• Title/Summary/Keyword: Artificial flaws

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Ultrasonic Signal Analysis with DSP for the Pattern Recognition of Welding Flaws

  • Kim, Jae-Yeol;Cho, Gyu-Jae;Kim, Chang-Hyun
    • International Journal of Precision Engineering and Manufacturing
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    • v.1 no.1
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    • pp.106-110
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    • 2000
  • The researches classifying the artificial flaws in welding parts are performed using the pattern recognition technology. For this purpose the signal pattern recognition package including user defined function is developed and the total procedure is made up the digital signal processing, feature extraction, feature selection, classfier design. Specially it is composed with and discussed using the ststistical classfier such as the linear discriminant function classfier, the empirical Bayesian classfier.

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Analysis of Vibration Modes of Small and Large Concrete Blocks Containing Flaws by Impact Resonance Method (충격 공진법에 의한 대소 경계조건하 콘크리트 블록 내부결함 신호의 해석)

  • Park, Seok-Kyun;Yoon, Seok-Soo
    • Magazine of the Korea Concrete Institute
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    • v.11 no.1
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    • pp.161-171
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    • 1999
  • Impact resonance testing was carried out on small and large concrete blocks containing several types of artificial flaws respectively. Quantitative analysis of the observed peak frequencies in the impact resonance tests identifies the possible normal modes of concrete blocks containing flaws. and enables to determine the depth and size of the flaws in concrete blocks. In this study, concrete can be treated as a homogeneous and isotropic material. The flaw size and location at each section of artificial flaw series in small and large concrete blocks, determined through two-dimensional scanning of impact point and real-time fast Fourier transform, are in good agreement with real size location, respectively. Consequently, quantitative analysis method of vibration modes in the impact resonance tests, which can be applied for homogeneous and isotropic material, can be useful for the detection of flaws in any case of small and large concrete blocks in this study.

Control of Tensile Behavior of Ultra-High Performance Concrete Through Artificial Flaws and Fiber Hybridization

  • Kang, Su-Tae;Lee, Kang-Seok;Choi, Jeong-Il;Lee, Yun;Felekoglu, Burak;Lee, Bang Yeon
    • International Journal of Concrete Structures and Materials
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    • v.10 no.sup3
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    • pp.33-41
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    • 2016
  • Ultra-high performance concrete (UHPC) is one of the most promising construction materials because it exhibits high performance, such as through high strength, high durability, and proper rheological properties. However, it has low tensile ductility compared with other normal strength grade high ductile fiber-reinforced cementitious composites. This paper presents an experimental study on the tensile behavior, including tensile ductility and crack patterns, of UHPC reinforced by hybrid steel and polyethylene fibers and incorporating plastic beads which have a very weak bond with a cementitious matrix. These beads behave as an artificial flaw under tensile loading. A series of experiments including density, compressive strength, and uniaxial tension tests were performed. Test results showed that the tensile behavior including tensile strain capacity and cracking pattern of UHPC investigated in this study can be controlled by fiber hybridization and artificial flaws.

A Feasibility Test for Flaw Detection in Overlay Weld of Reactor Upper Head Penetration Using Time of Flight Diffraction Technique (TOFD 기법을 활용한 원자로 상부헤드관통부 오버레이 용접부 결함 검출 가능성 평가)

  • Lee, Jeong Seok;Kim, Jin Hoi
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.10 no.1
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    • pp.15-19
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    • 2014
  • A Failure or degradation of reactor upper head penetration is a recurring problem due to long term operation at nuclear power plants. And a flaw in the reactor upper head penetration has caused unplanned plant shutdown for repair as well as high economic impact on the plants. Consequently, a detection of flaws is of the utmost importance. Prior to the replacement of reactor upper head penetration, some utilities have repaired the flaws of reactor upper head penetration generated by overlay weld. Until now, only the base metal in reactor upper head penetration has been inspected according to 10 CFR 50.55a and ASME code case N-729-1. Accordingly, it is difficult to detect manufacturing defects and repair defects in overlay weld. This paper presents a case study on the application of Time of Flight Diffraction technique for reactor head penetration mockup with artificial flaws in overlay weld. This study offers a way to understand the flaws detected in reactor upper head penetration overlay weld.

Characteristics of High Frequency Ultrasonic Transducer Employing Polyvinylidene Fluoride and Detectability of Flaw in Cr-Ni Steel (PVDF 수침용 고주파수 초음파 탐촉자의 검출장과 Cr-Ni 강에서의 결함 검출능 측정)

  • Kim, Byoung-Geuk;Lee, S.S.
    • Journal of the Korean Society for Nondestructive Testing
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    • v.17 no.1
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    • pp.23-30
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    • 1997
  • Recently high frequency ultrasonic transducers to employ polyvinylidene fluoride(PVDF) or polyvinylidene fluoride trifluoroethylene P(VDF-TrFE) have been used to detect small flaws in immersion testing. The detection field depending on the water path between the transducer and a specimen and the path in a tested specimen was measured using a PVDF transducer with nominal frequency 80MHz. Also, C-scan and B-scan were performed for the specimens made of Cr-Ni steel with the artificial flaws, the flat-bottom holes with diameter ranging from $50{\mu}m$ to $560{\mu}m$ at 12mm depth. As the result, the flaws with diameter larger than $280{\mu}m$ were detected, but the flaws with the ratio of diameter to wavelength smaller than about 0.48 were not detected. That the smaller flaws could not be detected was attributed to the attenuation of high frequency components in the steel specimens.

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Micro-Crack Healing on Soda-Lime Glass by Chemical Strengthening

  • Kim, Hyeong-Jun;Lee, Sung-Min;Maeng, Jeehun;Kim, Dong-hwan
    • Journal of the Korean Ceramic Society
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    • v.56 no.5
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    • pp.483-488
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    • 2019
  • We studied whether chemical strengthening can heal the flaws on soda-lime silicate glass. Artificial surface cracks were introduced on the glass by sharp indentation with various loads of 0.1 to 10 N. Then, the glasses with flaws were treated by ion-exchanging in KNO3 melt. The change in the dimension of the crack on glass was measured by a digital microscope and a scanning electron microscope. The chemical strengthening treatment enhances the strength of the glass with flaws. It is thought that the melted KNO3 not only forms the depth of the compressed layer of 7.5 ㎛, but also heals the cracks by infiltrating them and expanding the glass on both sides of the cracks. The critical length (2c) of the cracks on soda-lime glass that can be healed by chemical strengthening is 50 ㎛ or less.

Thermographic Defects Evaluation of Railway Composite Bogie (적외선열화상을 이용한 복합소재대차의 결함평가)

  • Kim, Jeong-Guk;Kwon, Sung-Tae;Kim, Jung-Seok;Yoon, Hyuk-Jin
    • Proceedings of the KSR Conference
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    • 2011.05a
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    • pp.548-553
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    • 2011
  • The lock-in thermography was employed to evaluate the defects in railway bogies. Prior to the actual application on railway bogies, in order to assess the detectability of known flaws, the calibration reference panel was prepared with various dimensions of artificial flaws. The panel was composed of polymer matrix composites, which were the same material with actual bogies. Through lock-in thermography evaluation, the optimal frequency of heat source was determined for the best flaw detection. Based on the defects information, the actual defect assessments on railway bogie were conducted with different types of railway bogies, which were used for the current operation. In summary, it was found that the novel infrared thermography technique could be an effective way for the inspection and the detection of surface defects on bogies since the infrared thermography method provided rapid and non-contact investigation of railway bogies.

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The Comparison of Acceptance Criteria and Flaw Size Measurement between ASME and RCC-M Code in Ultrasonic Examination (초음파검사시 ASME와 RCC-M CODE에 따른 결함 크기측정 및 허용기준 비교평가)

  • Kim, B.C.;Lim, H.T.;Lee, J.P.;Joo, Y.S.
    • Journal of the Korean Society for Nondestructive Testing
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    • v.8 no.1
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    • pp.6-11
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    • 1988
  • The comparison and analysis of flaw detectability, flaw sizing methods and allowable criteria in accordance with the applicable codes, ASME and RCC-M Code, in ultrasonic examination of pressure vessel in nuclear power plants were studied. Accordding to the codes, calibration blocks were made. The artificial flaws such as disc and band types in test specimens were machined. They were detected and evaluated with etch code requirements and measured values were compared with the actual flaws.

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Ultrasonic Phased Array Techniques for Detection of Flaws of Stud Bolts in Nuclear Power Plants

  • Lee, Joon-Hyun;Choi, Sang-Woo
    • Journal of the Korean Society for Nondestructive Testing
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    • v.26 no.6
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    • pp.440-446
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    • 2006
  • The reactor vessel body and closure head are fastened with the stud bolt that is one of crucial parts for safety of the reactor vessels in nuclear power plants. It is reported that the stud bolt is often experienced by fatigue cracks initiated at threads. Stud bolts are inspected by the ultrasonic technique during the overhaul periodically for the prevention of failure which leads to radioactive leakage from the nuclear reactor. The conventional ultrasonic inspection for stud bolts was mainly conducted by reflected echo method based on shadow effect. However, in this technique, there were numerous spurious signals reflected from every oblique surfaces of the thread. In this study, ultrasonic phased array technique was applied to investigate detectability of flaws in stud bolts and characteristics of ultrasonic images corresponding to different scanning methods, that is, sector and linear scan. For this purpose, simplified stud bolt specimens with artificial defects of various depths were prepared.

A Study on the Application of Digital Signal Processing for Pattern Recognition of Microdefects (미소결함의 형상인식을 위한 디지털 신호처리 적용에 관한 연구)

  • 홍석주
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.9 no.1
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    • pp.119-127
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    • 2000
  • In this study the classified researches the artificial and natural flaws in welding parts are performed using the pattern recognition technology. For this purpose the signal pattern recognition package including the user defined function was developed and the total procedure including the digital signal processing feature extraction feature selection and classifi-er selection is teated by bulk,. Specially it is composed with and discussed using the statistical classifier such as the linear discriminant function the empirical Bayesian classifier. Also the pattern recognition technology is applied to classifica-tion problem of natural flaw(i.e multiple classification problem-crack lack of penetration lack of fusion porosity and slag inclusion the planar and volumetric flaw classification problem), According to this result it is possible to acquire the recognition rate of 83% above even through it is different a little according to domain extracting the feature and the classifier.

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