• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2003.10a
• /
• pp.29-32
• /
• 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
• /
• v.9 no.4
• /
• pp.373-388
• /
• 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.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.27 no.3
• /
• pp.224-230
• /
• 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.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2018.05a
• /
• pp.263-264
• /
• 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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.24 no.8
• /
• pp.682-685
• /
• 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.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.34 no.3
• /
• pp.233-240
• /
• 2014

In this study, we investigated the dispersion characteristics of guided waves in thin films. Dispersion curves are essential for understanding not only the behavior of ultrasonic waves, but also the mechanical properties of thin films. Matrix techniques are presented for modeling ultrasonic waves in multilayered structures before being used to calculate the dispersion curves for Al-steel and Al-composite specimens. When compared with the dispersion curves obtained using the commercial program (Disperse), the dispersion curves generated from the transfer matrix method show its validity. These developed methods are used to obtain dispersion curves for Al thin films deposited on a Si substrate. The resulting dispersion curves enable observation of both dispersive and non-dispersive behavior for the guided waves, depending on the thickness of the thin films.

• Korean Journal of Materials Research
• /
• v.11 no.11
• /
• pp.972-977
• /
• 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
• /
• v.2 no.1
• /
• pp.65-69
• /
• 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
• /
• v.19 no.5
• /
• pp.285-291
• /
• 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.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2004.10a
• /
• pp.31-34
• /
• 2004

Carbon nanofiber exhibits superior and often unique characteristics of mechanical, electrical chemical and thermal properties. In this study, For improvement of the mechanical properties of composites, carbon nanofiber reinforced hybrid composites was investigated. For the effect of dispersion, The dispersion methods of solution blending and mechanical mixing were used. The mixing of solution blending method was used using ultrasonic. Dispersion of carbon nanofiber was observed by scanning electron microscope (SEM). Mechanical properties were measured by universal testing Machine (UTM).