• Title/Summary/Keyword: Initial Surface Defect

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Effect of Small Surface Defects in the Starting Material on Product Quality after Drawing (원소재의 미소 표면결함이 인발공정에 미치는 영향)

  • Nam, C.H.;Lee, I.K.;Lee, J.K.;Joun, M.S.
    • Transactions of Materials Processing
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    • v.23 no.3
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    • pp.159-163
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    • 2014
  • In the current study, the effect of small surface defects in the starting material including roughness, indentations, or scratches, which are perpendicular to the direction of drawing, on the product quality is investigated using the finite element method. An axisymmetric defect is assumed. Such defects are defined by a cylindrical defect area and two tapered regions connecting the defect area to the non-defective area of the material. Various conditions for these initial surface defects are considered, including defect depth, defect slope and defect length. To describe the plastic deformation of the defect in detail during the simulation, local remeshing is applied. Based on the finite element results, defect disappearance maps were generated. It was found that defect disappearance is significantly dependent on the defect depth and the defect length coupled with the defect slope.

A study on surface fatigue crack behavior of SS400 weldment (SS400 용접부의 표면피로균열거동에 관한 연구)

  • 이용복;조남익;박강은
    • Journal of Welding and Joining
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    • v.14 no.2
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    • pp.90-95
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    • 1996
  • In order to investigate characteristics of surface fatigue crack propagation from a pit shaped surface defect which frequently exists around welded joints, SS400 steel with thickness of 12mm, which has been generally used for structure members, was welded with submerged-arc butt type and machined for both surface. An initial surface defect of pit shape with the aspect ratio of 2 was made on the specimen. The initial defect was located at 5 different zones over the weldment : weld metal zone, boundary between weld metal and HAZ, HAZ, boundary between HAZ and base metal. Characteristics of surface fatigue crack propagation from the defect on each region under the same loading condition were investigated and compared.

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A study on surface fatigue crack behavior of SS400 welding Zone (SS400용접 부위의 표면 피로균열거동에 관한 연구)

  • 이용복;조남익;박강은
    • Proceedings of the KWS Conference
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    • 1995.10a
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    • pp.214-217
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    • 1995
  • In order to investigate characteristics of surface fatigue crack propagation from a pit shaped surface defect which frequently exists near weld joints, SS400 steel with thickness of 12mm, which generally used for structure members, was submerged-arc welded with butt type and machined for both surface. The weld joints were devided into 5 regions, weld metal, boundary between heat affected zone (HAZ), HAZ, boundary between HAZ and base metal, and base metal. Specimens from each region were machined for a pit shaped initial surface defect with aspect ratio of 2. characteristics of surface fatigue crack por pagation from the defect under the same loading condition were compared and discussed.

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Enhanced Stability of Organic Photovoltaics by Additional ZnO Layers on Rippled ZnO Electron-collecting Layer using Atomic Layer Deposition

  • Kim, Kwang-Dae;Lim, Dong Chan;Jeong, Myung-Geun;Seo, Hyun Ook;Seo, Bo Yeol;Lee, Joo Yul;Song, Youngsup;Cho, Shinuk;Lim, Jae-Hong;Kim, Young Dok
    • Bulletin of the Korean Chemical Society
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    • v.35 no.2
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    • pp.353-356
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    • 2014
  • We fabricated organic photovoltaic (OPV) based on ZnO ripple structure on indium tin oxide as electron-collecting layers and PTB7-F20 as donor polymer. In addition, atomic layer deposition (ALD) was used for preparing additional ZnO layers on rippled ZnO. Addition of 2 nm-thick ALD-ZnO resulted in enhanced initial OPV performance and stability. Based on photoluminescence results, we suggest that ALD-ZnO layers reduced number of surface defect sites on ZnO, which can act as electron-hole recombination center of OPV, and increased resistance of ZnO towards surface defect formation.

Long-term radiographic evaluation of infrabony defect treated by flap operation (치주판막술에 의해 치료된 골연하 결손부의 장기적 방사선학적 변화 양사의 관찰)

  • Bae, Sang-Ryul;Park, Jin-Woo;Suh, Jo-Young;Lee, Jae-Mok
    • Journal of Periodontal and Implant Science
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    • v.38 no.3
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    • pp.429-436
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    • 2008
  • Purpose: The goal of periodontal regenerative therapy is to replace bone, cementum, and periodontal ligament on a previously diseased root surface, which has suffered the loss of these supporting structures. To accomplish the regeneration, a number of surgical procedures have been advocated throughout the years. There seems to be a potential for some spontaneous periodontal tissue regeneration in the bottom of periodontal defect following open flap debridement alone. The aim of this study was to analyse the radiographic bone changes over 2-year after flap operation. Material and Methods: Patients attending the department of periodontics of Kyungpook National University Hospital were studied. Patients had clinical and radiographic evidence of infrabony defect(s). forty two sites of 33 patients aged 26 to 65 (mean age 45.5) were treated by flap operation with or without osseous surgery. Baseline and over 2-year follow-up radiographs were collected and evaluated for this study. Radiographic assessment includes a bone fill, bone crest change, defect resolution, and % of defect resolution. Pre- and post-treatment differences between variables (maxilla and mandible, gender, defect depth, defect angle) using the paired t-test were examined. Result: We observed 0.74 mm of bone fill, 0.66 mm of crestal resorption, 1.40 mm of defect resolution, and 27% of percentage of defect resolution. Mandible, women, deeper initial defect depth, narrower initial defect angle showed greater bone fill, defect resolution, and % of defect resolution. Conclusion: The results of this study suggest that the use of flap operation did enhance the outcome in terms of radiographically detectable bone fill. Both treatment resulted in some loss of crestal bone height.

Fatigue Characteristics of Work roll of Roughing Stand in Hot Strip Mill (열연 조압연 Work Roll의 피로 특성)

  • 이원호;김상준;이영호;장준상;이준정;김종근
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.4
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    • pp.819-827
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    • 1992
  • Investigations of the fatigue damage of roughing mill roll and experimentally. By the computer simulation for analysing the stresses on the roll surface and experimental hot rolling, the following results were drawn : The crakcs observed on the roll surface were initiated thermally in the initial stage of the rolling and propagated by repeated thermal and bending stresses. The size of the roll surface cracks smaller than 4.87mm could avoid the occurrence of tiny scab, surface defect of hot steel strip. Since the size of surface cracks observed on the roughing mill roll was very small, the fatigue damage of roll surface was found not to be the major factor for the formation of the scab.

An Efficient Detection Method for Rail Surface Defect using Limited Label Data (한정된 레이블 데이터를 이용한 효율적인 철도 표면 결함 감지 방법)

  • Seokmin Han
    • The Journal of the Institute of Internet, Broadcasting and Communication
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    • v.24 no.1
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    • pp.83-88
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    • 2024
  • In this research, we propose a Semi-Supervised learning based railroad surface defect detection method. The Resnet50 model, pretrained on ImageNet, was employed for the training. Data without labels are randomly selected, and then labeled to train the ResNet50 model. The trained model is used to predict the results of the remaining unlabeled training data. The predicted values exceeding a certain threshold are selected, sorted in descending order, and added to the training data. Pseudo-labeling is performed based on the class with the highest probability during this process. An experiment was conducted to assess the overall class classification performance based on the initial number of labeled data. The results showed an accuracy of 98% at best with less than 10% labeled training data compared to the overall training data.

Manufacture of 7000 Al Alloy with Superior Extrudability and Its Extrusion Limit Diagram (압출성 향상을 위한 고강도 7000계 알루미늄 합금의 제조 및 압출한계선도)

  • Ham, H.W.;Kim, B.M.;Cho, H.;Cho, H.H.
    • Transactions of Materials Processing
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    • v.8 no.5
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    • pp.482-490
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    • 1999
  • 7000 series Al alloy with good mechanical properties has been focused with tendency to reduce the components weight of aircraft and automobile. However, it is difficult to manufacture a sound extruded product because of segregation, grain growth, casting defect, surface defect, decreasing extrudability and so on. The objective of this study is to manufacture a new 7000 al alloy more than the extrudability of A7N01 and A7003 through controlling the weight (%) Mg, Zn, Si. Hot extrusion experiments on the axisymmetric rod are performed in 500℃ and also performed analysis of the same process using unmerical analysis method, a coupled rigid-thermoviscoplastic finite element method. Extrusion limit diagram was obtained for the developed alloy by FE-simulation in order to define the relationship of extrusion speed and initial billet temperature.

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Effects of Mg on corrosion resistance of Al galvanically coupled to Fe (Fe와 galvanic couple된 알루미늄의 내식성에 미치는 마그네슘의 영향)

  • Hyun, Youngmin;Kim, Heesan
    • Corrosion Science and Technology
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    • v.12 no.1
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    • pp.40-49
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    • 2013
  • Effects of magnesium and pH on corrosion of aluminum galvanically coupled to iron have studied by using potentio- dynamic and static tests for polarization curves, Mott-Schottky test for analysis of semiconductor property, and GD-AES and XPS for film analysis. Pitting potential was sensitive to magnesium as an alloying element but not to pH, while passive current was sensitive to pH but not to magnesium. It was explained with, instead of point defect model (PDM), surface charge model describing that the ingression of chloride depends on the state of surface charge and passive film at film/solution interface is affected by pH. In addition, galvanic current of aluminum electrically coupled to iron was not affected by magnesium in pH 8.4, 0.2M citrate solution but was increased by magnesium at the solution of pH 9.1. The galvanic current at pH 9.1 increased with time at the initial stage and after the exposure of about 200 minute, decreased and stabilized. The behavior of the galvanic current was related with the concentration of magnesium at the surface. It agreed with the depletion of magnesium at the oxide surface by using glow discharge atomic emission spectroscopy (GD-AES). In addition, pitting potential of pure aluminum was reduced in neutral pH solution where chloride ion maybe are competitively adsorbed on pure aluminum. It was confirmed by the exponential decrease of pitting potential with log of [$Cl^-$] around 0.025 M of [$Cl^-$] and linear decrease of the pitting potential. From the above results, unlike magnesium, alloying elements with higher electron negativity, lowering isoelectric point (ISE), are recommended to be added to improve pitting corrosion resistance of aluminum and its alloys in neutral solutions as well as their galvanic corrosion resistance in weakly basic solutions.

The Study on the Denuded Zone Formation of Czochralski-grown Single Crystal Silicon Wafer (I) (Czochralski 법으로 성장시킨 단결정 Silicon Wafer에서의 표면 무결함층(Denuded Zone) 형성에 관한 연구(I))

  • 김승현;양두영;김창은;이홍림
    • Journal of the Korean Ceramic Society
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    • v.28 no.6
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    • pp.495-501
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    • 1991
  • This study is intended to make defect-free region, denuded zone at the silicon wafer surface for semiconductor device substrates. In this experiment, initial oxygen concentration of starting material CZ-grown silicon wafer, various heat treatment combinations, denuding ambient and the amounts of oxygen reduction were measured, and then denuded zone (DZ) formation and depth were investigated. In Low/High anneal (DZ formation could be achieved), the optimum temperature for Low anneal was 700$^{\circ}C$∼750$^{\circ}C$. In case of High anneal, with the time increased, DZ depth was increased at 1000$^{\circ}C$, 1150$^{\circ}C$ respectively, but on the contrary, DZ depth was decreased at low temperature 900$^{\circ}C$. As well, out-diffusion time below 2 hours was unsuitable for effective Gettering technique even though the temperature was high, and DZ formation could be achieved when initial oxygen concentration was only above 14 ppm in silicon wafer.

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