• Journal of the Korean Institute of Gas
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• v.11 no.4
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• pp.64-72
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• 2007

Under the AE methods, the valid condition analysis and evaluation the leak etc, resulted by the AE signal pattern on the bottom plate of ground tank at full. In next more, the gradient of accumulation amplitude distribution analysis and comparison the energy, count, and duration time that noise of EMI signal were removed. EMI signal showed height-energy, count, and duration time, it also appeared great gradient of accumulation distribution. Then, with the pure remaining AE signals cluster analysis and location. It would possibly assume of damage with corrosion. Total cluster 20 and energy showed between the maximum 11,990 and 8,565 which is much lower than above figure and event number showed from 8 to 5. Even when it difficult to certify damage by open, as it is raised higher height-sensitivity and threshold by 60 dB. It would possibly presume of location source more accurately.

• The Journal of the Acoustical Society of Korea
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• v.36 no.4
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• pp.247-253
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• 2017

Generally, the vibration characteristics of refractory ceramics are identified by assuming them as isotropic materials. However, in practice, refractory ceramics exhibit anisotropic properties as they are manufactured by pressing ceramic powders along a particular direction. Therefore, in this research, the frequency responses of a refractory ceramic brick along its width, length, and height directions were acquired using finite element analysis by assuming that the ceramics had tetragonal symmetry in their material properties. The validity of the numerical analysis results was verified by comparing them with those from experimental measurements. Based on the frequency response, the thicknesses of the refractory brick along three different directions were estimated using the impact-echo technique. The maximum difference between the estimated and actual thicknesses was observed to be less than 5 %. This result confirms the effectiveness of the impact-echo technique along with anisotropic property characterization to evaluate the thickness of the refractory ceramic.

• Smart Structures and Systems
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• v.22 no.4
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• pp.481-493
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• 2018

Ultrasonic guided waves have attracted increasing attention for non-destructive testing (NDT) and structural health monitoring (SHM) of bridge cables. They offer advantages like single measurement, wide coverage of acoustical field, and long-range propagation capability. To design defect detection systems, it is essential to understand how guided waves propagate in cables and how to select the optimal excitation frequency and mode. However, certain cable characteristics such as multiple wires, anchorage, and polyethylene (PE) sheath increase the complexity in analyzing the guided wave propagation. In this study, guided wave modes for multi-wire bridge cables are identified by using a semi-analytical finite element (SAFE) technique to obtain relevant dispersion curves. Numerical results indicated that the number of guided wave modes increases, the length of the flat region with a low frequency of L(0,1) mode becomes shorter, and the cutoff frequency for high order longitudinal wave modes becomes lower, as the number of steel wires in a cable increases. These findings were used in design of transducers for defect detection and selection of the optimal wave mode and frequency for subsequent experiments. A magnetostrictive transducer system was used to excite and detect the guided waves. The applicability of the proposed approach for detecting and locating wire breakages was demonstrated for a cable with 37 wires. The present ultrasonic guided wave method has been found to be very responsive to the number of brokenwires and is thus capable of detecting defects with varying sizes.

• Journal of the Korean Geotechnical Society
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• v.27 no.11
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• pp.83-92
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• 2011

The random and heterogeneous pore structure is a significant factor that dominates physical and mechanical behaviors of soils such as fluid flow and geomechanical responses driven by loading. The characterization method using non-destructive testing such as micro X-ray CT technique which has a high resolution with micrometer unit allows to observe internal structure of soils. However, the application has been limited to qualitatively observe 2D and 3D CT images and to obtain the void ratio at macro-scale although the CT images contain enormous information of materials of interests. In this study, we constructed the 3D particle and pore structures based on sequentially taken 2D images of glass beads and quantitatively defined complex pore structure with void cell and void channel. This approach was enabled by implementing image processing techniques that include coordinate transformation, binarization, Delaunay Triangulation, and Euclidean Distance Transform. It was confirmed that the suggested algorithm allows to quantitatively evaluate the distribution of void cells and their connectivity of heterogeneous pore structures for glass beads.

• Journal of the Korea Computer Graphics Society
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• v.3 no.2
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• pp.27-34
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• 1997

3-D image modeling is in high demand for automated visual inspection and non-destructive testing. It also can be useful in biomedical research, medical therapy, surgery planning, and simulation of critical surgery (i.e. cranio-facial). Image processing and image analysis are used to enhance and classify medical volumetric data. Analyzing medical volumetric data is very difficult In this paper, we propose a new image modeling method based on tetrahedrization to improve the visualization of three-dimensional medical volumetric data. In this method, the trivariate piecewise linear interpolation is applied through the constructed tetrahedral domain. Also, visualization methods including iso-surface, color contouring, and slicing are discussed. This method can be useful to the correct and speedy analysis of medical volumetric data, because it doesn't have the ambiguity problem of Marching Cubes algorithm and achieves the data reduction. We expect to compensate the degradation of an accuracy by using an adaptive sub-division of tetrahedrization based on least squares fitting.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05a
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• pp.11-20
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• 2002

This paper describes the magnetic flux leakage(MFL) type non-destructive testing(NDT) system to detect the 3D defects on underground gas pipe. Magnetic systems with permanent magnets and yokes are analyzed by 3D non-lineal finite element method(FEM) with optimum design. In case of under-saturation of gas pipe, sensing signals are too weak to detect. In case of over-saturation, the changes of the sensing signals are too low to detect the defects sensitively. So, the operating points of the magnetic system are optimized to increase the changes of the MFL signals. The effects of the depth and size of the defects on the sensing signals are analyzed to define the range and resolution of the MFL sensors. To increase the sensor's sensitivity, the back-yoke sensors are introduced and tested.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.98-104
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• 2018

Nondestructive strength Equations are commonly used to determine the strength of concrete. However, the application of the existing equations may include many errors because this method is proposed on the basis of limited experimental parameters while actual bridges have various parameters such as conditions of concrete mixtures, properties of concrete strength, etc. Also, the error among the existing equations causes the confusion when engineers select the proper estimation equation for the concerned bridge. In this study, a series of the field inspection and the test have been performed on 297 existing bridges, in order to evaluate the bridges, based on the test results of the in-depth inspection, and the estimated strengths by means of the nondestructive strength equations are analyzed and compared with results of the core specimen strengths. According to results of analyses, the nondestructive strength equation proposed by CNDT Committee of Architectural Institute of Japan had high relationship with core strength. However, the strengths predicted by this equation, are underestimated when concrete's strengths are over 30 MPa, otherwise, they are overestimated. Also in this paper, based on the relationship between the estimated nondestructive concrete strengths and the core specimen strengths the modified strength equation through simple correlation analysis is proposed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.1 no.1
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• pp.23-26
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• 2000

In spot welded joint. Electronic Speckle Pattern Interferometry(ESPI) method using the Model 95 Ar laser a video system and an image processor was applied to measure the stress Unlike traditional strain gauges or Moire method, ESPI method has no special surface preparation or attachments and can be measured in-plane displacement with non-contact and real time. In this experiment, specimens are loaded in parallel with a load cell. The specimens are made of the cold rolled steel sheet with 1mm thickness, are attached strain. gauges. This study Provides an example of how ESPI has been used to measure stress and strain inspecimen. The results measured by ESPI are compared with the data which was measured by strain gauge method under tensile testing.

• Polymer(Korea)
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• v.28 no.4
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• pp.285-290
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• 2004

Nondestructive damage sensitivity of carbon nanotube(CNT) and nanofiber (CNF)/epoxy composites with their adding contents was investigated using electro-micromechanical technique. Carbon black (CB) was used only for the comparison with CNT and CNF. The fracture of carbon fiber was detected by acoustic emission (AE), which was correlated to the change in electrical resistance, ΔR under double-matrix composites (DMC) test. Stress sensing on carbon nanocomposites was performed by electro-pullout test under uniform cyclic loading. At the same volume fraction, the damage sensitivity for fiber fracture, matrix deformation and stress sensing were highest for CNT/epoxy composite, whereas for CB/epoxy composite they were the lowest among three carbon nanomaterials (CNMs). Damage sensitivity was correlated with morphological observation of carbon nanocomposites. Homogeneous dispersion among CNMs could be keying parameters for better damage monitoring. In this study, damage sensing of carbon nanocomposites could be evaluated well nondestructively by the electrical resistance measurement with AE.

• Journal of Welding and Joining
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• v.31 no.6
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• pp.90-95
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• 2013

Pipe inside clad welding is mainly used to the flow pipe of sub-sea or chemical plant. For the inside clad welding to the medium pipe with the diameter of about 12", TIG welding is frequently applied with filler metal. In this case, the clad welding has the very broad weld area over $10m^2$. And, the non-destructive test (NDT) such as ultrasonic test (UT) or radiographic testing (RT) should be conducted on the broad weld area, and it costs very high due to the time-consuming work. Therefore, the present study investigated the variation of arc voltage to develop the in-line quality monitoring system for the pipe inside TIG cladding. The 4 experimental parameters (current, arc length, wire feed position, and shield gas flow rate) varied to observe the change of arc voltage and to establish the model for the monitoring. The arc voltage was decreased when the wire was fed to the backward eccentric position(over 2mm), and the shield gas flow rate was insufficient under 10L/min. In the case of the backward eccentric position over 2mm, the bead appearance was not good and the dilution ratio was increased due to deep penetration. When the shield gas flow rate was lower than 10L/min, the bead surface was oxidized.