• 연구논문집
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• s.28
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• pp.229-238
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• 1998

Materials and parts required for nondestructive testing should be evaluated using with standard block. And it is ruled that standard blocks should be fabricated from same or similar material with test specimen. In order to manufacture and export materials and parts, quality assurance system should be required. In this paper, ultrasonic characteristics of ASTM 4340 steel ultrasonic standard block are investigated for nondestructive evaluation of udimet 720Li disc. Microstructures of udimet 720Li alloy are investigated using with optical and transmission electron microscope. Also ultrasonic transit time and attenuation are measured from high power ultrasonic analysis system with phase adjustment method. Conclusively, it is proved that 4340 steel ultrasonic standard block can be use for nondestructive evaluation of udimet 720Li disc.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.431-437
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• 2000

Standard Test Block(STB) for UT(Ultrasonic Testing) is a block approved by authoritative for material, shape and quality. STB is used for characteristic tests, sensitivity calibration and control of the time base range of UT inspection devices. The material, size and chemical components of STB should be strictly controled to meet the related standards such as ASTM and JIS because it has an effect upon sensitivity, resolution and reproductivity of UT. The STBs which are not approved are sometimes used because the qualified STBs are very expensive. So, the purpose of this study is to survey the characteristics, quality and usability of Non-Standardized Test Blocks. Non-Standardized Test Blocks did not meet the standard requirements in size or chemical components, and ultrasonic characteristics. Therefore if the Non-Standardized Test Blocks are used without being tested, it's likely to cause errors in detecting the location and measuring the size of the defects.

• Journal of the Korean Institute of Gas
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• v.2 no.4
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• pp.42-46
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• 1998

Miniaturized specimen technology Permits mechanical behavior to be determined using a minimum volume of material. The technology is useful in case of not collecting a large amount of materials from industrial equipments. Five kinds of accelerated degradation materials were prepared by isothermal aging heat treatment at $630^{\circ}C$. Three kinds of specimens were prepared for impact testing. In order to increase plastic constraint of subsize specimen, side-groove was introduced. Results between subsize and full size impact testing were compared. Size effects correlations were developed for the impact properties of turbine rotor material. These correlations successfully predict the ductile brittle transition temperature (DBTT) of full size Charpy impact specimens based on subsize specimen data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.6
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• pp.531-537
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• 2016

The damage and fracture of machine or structure are caused by the crack happened from the defect existed at the inside of material. The properties of crack propagation and growth characteristic must be considered because there are many cases at which these cracks are densely existed. Therefore, this study investigates the fracture property due to the position of crack and hole inside the standard compact tension (C. T.) specimen. When the concentrated load is applied eccentrically at the standard C. T. specimen, the fracture mechanical behavior due to the existence or non-existence and the position of hole near crack is investigated. As the result of analysis study, model 3 (in case of the distance of 2mm on the horizontal direction between the end part and hole as the specimen model existed with one hole near the crack) has the maximum deformation, stress and deformation energy of the most values among three models. As the distance between the crack and hole inside the specimen becomes nearer, the maximum stress becomes higher in cases of three models. Apart from the number of holes, it is seen that the maximum stress becomes higher near the crack when the hole exists near the crack inside the specimen. If the hole inside the machine or the mechanical structure is punctured by using the result of this study, it is thought that the occurred breakage or breakdown can be prevented by reducing the fracture stress happened at the specimen.

• The Monthly Technology and Standards
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• s.7
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• pp.92-102
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• 2002

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05c
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• pp.284-289
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• 1996

국산 원자로 압력용기강(ASME SA508 cl.3)을 대상으로 표준 샤피충격시험편(2 mm V- notch)과 피로균열(precracked Charpy) 시험편을 제작하여 계장화(instrumented)충격시험을 실시하고, 충격시험시 하중점(load point)의 변위(displacement) 혹은 시간의 변화를 하중의 변화와 함께 측정하였다. 측정결과를 파괴현상 및 파괴역학과 연계시켜 해석하므로서, 가능한한 소량의 시험편(혹은 시험공정)을 사용하여 필요로 하는 인성평가 관련 정보를 획득할 수 있도록 시도하였다. 그 결과, 파괴과정을 나타내는 하중의 변화를 이용하여 Shear fraction 을 예측할 수 있었고, 하중의 변화와 관계된 변위로부터 Lateral expansion을 추정할 수 있었다. 피로균열 시험편 시험결과로 부터는 충격시의 항복하중, 항복변위, 최고하중 등을 획득하여 균열크기의 함수로 표시되는 시험편 Compliance 를 계산하였고, Equivalent energy 법과 J-integral 법을 적용하여 원자로 압력용기강의 탄소성 동적파괴인 성을 평가할 수 있었다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.88-88
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• 2004

내압을 받는 압력관의 파괴는 원주방향의 응력이 주된 요인이므로, 압력관의 안전성을 평가를 위해서는 원주방향의 인장특성을 아는 것이 필요하다. 소형 압력관의 인장특성을 평가할 때, 정확한 원주방향의 인장특성을 알기 위해서는 관으로 가공된 후의 재료로 시험해야 하지만, 부피의 제약으로 인하여 원주방향으로의 표준 인장시험편을 제작하지 못하므로 가공하기 전의 재료의 물성치를 사용하고 있다. 이를 개선하고자 원주방향의 인장특성을 평가하기 위한 방법의 하나로 링 시험법(ring test)이 있다.(중략)

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.2
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• pp.90-98
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• 2006

Signals captured from a Combo calibration standard tube paly a crucial role in the evaluation of motorized rotating pancake coil (MRPC) probe signals from steam generator (SG) tubes in nuclear power plants (NPPs). Therefore, the Combo tube signals should be consistent and accurate. However, MRPC probe signals are very easily affected by various factors around the tubes so that they can be distorted in their amplitudes and phase angles which are the values specifically used in the evaluation. To overcome this problem, in this study, we explored possibility of simulation to be used as a practical calibration tool far the evaluation of real field signals. For this purpose, we investigated the characteristics of a MRPC probe and a Combo tube. And then using commercial software (VIC-3D) we simulated a set of calibration signals and compared to the experimental signals. From this comparison, we verified the accuracy of the simulated signals. Finally, we evaluated two defects using the simulated Combo tube signals, and the results were compared with those obtained using the actual field calibration signals.

• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.2
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• pp.357-363
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• 1995

Disbond size of adhesively bonded single lap and double lap joints CFRP composite specimens has been evaluated using acousto-ultrasonic(AU) technique. Frequency spectra for all specimens were obtained by measuring peak amplitude of the stress wave propagated through the bond-lines. By analyzing these frequency spectra, peak amplitude was found to be proportional to fractional bonding area and to be maxima at the fundamental and the third order higher harmonic frequencies of specimen thickness mode. The disbond size can be evaluated quantitatively and this technique can be applied to real structures if the reference specimens are prepared in advancve.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.9
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• pp.930-937
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• 2009

The estimation method of the fracture resistance curve for the pipe specimen was proposed using the load ratio method for the standard specimen. For this, the calculation method of the load - CMOD curve for the pipe specimen with the common format equation(CFE) was proposed by using data of the CT specimen. The proposed method agreed well with experimental data. The J-integral value and the crack extension were calculated from the estimated load - CMOD data. The fracture resistance curve was estimated from the calculated J-integral and the crack extension. From these results, it have been seen that the proposed method is reliable to estimate the J-R curve of the pipe specimen.