• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.3
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• pp.276-282
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• 2013

This paper proposes an ultrasonic method for measurement of linear and hysteretic interfacial stiffness of contacting surfaces between two steel plates subjected to nominal compression pressure. Interfacial stiffness was evaluated by the reflection and transmission coefficients obtained from three consecutive reflection waves from solid-solid surface using the shear wave. A nonlinear hysteretic spring model was proposed and used to define the quantitative interfacial stiffness of interface with the reflection and transmission coefficients. Acoustic model for 1-D wave propagation across interfaces is developed to formulate the reflection and transmission waves and to determine the linear and nonlinear hysteretic interfacial stiffness. Two identical plates are put together to form a contacting surface and pressed by bolt-fastening to measure interfacial stiffness at different states of contact pressure. It is found from experiment that the linear and hysteretic interfacial stiffness are successfully determined by the reflection and transmission coefficient at the contact surfaces through ultrasonic pulse-echo measurement.

• Journal of Welding and Joining
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• v.15 no.3
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• pp.109-117
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• 1997

The temperature gradient in weldment changes the transit time and distorts the direction of the ultrasound beam to the higher temperature regions due to the lower sound speed in the hotter regions of the weldment. This paper describes a ray-tracing method for calculating the effects of temperature gradients on ultrasonic propagation in fillet arc weldig. In the method, weldment is conceptually devided into a number of layers and the refraction and sound speed at each layer is calculated using the temperature which calculated from analytical solution. Calculating the time and location of echoes arrived from various interfaces around a molten weld pool determines the optimum location of ultrasonic transducers and the correct position of flaws.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.3
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• pp.82-88
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• 2003

The nondestructive internal quality evaluation of agricultural products has been strongly required from the needs for individual inspection. Recently, the ultrasonic wave has been considered as a solution fur this problem, and an ultrasonic system was constructed for the ultrasonic NDE of fruits and vegetables in our previous work. In this paper, the practical applicability of our ultrasonic system is tested fur the inspection of internal defects (central cavity) in Atlantic potato. Sound speed and RMS of transmitted ultrasonic wave signal were measured and classification algorithm using 2 dimensional stochastic analysis. was presented. Experimental results showed greater value of sound speed and RMS (root mean square) of transmitted signal in normal samples than in abnormal samples with cavity. Also a stochastic method to distinguish normal and abnormal showed fault detection rate less than 5%.

• Journal of Pharmaceutical Investigation
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• v.36 no.3
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• pp.185-192
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• 2006

The purpose of this study was to determine the effects of iontophoresis on transdermal delivery of procaine hydrochloride in healthy volunteers, as well as to the synergic effect of high voltage current or ultrasound on the efficacy of transdermal delivery of iontophoresis. Forty healthy volunteers were randomly assigned to four groups topical application group (TA), iontophoresis group (IT), pre-treatment of high voltage current stimulation with iontophoresis (HVS + IT), and pre-treatment of ultrasound application with iontophoresis (US + IT). All subjects received procaine iontophoresis on the forearm using direct current with 4 mA f3r 15 minutes. All subject was measured the duration of local anesthesia, pressure pain threshold, pain perception threshold using rectangular wave at 0.2 ms, 1 ms, 50 ms of rectangular current stimulation after procaine iontophoresis. For comparisons of the sensory characteristics and efficacy of iontophoresis between the groups, an one-way ANOVA and Kruskal-Wallis were used. The significant difference the duration of local anesthesia were found between the groups (p<0.001). The local anesthetic duration of IT, HVS+IT were significantly longer than TA. Meanwhile, the local anesthetic duration of US+IT was significantly longer than HVS+IT, IT and TA group (p<0.05). Also, the pressure pain threshold, pain perception threshold at 0.2 ms, 1 ms, 50 ms were significant difference between the groups (p<0.001). All sensory characteristics including pressure pain threshold, pain perception threshold of IT, HVS+IT was significantly increased than TA, whereas, US+1T was significantly increased HVS+1T, IT and TA (p<0.05). This study showed that the procaine iontophoresis have increase the duration of local anesthesia concomitantly pressure pain threshold and pain perception threshold of sensory nerve fibers such as $A-{\beta}$, $A-{\delta}$ and C fiber. This findings suggest that the iontophoresis enhanced the transdermal delivery of drug ions in vivo. The combination of ultrasound application and iontophoresis synergized the transdermal delivery of drug ions. It is suggests that an electric field, mechanical and heating property of ultrasound may contribute to synergic effect due to temporary changes of structure in the stratum corneum.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.4
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• pp.290-298
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• 2014

Ultrasonic thickness measurement is a non-destructive method to measure the local thickness of a solid element, based on the time taken for an ultrasound wave to return to the surface. When an element is very thin, it is difficult to measure thickness with the conventional ultrasonic thickness method. This is because the method measures the time delay by using the peak of a pulse, and the pulses overlap. To solve this problem, we propose a method for measuring thickness by using the power cepstrum and the minimum variance cepstrum. Because the cepstrums processing can divides the ultrasound into an impulse train and transfer function, where the period of the impulse train is the traversal time, the thickness can be measured exactly. To verify the proposed method, we performed experiments with steel and, acrylic plates of variable thickness. The conventional method is not able to estimate the thickness, because of the overlapping pulses. However, the cepstrum ultrasonic signal processing that divides a pulse into an impulse and a transfer function can measure the thickness exactly.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.3
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• pp.226-232
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• 2014

In the present study, the characteristics of laser ultrasound in the ablation regime are investigated using simulations and experiments. The laser ultrasonic technique has been recognized as a noncontact method in the field of nondestructive tests (NDTs). In hostile environments (such as hot temperatures), this method has various advantages over the conventional contact ultrasonic method. In particular, in the ablation regime, the laser ultrasonic technique is suitable for inspecting internal defects because of the high amplitude and directivity of the longitudinal wave. In this paper, a simulation model for laser ultrasound in the ablation regime was developed. This model was subsequently applied to a defective specimen using the B-scan method to locate defects. Finally, we performed an experimental test to verify the simulation results. Consequently, the simulation demonstrated good agreement with the experimental test.

• Journal of the Korean Wood Science and Technology
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• v.35 no.5
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• pp.16-23
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• 2007

This study was performed as part of a research project aimed at developing an ultrasonic computed tomography (CT) system of wood for field application. In this reports, we investigate the variation of wave velocities on the cross section of real size wooden structural member to confirm the reason of image distortion on CT image of wood, and then proposed a new image reconstruction method by considering the velocity variation on wood cross section. First of all, the effect of wood anisotropy on ultrasonic velocities of wooden members was investigated. Based on the relationship between ultrasonic velocity and annual ring angle, which was obtained from test results of small clear specimens, ultrasonic velocities of each measuring angle were predicted. Next, they were compared with the ultrasonic velocities measured on five wood disks. There were very large differences between predicted and measured results, thought to be caused by the skewing effect of ultrasound and the presence of juvenile-wood. Based on these findings, a new method was proposed to reconstruct cross-sectional image of wood. By using this method, some distortions on reconstructed images could be removed, and defects were more easily and clearly detected. The minimum size of detectable defect was decreased remarkably, from 33 mm to 13 mm. However, the size of the detected defect was enlarged and the position somewhat shifted to the specimen surface on the CT images, which was also thought to be caused by the skewing effect of ultrasound. Additional research has been planned to solve these problems.

• Composites Research
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• v.29 no.5
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• pp.288-292
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• 2016

In this paper, a novel ultrasonic propagation imaging system, called a full-field pulse-echo ultrasonic propagation imaging (FF PE UPI) system is introduced. The system nondestructively inspected targets with two-axis translation stage. The coincident laser beams for ultrasonic sensing and generation are scanned and pulse-echo mode laser ultrasounds are captured. This procedure makes it possible to generate full-field ultrasound in through-the-thickness direction as large as the scan area. Structural inspection results in the form of full-field ultrasonic wave propagation videos are introduced, which are painted sandwich control surfaces. In addition, the inspection results of FF PE UPI system are compared with conventional ultrasonic testing methods such as waterjet and portable C-scan.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.1
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• pp.1-7
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• 2004

The angular dependence (or profile) of backscattered ultrasound was measured for steel specimens with a range of surface roughness, $1{\sim}71{\mu}m$. Backscattering profiles at or near the Rayleigh angle still showed roughness dependence while the assessment of surface roughness via normal profile became impossible due to the paint layer masking the roughness. The peak amplitude directly radiated at the Rayleigh angle was proportional to the surface roughness, while the averaged peak amplitude radiated from the backward propagating Rayleigh wave, produced by reflection at a corner, was inversely proportional. In the painted specimens, the linearity of direct backward radiation with the roughness was observed even at the roughness of less than three hundredths of a wavelength, and the abnormal multiple bark reflection caused by periodic roughness disappeared.

• Korean Journal of Metals and Materials
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• v.49 no.12
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• pp.924-929
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• 2011

It is well known that grain boundary cavitation is the main failure mechanism in austenitic stainless steel under tensile hold creep-fatigue interaction conditions. The cavities are nucleated at the grain boundary during cyclic loading and grow to become grain boundary cracks. The attenuation of ultrasound depends on scattering and absorption in polycrystalline materials. Scattering occurs when a propagation wave encounters microstructural discontinuities, such as internal voids or cavities. Since the density of the creep-fatigue cavities increases with the fatigue cycles, the attenuation of ultrasound will also be increased with the fatigue cycles and this attenuation can be detected nondestructively. In this study, it is found that individual grain boundary cavities are formed and grow up to about 100 cycles and then, these cavities coalesce to become cracks. The measured ultrasonic attenuation increased with the cycles up to cycle 100, where it reached a maximum value and then decreased with further cycles. These experimental measurements strongly indicate that the open pores of cavities contribute to the attenuation of ultrasonic waves. However, when the cavities develop, at the grain boundary cracks whose crack surfaces are in contact with each other, there is no longer any open space and the ultrasonic wave may propagate across the cracks. Therefore, the attenuation of ultrasonic waves will be decreased. This phenomenon of maximum attenuation is very important to judge the stage of grain boundary crack development, which is the indication of the dangerous stage of the structures.