• Journal of Power System Engineering
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• v.10 no.1
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• pp.77-82
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• 2006

In this study, dissimilar friction welding were produced using 15mm diameter solid bar in chrome molybedenum steel(SCM440) to carbon steel(S45C) to investigate their mechanical properties and the relationship between the weld parameters and the nondestructive coefficients, such as AE counts and ultrasonic attenuation coefficient. The main friction welding parameters were selected to endure good quality welds on the basis of visual examination, tensile tests, Vickers hardness surveys of the bond of area and heat affected zone. The specimens were tested as-welded and post weld heat treated(PWHT). The tensile strength of the friction welded steel bars was increased up to 100％ of the S45C base metal under the condition of all heating time. The ductility of PWHT specimens is higher than as-welded.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.2
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• pp.180-185
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• 2004

Conventional ultrasonic examination to detect micro and small surface cracks is based on the pulse-echo technique using a normal immersion focused transducer with high frequency, or an angle-beam transducer generating surface waves. It is difficult to make an automatic ultrasonic system that can detect micro and small surface cracks and position in a large structure like steel and ceramic rolls, because of the huge data of inspection and the ambiguous position data of the transducer. In this study, a high-precision scanning acoustic microscope with a 10MHz large-aperture transducer has been used to assess the existence, position and depth of a surface crack from the real-time A, B, C scans obtained by exploiting the ultrasonic diffraction. The ultrasonic method with large aperture transducer has improved the accuracy of the crack depth assessment and also the scanning speed by ten times, compared with the conventional ultrasonic methods.

• 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.22 no.2
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• pp.132-139
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• 2002

The grain size of aluminum alloy was refined to the submicrometer level by using equal-channel angular pressing(ECAP). The effect of grain size refinement was evaluated by the tensile test, micro-hardness test, microstructure observations, ultrasonic test and acoustic emission test. The strength and the Vickers hardness were increased significantly according to grain size refinement after equal-channel angular pressed. The ultrasonic velocity was faster after equal-channel angular pressed, and the high frequency range appeared. The results of the ultrasonic velocity and the frequency range are expected to be basic data that can prove the grain size refinement

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.1
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• pp.11-22
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• 1997

It is very essential to get the accurate classification of defects in primary pressure vessel and piping welds for the safety of nuclear power plant. Ultrasonic testing has been widely applied to inspect primary pressure vessel and piping welds of nuclear power plants during PSI / ISI. Classification of flaws in weldments from their ultrasonic scattering signals is very important in quantitative nondestructive evaluation. This problem is ideally suited to a modern ultrasonic Pattern recognition technique. Here, a brief discussion on systematic approach to this methodology is presented including ultrasonic feature extraction, feature selection and classification. A stronger emphasis is placed on Fuzzy-UTSCS (UT signal classification system) as efficient classifiers for many practical classification problems. As an example Fuzzy-UTSCS is applied to classify flaws in ferrite pressure vessel weldments into two types such as linear and volumetric. It is shown that Fuzzy-UTSCS is able to exhibit higher performance than other classifiers in the defect classification.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.5
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• pp.464-474
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• 2003

Ultrasonic imaging of 3-D structures for nondestructive evaluation must provide readily recognizable images with enough details to clearly show various flaws that may or may not be present. Typical flaws that need to be detected are miniature cracks, for instance, in metal pipes having aged over years of operation in nuclear power plants; and these sub-millimeter cracks or flaws must be depicted in the final 3-D image for a meaningful evaluation. As a step towards improving conspicuity and thus detection of flaws, we propose a pulse-echo ultrasonic imaging technique to generate various 3-D views of the 3-D object under evaluation through strategic scanning and processing of the pulse-echo data. We employ a 2-D Wiener filter that filters the pulse-echo data along the plane orthogonal to the beam propagation so that ultrasonic beams can be sharpened. This three-dimensional processing and display coupled with 3-D manipulation capabilities by which users are able to pan and rotate the 3-D structure improve conspicuity of flaws. Providing such manipulation operations allow a clear depiction of the size and the location of various flaws in 3-D.

• Journal of Ocean Engineering and Technology
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• v.15 no.3
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• pp.87-92
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• 2001

In this studies, joint time-frequency analysis techniques were applied to analyze ultrasonic signals in the degraded austenitic 316 stainless steels, to study the evolution of damage in these materials. It was demonstrated that the nonstationary characteristics of ultrasonic signals could be analyzed effectively by these methods. The WVD was more effective for analyzing the attenuation and frequency characteristics of the degraded materials through ultrasonic. It is indicated that the joint time-frequency analysis, WVD method, should also be useful in evaluating various damages and defects in structural members.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.121-124
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• 2003

This paper shows shear wave behavior of CFRP(carton fiber reinforced plastics) composite laminates as a polar grid form to evaluate vibration pattern of ultrasonic transducers, which gives measured modelling fundamental contents of nondestructive evaluation. This modelling decomposes the transmission of a linearly polarized wave into orthogonal components through each ply of a laminate. It is found that a high probability shows between the model and measurement system in characterizing lay up of CFRP composite laminates. Also evaluating quantitatively the defects in CFRP laminates who found to be possible of normalized frequency obtained from 2D-FFT technique based on C-scan method. Thus, the technique is proven to be one of the useful means to evaluate any internal defect in CFRP composite laminates.

• Journal of the Korean Society of Safety
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• v.12 no.2
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• pp.3-16
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• 1997

In modern high performance engineering applications, the structural integrity of materials and structures are quite often evaluated using fracture mechanics. This evaluation in turn requires information on the flaw geometry (location, type, shape, size, and orientation). The ultrasonic nondestructive evaluation (NDE) method is one technique that is commonly used to provide such information. Flaw classification (determination of the flaw type ) and flaw sizing (prediction of the flaw shape, orientation and sizing parameters) are very important issues for quantitative ultrasonic NDE. In this paper new approaches to both classification and sizing of flaws are described together with extensive review of previous works on both topics. In the area of flaw classification, a methodology is developed which can solve classification problems using probabilistic neural networks, and in the area of flaw sizing, a time-of-flight equivalent (TOFE) sizing method is presented. The techniques proposed here are in a form that can be used directly in many practical applications to quantitative estimates of the flaw's significance.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.651-658
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• 2012

This paper concentrates on the evaluation of microcracks in thermal damaged concrete on the basis of the nonlinear ultrasonic modulation technique. Since concrete structure exposed to high temperature accompanies the development of microcracks due to the physical and chemical changes from temperature and exposed time, the adoption of nonlinear approach is required. Instead of using the conventional ultrasonic nondestructive methods which have the limitation in evaluating excessive microcracks, accordingly, a nonlinear ultrasonic modulation method which shows better sensitivity in quantifying microcracks is introduced. Upon the analysis for the modulation of ultrasonic wave and low frequency impact to measure the nonlinearity parameter, which can be used as an indicator of thermal damage, the verification processes for the introduced technique are followed: SEM investigation and permeable pore space test are performed to characterize thermally induced microcracks in concrete, and ultrasonic pulse velocity tests are performed to confirm the outstanding sensitivity of nonlinear ultrasonic modulation technique. In advance, compressive strength of thermal damaged concrete is measured to represent the effect of microcracks on performance degradation. Correlation studies between experimental data and measured data show that nonlinear ultrasonic modulation technique can effectively be used to quantify thermally induced microcracks, and to estimate the compressive strength of thermally damaged concrete.