• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.4
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• pp.342-348
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• 2003

Ultrasonic backscattering profiles of the Zr plates(with a thickness of 1.32mm) with/without Be-Zr alloy layer(with a thickness of $100{\mu}m$) were measured at various incidence positions to evaluate the characteristics of Be diffusion layer. Four principal subprofiles were observed in the backward ultrasound radiated from leaky Lamb waves. The angles and the intensities of the subprofile peaks decreased by the stiffening effect of Be layer. Generation and change of the subprofiles were explained by the acoustical property, collective group velocity and leaky factor difference of the plates under consideration. Backward radiation subprofiles turned out to be an useful method for evaluating thin diffusion layers on plates.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.211-216
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• 2008

In this study, we have developed a program which can calculate phase and group velocities, attenuation and wave structures of each mode in multi-layered plates. The wave structures of each mode are obtained, varying material properties and number of layers. The key in the success of guided wave NDE is how to optimize the mode selection scheme by minimizing energy loss when a structure is in contact with liquid. In this study, the normalized out-of-plane displacements at the surface of a free plate are used to predict the variation of modal attenuation and verily the correlation between attenuation and wave structure. It turns out that the guided wave attenuation can be efficiently obtain from the out-of-plane displacement variation of a free wave guide alleviating such mathematical difficulties in extracting complex roots for the eigenvalue problem of a liquid loaded wave guide. Through this study, the concert to optimize guided wave mode selection is accomplished to enhance sensitivity and efficiency in nondestructive evaluation for multi-layered structures.

• Journal of the Korean Society for Nondestructive Testing
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• v.37 no.1
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• pp.29-36
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• 2017

Recently, KTX (Korean Train Express) train stoppage accidents were mainly caused by malfunctioning equipment, aging and cracking of railway vehicles, crack breakages of brake disks, and breakages of brake disks. Breakage of brake disk can cause large-scale casualties such as high-speed collision and concern about derailment by hitting lower axle and wheel. Therefore, in this study, a brake disk with solid and ventilation type, which is the brake disk of a KTX train was modeled, and a dynamometer system was constructed to operate the disk. A Rayleigh wave was used to inspect the surface of the brake disk. An ultrasonic inspection module was developed for the brake disk by using a local immersion method due to the difficulty involved in ultrasonic inspection using an existing immersion method. In addition, the surface defects of the brake disk were evaluated using a dynamometer mock-up system and an ultrasonic inspection module of the brake disk.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.412-421
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• 2023

Ultrasound brain stimulation is spot-lighted by its capability of inducing brain cell activation in a localized deep brain region and ultimately treating impaired brain function while the efficiency and directivity of neural modulation are highly dependent on types of stimulus waveforms. Therefore, to optimize the types of stimulation parameters, we propose a cell-cultivable ultrasonic transducer having a series stack of a spin-coated polymer piezoelectric element (Poly-vinylidene fluoride-trifluorethylene, PVDF-TrFE) and a parylene insulating layer enhancing output acoustic pressure on a glass-coverslip which is commonly used in culturing cells. Due to the uniformity and high accuracy of stimulus waveform, tens of neuronal cell responses located on the transducer surface can be recorded simultaneously with fluorescence microscopy. By averaging the cell response traces from tens of cells, small changes to the low intensity ultrasound stimulations can be identified. In addition, the reduction of stimulus distortions made by standing wave generated from reflections between the transducers and other strong reflectors can be achieved by placing acoustic absorbers. Through the proposed ultrasound transducer, we could successfully observe the calcium responses induced by low-intensity ultrasound stimulation of 6 MHz, 0.2 MPa in astrocytes cultured on the transducer surface.

• Clean Technology
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• v.23 no.1
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• pp.90-94
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• 2017

These days much efforts are being dedicated to wind power as a potential source of renewable energy. To maintain effective and uniform generation of energy, defect preservation of turbine blade is essential because it directly takes effects on the efficiency of power generation. For the effective maintenance, early measurements of blade defects are very important. However, current technologies such as ultrasonic waves and thermal imaging inspection methods are not suitable because of long inspection time and non-real time inspection. To supplement the problems, the study introduced a method for real time defect monitoring of a blade surface based on surface wave technology. We examined the effect of various parameters such as micro-cracks and peelings on the propagation of surface wave.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.31-37
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• 2000

Metal matrix composites(MMCs) are rapidly becoming one of the strongest candidates for structural materials for many high temperature application. Among the high temperature environment, thermal shock is known to cause significant degradation in most MMC system. Therefore, the nondestructive evaluation on thermal shock damage behavior of SiC/A16061 composite has been carried out using ultrasonic surface and SH-waves. For this study, Sic fiber reinforced metal matrix composite specimens fabricated by a squeeze casting technique were thermally cycled in the temperature range 25~$400^{\circ}C$ up to 1000 cycles. Three point bend test was conducted to investigate the effect of thermal shock damage on mechanical properties. The relationship between thermal shock damage behavior and the change of ultrasonic velocity and attenuation were discussed by considering SEM observation of fracture surface.

• 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.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.1
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• pp.1-10
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• 2011

Recently harbor remodeling projects are seriously considered to enhance the loading and unloading capability of old container terminals and to make decrepit ports as eco-friendly harbor and waterfront spaces in many countries. In such a case, quantitative and qualitative evaluations on concrete harbor facilities are mandatory to determine the current structural integrity condition of aged materials. Once the remodeling project is determined to be carried out, the reusability of individual structural members and facilities including caissons, cell-blocks, and tetra-pods need to be decided based on the simple and economic visual inspection and/or nondestructive testing. In this study, the systematic quantitative evaluation procedure for determining the structural integrity condition and the reusability is studied based the nondestructive testing and evaluation methods. Conventional methods including Schmidt hammer test and ultrasonicpulse velocity methods and elastic wave based methods including impact echo test and surface wave test are applied to the old harbor facilities in five different sites. The compressive tests are also carried out to determine the elastic modulus and compressive strength of concrete materials.

• Journal of Korean Tunnelling and Underground Space Association
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• v.2 no.3
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• pp.37-45
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• 2000

In recent years two reflection methods, i.e. GPR and seismic Impact-Echo, are usually performed to obtain the information about tunnel lining structures composed of concrete lining, shotcrete, water barrier, and voids at the back of lining. However, they do not lead to a desirable resolution sufficient for the inspection of tunnel safety, due to many problems of interest including primarily (1) inner thin layers of lining structure itself in comparison with the wavelength of source wavelets, (2) dominant unwanted surface wave arrivals, (3) inadequate measuring strategy. In this sense, seismic physical modeling is a useful tool, with the use of the full information about the known physical model, to handle such problems, especially to study problems of wave propagation in such fine structures that are not amenable to theory and field works as well. Thus, this paper deals with various results of seismic physical modeling to enable to show a possibility of detecting the inner layer boundaries of tunnel lining structures. To this end, a physical model analogous to a lining structure was built up, measured and processed in the same way as performed in regular reflection surveys. The evaluated seismic section gives a clear picture of the lining structure, that will open up more consistent direction of research into the development of an efficient measuring and processing technology.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.7
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• pp.647-652
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• 2016

Guided waves can be used for the inspection of long range pipelines. Surface corrosion is often found as a major defect type in pipelines. The reciprocity relation is a well-established theorem by which one can simplify complicated mathematical expressions. The approach has been already applied to plate and half-space structures to obtain the closed-form solutions of scattered amplitude. However, results for the case of cylindrical structures have not been reported yet. In this paper, the scattering of torsional waves, which is widely used in commercial applications, is explored by the reciprocity theorem approach. Obtaining closed-form solutions of the amplitudes of propagating waves is much simplified by using the reciprocal relation. The scattered amplitudes for elliptical and rectangular defect shapes are calculated with respect to defect depth and width, at frequencies between 0 and 500 kHz. The amplitude shows the periodic result as a function of frequency. The derived closed-form solutions can play a significant role in quantitative signal interpretation.