• Polymer(Korea)
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• v.26 no.2
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• pp.270-278
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• 2002

In this study, the fracture behavior by low velocity impact damage and the tendencies of impact energy absorption were investigated. Low velocity impact tests were performed using a mini tower drop weight impact tester, and graphite powder, carbon black and milled carton fiber were chosen as additives. Addition of graphite powder increased the maximum load and maintained the stress long until the total penetration happened. At the content of 9 vol%, they showed the maximum of 42% improvement in impact strength compared composites containing no additives. At the test with low impact energy of 0.4 J, impact energy was consumed by delamination in the composite containing no additives, however, as graphite contents increased, the tendency of failure changed to the penetration of the specimen.

• Magazine of the Korea Concrete Institute
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• v.9 no.3
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• pp.179-187
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• 1997

콘크리트는 여러 구성 성분들이 불규칙적인 배열을 이루어 형성된 복합재료이지만, 과거에는 이 재료를 하나의 단종재료로 간주하여 해석하였기 때문에, LEFM에서 사용되는 파괴인성계수만으로는 콘크리트의 파괴역학적 접근이 어렵다는 것 이외에는 파괴인성계수들의 크기의존성에 대한 이유라든가, 실험을 통해서 관측된 구조물 두께 방향으로의 서로 다른 깊이의 균열 진행 현상에 대해서는 설명하기가 어려웠다. 따라서 본 연구는 콘크리트를 하나의 복합재료로써 각각의 구성요소들이 차지하고 있는 체적비 및 배열상의 효과를 고려하여 복합재료의 파괴거동을 해석하고, 구성재료의 수와 파괴인성계수와의 상관관계를 분석하였다. 각각의 구성요소들을 연립변형모드( SD mode)로 배열시킨 조건에서 복합재료역학개념에 입각하여 해석한 결과, 일반적으로 실험이나 비선형파괴역학 해석과 같이 하중-변위곡선 상단부에서 비선형 거동이 관측되었다. 또한 임계응력확대계수( $K_IC$)나 파괴에너지($G_r$)는 구성원의 수나 보의 크기에 대해서 거의 무관한 값을 나타내지만, 임계군열선단개구변위 ($CTOD_c$)는 크기에 영향을 받음을 보여 주었다. 균열의 진행속도는 균열이 진행될수록 감소하며, 파괴인성이 작은 구성원에서부터 균열이 발생되어 결과적으로 보의 두께 방향으로 서로 다른 크기의 균열길이가 생성됨이 관측되었다.

• Journal of Energy Engineering
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• v.22 no.4
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• pp.327-332
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• 2013

일본 연구에서는 열충격 시험을 통한 태양전지의 파괴모드에 따른 전기적 특성을 분석하였다. 시편은 Photovoltaic Module을 만들기 전 3 line Ribbon을 Tabbing한 단결정 Solar Cell을 제작하였다. 열충격 시험 Test 1의 온도조건은 저온 $-40^{\circ}C$, 고온 $85^{\circ}C$, Test 2는 저온 $-40^{\circ}C$, 고온 $120^{\circ}C$에서 Ramping Time을 포함하여 각각 15분씩, 총 30분을 1사이클로 500사이클을 각각의 조건으로 수행하였다. 열충격 시험 후 Test 1에서는 4.0%의 효율 감소율과 1.5%의 Fill Factor 감소율을 확인하였으며, Test 2에서는 24.5%의 효율 감소율과 11.8%의 Fill Factor 감소율을 확인하였다. EL(Electroluminescence)촬영 및 단면을 분석한 결과, Test 1과 Test 2 시편 모두 Cell 표면 및 내부에서의 Crack이 발견되었다. 하지만, Test 2의 시험이 Test 1보다 가혹한 온도조건의 시험으로 인해 Test 1에서 나타나지 않았던, Cell 파괴를 Test 2에서 확인하였다. 결국, Test 1에서 효율의 직접적인 감소 원인은 Cell 내부에서의 Crack이며, Test 2에서는 Cell 내부에서의 Crack 및 Cell 파괴로 인한 Cell 자체의 성능저하로 효율이 크게 감소한다는 것을 본 실험을 통하여 규명하였다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.92-100
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• 2015

The aim of this study is to evaluate the fracture characteristics of ductile fiber reinforced cement based composites with 1.5 volume ratio of polyvinyl alcohol and steel fiber by high velocity impact of steel projectile. We used gunpowder impact facility to evaluate the fracture characteristics of ductile fiber reinforced cement based composites by collision of steel projectile, and the impact velocity was from about 150 to 1,000m/s. The results of evaluation on the fracture characteristics of ductile fiber reinforced cement based composites were penetration grade, which is the kinetic energy more than three times of no-fiber reinforced specimen (Plain). In addition, ductile fiber reinforced cement based composites did not occurred critical damage other than the debris. In the case of mass loss, Plain specimen was proportional to kinetic energy of steel projectile, while ductile fiber reinforced cement based composites was not significantly affected by kinetic energy of steel projectile. In particular, this tendency had a close relationship with the fracture characteristics of back side of specimens, and the scabbing inhibiting efficiency of PVA specimen was higher than S specimen. In the results of verifying relationship between front and back side calculated by local damage, scabbing occurred at the region close to the back side in the ductile fiber reinforced cement based composites unlike Plain specimen. Thus, in this study, we examined principal fracture behaviors of ductile fiber reinforced cement based composites under collision of steel projectile, and verified that impact resistance performance was improved as compared to Plain specimen.

• The Journal of Engineering Geology
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• v.32 no.4
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• pp.597-610
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• 2022

Knowledge of the failure behavior of friction materials considering their intermediate principal stress is related to an understanding of situations where these materials might be used: for example, the stability of deep-seated boreholes and fault slip analysis. This study designed equipment for physically implementing true triaxial compression and used it to assess specimens of plaster, a friction material. The material's mechanical behaviors are discussed based on the results. The applicability of the 3D failure criteria are also reviewed. The tested specimens were molded cuboids of width, length, and height 52, 52, and 104 mm, respectively. A total of 24 true triaxial compression tests were performed under various combinations of 𝜎₃ and 𝜎₂ conditions. Conventional uniaxial and triaxial compression tests were employed to estimate the mechanical properties of the plaster for use as parameters for 3D failure criteria. Examining the stress-strain relations of the plaster materials showed that a large difference between the intermediate principal stress and the minimum principal stress indicated strong brittle behavior. The mechanical behavior of the plaster used here reflects the change of intermediate principal stress. Nonlinear multiple regression analysis on the test data in the principal space showed that the modified Wiebols-Cook failure criterion and the modified Lade failure criterion were the most suitable 3D failure criteria for the tested plaster.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1993.05a
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• pp.15-19
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• 1993

지구의 환경 문제는 국제적으로 점차 그 중요성이 증대되고 있다. 지구에 인류가 존재하는 한 환경은 오염될 수밖에 없으며 그 결과 지구 생태계의 커다란 변화가 다가올 것이라는 것은 주지의 사실이다. 따라서 지구 환경의 보존을 위해 에너지 이용 효율성을 제고해야 하며, 청정 에너지의 개발, 사용으로 온실 효과의 주범인 $CO_2$ 발생량을 줄이기 위해 화석 연료의 사용을 억제할 수 있는 대책과 화석 연소로부터 발생되는 NO$_{x}$ 나 SO$_{x}$ 등에 의한 산성비로 생태계의 파괴를 막을 수 있는 청정 에너지의 개발을 위한 사회, 환경적인 정책적 제도 도입이 활발히 진행되고 있다. (중략)

• Journal of the Korean Society of Safety
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• v.12 no.4
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• pp.249-256
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• 1997

1973년 OPEC가 원유 수출을 규제하면서 일어난 석유 위기는 국내는 물론 세계에 큰 충격을 주었다. 더욱 석유, 석탄 등의 화석연료 중 석유자원의 고갈에 대한 불안과 화석연료의 연소로 인한 대기오염, 환경파괴에 대한 불안이 증대되었다. 이를 계기로 화석연료를 대신하는 새로운 에너지 자원의 개발과 효율적인 에너지 이용시스템의 개발이 세계 각국에서 착실히 진행되었다. 즉, 에너지 정세의 변화, 지구 환경문제의 대응, 새로운 에너지 기술개발 대책은 절대적으로 필요하고, 21세기의 장기 전망에서 보면, 에너지 문제는 매우 심각한 사태라는 것은 의심할 여지가 없다.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.1
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• pp.39-47
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• 2007

It is investigated how KOH and Rthylenediamine(EDA) treatment conditions on Polyimide film surface affect the interfacial fracture energy between electroless plated Ni and Polyimide film by $180^{\circ}$ peel test. Estimated values of interfacial fracture energy were 24.5 g/mm and 33.3 g/mm for the KOH treatment times under 1 and 5 minutes, respectively, while, those were 31.6 g/mm and 22.3 g/mm for EDA treatment times under 1 and 5 minutes, respectively. Interfacial bonding between electroless plated Ni and Polyimide seems to be dominated by chemical bonding effect rather than mechanical interlocking effect. It is found that chemical treatment produces carboxyl and mine functional groups which are closely related the interfacial bonding mechanism. Finally, it is speculated that interfacial fracture energy seems to be controlled by O=C-O bonding near cohesive failure region.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.1
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• pp.359-368
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• 1996

For fuel economy and pollutant reduction, the interests in lean burn has increased recently. The purpose of this research is to develop a High Frequency Ignition System (HIS) that can make powerful ignition. We studied relations between performance of HIS and probability of inflammation under various ignition conditions. It is concluded that the portion of capacitance energy to the total energy is comparatively larger and that the optimum spark interval and spark duration are dependent upon conditions of Constant Volume Combustion Chamber.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.4
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• pp.47-52
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• 2008

Important factor in designing a breakaway sign support is the velocity change of the impact vehicle. It is measured from the crash test or can be calculated by 3-D Finite Element Analysis. It can also be calculated with relative ease utilizing energy and momentum conservation. In this paper a formula to calculate the velocity change of a car during the time of impact against a small sign is derived utilizing the energy and momentum balance. Using the formula, parametric studies were conducted to find that impact speed, separation force and Breakaway Fracture Energy(BFE) of the posts which represent the degree of fixedness to the foundation are the important factor to vehicle's speed change. It is shown that speed change is larger in the lower speed impact and to the posts with large separation force and BFE.