• 한국신뢰성학회지:신뢰성응용연구
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• 제12권3호
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• pp.177-186
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• 2012

This paper presents a comparison of the failure mechanism for high power converted white LEDs(3W) with the commercially available YAG:Ce and silicate phosphor. We carry out the normal aging life test for 10,000 hours, the high temperature aging test for 8,000 hours, the high temperature and humidity aging test for 8,000 hours and the current aging testing for 5,000 hours. The optical and electrical parameters of LEDs were monitored, such as lumen, correlated color temperature (CCT), chromaticity coordinates(x, y), thermal resistance, I -V curve and spectrum intensity. The stress induced a luminous flux decay on LED in all experiments and causes a failure. So we try to find out what's a main failure mechanism for a high power LED.

• 대한전기학회논문지:전력기술부문A
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• 제54권10호
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• pp.480-486
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• 2005

This paper proposes a method to consider an aging failure probability and survival probability of power system components, though only aging failure probability has been considered in existing mean life calculation. The estimates of the mean and its standard deviation is calculated by using Weibull distribution, and each estimated parameters is obtained from Data Analytic Method (Type H Censoring). The parameter estimation using Data Analytic Method is simpler and faster than the traditional calculation method using gradient descent algorithm. This paper shows calculation procedure of the mean life and its standard deviation by the proposed method and illustrates that the estimated results are close enough to real historical data of combustion turbine generating units in Korean systems. Also, this paper shows the calculation procedures of a probabilistic failure prediction through a stochastic data analysis. Consequently, the proposed methods would be likely to permit that the new deregulated environment forces utilities to reduce overall costs while maintaining an are-related reliability index.

• JSTS:Journal of Semiconductor Technology and Science
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• 제14권1호
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• pp.124-130
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• 2014

In highly reliable and durable systems, failures due to aging might result in catastrophes. Aging monitoring techniques to prevent catastrophes by predicting such a failure are required. This paper presents a scan-based on-line aging monitoring scheme which monitors aging during normal operation and gives an alarm if aging is detected so that the system users take action before a failure occurs. We illustrate our modified scan chain architecture and aging monitoring control method. Experimental results show our simulation results to verify the functions of the proposed scheme.

• Journal of Electrical Engineering and Technology
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• 제9권3호
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• pp.957-963
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• 2014

Converter transformers play important roles in high-voltage direct current transmission systems. This paper presents experimental and analysis results of the combined electrical and thermal aging of oil-impregnated paper at pulsating DC voltages. Breakdown voltages and time-to-breakdown of oil-paper specimens were measured by using short-time and constant-stress tests. The breakdown characteristics of combined electrical and thermal aging on insulation system were discussed. According to the relationship between failure time and aging temperature, the two-parameter Weibull model was improved. On the basis of the competing risk algorithm and the improved Weibull model, the two factors failure model was calculated. And the influence of temperature in the insulation system has been analyzed. This model performs better than the two-parameter Weibull model when both time and temperature are considered as variables in estimating the lifetime of oil-paper insulation.

• 한국산학기술학회논문지
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• 제21권11호
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• pp.595-601
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• 2020

10년 이상 보관된 니트로셀룰로오스 (Nitrocellulose, 니트로셀룰로오스) 재질의 화약용기 안전 검사를 진행하는 과정 중 화약이 보관되어진 용기에 균열이 발생한 것을 확인하여 고장 원인 분석 시험을 실시하였다. 고장이 발생한 데에 영향을 준 요인을 선별하기 위해 먼저 고장수목분석(Fault Tree Analysis, FTA)을 통해 고장 요인 및 원인에 대해 탐구하였으며, 보관 시 발생할 수 있는 내·외부적인 요인 및 환경에 대한 영향성을 확인한 결과 열에 의해 화학 반응이 가속화되어 발생한 화약용기의 물성 변화가 고장의 원인인 것으로 추정하였다. 이를 확인하기 위해 자연 노화된 화약용기를 이용하여 열충격시험, 양립성 시험 등의 환경시험을 수행하여 고장의 원인 분석을 수행하였으며, 가속노화시험을 통해 고장 재현 시험을 실시하였다. 이를 통해 앞선 고장수목분석 결과와 같이 열과 화약에 의해 화학 반응이 가속화되는 것을 확인할 수 있었으며, 화약용기의 물성이 변화하는 것을 확인하였다. 또한, 열 노화에 의한 수명 추정을 위해 아레니우스 모델(Arrhenius Model)을 이용하여 화약용기의 사용 수명을 추정하였다.

• 대한임베디드공학회논문지
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• 제13권3호
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• pp.143-149
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• 2018

It has become ever harder to design reliable circuits with each nanometer technology node; under normal operation conditions, a transistor device can be affected by various aging effects resulting in performance degradation and eventually design failure. The reliability (aging) effect has traditionally been the area of process engineers. However, in the future, even the smallest of variations can slow down a transistor's switching speed, and an aging device may not perform adequately at a very low voltage. Therefore, circuit designers need to consider these reliability effects in the early stages of design to make sure there are enough margins for circuits to function correctly over their entire lifetime. However, such an approach excessively increases the size and power dissipation of a system. As the impact of reliability, new techniques in designing aging-resilient circuits are necessary to reduce the impact of the aging stresses on performance, power, and yield or to predict the failure of a system. Therefore, in this paper, a novel low power on-chip self-tuning circuit considering the aging effects has been proposed.

• Journal of Computing Science and Engineering
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• 제2권2호
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• pp.200-219
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• 2008

The effective management of uncertainty is one of the most fundamental problems in medical decision making. According to the literatures review, most medical decision models rely on point estimates for input parameters. However, it is natural that they should be interested in the relationship between changes in those values and subsequent changes in model output. Therefore, the purpose of this study is to identify the ranges of numerical values for which each option will be most efficient with respect to the input parameters. The Nonhomogeneous Poisson Process(NHPP) was used for describing the behavior of aging chronic diseases. Three kind of failure models (linear, exponential, and power law) were considered, and each of these failure models was studied under the assumptions of unknown scale factor and known aging rate, known scale factor and unknown aging rate, and unknown scale factor and unknown aging rate, respectively. In addition, this study illustrated developed method with an analysis of data from a trial of immunotherapy in the treatment of chronic Granulomatous disease. Finally, the proposed design of Bayesian value of information analysis facilitates the effective use of the computing capability of computers and provides a systematic way to integrate the expert's opinions and the sampling information which will furnish decision makers with valuable support for quality medical decision making.

• The Journal of Advanced Prosthodontics
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• 제7권2호
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• pp.108-114
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• 2015

PURPOSE. The aim of this study was to evaluate effect of different surface treatment methods on the bond strength between aged composite-resin core and luting agent. MATERIALS AND METHODS. Seventy-five resin composites and also seventy-five zirconia ceramic discs were prepared. 60 composite samples were exposed to thermal aging (10,000 cycles, 5 to $55^{\circ}C$) and different surface treatment. All specimens were separated into 5 groups (n=15): 1) Intact specimens 2) Thermal aging-air polishing 3) Thermal aging- Er:YAG laser irradiation 4) Thermal aging- acid etching 5) Thermal-aging. All specimens were bonded to the zirconia discs with resin cement and fixed to universal testing machine and bond strength testing loaded to failure with a crosshead speed of 0.5 mm/min. The fractured surface was classified as adhesive failure, cohesive failure and adhesive-cohesive failure. The bond strength data was statistically compared by the Kruskal-Wallis method complemented by the Bonferroni correction Mann-Whitney U test. The probability level for statistical significance was set at ${\alpha}$=.05. RESULTS. Thermal aging and different surface treatment methods have significant effect on the bond strength between composite-resin cores and luting-agent (P<.05). The mean baseline bond strength values ranged between $7.07{\pm}2.11$ and $26.05{\pm}6.53$ N. The highest bond strength of $26.05{\pm}6.53$ N was obtained with Group 3. Group 5 showed the lowest value of bond strength. CONCLUSION. Appropriate surface treatment method should be applied to aged composite resin cores or aged-composites restorations should be replaced for the optimal bond strength and the clinical success.

• Composites Research
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• 제21권6호
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• pp.23-30
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• 2008

본 논문에서는 자연 노화가 필라멘트 와인딩으로 제작된 압력용기의 강도 분포와 구조 사용 수명에 미치는 영향을 연구하였다. 자연 노화에 따라 변화되는 섬유 방향 파괴 변형률을 설계 확률 변수로 하는 확률 강도 해석을 수행하였다. 이때 확률강도 해석은 정확한 파열 압력을 예측하기 위해 연속 파손 모드가 고려되었고, 비선형 한계식의 해를 구하기 위해 FORM방법이 이용되었다. 해석을 통해 노화 시간별 파괴 확률 분포 선도를 구하였다. 복합재 구조물의 특성상 재료 물성 및 제작 공정 변수 영향으로 제품의 성능 변동성이 비교적 크게 나타났고, 노화로 인한 압력용기의 파열 압력 저하 현상은 대부분 10년 이내에서 발생하였다. 임의 적층의 복합재 압력 용기를 모델로 하여 수명을 평가한 결과, 파괴 확률 2.5%와 안전율 1.3을 고려한 설계 압력 3,250psi기준으로 약 13년의 사용 수명이 평가되었다.

• 한국추진공학회지
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• 제25권3호
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• pp.26-41
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• 2021

Titanium hydride potassium perchlorate (THPP)는 일반적으로 널리 사용되는 착화제로 추진 시스템에서 중요한 역할을 수행해오고 있지만, '노화'라는 현상으로 인하여 THPP의 요구 성능 변화, 심지어는 system failure가 초래될 수 있다. 본 연구에서는 다양한 상대습도 조건에서 노화된 THPP의 열역학적 특성 및 성능, 점화 특성 변화를 상세한 열분석과 점화 실험을 통해 밝혔다. 그리고 형태학적 분석과 조성 변화를 통해 노화에 따른 THPP의 물리·화학적인 변화 또한 확인하였다. 결론적으로, 열노화는 산화제 분해로 인하여 활성화 에너지 감소/반응성 증가로 이어지고 수분노화는 연료 산화로 인하여 활성화 에너지 증가/반응성 감소와 같은 경로를 따름을 최종적으로 확인해볼 수 있었다.