• Proceedings of the Korean Information Science Society Conference
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• 2004.10a
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• pp.646-648
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• 2004

네트워크 기반 컴퓨터 시스템이 각종 악의적 공격에 의해 손상되더라도, 지속적인 서비스를 제공할 수 있게 해주는 침입 감내시스템(Intrusion Tolerance Systems) 설계기법의 중요한 요소 기술 중의 하나는 컴퓨터 시스템의 정량적 신인도(Dependability) 분석이라 할 수 있다. 본 논문에서는 침입 감내시스템의 신인도를 분석하기 위해 자율컴퓨팅(Autonomous Computing)의 핵심 기술인 자가 치유(Self-healing) 메커니즘을 적용하였다. 즉, 주 서버와 보조서버로 구성된 이중계 침입 감내시스템의 상태천이(State Transition)를 자가치유 메커니즘의 두 가지 요소(결함모델 및 시스템반응)를 활용하여 분석하였으며, 시뮬레이션 실험을 통해 침입 감내시스템의 가용도(Availability)를 정량적으로 정의하였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.11a
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• pp.29-29
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• 2007

본 연구에서는 분산강화 스테인리스강을 이용하여 케비테이션 발생 시 고체입자충격에 의한 재료의 침식메커니즘 및 침식저항성을 고찰하고자 하였다. 케비테이션 시간에 따른 침식저항성 측정결과, 기존재료에 비해 분산강화된 시편의 무게손실량이 낮았으며 침식잠복기가 짧고 침식속도가 낮아 전반적으로 우수한 저항성을 보였다. 이것은 침식표면의 손상메커니즘 관찰을 통해 확인할 수 있었다.

• The Journal of the Korea institute of electronic communication sciences
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• v.19 no.4
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• pp.669-676
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• 2024

This study aims to evaluate battery damage and heat transfer mechanisms through fire tests on lithium-ion batteries, and to explore ways to improve the efficiency and safety of battery management systems (BMS). Temperature changes in each sector are measured at points T1, T2, and T3 observing and recording the reactions of surrounding cells for 10 minutes after applying electricity to the ignition electrode. The results show that the batteries in sectors A and B fully ignite, causing severe physical damage, while the batteries in sector C do not ignite and sustain minimal damage. This confirms that the distance between sectors plays a crucial role in reducing ignition and heat propagation. The study suggests that considering the distance between sectors in the design of thermal management systems for lithium-ion batteries can significantly mitigate ignition and heat spread. Future experiments with various battery models and conditions will further propose the ways to enhance the efficiency and safety of BMS.

• Journal of the KSME
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• v.52 no.7
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• pp.45-49
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• 2012

폴리머 재료들이 포함된 전자 패키지의 신뢰성 문제는 습기의 영향이 매우 크다. 습기와 연관된 파손을 분석하기 위해서는 폴리머 재료들의 흡습 특성을 측정하는 것이 매우 중요하며, 습기 확산 메커니즘 및 폴리머의 손상과 접착력 저하에 대한 엄밀한 연구가 필요하다.

• Tunnel and Underground Space
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• v.16 no.6 s.65
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• pp.476-485
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• 2006

During blasting, both shock wave and gas are generated in detonation process of explosives and the generated wave and gas expansion may create new fractures and damage rock mass. In order to explain and understand completely the fracture mechanism by blasting, we have to consider both effects of the wave and gas expansion simultaneously. In this study, we use a discrete element code, PFC2D and develop an algorithm which is capable of modeling both detonation and gas pressures acting on blasthole wall and visualizing generated cracks within rock mass. Moreover, the gas-pressure modeling method which applies a corresponding external force of gas pressure to parent particles of radial fractures is adopted to simulate a coopting between rock mass and gas penetrating created radial fractures. The developed algorithm is verified by reproducing numerical simulations of a lab-scale test blast successfully.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.10
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• pp.856-865
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• 2008

Damage mechanisms in bending piezoelectric actuators under electric fatigue loading are addressed in this work with the aid of an acoustic emission (AE) technique. Electric cyclic fatigue tests have been performed up to $10^7$ cycles on the fabricated bending piezoelectric actuators. An applied electric loading range is from -6 kV/cm to +6 kV/cm, which is below the coercive field strength of the PZT ceramic. To confirm the fatigue damage onset and its pathway, the source location and distributions of the AE behavior in terms of count rate and amplitude are analyzed over the fatigue range. It is concluded that electric cyclic loading leads to fatigue damages such as transgranular damages and intergranular cracking in the surface of the PZT ceramic layer, and intergranular cracking even develops into the PZ inner layer, thereby degrading the displacement performance. However, this fatigue damage and cracking do not cause the final failure of the bending piezoelectric actuator loaded up to $10^7$ cycles. Investigations of the AE behavior and the linear AE source location reveal that the onset time of the fatigue damage varies considerably depending on the existence of a glass-epoxy protecting layer.

• Journal of the Korea Concrete Institute
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• v.21 no.4
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• pp.457-464
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• 2009

Fiber is an important ingredient in fiber-reinforced cement composite (FRCC) which can control fracture of cement composite by bridging action. In compliance with the action of the fiber and the aggregate size, it also showed a different failure mechanism. For practical application, it is needed to investigate the fracture behavior of the FRCC and to understand the micro-mechanism of cement matrix with reinforcing fiber. In order to evaluate a characteristics of fracture process in the FRCC, acoustic emission (AE) technique was used for the analysis and evaluation of FRCC damage by acoustic emission under flexural and cyclic compressive loadings. The AE signals were monitored by AMSY4 AE instrument during the entire loading period. The specimens are reinforced with 0, 1.0, 1.5 and 2.0% (by volume) Polyvinyl alcohol (PVA) fiber. The test results showed that the damage progress of the FRCC was characteristic for the fiber replacement ratio. As a result of analyzing the felicity ratio (FR) values, it is shown that this values can be used for evaluating the degree of FRCC damage. On the whole the felicity ratio values of FRCC are shown between 0.4 and 1.1. And, the AE kaiser effect was shown in the all FRCC specimen. In addition, the damage behavior and the microscopic fracture process of the FRCC are evaluated using the AE parameters, such as calm ratio, b-value and felicity ratio. The purpose of this reserch was to advance the state of knowledge regarding the applicability of acoustic emission as an evaluation method for FRCC.

• Composites Research
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• v.24 no.4
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• pp.36-40
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• 2011

This paper described analysis of acoustic emission parameter for the damage evaluation of type II vehicle fuel tank during fracture test. The observation of Kaiser effect, Felicity effect and creep effect is the means of damage evaluation method. It is possible to evaluate tank damage by the ratio of hit of over 60 dB and total hit. Damage mechanism of pressure tank can be estimated by analysis of average rise time, average amplitude.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.391-398
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• 2016

Acoustic emission (AE) is one of the most powerful techniques for detecting damages and identify damage location during operations. However, in case of the source location technique, there is some limitation in conventional AE technology, because it strongly depends on wave speed in the corresponding structures having heterogeneous composite materials. A compressed natural gas(CNG) pressure vessel is usually made of carbon fiber composite outside of vessel for the purpose of strengthening. In this type of composite material, locating impact damage sources exactly using conventional time arrival method is difficult. To overcome this limitation, this study applied the previously developed Contour D/B map technique to four types of CNG storage tanks to identify the source location of damages caused by external shock. The results of the identification of the source location for different types were compared.

• Journal of Conservation Science
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• v.36 no.5
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• pp.368-382
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• 2020

It was confirmed that a white porcelain figurine in underglaze iron was damaged after exhibition. This study analyzes the current state of salt damage on the artifact and identifies the factors contributing to its deterioration by examining the material characteristics of the artifact and exhibition environment. The analysis will thus assist in preparing a conservation scheme for artifacts. The crystallized carbonate on the surface of the white porcelain figurine is a water-soluble alkali salt with high hygroscopicity and high solubility in water. This solubility increases as the temperature increases. The figurine was low-fired at approximately 1000℃. A lead glaze was applied, and thin cracks were formed on the glazed surface, indicating poor surface properties. Our analysis suggested that the showcase used in the exhibition likely created a moist environment resulting from condensation, as it was exposed to high temperature and relative humidity, particularly in comparison to the exhibition room where the temperature was regulated using an air conditioner. In addition, the artifacts in the showcase were exposed to sudden changes in temperature and relative humidity as the air conditioner was repeatedly turned on and off. Therefore, it can be deduced that the soluble salt remaining on the white porcelain figurine moved toward the surface of the relatively weak glaze as a result of the temperature, and the crystallized salt exacerbated surface damage as the moisture evaporated in a dry environment.