• Journal of the Korean Society for Nondestructive Testing
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• v.13 no.4
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• pp.9-17
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• 1994

It is well recognized recently that ultrasonic technique is one of the most widely used methods of nondestructive evaluation to characterize material properties of nonconventional engineering materials. Therefore it is very important to understand physical phenomenon on propagation behavior of elastic wave in these materials, which is directly associated with ultrasonic signals in the test. In this study, the theoretical analysis on multi-scattering of harmonic elastic wave due to the particulate with interface between matrix and fiber in metal matrix composites(MMCs) was done on the basis of Lax's quasi-crystalline approximation and extinction theorem. SiC particulate (SiCp) reinforced A16061-T6 composite material was chosen for this analysis. From this analysis, frequency dependences of phase velocity and amplitude attenuation of effective plane wave due to the change of volume fraction of SiC particulate were clearly found. It was also shown that the interface condition between matrix and fiber in MMCs gives a direct effect on the variation of phase velocity of plane wave in MMCs.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.373-380
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• 2000

It is useful to use NDE methods to assess the mechanical properties of materials since destructive methods are time-consuming and usually require cutting of sample from the material/component. In the present research, ultrasonic characteristics have been utilized to evaluate changes of mechanical properties due to heat treatment temperature and condition. The attenuation coefficient of ultrasonic wave increased as the heat treatment temperature because the grain size increased in size as the temperature. The attenuation coefficient decreased as the heat treatment has been progressed (quenched, tempered, PWHT). In the case of ultrasonic velocity measurement, velocity difference between quenched and tempered/PWHT was 40 m/s. There was a good relationship between the attenuation coefficient and the toughness. The relationship can be used for the nondestructive evaluation of the forged reactor vessels. Moreover, the method may be effectively used in the field application.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.2
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• pp.110-117
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• 1999

In order to ultrasonically evaluate creep cavities pure copper samples were subjected to creep test and their microstructures were examined. Ultrasonic velocities. frequency-dependent magnitude spectra and attenuations were measured on a series of copper samples obtained from the different stages of creep test. Velocities measured in three directions with respect to the loading axis decreased and their anisotropy increased as a function of the creep-induced porosity. The anisotropic behavior could be attributed to the progressive change of pore shape and preferred orientation as the creep advanced. The 2% porosity by volume decreased the longitudinal and shear wave velocities by 11% and 4%, respectively. Furthermore, both velocities decreased nonlinearly with the porosity. As the creep damage developed, the magnitude spectra lost high frequency components and their central frequencies shifted to lower values. The attenuation showed almost linear behavior in the frequency range used. Normalized velocity, central frequency shift and attenuation slope were selected as nondestructive evaluation parameters. These results were presented and showed good relations with the porosity content.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.445-450
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• 2000

The integrity of the turbine rotors can be assessed by measuring reversible permeability and Vickers hardness of the aged rotors at service temperature. The measurement system of reversible permeability, which measured by applied alternating perturbing magnetic field, was constructed in order to evaluate material degradation, nondestructively. The test specimen was 1Cr-1Mo-0.25V steel used widely for turbine rotor material, and the specimens were prepared by the isothermal heat treatment at $630\;^{\circ}C$. The reversible permeability of the test materials were measured at room temperature. The peak interval of reversible permeability and Vickers hardness decreased with the increase of degradation. The degradation of test material may be determined nondestructively by the lineality of Vickers hardness and the peak interval of reversible permeability.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.1
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• pp.25-33
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• 1999

Since concrete is an inhomogeneous material consisting of larger aggregates and sand embedded in a cement paste matrix, it relatively shows a complex failure mechanism. In order to assure the reliability of concrete structure. microscopic fracture behavior and internal damage progress of concrete under the loading should be fully understood. In this study, an acoustic emission(AE) technique has been used to clarify microscopic failure mechanism and their corresponding AE signal characteristics of concrete under three-point bending test. In addition 2-dimensional AE source location has been performed to monitor the progress of an internal damage and the successive crack growth behavior during the loading. The relationship between AE signal characteristics and microscopic fracture mechanism is discussed.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.6
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• pp.411-419
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• 1999

It has been well recognized that a long term service at elevated temperature of $350^{\circ}C{\sim}550^{\circ}C$ induces embrittlement damage due to carbide precipitation and/or P, Sb and Sn segregation at grain boundaries and thereby deteriorates the grain boundary strength of heat resisting components in the energy-related plants. Therefore, it is very important to assess quantitatively the extent of embrittlement damage of heat resisting components to secure the reliable and efficient service condition and to prevent brittle failure in service. However, because fracture tests are limited in size and number of specimen obtained from the structural components, nondestructive test method is required. In this study, the optimum electrochemical parameters are investigated and discussed to evaluate nondestructive embrittlement damage for aged 2.25Cr-1Mo steels by means of electrochemical polarization test method (ECPTM) in proper corrosive environment. In addition, the electrochemical test results are compared with embrittlement degree evaluated by semi-nondestructive SP test.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.3
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• pp.205-211
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• 2003

Acoustic emission (AE) technique has been applied to not only mechanical property testing but also on-line monitoring of the el)tire structure or a limit zone only. Although several AE devices have already been developed for the on-line monitoring, the price of these systems is very high and it is difficult for the field to apply yet. In this study, wc developed a specially designed PC-based source location system using the A/D board. The source location technique is very important to identify the source, such as crack, leak detection. However, since the AE waveforms obtained from transducers are very difficult to distinguish the defect signals, therefore, it is necessary to consider the signal analyses of the transient waveform. Wavelet Transform (WT) is a powerful tool for processing transient signals with temporally varying spectra that helps to resolve high and low frequency transients components effectively In this study, the analyses of the AE signals are presented by employing the WT analyses. AE results are compared the PC-based source location system using A/D board with the commercial AE system.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.3
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• pp.188-194
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• 2016

We propose an acousto-optic technique for the nondestructive evaluation of adhesion properties of a Pt/Ti thin-film interface. Since there are some problems encountered when using prevailing techniques to nondestructively evaluate the interfacial properties of micro/nano-scale thin-films, we applied an interferometer that combined the acoustic and optical methods. This technique is based on the Michelson interferometer but the resultant surface of the thin film specimen makes interference instead of the mirror when the interface is excited from the acoustic transducer at the driving frequency. The thin film shows resonance-like behavior at a certain frequency range, resulting in a low-contrast fringe pattern. Therefore, we represented quantitatively the change in fringe pattern as a frequency spectrum and discovered the possibility that the interfacial adhesion properties of a thin film can be evaluated using the newly proposed technique.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.10
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• pp.108-114
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• 2018

Due to the development of nondestructive testing techniques, methods of inspecting cracks in mechanical parts have drawn attentions. Among various non-destructive testing methods the acoustic resonance method which analyzes the natural frequencies has been developed into a technique suitable for the prompt judgements of the existence of the defects in the mechanical parts. In this study, we investigated the crack inspection technique to examine the cracks in the yoke tubes by using the acoustic resonance method and realized the system to quickly detect the cracks. A 24bit ADC circuit and an MCU were installed for the smooth data collection, and a TCP / IP communication interface was configured for the data communication with PC. We used a microphone as a sensor measuring the vibrations. We constructed an analysis software to obtain the frequency spectra of the vibrations, to find the existence of the cracks, and to feedback to the user. Tests were conducted using the yoke tubes manufactured in the real industrial field. The tests were successfully conducted to distinguish the good products from the defective (cracked) products and confirmed that they can be employed in the actual industrial field.

• Journal of the Korean Society for Nondestructive Testing
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• v.14 no.3
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• pp.151-156
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• 1994

Exertion has been made to develop high-temperature (about $250{\sim}650^{\circ}C$) immersion ultrasonic sensor for the visualization of objects, temperature measurement, dimensional check, or nondestructive testing of welds under liquid sodium. In this study, the feasibility of the ultrasonic sensor taking advantage of a strip waveguide was confirmed by water-experiment. The lowest order of antisymmetric Lamb wave was used in the frequency range with negligible dispersion. This plate wave was excited in the stainless steel strip waveguide of 1.0mm thickness and 13mm width by the comb-structure transducer of 2.3MHz frequency. Its attenuation coefficient was 1.2dB/m in air and 380dB/m in water. The signal to noise ratio of 25dB was obtained from a planar reflector 270mm away from the beam aperture of $13mm{\times}39mm$ size.