependence of the crack signal was explored with the excit...
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The nondestructive evaluation (NDE) for the crack inside a graphite slab was investigated by using the high-T-c SQUID NDE system in unshielded environment. The crack-depth dependence of the crack signal was explored with the excitation frequency varied from 2 to 20 kHz. It was found that the phase of the crack signal is a linear function of the crack depth for various excitation frequencies. In addition, for both graphite and aluminum, the slope of the linear phase depth relation scaled in an empirical equation with the skin depth as the only variable. The empirical equation was useful in determining the proper excitation frequency for the eddy-current NDE of conductive samples. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 6]
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The ultrasonic pulse velocity (UPV) method has been used for decades to characterize concrete structures. In this method, ultrasonic transducers are attached to the concrete surface using a coupling agent. The coupling process is ...
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The ultrasonic pulse velocity (UPV) method has been used for decades to characterize concrete structures. In this method, ultrasonic transducers are attached to the concrete surface using a coupling agent. The coupling process is both time and labor intensive and, in some cases, may limit the ability to collect data. This paper describes the development of a fully contact-less (air-coupled) UPV method. By adding a matching layer between the transducer crystal and air and using signal processing methods, air-coupled through-thickness compression wave measurements in concrete are made possible. A scanning test setup was proposed and applied to a concrete test specimen that had different thicknesses and contained internal defects. The thicknesses of the test specimen represent realistic values for concrete elements. Experimental results show that defects and thickness variations within the concrete were visualized when the UPV data were presented in a two-dimensional (2D) scan image. A data interpretation algorithm was used to accurately locate the embedded defects within the test specimen.
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This paper describes a novel application of ultrasonic Lamb waves combined with network methods for data analysis for a non-destructive evaluation of the adhesive fillet size in the cusp of an aluminium T-peel joint. The ultrasoni...
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This paper describes a novel application of ultrasonic Lamb waves combined with network methods for data analysis for a non-destructive evaluation of the adhesive fillet size in the cusp of an aluminium T-peel joint. The ultrasonic signals were transmitted and received using a purpose-built cross correlator system, which generated filtered pseudo-random binary sequences tailored to excite s0 and a1 wave modes in the specimens. Signals received after propagation across the joint area were analysed in the modulus frequency domain by means of a standard fast Fourier transform. Simple statistical measures (such as mean and standard deviation) applied to peaks in the frequency spectra did not provide a robust basis for automatic discrimination between classes of bond fillet size, with 'recognition' success being of the order of chance alone. The most basic form of artificial neural network, the linear network, was then trained to recognize bond fillet radius as belonging to one of three categories of size. When presented with regions of bond fillet that were not included in its training data, it was able to 'recognize' fillet sizes with a success rate of 95%. The sensitivity of the method to experimental arrangements was examined by comparing the results obtained with well-collimated water-coupled transducers with those obtained by using mode-converting contact probes, which exhibited greater angular dispersion in the excited waves. Comparisons were made between different transducer excitations designed to excite s0 alone, a1 alone, s0 and a1 together and also a broadband excitation. Various training protocols for the network were also compared as were the results of output thresholding to minimize the number of wrong decisions made by the network. Overall we find that the best fillet size recognition performance was obtained with the broadband excitation applied to mode-converting wedge transducers set on either side of the bond. [References: 13]
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To contain high-pressure gases inside a pressure vessel a seal is often made in a thin-walled tube, known as the stem tube, that connects the gas reservoir and the vessel. This seal can be achieved through the use of a resistance ...
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To contain high-pressure gases inside a pressure vessel a seal is often made in a thin-walled tube, known as the stem tube, that connects the gas reservoir and the vessel. This seal can be achieved through the use of a resistance pinch weld that forms with only a limited amount of melting occurring. The lack of melting makes applying traditional post-weld nondestructive evaluation (NDE) techniques extremely difficult. The welds of interest here are made from 304L stainless steel (typically 3.8 mm diameter and 38 mm long) and have a non-uniform geometry that does not inherently lend itself to either eddy current or static field SQUID-based measurement techniques. We perform these NDE measurements with both the sample and the SQUID located inside local electromagnetic shielding. SQUID data are presented as individual time series traces for a set of welds that were fabricated using a broad range of fabrication parameters, and a comparison is made between the SQUID-based results and the known parameters. With the limited spatial resolution offered by our present SQUID system, it is not clear if weld quality can be evaluated from purely SQUID-based results.
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The paper investigates innovative designs of piezoelectric actuators for structural health monitoring (SHM). Periodic configurations are proposed as an effective means to provide actuators and sensors with strong, frequency depend...
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The paper investigates innovative designs of piezoelectric actuators for structural health monitoring (SHM). Periodic configurations are proposed as an effective means to provide actuators and sensors with strong, frequency dependent directional characteristics, which allow beam steering through a sweep of the excitation frequency. The concept has the potential to enable in situ monitoring of critical components through strongly focused actuation (and/or sensing) and directional scanning capability, which may be achieved with very limited hardware requirements. Beam steering is achieved by exploiting interference phenomena generated by the spatial periodicity of the array and the simultaneous activation of its components. Such interference phenomena produce waves with frequency dependent directional characteristics, which allow directional scanning to be performed simply through a frequency sweep. The need for beam-forming algorithms and associated hardware is thus avoided. The concept is illustrated by considering 2D arrays of point sources of various topologies. The case of a thin membrane supporting the propagation of SV waves is first presented to provide a simple frame work of analysis. The case of Lamb waves in a thin plate is then considered to demonstrate the validity and the practicality of the proposed approach.
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Coupling media are necessary to ensure that transducers bond to wood specimens to minimize coupling losses and improve the accuracy of ultrasonic measurements. There are several types of coupling media available, and the optimal c...
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Coupling media are necessary to ensure that transducers bond to wood specimens to minimize coupling losses and improve the accuracy of ultrasonic measurements. There are several types of coupling media available, and the optimal choice is not known. In this work, we analyzed the results of ultrasonic wave attenuation for 0.1-MHz longitudinal and transverse transducers with six different materials as coupling media in nine species of Brazilian wood with densities in the range 700–1170 kg/m3. Tests were performed using constant pressure on the transducer and with wave propagation in the longitudinal direction. For transverse transducers, the polarization was in the radial and tangential directions. The results were analyzed statistically and showed that, for attenuation in both longitudinal and transverse waves, the material used for coupling had significant effects, whereas the wood species had no effect. For longitudinal waves, the statistical evaluation showed that the coupling material performance was strongly dependent on the species of wood, but it was not possible to observe any tendency of behavior associated with specific anatomical properties.
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