• Title/Summary/Keyword: Structure Defects

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The effects of temperature and vacancy defect on the severity of the SLGS becoming anisotropic

  • Tahouneh, Vahid;Naei, Mohammad Hasan;Mashhadi, Mahmoud Mosavi
    • Steel and Composite Structures
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    • v.29 no.5
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    • pp.647-657
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    • 2018
  • Geometric imperfections may be created during the production process or setting borders of single-layer graphene sheets (SLGSs). Vacancy defects are an instance of geometric imperfection, so investigating the effect of these vacancies on the mechanical properties of single-layer graphene is extremely important. Since very few studies have been conducted on the structure of imperfect graphene (with the vacancy defect) as an anisotropic structure, further study of this defective structure seems imperative. Due to the vacancy defects and for the proper assessment of mechanical properties, the graphene structure should be considered anisotropic in certain states. The present study investigates the effects of site and size of vacancy defects on the mechanical properties of graphene as an anisotropic structure using the lekhnitskii interaction coefficients and Molecular Dynamic approach. The effect of temperature on the severity of the SLGS becoming anisotropic is also investigated in this study. The results reveal that the amount of temperature has a big effect on the severity of the structure getting anisotropic even for a graphene without any defects. The effect of aspect ratio, temperature and also size and site of vacancy defects on the material properties of the graphene are studied in this research work. According to the present study, using material properties of flawless graphene for imperfect structure can lead to inaccurate results.

Evaluation of Fatigue Strength and Characteristics of Fatigue Crack Closure in SM35C Steel (중탄소강의 피로크랙 개폐구의 특성 및 피로강도의 평가)

    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.6 no.1
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    • pp.45-50
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    • 1997
  • It is not clearly known how surface defects or inclusions of a medium carbon steel affect a fatigue strength. In this study, we used SM35C specimens with spheroidized cementite structure to eliminate dependence of micro structure of fatigue crack. The investigation was carried out by behavior of crack closure at non-propagation crack and effect of the fatigue limit according to the artificial defects size. Experimental findings are obtained as follows : (1) Fatigue crack initiation point of medium carbon steel with spheroidized cementite structure is at the surface defects. (2) Non-propagating crack length of smooth specimen is equal to the critical size of defect. (3) Considering the opening and closure behavior of fatigue crack, the defect shape results in various crack opening displacement, while it does not affects the fatigue limit level of medium carbon steel with spheroidized cementite structure. (4) The critical length of the non-propagation crack of smooth specimen is the same as critical size of defect in transient area which determines threshold condition in steel with spheroidized cementite structure.

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The Management Method for Preventing Frequent Defect about Each Inspection Part from The Data Analysis of Pre-qualification of Residential Building Reconstruction (주택 재건축 예비평가 자료분석을 통한 분야별 주요결함 발생현황 및 유지관리방안 고찰)

  • Bae, Cheol-Hak;Lee, Sung-Ok;Ji, Myoung-Ho
    • Journal of the Korean housing association
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    • v.21 no.6
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    • pp.71-80
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    • 2010
  • The purpose of this study is to classify defects of the residential building by analyzing the defect specified by prequalification of residential building reconstruction and to suggest the solution of the problem which can be arisen during each stage of plan, construction and maintenance. By sorting the main defects which is specified by pre-qualification of residential building reconstruction for three years from August 2006 to August 2009 into 4 catagories and analyzing the cause of the defects, we draw the way of maintenance to prevent the defects and make pleasant residential environment. The reason for the frequent defects from residential building is mainly deterioration. It occured on the finishing more than on the structure, which means that residents can find defects easier on the finishing than the structure and clear the demand for repair. The result of analyzing of pre-qualification of residential building reconstruction is that the defects mostly caused small, masonry constructed and lower apartment. The apartment which is not into legal right for maintenance naturally have more defects than the others. In conclusion, it is necessary to establish a law of obligation duty of the maintenance of small apartment.

Hole Defects on Two-Dimensional Materials Formed by Electron Beam Irradiation: Toward Nanopore Devices

  • Park, Hyo Ju;Ryu, Gyeong Hee;Lee, Zonghoon
    • Applied Microscopy
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    • v.45 no.3
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    • pp.107-114
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    • 2015
  • Two-dimensional (2D) materials containing hole defects are a promising substitute for conventional nanopore membranes like silicon nitride. Hole defects on 2D materials, as atomically thin nanopores, have been used in nanopore devices, such as DNA sensor, gas sensor and purifier at lab-scale. For practical applications of 2D materials to nanopore devices, researches on characteristics of hole defects on graphene, hexagonal boron nitride and molybdenum disulfide have been conducted precisely using transmission electron microscope. Here, we summarized formation, features, structural preference and stability of hole defects on 2D materials with atomic-resolution transmission electron microscope images and theoretical calculations, emphasizing the future challenges in controlling the edge structures and stabilization of hole defects. Exploring the properties at the local structure of hole defects through in situ experiments is also the important issue for the fabrication of realistic 2D nanopore devices.

A Study on the Analysis of causes & minimizing of Defects at Composite Materials Sandwich Aircraft Structure in Autoclave Processing (항공기용 복합재료 샌드위치 구조물의 오토클레이브 성형시 발생되는 결함 원인 분석과 그 최소화 방안)

  • 권순철;임철문;최병근;이세원;한중원;김윤해
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2000.11a
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    • pp.29-33
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    • 2000
  • The purpose of this paper is to determine the effect of the autoclave inner pressure rate, heat-up rate, tool round angle, Thickness of core, height of joggle on defects, and to minimize the defects of aircraft sandwich structure reinforced with honeycomb core occurred in autoclave processing. The results showed that the geometry of aircraft sandwich structure and tool such as tool round angle, Thickness of core, height of joggle, and the autoclave cure conditions such as inner pressure rate, heat up rate strongly affected the core movement, core wrinkle, bridge phenomenon of prepreg and depression of core that occurred in autoclave processing.

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Corner Inspection of Autoclave-cured L-shaped Composite Structure using Pulse-echo Rotation Scanning Scheme based on Laser Ultrasonic (레이저 초음파 기반 반사식 회전 검사 기법을 이용한 오토클레이브 가공 L 형 복합재 구조물의 모서리 검사)

  • Lee, Young-Jun;Lee, Jung-Ryul;Hong, Sung-Jin
    • Composites Research
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    • v.31 no.5
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    • pp.246-250
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    • 2018
  • In this paper, laser ultrasonic rotation scanning method was proposed to inspect and visualize defects in corner section of curved composite structure. L-shaped composite specimen with defects in its corner section were inspected using laser ultrasonic rotation scanning method. L-shaped specimens had artificial defects at three different depths to simulate delamination damage. All artificial defects were detected clearly in different time-of-flight according to their depths. Inspection result showed that the proposed method is suitable to inspect round corner section of curved composite structure without any special tools.

Laser-Ultrasonics Application for Non-Contact and Non-destructive Evaluation of Structure (구조물의 비접촉 비파괴 검사를 위한 레이저 초음파법 적용)

  • Kim Jae-Yeal;Song Kyung-Seok;Yang Dong-Jo
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.14 no.4
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    • pp.49-54
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    • 2005
  • Measuring defects on the inside and on the surface of a steel structure is very important technology in order to predict the life span of the structure. In particular, a place with a high probability that it may contain defects is a welded part and it is very important to check defects in the part, absence/presence of non-uniform substances, its shape, and the location. Many non-destructive tests can be applied, but the ultrasonic flow detection test is widely used with some advantages. The ultrasonic flow detection test, however, cannot be applied when there is a problem by a contact medium between PZT and a specimen, in case of a small and complicated shape or a moving object or when the specimen is hot. In this study, to solve the problems of the contact ultrasonic flow detection test, the non-contact ultrasonic flow detection test for sending/receiving ultrasonic waves using lasers was described. I intended to develop a non-destructive detection system applying the laser application ultrasonic test to a steel structure by detecting the defects inside of and on the surface of the specimen.

A comparative study of electrical properties of arachidic acid LB films in the Al/LB/Al and Au/LB/Au electrode structure (Al/LB/Al, Au/LB/Au 전극 구조에서 arachidic acid LB막의 전기적 특성에 관한 비교 연구)

  • 오세중;김정수
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.44 no.10
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    • pp.1311-1316
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    • 1995
  • The electrical properties of the Langmuir-Blodgett (LB) films layered with arachidic acid were studied at the room temperature. The sample was formed with 2 different structure ; One was Al/LB/Al and the other was Au/LB/Au. The precise structure of Al/LB/Al was considered as Al/Al$_{2}$O$_{3}$/LB/Al, because the natural oxide layer was formed on surface of lower Al electrode. The electrical conductivity of Al/Al$_{2}$O$_{3}$/LB/Al structure was determined the value of 3.5 * 10$^{-14}$ S/cm from the measurement of current-voltage (I-V) characteristics. The sample with the structure of Au/LB/Au was made to eliminate the influence of oxide layer in the electrical properties of the LB films. The short circuit current was observed in this sample from the I-V characteristics. To verify the reason of short circuit current generation, copper decoration method was employed to the 15 layers of LB films deposited on the Al and Au electrode each. The defects were shown on the films deposited with Au electrode. This results means that the defects on the LB films which layered with the Au electrode were contributed to the short circuit current. Several films (15, 31, 51, 71L) were deposited on the Au electrode and measured the size of defects with the copper decoration method. The size of defects becomes smaller as the film layer was increased. We conclude that the existence of defects affects the short circuit current generation.

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Electronic properties of graphene nanoribbons with Stone-Wales defects using the tight-binding method

  • M.W. Chuan;S.Z. Lok;A. Hamzah;N.E. Alias;S. Mohamed Sultan;C.S. Lim;M.L.P Tan
    • Advances in nano research
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    • v.14 no.1
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    • pp.1-15
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    • 2023
  • Driven by the scaling down of transistor node technology, graphene became of interest to many researchers following the success of its fabrication as graphene nanoribbons (GNRs). However, during the fabrication of GNRs, it is not uncommon to have defects within the GNR structures. Scaling down node technology also changes the modelling approach from the classical Boltzmann transport equation to the quantum transport theory because the quantum confinement effects become significant at sub-10 nanometer dimensions. The aim of this study is to examine the effect of Stone-Wales defects on the electronic properties of GNRs using a tight-binding model, based on Non-Equilibrium Green's Function (NEGF) via numeric computation methods using MATLAB. Armchair and zigzag edge defects are also implemented in the GNR structures to mimic the practical fabrication process. Electronic properties of pristine and defected GNRs of various lengths and widths were computed, including their band structure and density of states (DOS). The results show that Stone-Wales defects cause fluctuation in the band structure and increase the bandgap values for both armchair GNRs (AGNRs) and zigzag GNRs (ZGNRs) at every simulated width. In addition, Stone-Wales defects reduce the numerical computation DOS for both AGNRs and ZGNRs. However, when the lengths of the structures increase with fixed widths, the effect of the Stone-Wales defects become less significant.

Study of the Effects of the Antisite Related Defects in Silicon Dioxide of Metal-Oxide-Semiconductor Structure on the Gate Leakage Current

  • Mao, Ling-Feng;Wang, Zi-Ou;Xu, Ming-Zhen;Tan, Chang-Hua
    • JSTS:Journal of Semiconductor Technology and Science
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    • v.8 no.2
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    • pp.164-169
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    • 2008
  • The effects of the antisite related defects on the electronic structure of silica and the gate leakage current have been investigated using first-principles calculations. Energy levels related to the antisite defects in silicon dioxide have been introduced into the bandgap, which are nearly 2.0 eV from the top of the valence band. Combining with the electronic structures calculated from first-principles simulations, tunneling currents through the silica layer with antisite defects have been calculated. The tunneling current calculations show that the hole tunneling currents assisted by the antisite defects will be dominant at low oxide field whereas the electron direct tunneling current will be dominant at high oxide field. With increased thickness of the defect layer, the threshold point where the hole tunneling current assisted by antisite defects in silica is equal to the electron direct tunneling current extends to higher oxide field.