• Corrosion Science and Technology
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• 제4권3호
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• pp.108-113
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• 2005

One of the recent safety issues in the pressurized heavy water reactor (PHWR) is the cracking of the feeder pipe. Because of the limited accessibility to the cracked region and a high dose of radiation exposure, it is difficult to inspect all the pipes with the conventional ultrasonic method. In order to solve this problem, a long-range guided wave technique has been developed. A computer program to calculate the dispersion curves in the pipe was developed and the dispersion curves for the feeder pipes in PHWR plants were determined. Several longitudinal and/or flexural modes were selected from the review of the dispersion curves and an actual experiment has been carried out with the specific alignment of the piezoelectric ultrasonic transducers. They were confirmed as L(0,1)) and/or flexural modes(F(m,2)) by the short time Fourier transformation(STFT) and were sensitive to the circumferential cracks, but not to the axial cracks in the pipe. An electromagnetic acoustic transducers(EMAT) was designed and fabricated for the generation and reception of the torsional guided wave. The axial cracks were detected by a torsional mode(T(0,1)) generated by the EMAT.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 추계학술발표대회 논문집
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• pp.29-32
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• 2003

Multi -walled carbon nanotube(MWNT)/poly(methyl methacrylate) composites were fabricate d through film casting. Manufacturing process was established using a ultrasonic cleaner and a homogenizer. Acetone was used as a solvent to melt PMMA and mix with MWNT. The ultrasonic cleaner performed an important role in producing MWNT/MMA nanocomposites. Ultrasonic energy was utilized to disperse MWNT in acetone. Also, melting PMMA in acetone and mixing MWNT and PMMA were achieved using the homogenizer. It was confirmed that the nanohlbes were well dispersed in PMMA according to SEM images.

• Structural Monitoring and Maintenance
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• 제9권4호
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• pp.373-388
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• 2022

A USW based diagnostic procedure is presented for estimating the depth of surface-breaking cracks. The diagnosis is demonstrated on seven lab-scale SFRC beam specimens, which are subjected to the CMOD controlled three-point bending test to create real bending cracks. Then, the recorded multiple ultrasonic signals are examined with the signal processing techniques, including wavelet transform and two-dimensional Fourier transform, to investigate the relationships between the crack depth and two diagnostic indices, namely the attenuation coefficient and dispersion index (DI). Finally, the reliabilities of these indices for depth estimation are verified with the visually measured crack depths as well as the crack features obtained with a digital image processing algorithm. It is found that the DI outperforms the attenuation coefficient in depth estimation, where this index displays good agreement with the visual inspection for 86% of the inspected specimens.

• 비파괴검사학회지
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• 제27권3호
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• pp.224-230
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• 2007

This work is aimed to explore a possibility of using the generalized Lamb waves for nondestructive evaluation of the bonding quality of layered substrates. For this purpose, we prepared two sets of specimens with imperfect bonding at their interfaces; 1) TiN-coated specimens with various wear conditions, and 2) CVD diamond specimens with various cleaning conditions. A dispersion simulation performed for layered substrates with imperfect interfaces are carried out to get the characteristics of dispersion curves that can be used for bonding quality evaluation. Then the characteristics of dispersion curves of the fabricated specimens are experimentally determined by use of an ultrasonic backward radiation measurement technique. The results obtained in the present study show that the lowest velocity mode (Rayleigh-like) of the generalized Lamb waves are sensitively affected by the bonding quality. Therefore, the generalized Lamb waves can be applied for nondestructive evaluation of imperfect bonding quality in various layered substrates.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2018년도 춘계 학술논문 발표대회
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• pp.263-264
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• 2018

Recently, interest in making nanocomposite materials for construction utilizing the excellent physical properties of nano materials is increasing. In this study, basic properties of mortar were evaluated by the dispersion condition of cellulose nano-crystals (CNCs) extracted from nanocellulose and the feasibility of the study was examined. As a result, it was confirmed that the flexural strength and the compressive strength were increased by increasing the dispersion time of the CNCs and by using the ultrasonic dispersing device and the magnetic stirrer together.

• 한국전기전자재료학회논문지
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• 제24권8호
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• pp.682-685
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• 2011

An engine oil sensor based on multiwall carbon nanotubes was fabricated with screen printing method. Since carbon nanotubes are generally intertwined, dispersion of the carbon nanotubes in the binding agent (ethyl cellulose, a-terpineol, frit) is a key factor for large yield of engine oil sensor. By conventional dispersion method, a hand-mill method, the maximum yield was 80% at most. However, we used the hand ultrasonic, in order to increase the yield of the sensors. As a results, our engine oil sensor fabricated by the screen printing method shows excellent yield rate of 97%, when we dispersed a paste by the hand ultrasonic method.

• 비파괴검사학회지
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• 제34권3호
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• pp.233-240
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• 2014

나노/마이크로 소자의 개발이 활발해짐에 따라 나노/마이크로 박막의 기계적 물성의 정밀 측정에 대한 필요성이 점차 커지고 있다. 기존의 파괴적인 방법의 한계를 극복하기 위한 방법으로, 유도초음파를 이용한 비파괴적인 박막 물성 방법에 대한 관심이 늘어나고 있다. 유도초음파를 이용하여 박막의 물성을 측정하는 실험을 설계하거나, 물성 측정에 대한 실험 결과를 이해하는데 있어 박막의 분산선도를 이해하는 것은 필수적이라 할 수 있다. 본 연구에서는, 전달 행렬법을 이용하여 박막의 분산선도를 계산하는 방법을 제시하고, 이를 금속 박막에 적용하여 그 특성을 관찰하였다. 전달 행렬법을 이용하여 다층판에서의 주파수에 따라 유도초음파가 전파하는 속도를 계산하여 상용 프로그램과 비교하여 그 타당성을 확인하였다. 이러한 방법을 Si 기판 위에 증착된 Al 금속 박막에 적용하여 얻은 분산곡선의 분석을 통해, 박막의 두께 조건에 따른 모드와 분산 및 비분산 특성이 나타나는 구간을 관찰할 수 있었다.

• 한국재료학회지
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• 제11권11호
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• pp.972-977
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• 2001

It was investigated the effect of ultrasonic treatment on magnetic property of ultra fine magnetic Fe powders ($\alpha$-Fe) for magnetic tape. The properties were characterized with vibrating sample magnetometer (VSM), particle size analyzer (PSA) and scanning electron microscope (SEM). At 4hours ultrasonic treatment of 70 kHz, magnetic properties such as squareness ratio (S.Q. : 0.8868), orientation ratio (O.R. : 2.45) and switching field distribution (S.F. D. : 0.394) before taping were relatively enhanced. Cumulative particle size distribution of less than 5$\mu\textrm{m}$ fine powder was above 90% below 1 hour leaving time after ultrasonic treatment and it was supposed that ultrasonic treatment prevent aggregation. The magnetic values of S.Q. and S.F.D. of tape manufactured at 70 kHz and 4hour ultrasonic treatment were improved from 0.7747, 0.3818 to 0.8037, 0.3706, respectively. Electro-magnetic property used as in-output signal characteristic was improved, which showed that ultrasonic treatment developed the magnetic properties.

• Safety and Health at Work
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• 제2권1호
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• pp.65-69
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• 2011

Objectives: Carbon nanotubes are an important new class of technological materials that have numerous novel and useful properties. Multi-walled carbon nanotubes (MWCNTs), which is a nanomaterial, is now in mass production because of its excellent mechanical and electrical properties. Although MWCNTs appear to have great industrial and medical potential, there is little information regarding their toxicological effects on researchers and workers who could be exposed to them by inhalation during the handling of MWCNTs. Methods: The generation of an untangled MWCNT aerosol with a consistent concentration without using surfactants that was designed to be tested in in vivo inhalation toxicity testing was attempted. To do this, MWCNTs were dispersed in deionized water without the addition of any surfactant. To facilitate the dispersion of MWCNTs in deionized water, the water was heated to $40^{\circ}C$, $60^{\circ}C$, and $80^{\circ}C$ depending on the sample with ultrasonic sonication. Then the dispersed MWCNTs were atomized to generate the MWCNT aerosol. After aerosolization of the MWCNTs, the shapes of the NTs were examined by transmission electron microscopy. Results: The aerosolized MWCNTs exhibited an untangled shape and the MWCNT generation rate was about 50 $mg/m^3$. Conclusion: Our method provided sufficient concentration and dispersion of MWNCTs to be used for inhalation toxicity testing.

• Tribology and Lubricants
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• 제19권5호
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• pp.285-291
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• 2003

Ultrasonic vibrator is an equipment which atomizes and homogenization the oils by breaking the oil particles with ultrasonic cavitation, and would improve the properties. The present study deal with the ultrasonic breaking systems which recycle the shipborne waste oil into usable oil to be burnt. The first place, experimental studies were carried out to investigate the homogenizing effect of the waste oils by ultrasonic cavitation. Variation of the properties(viscosity, specific gravity and pH) and the matrix structures for the various shipborne waste oils were interpreted to analyse the breaking, dispersion effects by ultrasonic cavitation. The experimental results can be useful to the development of waste oil disposing systems.