• 한국세라믹학회지
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• 제48권5호
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• pp.458-462
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• 2011

The strength of ceramic was improved by lamination by suppressing the propagation of cracks with compressive residual stress in the face layer of the laminate. Hot pressed SiAlON+SiC/SiC/SiAlON+SiC laminate discs were fabricated for tailored residual stress. The residual stress in this laminate was studied by X-ray diffraction (XRD). There was considerable compressive residual stress in the face layer. A Finite Element Analysis (FEA) was performed to support the measured XRD results and to determine the stress field in the laminate. The residual stress measured by XRD had satisfactory agreement with the analytically calculated and FEA values. The measured value by XRD was -385 ${\pm}$ 20 MPa over most of the face layer. The calculated and FEA values were -386 MPa and -371MPa, respectively. FEA also showed significantly modified stresses and the maximum tensile stress near the edge region which are possible crack generators in the presence of flaws or contact damage.

• 한국멀티미디어학회:학술대회논문집
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• 한국멀티미디어학회 2004년도 춘계학술발표대회논문집
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• pp.263-266
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• 2004

본 논문에서는 터널 구조물에서 발생하는 균열의 인식과 이에 대한 정보를 획득하기 위한 방법에 대한 연구를 수행하였다. 터널 구조물에서 발생하는 균열의 경우, 건설 분야의 특수성 때문에 기존의 경계점 인식(edge detection) 알고리즘을 적용하는 경우 정밀도 저하의 문제가 발생한다. 이러한 문제점을 해결하고 더불어 정밀도를 향상시킬 수 있는 방법으로 영상에서 균열을 인식하는 균열 인식 단계와 인식된 균열의 길이, 두께 등을 측정하는 균열 정보 획득 단계로 구분하였다. 균열 인식 단계에서는 균열의 시작점과 끝점을 기준으로 휴리스틱(Heuristic) 알고리즘을 사용하여 픽셀 값의 분포에 따라 균열의 중심선을 계산하여 균열을 인식한다. 균열 정보 획득 단계에서는 균열 인식 단계에서 얻은 정보를 통해 균열의 길이, 진행 방향 정보, 그리고 균열의 두께를 계산한다. 균열의 길이 및 진행 방향 정보는 균열 인식 단계에서 얻어진 정보를 통하여 계산하며, 균열 두께 측정은 각 픽셀의 누적 값을 이용하여 계산하는 원형 검출기(Daugman 알고리즘)를 변형하여 사용하였다.

• Smart Structures and Systems
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• 제23권4호
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• pp.373-385
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• 2019

A study concerning the strength of brittle materials is presented in this paper. The failure behavior was investigated examining the plane of the crack after the failure and comparing the results obtained with those deriving from the fracture mechanics theory. Although the proposed methods are valid in general for brittle materials, the experiment was performed on glass because the results are more significant for this. Glass elements of various sizes and different edge finishes were subjected to bending tests until collapsing. The bending results were studied in terms of failure load and energy dissipation, and the fracture surfaces were examined by means of microscopic analysis, in which the depth of the flaw and the mirror radius of the fracture were measured and the strength was calculated. These results agreed with those obtained from the fracture mechanics analysis.

• 한국초전도ㆍ저온공학회논문지
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• 제12권2호
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• pp.5-8
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• 2010

In this study, the effect of bending strain on the transport property and critical current of lap and butt-jointed (non-laminated) BSCCO tapes has been investigated. The samples were joined using a mechanically controlled jointing procedure. To achieve a uniform thickness at the joint a single point loading contact has been devised. GFRP mandrels with different bending radii which support the sample during bending have been used. $I_c$ have been measured at 77 K and self field. In the case of easy bending test for jointed BSCCO tapes, sudden degradation of $I_c$ is caused by the local strain concentration due to non uniform deformation at the edge parts of the joint. In the case of hard bending test of jointed BSCCO tapes transverse macroscopic crack at specific subsection caused a large $I_c$ degradation. The transport property of jointed BSCCO tapes in each bending mode was discussed with the damage morphology occurred.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2022년도 추계학술발표대회
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• pp.881-883
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• 2022

고객사에 납품하는 웨이퍼의 안정적인 공급을 위한 웨이퍼 엣지의 결함 검출 장비다. 본 연구에서는 OpenCV와 임베디드 시스템, 머신러닝, 전자 회로 그리고 센서/카메라 기술을 핵심 기술로 R&D 한다. 고객사에서 불량 웨이퍼 발생에 대응하기 위한 장비의 데이터를 생산하여 고객과의 신뢰도 향상 및 유지를 할 수 있다. 그리고 결함이 특정 공정 지점에서 발생하는지 탐색할 수 있다.

• 마이크로전자및패키징학회지
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• 제24권1호
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• pp.103-111
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• 2017

본 연구에서는 전동차의 전력 변환 장치로 많이 사용되고 있는 고전압 대전류용(3,300 V/1200 A급) insulated gate bipolar transistor(IGBT) 모듈에 대하여 열 사이클 조건하에서의 열-기계적 응력해석 및 피로수명해석을 수행하였다. 특히 최근 고전압 IGBT용으로 개발되고 있는 구리(copper) 와이어, 리본(ribbon) 와이어를 사용하였을 경우의 응력 및 피로수명을 기존의 알루미늄 와이어와 비교하여 분석하였다. 알루미늄 와이어 보다는 구리 와이어에 응력이 3배 이상 많이 발생하였다. 리본 와이어의 경우 원형 와이어 보다 응력이 더 크게 발생하며, 구리 리본 와이어의 응력이 제일 높았다. 칩과 direct bond copper(DBC)를 접합하고 있는 칩 솔더부의 피로해석을 수행한 결과, 솔더의 크랙은 주로 솔더의 모서리에서 발생하였다. 원형 와이어를 사용할 경우 솔더의 크랙은 약 35,000 사이클에서 발생하기 시작하였으며, 알루미늄 와이어 보다는 구리 와이어에서의 크랙의 발생 면적이 더 컸다. 반면 리본 와이어를 사용하였을 경우 크랙의 면적은 원형 와이어를 사용하였을 경우보다 적음을 알 수 있다. DBC와 베이스 플레이트 사이에 존재하는 솔더의 경우 크랙의 성장 속도는 와이어의 재질이나 형태에 관계없이 비슷하였다. 그러나 칩 솔더에 비하여 크랙의 발생이 일찍 시작하며, 40,000 사이클이 되면 전체 솔더의 반 이상이 파괴됨을 알 수 있었다. 따라서 칩 솔더 보다는 DBC와 베이스 플레이트 사이에 존재하는 솔더의 신뢰성이 더 큰 문제가 될 것으로 판단된다.

• 터널과지하공간
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• 제29권3호
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• pp.184-196
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• 2019

본 연구에서는 화강암 시편에서 수압 파쇄법에 의해 생성된 미세균열의 3차원 형상을 X-ray CT 영상과 딥러닝을 이용하여 추출하였다. 실험으로 생성된 미세균열은 X-ray CT 영상 상에서 일반적인 영상처리방법으로는 추출하기 매우 어렵고 육안으로만 관찰이 가능한 형태를 지닌다. 하지만 본 연구에서 제안한 합성곱 신경망(Convolutional neural network) 기반 인코더-디코더(Encoder-Decoder) 구조의 딥러닝 모델을 통해 미세균열을 정량적으로 추출할 수 있었다. 특히 픽셀 단위의 미세균열 추출을 위해 인코딩 과정에서 소실되는 정보를 디코딩 과정으로 직접 전달하는 디코더 모델을 제안하였다. 또한, 딥러닝 기반 신경망 학습에 필요한 데이터의 수를 증가시키기 위해 이미지의 분할(Division), 회전(Rotation), 그리고 반전(Flipping) 등으로 데이터를 생성하는 영상 증대 방법을 적용하였으며 이때 최적의 조합을 확인하였다. 최적의 영상 학습 데이터 증대 방법을 적용하였을 때 검증 데이터뿐만 아니라 테스트 데이터에서의 성능 향상을 확인하였다. 학습 데이터의 원본 개수가 딥러닝 기반 신경망의 균열 추출 성능에 미치는 영향을 확인하고 딥러닝 기술을 사용하여 성공적으로 미세균열을 추출하였다.

• Journal of Mechanical Science and Technology
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• 제18권5호
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• pp.770-779
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• 2004

This paper describes the micro cutting of wear resistant tungsten carbides using PCD (Poly-Crystalline Diamond) cutting tools in performance with SEM (Scanning Electron Microscope) direct observation method. Turning experiments were also carried out on this alloy (V50) using a PCD cutting tool. One of the purposes of this study is to describe clearly the cutting mechanism of tungsten carbides and the behavior of WC particles in the deformation zone in orthogonal micro cutting. Other purposes are to achieve a systematic understanding of machining characteristics and the effects of machining parameters on cutting force, machined surface and tool wear rates by the outer turning of this alloy carried out using the PCD cutting tool during these various cutting conditions. A summary of the results are as follows: (1) From the SEM direct observation in cutting the tungsten carbide, WC particles are broken and come into contact with the tool edge directly. This causes tool wear in which portions scrape the tool in a strong manner. (2) There are two chip formation types. One is where the shear angle is comparatively small and the crack of the shear plane becomes wide. The other is a type where the shear angle is above 45 degrees and the crack of the shear plane does not widen. These differences are caused by the stress condition which gives rise to the friction at the shear plane. (3) The thrust cutting forces tend to increase more rapidly than the principal forces, as the depth of cut and the cutting speed are increased preferably in the orthogonal micro cutting. (4) The tool wear on the flank face was larger than that on the rake face in the orthogonal micro cutting. (5) Three components of cutting force in the conventional turning experiments were different in balance from ordinary cutting such as the cutting of steel or cast iron. Those expressed a large value of thrust force, principal force, and feed force. (6) From the viewpoint of high efficient cutting found within this research, a proper cutting speed was 15 m/min and a proper feed rate was 0.1 mm/rev. In this case, it was found that the tool life of a PCD tool was limited to a distance of approximately 230 m. (7) When the depth of cut was 0.1 mm, there was no influence of the feed rate on the feed force. The feed force tended to decrease, as the cutting distance was long, because the tool was worn and the tool edge retreated. (8) The main tool wear of a PCD tool in this research was due to the flank wear within the maximum value of $V_{max}$ being about 260 $\mu\textrm{m}$.

• Geomechanics and Engineering
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• 제15권2호
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• pp.721-728
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• 2018

The surrounding rock mass contains cracks and joints which are distributed randomly around tunnels, and in the process of tunnel blasting excavation, radial cracks could also be induced in the surrounding rock mass. In order to clearly understand the impact of radial cracks on tunnel stability, tunnel model tests and finite element numerical analysis were implemented in this paper. Two kinds of materials: cement mortar and sandstone, were used to make tunnel models, which were loaded vertically and confined horizontally. The tunnel failure pattern was simulated by using RFPA2D code, and the Tresca stresses and the stress intensity factors were calculated by using ABAQUS code, which were applied to the analysis of tunnel model test results. The numerical results generally agree with the model test results, and the mode II stress intensity factors calculated by ABAQUS code can well explain the model test results. It can be seen that for tunnels with a radial crack emanating from three points on tunnel edge, i.e., the middle point between tunnel spandrel and its top with a dip angle $45^{\circ}$, the tunnel foot with a dip angle $127^{\circ}$, and the tunnel spandrel with $135^{\circ}$ with tunnel wall, the tunnel model strength is about a half of the regular tunnel model strength, and the corresponding tunnel stability decreases largely.

• Journal of Welding and Joining
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• 제34권5호
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• pp.70-76
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• 2016

In this study, Microstructure and tensile properties in arc brazed joints of 1000MPa grade DP steel using Cu-Si insert metal were investigated. The fusion zone was composed of Cu phase which solidified a little Fe and Si. The former phase formed due to dilute the edge of base material by arc, although Fe was not solid solution in Cu at the room temperature. Cu3Si particles formed by crystallization at $1100^{\circ}C$ during faster cooling. After the tensile shear test, there are no differences between the brazed joint efficiencies. The maximum joint efficient was about 37% compared to strength of base metal. It is better than that of arc brazed joint of DP steel using Cu-Sn filler metal. Fracture position of all brazing conditions was in the fusion zone. Crack initiation occurred at three junction point which was a stress singularity point of upper sheet, lower sheet and the fusion zone. And then crack propagated across the fusion zone. The reason why the fracture occurred at fusion zone was that the hardness of fusion zone was lower than that of base material and heat affected zone. The correlation among maximum load and hardness of fusion zone and EST at fractured position was $R^2=0.9338$. Therefore, this means that hardness and EST can have great impact on maximum load.