• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.4
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• pp.315-321
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• 2003

The integrity of the turbine rotors can be assessed by measuring the material properties at service temperature. In order to evaluate the remanent life of turbine rotor steel nondestructively, a measurement system of reversible magnetic permeability using an alternating perturbing magnetic field was constructed. We present a new non-destructive method to evaluate the remanent life of 1Cr-1Mo-0.25V steel using the value of reversible magnetic permeability. This method is based on the existence of reversible magnetic permeability in the differential magnetization around the coercive field strength. We measured the first harmonics voltage induced in a coil using a lock-in amplifier tuned to an exciting frequency. The Results of reversible magnetic Permeability and Wickers hardness on the aged samples show that the peak interval of reversible magnetic permeability (PIRMP) and Vickers hardness decreases as aging time increases. A softening curve is obtained from the correlation between Vickers hardness and the PIRMP. This curve can be used as a non-destructive method to evaluate the remanent life of turbine rotor steel.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.2
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• pp.588-594
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• 2020

This study proposes non-destructive rebound-hardness and ultrasonic testing methods to more accurately evaluate the residual structural performance of reinforced concrete structures in a fire. Techniques are also proposed to assess the stiffness used in the deflection calculation with natural frequencies obtained by vibration tests. In the compressive strength evaluation using rebound hardness, the residual compressive strength of thick specimens and a larger water/cement (W/C) ratio were shown to be large. The homogeneity of concrete at high temperature compared to ambient temperature conditions was assessed by the velocity of ultrasonic waves that penetrate the concrete, and it followed W/C or thickness of slab makes little different results. To assess the stiffness of fire-damaged slabs and increase in deflection, the natural frequency was measured by vibration tests and incorporated into the equation of the stiffness. The application of this technique to the slab experiment showed that it can be a very reasonable evaluation technique. In addition, to evaluate the residual strength of a member after fire, a test of the strength of a component was carried out during and after heating.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.37 no.1
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• pp.27-36
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• 2000

As a potential approach for non-destructive testing of concrete structures, we evaluate the time-of-flight (TOF) ultrasound tomography technique In conventional X ray tomography, the reconstructed Image corresponds to the internal attenuation coefficient However, in TOF ultrasound tomography, the reconstructed Image is proportional to the retractive index of the medium Because refractive effects are minimal for X-rays, conventional reconstruction techniques are applied to reconstruct the Image in X-ray tomography However, since ultrasound travels in curved path, due to the spatial variations in the refractive index of the medium, the path must be known to correctly reconstruct the Image. Algorithm for determining the ultrasound path is developed from a Geometrical Optics point view and the image reconstruction algorithm, since the paths are curved It requires the algebraic approach, namely the ART or the SIRT Here, the difference between the computed and the measured TOP data is used as a basis, for the iteration process First the initial image is reconstructed assuming straight paths. It then updates the path based on the recently reconstructed image This process of reconstruction and path determination repeats until convergence The proposed algorithm is evaluated by computer simulations, and in addition is applied to a real concrete structure.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.3
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• pp.275-283
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• 2002

To detect the position and depth of buried underground utilities, method of Ground Penetrating Radar(GPR) survey is the most commonly used. However, the skin-depth of GPR is very shallow, and in the places where subsurface materials are not homogeneous and are compose of clays and/or salts and gravels, GPR method has limitations in application and interpretation. The aim of this study is to overcome these limitations of GPR survey. For this purpose the site where the GPR survey is unsuccessful to detect the underground big pipes is selected, and soil tests were conducted to confirm the reason why GPR method was not applicable. Non-destructive high-frequency electromagnetic (HFEM) survey was newly developed and was applied in the study area to prove the effectiveness of this new technique. The frequency ranges $2kHz{\sim}4MHz$ and the skin depth is about 30m. The HFEM measures the electric field and magnetic field perpendicular to each other to get the impedance from which vertical electric resistivity distribution at the measured point can be deduced. By adopting the capacitive coupled electrodes, it can make the measuring time shorter, and can be applied to the places covered by asphalt an and/or concrete. In addition to the above mentioned advantages, noise due to high-voltage power line is much reduced by stacking the signals. As a result, the HFEM was successful in detecting the buried underground objects. Therefore this method is a promising new technique that can be applied in the lots of fields, such as geotechnical and archaeological surveys.

• Journal of the Korean Society for Nondestructive Testing
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• v.16 no.4
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• pp.225-233
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• 1997

This study is performed to establish a non-destructive evaluation method for metal matrix composite using ultrasonic technique. The specimen is made of SiC/AC8A metal matrix composite by squeeze-casting method. Three kinds or reinforced particles are prepared as 4.86, 8.09 and $11.44{\mu}m$ to investigate the effect of size on the mechanical and ultrasonic properties of metal matrix composite. In addition, four different volume fractions (14, 22.5, 27.5, 35%) of reinforced particles are prepared per each size to examine the effect of volume fraction on the ultrasonic properties. From this specimen, the availability and precision of measurement of Young's modulus are examined and the evaluation method for microstructure of metar matrix composite using the speed of sound and attenuation factor is also reviewed. The results show that the Young's modulus measured by ultrasonic method is as effective as that measured by mechanical method. It is also known that the size and volume fraction of reinforced fiber are precisely evaluated using the speed of sound and attenuation factor.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.1
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• pp.75-82
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• 2007

As one of the main support systems, rock bolts play a crucial role in the reinforcement of tunnels. Numerical and experimental studies using a transmission method of ultrasonic guided waves are performed to evaluate the integrity of rock bolts encapsulated by grouting paste. Numerical simulations using "DISPERSE" are carried out for the selection of the optimal experimental setup, i.e. non-destructive testing (NDT) system of the rock bolt. Based on results of the numerical simulation, the calculated frequency range for NDT testing is between 20kHz and 70kHz with the first longitudinal L(1) mode. Laboratory transmission tests are performed by attaching the piezo electric sensor at the tip of the rock bolt before embedding. Both of analytical and experimental results show that the amplitude of signals as well as the wave velocity increases with increase in the defect ratio of grouting paste. The defect in grouting paste means that the space around the rock bolt is not fully filled with the grouting paste. Experimental results also show that the increase of the wave velocity is more sensitive to the defect ratio increase than that of the amplitude. This study demonstrates that the transmission technique of ultrasonic guided waves may be a valuable tool in the evaluation of the rock bolt integrity.

• Geophysics and Geophysical Exploration
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• v.16 no.2
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• pp.79-90
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• 2013

Geophysical investigation in non-destructive testing is economically less expensive than boring testing and providing geotechnical information over wide-area. But, it provides only limited geotechnical information, which is hardly used to the design. Accordingly, we performed electrical resistivity experiments on large scale of soil model to analyze the correlation between electrical resistivity response and soil water contents. The soils used in the experiments were the Jumunjin standard sand and weathered granite soil. Each soil particle size distribution and coefficient of uniformity of experimental material obtained in the experiments were maintained in a state of the homogeneous. The specifications of the model used in this study is $160{\times}100{\times}50$(cm) of acrylic, and each soil was maintained at the height 30 cm. The water content were measured using the 5TE sensors (water contents sensors) which is installed 7 ~ 8 cm apart vertically by plugging to floor. The results of the resistivity behavior pattern for Jumunjin standard sand was found to be sensitive to the water content, while the weathered granite soil was showing lower resistivity over the time, and there was no significant change in behavior pattern observed. So, it results that the Jumunjin standard sand's particle current conduction was better than the weathered granite soil's particle through contact with the distilled water. This lab test was also compared with the result of a test bed site composed of similar weathered soil. It was confirmed that these experiments were underlying research of non-destructive investigation techniques to improve the accuracy to estimate the geotechnical parameter.

• Journal of the Korean Institute of Gas
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• v.17 no.5
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• pp.64-68
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• 2013

Non destructive testing(NDT) methods of electrofusion(EF) joints of thermoplastics pipes are required for fusion joint safety and for the long term reliability of a pipe system. Electrofusion joints, which are joined at the proper fusion process and procedures, may encounter defects due to the difference of ovality between pipes and coupling, improper fusion process or porosity result from electrofusion joining. These defects can cause the failure of pipeline and by extension, they can be caused the limit to expand the use of plastics pipes. This paper studies inspection results using ultrasonic imaging method for damaged polyethylene electrofusion joints. Gas was leaking from 250mm diameter polyethylene electrofusion joints at February 2004 which was electrofused at December 1994 and operation pressure was 2.45kPa. First, surface inspection was conducted and then in order to find the types of defects examination using ultrasonic imaging method was performed. Lack of fusion and inappropriate inserting for polyethylene pipes into electrofusion coupling were found and causes of the gas leak were judged that misalignment and insert defect. Cutting inspection was performed and each inspection results were compared to. Results of ultrasonic imaging method and cutting inspection were the same.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.2
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• pp.193-201
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• 2021

The welding has a high proportion of the production and drying of ships or offshore plants. Non-destructive testing is carried out to verify the quality of welds in Korea, radiography test (RT) is mainly used. Currently, most shipyards adopt analog-type techniques to print the films through the shoot of welding parts. Therefore, the time required from radiography test to pass or fail judgment is long and complex, and is being manually carried out by qualified inspectors. To improve this problem, this paper covers a platform for scanning and digitalizing RT films occurring in shipyards with high resolution, accumulating them in management servers, and applying artificial intelligence (AI) technology to detect welding defects. To do this, we describe the process of designing and developing RT film scanning equipment, welding inspection information integrated management platform, fault reading algorithms, visualization software, and testing and verification of each developed element in conjunction.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.137-143
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• 2008

The spherical glasses lenses are typically classified into two groups such as (+) diopter lens and (-) diopter lens by the refractive power index. The thermal deformation of a lens is occurred by external heat source and is changed respected to the diopter of a lens. In this paper, the thermal deformation of spherical glasses lenses were quantitatively measured by using ESPI (electronic speckle pattern interferometry) which has an advantage that the non-contact, non-destructive and precise deformation measurement is available due to the coherency characteristic. The temperature changes were measured by IR camera. It makes experiments over 14 types of the plastic glasses lenses. From the results, it was confirmed that the larger diopter lens showed the less thermal deformation in case of the (+) diopter lens. On the other hand, the thermal deformation of the (-) diopter lens was measured with uniform pattern when the same temperature changes were applied. Also, it was found that the thermnal deformation of the (+) diopter lens is less than that of the (-) diopter lens. Therefore, it is expected that when the thermal deformation is occurred to the various types of the lens, the variation of the focal length caused by the thermal distortion of a lens would be measured quantitatively.