• Applied Chemistry for Engineering
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• v.21 no.2
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• pp.205-210
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• 2010

In this study, a brass electrode gas discharge tube (GDT) was prepared to investigate its discharge characterization, which affects surge protection efficiency and lifetime of GDT. Discharge characterization of GDT using a brass electrode was investigated by changing applied voltage gradient and nitrogen gas pressure inside the GDT. As applied voltage gradient in GDT increased, electrical breakdown voltage and threshold energy largely increased and electrical breakdown time delay decreased. It was found that electrical breakdown voltage, electrical breakdown time delay, and threshold energy were largely decreased with decreasing the nitrogen gas pressure in GDT. As a result, electrical breakdown voltage, electrical breakdown time delay, threshold energy needed to be decreased to increase surge protection efficiency and lifetime. It was also found that the nitrogen gas pressure of GDT influenced strongly the performances as well as life span of it.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.4
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• pp.67-80
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• 1989

This Paper is concerned with the fracture behavoir of Unidirectional Laminate(UD) and the characteristic length of Multidirectional Laminate(MD) around hole under the Uniform Tensial Strain. Two fracture mechanical concepts of the Waddoups-Eisenman-Kaminski(WEK) model based on the Linear Elastic Fracture Mechanics(LEFM) and the Whitney-Nuismer Model based on Point and Average Stress Criteria were applied. The characteristic length of a laminate with a hole is then obtained using the coefficient of stress reduction and the experimental results, and it can be utilized in predicting the stress level at which the specimen will fracture. The results of the fracture characteristics and the strength of the specimens having a hole in the center can be used as the important experimental data in the research branch of the mechanical fastening of laminated structures. The Ultrasonic scanning and the Acoustic Emission(AE) method were utilized in order to find out the initial defects and the fracture behavior, respectively.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.4
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• pp.43-45
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• 2001

For photosensitive and micro-structuring in $Li_2O-A1_2O_3-SiO_2$glasses by laser treatment, Nd:YAG laser in 355 nm and 1064 nm wavelength was irradiated to the glass to investigate fracture characterization and optical changes. The fractured glass surfaces irradiated by 1064 nm laser was observed by Scanning Electron Microscope(SEM) and optical microscope, and optical changes caused by 355 nm later was identified from absorption spectra. In this study, it could be expected that the laser treatment technology will be utilized for 3-dimensional micro-structure, internal waveguide, optical memory by optical absorption changes in glass matrix.

• Proceedings of the KIEE Conference
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• 2006.10a
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• pp.217-219
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• 2006

본 논문은 초고압용 XLPE 케이블의 절연/단도전의 계면특성 향상을 위해 계면활성제 부가를 통한 절연파괴전압 향상에 관한 것으로, 계면구조의 변화와 이에 따른 절연파괴전압의 상관성을 밝히고자 하였다. 이를 위해, 계면확성제의 함량에 따른 절연/반도전 계면에서의 결정 미세구조(라멜라 밀도와 분자배향)를 스침각 X-ray와 TEM분석을 통해 밝히고, 이를 절연파괴 특성과의 상관성을 밝혔다. 연구결과, 사용되는 기저고분자와 첨가제 간의 정합성과 최적의 첨가제 함량이 절연재료의 파괴강도에 큰 영향이 있음을 알 수 있었다. 즉, 과도한 첨가제의 부가로 인하여 계면으로 이동한 계면활성제 간에 인력으로 뭉치게 되고(aggregation), 결국 국부적인 도메인을 형성하여 절연파괴 개시부로 작용할 수 있게 된다. 이를 스침각 X-ray (Gl-SAXS)를 통하여 라멜라 밀도 및 배향을 정량화 할 수 있으며, 이는 XLPE 전력케이블의 반도전 재료의 처방 및 계면특성 정량화 기법으로 유효하게 사용될 수 있을 것이다.

• Tunnel and Underground Space
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• v.19 no.2
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• pp.95-106
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• 2009

Numerical analysis of the progressive failure of a rock slope was conducted using a 3-D rock joint element considering fracture mechanics and subcritical crack growth of asperities in the rock joints. Even though the stress state in the rock slope is not changing, the elapse of time causes subcritical crack growth to break asperities in the joints. The increase of broken asperities causes failure of joints in the rock slope and the increase of failed joints results in failure of a jointed rock slope. As a result, the progressive failure of a jointed rock slope due to the gradual breaking of small asperities along joints generated by subcritical crack growth occurs at a lower stress than if rock failure occurred by exceeding the static strength or fracture toughness.

• Journal of the Korean Wood Science and Technology
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• v.24 no.4
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• pp.64-73
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• 1996

고인성 종이의 탄성-소성 파괴를 파괴역학을 이용하여 분석하였다. 탄성-소성 물질의 파괴에 있어서 균열이 언제 진행되기 시작하는지 이론적 판단 기준을 유도하고, mode I 파괴를 linear image strain analysis(LISA)로 관찰한 후, 파괴역학 변수들을 계산하였다. 크랙(crack)이 있는 물질에 외부하중이 작용할 때 변형율 에너지 발산 속도(strain energy release rate)가 그 물질이 견딜 수 있는 파괴저항(fracture resistance)에 도달하면 안정적인 파괴가 진행된다. 이를 이용하여 크랙의 초기 진행시 결점주위의 응력, 파괴저항, 크랙 진행거리, 기하인자(geometry factor) 등을 구하였다. 이 변수들은 종이의 파괴역학적 특성을 정량적으로 나타내므로 유용하게 활용될 수 있을 것이다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.523-524
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• 2006

본 논문에서는 질소와 이산화탄소를 완충기체로 사용하는 경우의 혼합가스에 대해 가스절연설비 내부의 이물질에 의한 절연파괴특성을 모의하기 위한 침-평판 전극구조에서의 침전극 재질을 연철, 고탄소강, 스테인레스강 등으로 구성한 경우 혼합가스의 절연파괴 특성에서 나타나는 전극 재질에 의한 영향을 실험적으로 검토해 보았다. 실험 결과 연철제 전극과 고탄소강제 전극의경우에는 혼합가스의 절연파괴특성에서 유사한 N-특성이 나타남을 확인할 수 있었으나 스테인레스 강제 전극의 경우에는 다소 상이한 양상이 나타났다. $SF_6$계 혼합가스의 경우에는 순 $SF_6$의 경우와 동일하게 코로나 안정화작용에 의한 N-특성이 발현됨이 일반적인 특성으로 알려져 있으나 본 실험 결과에 의하면 침전극 재질에 따라 다소 상이한 양상이 나타날 수 있음을 관측하였다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.5
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• pp.469-485
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• 2016

The failure of rock mass around deep tunnel, different from shallow tunnel largely affected by discontinuities, is dominated by magnitudes and directions of stresses, and the failures dominated by stresses can be divided into ductile and brittle features according to the conditions of stresses and the characteristics of rock mass. It is important to know the range and the depth of the V-shaped notch type failure resulted from the brittle failure, such as spalling, slabbing and rock burst, because they are the main factors for the design of excavation and support of deep tunnels. The main features of brittle failure are that it consists of cohesion loss and friction mobilization according to the stress condition, and is progressive. In this paper, a three-dimensional numerical model has been developed in order to simulate the brittle behavior of rock mass around deep tunnel by introducing the bi-linear failure envelope cut off, elastic-elastoplastic coupling and gradual spread of elastoplastic regions. By performing a series of numerical analyses, it is shown that the depths of failure estimated by this model coincide with an empirical relation from a case study.

• Journal of the Korea Concrete Institute
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• v.18 no.3 s.93
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• pp.439-445
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• 2006

For investigating self-diagnosis applicability, a method based on monitoring the changes in the electrical resistance of hybrid FRP(having electrical property) reinforced concrete has been tested. Then after examining change in the value of electrical resistance of carbon fiber in CFRP(non-hybrid type), CFGFRP and CFAFRP(hybrid type) before and after the occurrence of cracks and fracture in non-hybrid and hybrid FRP reinforced concrete at each flexural weight-stage, the correlations of each factors(the changes in electrical resistance and load as a function of strain, deflection) were analyzed. As the results, it is clarified that when the carbon fiber tows fracture, the electrical resistance of it increase largely, and afterwards hybrid FRP composites can be resist the load due to the presence of the reinforced fiber, for example, glass fiber or aramid fiber tows. Therefore, it can be recognized that hybrid FRP(including carbon fiber) reinforcing bar could be applied for self-diagnosis of fracture in reinforced FRP concrete fracture.

• Tunnel and Underground Space
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• v.19 no.4
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• pp.304-317
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• 2009

Most crystalline rocks have much higher compressive strength than tensile strength and show brittle failure. In-situ rock mass, strong enough in general sense, often fails in brittle manner when subjected to high stress exceeding strength in due of geometrically induced stress concentration or of high initial stress. Therefore, it is necessary to verify the brittle failure characteristics of rock and rock mass for proper stability assessment of underground structures excavated in great depths. In this study, damage controlled tests were conducted on biotite-granite and granitic gneiss, which are the two major crystalline rock types in Korea, to obtain the strain dependency characteristics of the cohesion and friction angle. A Cohesion-Weakening Friction-Strengthening (CWFS hereafter) model for each rock type was constructed and a series of compression tests were carried out numerically while varying confining pressures. The same tests were also conducted assuming the rock is Mohr-Coulomb material and results were compared.