• Journal of the Korean Society for Nondestructive Testing
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• v.7 no.1
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• pp.18-31
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• 1987

For the purpose of domestic production of ultrasonic transducer, experiments on material selection for backing and matching layer, and electrical impedance matching between transducer and equipment were performed. The characteristics of manufactured transducers with experimental results were analyzed and compared with foreign products. Through the evaluation of the transducers manufactured and the comparision with foreign products, it is confirmed that the transducers manufactured show the good performance characteristics and efficiency.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.5 no.1
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• pp.14-19
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• 2009

NDE(Nondestructive examination) detects a flaw or discontinuity in materials. Flaws detected by the examination shall be evaluated for the decision basis of the integrity. The internal flaws of forging products can be detected by UT. However, UT has detection limits because of its reflected signal weakness. Normally, a 1mm or less flaw is known as the limit. If a flaw was detected, the size of flaw would be evaluated by AVG(or DGS) technique. To verify the evaluation data, alternative examination methods are needed. But there is no alternative examination methods until now. In this study, Phased array ultrasonic technique can be used to size the flaws in the generator rotor with focused beam of ultrasonic wave as a supplement method of AVG. Also, the phased array ultrasonic technique described enables the shape of flaw to be depicted exactly.

• Journal of the Korean Society for Nondestructive Testing
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• v.9 no.2
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• pp.18-24
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• 1989

Computer-aided high frequency ultrasonic is applied to aluminum oxide(85w%, 94w%, 96w%, and 99w%) MOR(modulus of rupture) samples to evaluate mechanical properties such as density variation, pore content, elastic modulus, shear modulus, and poisson's ratio. Ultrasonic wave velocity and attenuation measurement techniques were used as an evaluator of such properties. Pulse-echo C-Scan images with different fate setting method using 50MHz center frequency 1 inch focal length transducer allows evaluation of density variation and pore content. Elastic modulus calculated with the relation of density and ultrasonic velocity. It shows good reliability as compared with resonance method. Sintered density variation of $0.025g/cm^{3}$, that is 0.6% of theoretical density in $Al_{2}O_{3}$ samples can be observed by ultrasonic velocity measurement. Attenuation measurement method qualitatively agree with 4-point fracture testing result concerning of porosity content.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.2
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• pp.103-109
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• 2005

Fiber reinforced plastic material should be inspected in fabrication process in order to enhance quality by prevent defects such as delamination and void. Generally, ultrasonic technique is widely used to evaluate FRP. In conventional ultrasonic techniques, transducer should be contacted on FRP. However, conventional contacting method could not be applied in fabrication process and novel non-contact evaluating technique was required. Laser-based ultrasonic technique was tried to evaluate CFRP plate. Laser-based ultrasonic waves propagated on CFRP were received with various transducers such as accelerometer and AE sensor in order to evaluate the properties of waves due to the variation of frequency. Velocities of laser-based ultrasonic waves were evaluated for various fiber orientation. In addition, laser interferometry was used to receive ultrasonic wave in CFRP and frequency was analysed.

• Journal of Power System Engineering
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• v.19 no.5
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• pp.60-66
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• 2015

Embrittlement of material by hydrogen charging should be cleared for safety of storage vessel of hydrogen and components deal with hydrogen. A stainless steel is generally used as materials for hydrogen transportation and storage, and it has a big advantage of corrosion resistance due to nickel component in material. In this study, microscopic damage behavior of stainless steel according to the hydrogen charging time using nondestructive evaluation was studied. The surface of stainless steel became more brittle as the hydrogen charging time increased. The parameters of nondestructive evaluation were also changed with the embrittlement of stainless steel surface by hydrogen charging. Ultrasonic test, which is the most generalized nondestructive technique, was applied to evaluate the relationship between the ultrasonic wave and mechanical properties of stainless steel by hydrogen charging. The attenuation coefficient of ultrasonic wave was increased with hydrogen charging time because of surface embrittlement of stainless steel. In addition, acoustic emission test was also used to study the dynamic behavior of stainless steel experienced hydrogen charging. AE event at the hydrogen charged specimen was obviously decreased at the plastic zone of stress-strain curves, while the number of event for the specimen of hydrogen free was dramatically generated when compared with the specimens underwent hydrogen charging.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.4
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• pp.293-298
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• 2009

The ultrasonic atomic force microscope(UAFM) has been developed in order to enhance the characterization technology for nano-scale surface combining ultrasonic property to atomic force microscope. This UAFM technique enables elasticity imaging due to the physical properties on the heterogeneous surface in addition to the novel topography of surface height in the nano-surface layer. In this study, the prototype UAFM system was constructed and applied to several materials, silicon deposited wafer, spherodized cold heading steel, and carbon fiber reinforced plastic specimen. Clear elastic contrast was successfully obtained using this developed prototype UAFM.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.2
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• pp.130-137
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• 2000

Ultrasonic technique which is one of the most common and reliable nondestructive evaluation techniques has been applied to evaluate the integrity of structures by analyzing the characteristics of signal scattered from internal defects. Therefore, the numerical analysis of the ultrasonic scattered field is absolutely necessary for the accurate and quantitative estimation of internal defects. Various modeling techniques now play an important role in nondestructive evaluation and have been employed to solve elastic wave scattering problems. Because the elastodynamic boundary element method is useful to analyze the scattered field in infinite media. it has been used to calculate the ultrasonic wavefields scattered from internal defects. In this study, a review of the boundary element method used for elastic wave scattering problems is presented and, as examples of the boundary element method, the scattered fields due to a circular cavity subjected to incident SH-wave and due to a surface-breaking crack subjected to incident Rayleigh wave are illustrated.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.3
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• pp.242-247
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• 2009

The ability of time reversal techniques to focus ultrasonic beams on the source location is important in many aspects of ultrasonic nondestructive evaluation. In this paper, we investigate the time reversal beam focusing of ultrasonic array sensors on a defect in layered media. Numerical modeling is performed using the commercially available software which employs a time domain finite difference method. Two different time reversal approaches are considered - the through transmission and the pulse-echo. Linear array sensors composed of N elements of line sources are used for signal reception/excitation, time reversal, and reemission in time reversal processes associated with the scattering source of a side-drilled hole located in the second layer of two layer structure. The simulation results demonstrate the time reversal focusing even with multiple reflections from the interface of layered structure. We examine the focusing resolution that is related to the propagation distance, the size of array sensor and the wavelength.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.1
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• pp.1-21
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• 2001

It will be shown how models can simulate all the elements of an ultrasonic NDE measurement system, including the pulser/receiver, cabling, transducer(s), and the acoustic/elastic waves fields. When combined, these models form what is called the electroacoustic measurement model. It will be demonstrated how this electroacoustic measurement model can be used to conduct parametric transducer and system studies and how the model can form the basis for experimentally characterizing all the elements of the ultrasonic measurement system, using purely electrical measurements.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.190-194
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• 2003

Two different types of nondestructive evaluation (NDE) techniques were employed to investigate the tensile behavior of ceramic matrix composites (CMCs). Two NDE methods, ultrasonic testing (UT) and infrared (IR) thermography, were used to assess defects and/or damage evolution before and during mechanical testing. Prior to tensile testing, a UTC-scan and a xenon flash method were performed to obtain initial defect information in light of UT C-scans and thermal diffusivity maps, respectively. An IR camera was used for in-situ monitoring of progressive damages. The IR camera measured temperature changes during tensile testing. This paper has presented the feasibility of using NDE techniques to interpret structural performance of CMCs.