• 소성∙가공
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• 제6권3호
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• pp.221-226
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• 1997

Chevron crack in cold extrusion has been studied in view of deformation conditions and material characteristics. There is V formed chevron crack is occasionally occurred in core part of shaft by multistage free extrusion. Although many research results were reported and theoretical analyses were accompanied, in this study we discussed practical method to prevent chevron crack in the field of working conditions and material characteristics. We have found that chevron crack is eliminated under condition of high hydrostatic state in deformation and decreased segregation, refinement of micro structure of materials.

• Journal of Welding and Joining
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• 제13권2호
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• pp.82-95
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• 1995

This paper discusses distribution of thermal stress, strain at near the joint and investigates the reliability of solder joints of electronic devices on a printed circuit board. As Electronic devices are composed of different materials, thermal stresses generate at near the interface, such as solder joints and interface between lC device and lead frame pad due to the differences of thermal expansion coefficients, As results of thermal stress, strain, micro crack often occurs thermal fatigue fracture at the interface of different materials, The initiation and propagation of micro crack depend on the environmental conditions, such as storage temperature and thermal cycling. Finally, this paper experimentally shows a way to suppress micro cracks by using Fe-Ni alloy clad lead frame, and investigates crack and thermal fatigue fracture of TSOP(Thin small outline package) type on printed circuit board.

• 대한기계학회논문집
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• 제9권5호
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• pp.564-571
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• 1985

본 논문에서는 미시조직인자를 변화시킨 마르텐사이트-페라이트 복합조직강을 준비하여 균열선단 및 안정영역의 파괴양상과 파괴저항과의 관계를 검토하였다.

• 반도체디스플레이기술학회지
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• 제15권3호
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• pp.6-11
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• 2016

Silicon wafer is one of main materials in solar cell. Micro-cracks in silicon wafer are one of reasons to decrease efficiency of energy transformation. They couldn't be observed by human eye. Also, their shape is not only various but also complicated. Accordingly, their shape classification is absolutely needed for manufacturing process quality and its feedback. The performance of typical classification techniques which is principal component analysis(PCA), neural network, fusion model to integrate PCA with neural network, and support vector machine(SVM), are evaluated using pattern features of micro-cracks. As a result, it has been confirmed that the SVM gives good results in micro-crack classification.

• 콘크리트학회논문집
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• 제19권6호
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• pp.707-715
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• 2007

다공질성 특성을 갖는 콘크리트는 충분한 다짐과 양생 조건에서 장수명을 갖으며, 유해 물질의 주요 경로는 공극이다. 그러나 균열이 발생한 콘크리트의 경우, 균열은 염소이온과 같은 유해 물질의 우선적인 침투 경로가 된다. 균열이 염소에 미치는 영향은 균열폭과 균열 깊이의 크기에 의존한다. 본 연구는 미세균열이 콘크리트의 염소이온 침투에 미치는 영향을 다룬 실험적 연구로서, 연구 목적은 균열폭과 균열 깊이 등의 균열 크기 효과가 염소이온에 미치는 영향을 고찰하는 것이다. 균열을 통한 염소이온의 침투를 시각화 하기 위하여, 급속 염소이온 침투 실험인 RCM (rapid chloride migration) 실험을 수행하였다. 균열폭과 균열 깊이는 전자 현미경으로 관찰하였고, 평균적인 균열폭을 산정하기 위하여 균열 개구 변위가 측정되었다. 다양한 균열 크기에 따른 염소이온의 침투 깊이 및 염소이온 확산계수의 변화율로부터 염소이온이 침투되지 않는 균열 깊이 및 이에 대응한 균열폭이 도출되었다.

• 대한기계학회논문집
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• 제11권6호
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• pp.953-962
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• 1987

본 연구에서는 국산 구조용강의 SM 45C 와 SUS 304 재를 최고 강도치가 나타 나는 압접조건하에서 압접하여 우재료의 용착금속부, 열영향부, 각 모재부 소정의 장 소에 미소원공을 가공한 시험편을 토대로 피로크랙의 발생 및 전파거동을 응력 레벨의 고저를 고려하여 고찰하였다.

• 콘크리트학회논문집
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• 제12권3호
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• pp.39-46
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• 2000

This study is to investigate the watertightness properties of waterproofing admixture mixed redispersible polymer and siliceous powder. Series I deals with change in micro-structure of mortar by waterproofing admixture according to the water/cement ratios of 0.5, 0.6, 0.7 and 0.8 Crystal growth in micro-structure was observed through SEM to estimate on the watertightness effect of it. SeriesII deals with watertightness properties of waterproofing admixture on water permeability coefficient, crack restoration capacity and carbonation depth. SeriesII deals with watertightness properties of waterproofing admixture on water permeability coefficient, crack restoration capacity and carbonation depth. The result of this study can be summarized as follows. 1) Fluidity of mortar and concrete was increased by adding waterproofing admixture. 2) From observation through SEM. Crystals grew larger and denser in micro-structure as fiberic crystalization. 3) Waterproofing admixture is good watertightness properties in a level of high water/cement ratios and long limit of time. 4) Crack restoration capacity was appeared and durability was progressed by waterproofing admixture.

• 한국정밀공학회지
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• 제12권2호
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• pp.5-13
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• 1995

Various techniques to measure fracture toughness which is an important parameter to predict fracture behavious of structural materials have been reported. Among these mathods, this paper describes the micro-Vickers indentation crack method to estimate the fracture toughness of some WC-Co composites. Two indentation crack patterns (such as radial-median cracks (orhalf-penny cracks) and Palmqvist cracks generated during indentation) are referred precisely. The fracture toughness of WC-4.7wt%Co, WC-6wr%Co and WE-9wr%Co composites were estimated by using some equations given by Shetty et al., Nihara et al. in this study. We show the reliability of indentation method by comparing the results with those from literatures. The appropriate equation to estimate the fracture toughness in the case of WC-Co composite is given. In addition, some technical informations in terms of the crack length by indentation in estimating the existence of the surface residual stress that prevents to obtain an accurate fracture toughness are presented.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.535-538
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• 2005

The problem of the crack which occures from the reinforced concrete structure. could be caused by the complexed factors. When the crack happen, it caused fatal blemish to manage and maintain the structure such as structural problem, licking, spalling, viewing Even though they study and work hard to solve this kind of problem in the world, there are no countermeasure for perfect prevention of crack. After the crack checked out, a method of repair-reinforcement has been sutdied and operated actively. In this experiment, studied durability of repair material. Experiment wave and durability of epoxy and urethane's were shown good result, and micro cement's durability displayed result that is not good. Result of a repeat tired experiment displayed result that micro cement is bad.

• 오토저널
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• 제13권1호
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• pp.57-65
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• 1991

It is experimented under rotary bending stress that the spacing of two micro hole flaws is adjacent and that it is distant. In order to observe the behavior of fatigue crack propagation, two kinds of specimens are tested under constant stress and periodic overstressing. Although the crack occurs faster when two micro-hole flaws are adjacent than when they are distant, but there is no difference of the number of fracture cycles between two. The crack propagates slower under low-high block stress than under high-constant stress, and it propagates faster under high-low block stress than under low-constant stress. The influence of two-step block stress is serious right after the stress varies.