• Journal of the Society of Disaster Information
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• v.12 no.2
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• pp.144-149
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• 2016

Nowaday, most of the low-rise concrete structures which have less than five stories were built before the intensified seismic code was established 2005. According to the fact that our country is not a safety zone ay more, studies are need to reinforce the seismic performance of that structures. The basic frame of low-rise structure are consist of beams and columns with partition walls, therefore that are very weak about secondary wave of earthquake because of the high stiffness. The partition wall are consist of open channel for sunlight or ventilation and intermediate wall. The intermediate walls will enhance the stiffness of columns, but will cause shear failure with short column effects because of the reduced effective depth. But we don't have studies and adequate design code for partition wall effects, therefore some more studies are need for these facts.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.2
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• pp.130-137
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• 2000

Ultrasonic technique which is one of the most common and reliable nondestructive evaluation techniques has been applied to evaluate the integrity of structures by analyzing the characteristics of signal scattered from internal defects. Therefore, the numerical analysis of the ultrasonic scattered field is absolutely necessary for the accurate and quantitative estimation of internal defects. Various modeling techniques now play an important role in nondestructive evaluation and have been employed to solve elastic wave scattering problems. Because the elastodynamic boundary element method is useful to analyze the scattered field in infinite media. it has been used to calculate the ultrasonic wavefields scattered from internal defects. In this study, a review of the boundary element method used for elastic wave scattering problems is presented and, as examples of the boundary element method, the scattered fields due to a circular cavity subjected to incident SH-wave and due to a surface-breaking crack subjected to incident Rayleigh wave are illustrated.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.6
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• pp.559-565
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• 2004

Two different methods were used for the scattering analysis of side-drilled holes(SDH). The scattering models include an explicit model based on the Kirchhoff approximation and the solution of the exact separation of variables. The far-field scattering amplitude was calculated and their time-domain results were compared for the case of shear vertical wave. The exact solution predicts the existence of the creeping wave. The Kirchhoff approximation agreed to the exact solution, except the case of the creeping wave. Two measurement models were introduced to predict the response from the SDHs for the case of immersion, pulse-echo testing. The received voltage was calculated for the case of the shear vertical waves with the incident angle of $45^{\circ}$ to the SDH with the diameter of 1mm, and compared with the experimental results.

• The Journal of the Acoustical Society of Korea
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• v.16 no.1
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• pp.39-46
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• 1997

In this paper, the PA(PhotoAcoustic) signals excited in metals by Xef, KrF excimer laser pulse were detected by a PZT transducer, and its transforming machanism and directivity patterns were analysed. The laser energy density in irradiation spot divides the PA trasnsorming machanism to be classified into thermoelastic and plasma regime, and the transforming machanisms in two regimes are different from each other. Based on theoretical model, it is predicted that shear wave is greater than longitudinal in the thermoelastic regime and longitudinal is greater than shear wave by reaction force in plasma regime. These predictions were verified through experiments by using of the XeF excimer pulsed laser of 480nm center-wavelength and the KrF excimer pulsed laser of 248nm. Also, for its directivity pattern, an arrival angle of the maximum longitudinal energy was around $60^{\circ}$ and maximum shear energy was around $30^{\circ}$ in the thermoelastic regime, and an arrival angle of maximum longitudinal energy was shown on nomal to the surface and maximum shear energy was represented in about $30^{\circ}$ in plasma regime.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.365-368
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• 2000

자왜 재료는 자계 포화 이하에서 비선형 특성을 갖는다고 알려져 있다. 그러나 지금까지 비선형 특성을 표현하는 자왜 재료의 구조 방정식을 유도한 사례는 전무한 실정이다 본 연구에서는 자계 포화 이하에서 비선형 특성을 갖는 자왜 재료의 비선형 구조 관계식을 유도하였다. 나아가 유도된 구조 관계식을 이용하여 자왜 재료 내의 파동 방정식을 정식화하였다. 그리고 비선형 특성을 갖는 자왜 재료에서 평면파가 자계 방향을 따라 전파될 때 이방성 자왜 재료를 등방성 재료로 가정하여 종파와 횡파 속도를 구하였다.

• 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 of Manufacturing Technology Engineers
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• v.6 no.1
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• pp.27-33
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• 1997

A neural network approach has been developed to determine the depth of a surface breaking crack in a steel plate from ultrasonic backscattering data. The network is trained by the use of feedforward three-layered network together with a back-scattering algorithm for error correction. The signal used for crack insonification is a mode converted 70$^{\circ}$transverse wave. A numerical analysis of back scattered field is carried out based on elastic wave theory, by the use of the boundary element method. The numerical data are calibrated by comparison with experimental data. The numerical analysis provides synthetic data for the training of the network. The training data have been calculated for cracks with specified increments of the crack depth. The performance of the network has been tested on other synthetic data and experimental data which are different from the training data.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.10a
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• pp.119-126
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• 2001

유리와 같이 취성이 큰 재료의 파단면을 주의하여보면 반원형의 곡선이 이따금씩 여러개 나타나 있는 것을 볼 수 있다. 이것은 진행 중에 있는 균열이 어떠한 부분으로부터 나온 음파(횡파)와 만났을 때 일어나는 흔적으로 Wallner선 이라고 한다. 초음파 Fractography는 파괴 시험시 강력한 초음파를 사용하여 파단면에 이와 같은 Wallner 선을 인공적으로 발생시켜, 파면해석을 통하여 파괴속도등 파괴연구에 필요한 정보를 얻는 수법이다. 이 수법은 유리와 같은 비정질 탄성태의 파괴속도 측정을 위해 Kerkhof에 의해 최초로 고안되었으며, 수지와 같은 점탄성재료에 대해서는 Takahashi에 의하여 PMMA(Polymethy1 Methacrylate)재에 강력한 초음파를 사용하여 그 가능성이 제기된 이후 PMMA와 EPOXY재등의 점탄성재료의 파괴속도측정과 파괴강성등의 측정에 본격적으로 연구되기 시작하였다.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1997.11a
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• pp.15-24
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• 1997

최근 우리나라에도 많은 지진사례가 보고되고 있으며, 이러한 지진하중은 원전설비 및 각종 기계설비등의 가동중 파손을 유발시킬 수 있는 잠재적 위험성이 높다. 이에 지진하중에 대한 안전성 확보의 필요성이 점차 대두되고 있다. 지진하중은 종ㆍ횡파에 의한 인장ㆍ압축이 반복되는 역사이클하중(reverse cyclic loading)형태로, 현재까지는 이를 고려한 설계개념이 미흡한 실정이며 이에 대한 파괴물성치의 확보는 물론 파괴물성치 평가 절차도 확립되어 있지 않은 상태이다. 따라서 지진하중에 대한 안전성확보를 위해서는, 역사이클 하중이 재료의 파괴특성 특히, 파괴저항(J-R)곡선에 미치는 영향이 고찰되어야 할 것이다. (중략)

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.04a
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• pp.61-65
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• 2001

A new flaw detection technique using by SH angle beam method has been discussed. The SH-wave is horizontally polarized shear wave and the surface SH wave has a characteristic of traveling along near surface layer. The surface SH wave technique is valuable for the detection of fatigue cracks at fillet weld heels which cannot be detected by other ultrasonic technique such as angle beam technique and The dispersion curves of it has simple characterization. In this work, using these beneficial chraterization, quality evaluation of spot weld with ultrasonic sound intensity of SH-wave passing through nugget area of spot weld are verified experimentally.