• Proceedings of the KSME Conference
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• 2004.04a
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• pp.336-341
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• 2004

This research investigates the feasibility of ultrasonic microscope for nondestructive assessment of thermal degradation in artificially aged commercial Co-base superalloy, FSX414. This alloy has been used for high temperature structure applications such as stationary gas turbine blade and nozzle chamber in fossil plant. Microstructural change was found that the fine carbides became coarser and spheroidized in matrix as aging time increased. The leaky surface acoustic wave velocity gradually decreases by a maximum of 4.7% with increasing aging time up to 4,000hours. However, the longitudinal wave velocity has a little change. Also, it has a good correlation between leaky surface acoustic wave velocity and Vickers hardness. Consequently, LSAW can be used to examine the degree of degradation in thermally aged Co-base superalloy.

• 연구논문집
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• s.31
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• pp.149-156
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• 2001

Hydrogen damage affects carbon steel tubes in many fossil-fuel-fired boilers, often causing large tube ruptures that necessitate an immediate shutdown. Therefore, equipment handling high-temperature, high-pressure hydrogen must undergo careful periodic inspection because of its susceptibility to hydrogen attack. This paper describes the application of an ultrasonic technique for detecting the presence of hydrogen damage in utility boiler tubes. The accuracy of the technique has been shown in laboratory tests. However, it is difficult to evaluate hydrogen attack quantitatively by this technique, because ultrasonic wave is influenced by the test conditions and the material itself.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.72-72
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• 2004

대부분의 금속 재료는 제조 공정 중에 인장, 압축, 압연, 압출, 인발 등 소성 변형을 수반하는 가공의 단계를 거치게 된다. 가공 단계에서 가해준 변형률 및 이에 따라 형성된 전위구조 등은 생산재의 기계적 성질에 많은 영향을 미친다. 그리고 소성 변형이 수반되는 또 하나의 과정은 피로, 크리프 손상 등의 소성 변형을 수반하게 되는 기계적 손상이다 이러한 기계적 손상에 의해서도 전위가 도입되며, 전위의 집적부위에서 균열이 생성되기도 한다. 따라서 기계적 손상을 비파괴적으로 평가하는데 있어서도 소성 변형의 영향을 파악하는 것이 하나의 중요한 문제가 된다.(중략)

• The Journal of the Acoustical Society of Korea
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• v.9 no.2
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• pp.5-13
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• 1990

In this paper, 50MHz reflection ultrasonic microscope system with small aperture acoustic lens has been constructed in order to study the defects which lay deep in thick specimens, and acoustic images of multilayered media have been analyzed. Output characteristics of this system for multilayered media have been influenced by acoustic attenuation, aberration in specimen, type of lens and the properties of a defect, and it has been used for image processing of the multilayered I.C. and the bonding layer. In experimental results, it has been shown that small aperture ultrasonic microscope system was powerful tool for inspection of thick specimens such as electronic device, bonding layer, quality of ceramic materials.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.6 no.1
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• pp.16-22
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• 2010

Cast austenitic stainless steel(CASS) is used in the primary cooling piping system of nuclear power plant for it's relative low cost, corrosion resistance and easy of welding. However, the coarse-grain structure of cast austenitic stainless steel can strongly affect the inspectability of ultrasonic testing. The major problems encountered during inspection are beam skewing, high attenuation and high background noise of CASS component. So far, the best inspection performance involving CASS components have been achieved using low frequency TRL(Transmitter/Receiver side-by-side L wave) angle beam probe. But TRL technique could not detect shallow defect and it contains an uncertainty for sizing capability. Currently, most of researchers are studying to overcome these challenge issue. In this study, low-frequency phased array TRL technique used to detect and sizing the flaws in CF8A cast austenitic stainless steel.As conclusion, we could detect and size not only axial flaw but also circumferential flaw using low frequency phased array technique.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.1
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• pp.46-53
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• 2000

Magnetostrictive sensors which can be used effectively to detect flaws in pipe were fabricated. The optimal conditions to obtain the maximum generation efficiency of the ultrasonic wave were established. In case of the used steel pipe the optimal magnetic field was $250{\sim}350Oe$ and the coil width of 15mm showed the best efficiency for generating a wave with the frequency of 180 kHz. In the best condition, the wave can propagate further than 50m without serious attenuation. The amplitude of the ultrasonic wave reflected from artificial flaw had a good linear relationship to the cross-sectional area of the flaw.

• Journal of Biomedical Engineering Research
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• v.26 no.1
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• pp.55-63
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• 2005

A novel imaging system for High-resolution Ultrasonic Transmission Tomography (HUTT) and soft tissue differentiation methodology for the HUTT system are presented. The critical innovation of the HUTT system includes the use of sub-millimeter transducer elements for both transmitter and receiver arrays and multi-band analysis of the first-arrival pulse. The first-arrival pulse is detected and extracted from the received signal (i.e., snippet) at each azimuthal and angular location of a mechanical tomographic scanner in transmission mode. Each extracted snippet is processed to yield a multi-spectral vector of attenuation values at multiple frequency bands. These vectors form a 3-D sinogram representing a multi-spectral augmentation of the conventional 2-D sinogram. A filtered backprojection algorithm is used to reconstruct a stack of multi-spectral images for each 2-D tomographic slice that allow tissue characterization. A novel methodology for soft tissue differentiation using spectral target detection is presented. The representative 2-D and 3-D HUTT images formed at various frequency bands demonstrate the high-resolution capability of the system. It is shown that spherical objects with diameter down to 0.3㎜ can be detected. In addition, the results of soft tissue differentiation and characterization demonstrate the feasibility of quantitative soft tissue analysis for possible detection of lesions or cancerous tissue.

• Journal of Conservation Science
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• v.31 no.3
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• pp.267-278
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• 2015

In this study, the elastomer cover, a new contact material, was developed to establish the customized ultrasonic measurement considering surface irregularities of stone cultural heritages. The cover exhibits high elastic force and wear resistance because it has tensile strength of 17MPa and elongation of 625%. In addition, as a result of comparative experiments for the seven types according to transducers and contact materials including the elastomer cover, rock surface irregularities significantly affect attenuation of ultrasonic velocity. The phenomenon was more noticeable in the chiseling finish and indirect transmission measurement rather than the dabbed finish and direct transmission measurement. However, the Type F using the exponential transducer and elastomer cover showed stable P-wave velocity and high amplitude regardless of the surface irregularities. This because the elastomer cover sufficiently sticks to surface irregularities and removes pores between a transducer and a rock specimen. Therefore, the Type F should be used for the ultrasonic measurement of stone cultural heritages with surface irregularities.

• Journal of the Korea Convergence Society
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• v.9 no.4
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• pp.161-167
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• 2018

The amount of CNG was measured using a pressure sensor in the case of CNG vehicles. However, the current measurement method causes anxiety to the driver because it is difficult to measure the detailed amount of CNG according to various environmental conditions. This study was performed to measure the amount of CNG in CNG fuel system, and presented the method of measurement by simulating the detection system of CNG. In this experiment, a detection simulator with an ultrasonic sensor in CNG tank of Type-3 was designed, and the reception signal of the ultrasonic sensor was verified by reducing the pressure from 100 bars to 0 bars (increment=5 bars) using compressed air. As a result, the output signal voltage of the ultrasonic sensor decreased as the pressure in the tank decreased, and the it was verified that the shape of the graph was linearity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.695-700
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• 2010

Material properties of the lock plate, which covers the gas-turbine blade, are studied using ultrasonic guided waves. The lock plate is a crucial part of a gas-turbine power plant. The wave velocity and attenuation coefficient are measured to investigate the changes in the material properties under three heat-treatment conditions. Compared to the destructive mechanical tests, the material characterization of Inconel X-750 can be performed more efficiently and nondestructively by using ultrasonic guided waves; this characterization helps identify the changes occurring in its elastic moduli and Poisson's ratio under different heat-treatment conditions. The wave velocity and hardness of Inconel X-750 are proportional to each other. This nondestructive technique for the measurement of material properties can be widely used in various industries to avoid catastrophic failure. It is also expected that the guided-wave technique can be applied as a new cost- and time-saving inspection tool for longer and wider inspection ranges.