The high-level nuclear waste (HLW) repository is a 500-1,000 m deep geological disposal system with a very long life expectancy for disposing of high-level waste, which is known to have a half-life of several thousand years. This repository is subject to harsh environmental conditions, such as high temperature and radiation from high-level waste, that can cause deterioration and crack. When radiation escapes through cracks, it can injure persons on the ground. Therefore, it is essential to install a sensor that can detect problems such as cracks. But, since the high-level nuclear waste (HLW) repository is sealed with bentonite and backfill, the sensor cannot be removed or replaced once it has been installed. Therefore, it is necessary to develop a highly durable monitoring sensor that can withstand harsh environmental conditions. Before attempting to improve durability, it is first required to assess durability quantitatively. And an accelerated life test is a widely used method for assessing durability. However, it is important to obtain the same failure mode when conducting a reliability test, such as an accelerated life test. If the accelerated life test is conducted using different failure modes, the dependability of the results is inevitably diminished. Therefore, in this study, a representative failure mode for the piezoelectric sensor used in the accelerated life test was derived through experiments and literature research.

The high-level waste disposal system is an underground structure exposed to complex environmental conditions such as high temperature, radiation, and groundwater. The high-level waste disposal causes structural cracks and deterioration over time. However, since the high-level waste disposal system is a structure that should be operated for a very long time, developing a high-durability monitoring sensor to detect cracks and deterioration is essential. The durability of the sensor can be evaluated by predicting the expected life through the accelerated life test, one of the reliability qualification tests. The most important factor in the accelerated life test design is setting the harsh stress level. This study figured out the harsh stress level of the piezoelectric sensor, which is commonly used for underground structure monitoring. It is possible to determine the appropriate stress level for the accelerated life test by investigating the harsh stress level for the temperature factor. It will contribute to more accurate life expectancy prediction.

The high-level nuclear waste disposal system is a structure with a very long life expectancy, and deterioration and cracking of the structure may occur over time. In addition, the high-level nuclear waste disposal system is in complex extreme conditions such as high temperature, groundwater, and radiation. Therefore, we need to develop a highly durable monitoring sensor that can detect the deterioration and crack of structures in extreme conditions. Since the durability of a sensor is closely related to the sensor lifetime, it is essential to predict the sensor lifetime accurately. The sensor lifetime can be predicted through the reliability qualification test. Among them, the accelerated life test conducted under harsh conditions is widely used as a method to shorten the test period. The major factor in carrying out the accelerated life test is to set the appropriate harsh conditions. Therefore, this study experimentally derived the operating limit of the monitoring sensor. It is essential to set the proper harsh conditions when performing the accelerated life test. Through this study, it is judged that it will be helpful in determining the appropriate stress level when performing the accelerated life test for accurate lifetime prediction.

In this study, an accelerated weathering test was performed to examine the variation of thermal insulation performance according to the service life. A widely used class 1 thermal screen (matt georgette + polyethylene (PE) foam + chemical cotton + felt + matt georgette) was selected as the target thermal screen. The ultraviolet irradiation that reached the target thermal screen specimen (60 x 60cm) was 5mW/cm2. Thus, the ultraviolet irradiance was set to 5mW/cm2, and the exposure periods of accelerated weathering conditions on the specimens were set to 0, 282, 847, and 1412h. The radiation exposure periods of the weathering conditions for 0, 282, 847, and 1412h indicate the amount of ultraviolet accumulation for 0, 1, 3, and 5years, respectively. In the accelerated weathering test, the target specimens that completed each exposure phase were subjected to the hotbox test to analyze their thermal insulation performances. Consequently, the thermal insulation performance of the multi-layer thermal screen was estimated to degrade rapidly after approximately two years. In the accelerated weathering condition, a quadratic function model was used to calculate the expected service life, since it adequately described the variation in thermal insulation of the thermal screen according to time. The results showed that when the thermal insulation performance degraded by 5, 10, 20, and 30%, the expected service lives were 2.5, 3.3, 4.5, and 5.5years, respectively.

Universal joint damage occurred during the operation of a combat vehicle. Damage to the internal bushing and cracks of the rubber cover occurred, and a design change was promoted based on the cause analysis and improvement measures. The failure of the bushing is due to the occurrence of expansion due to fatigue load when the rotation proceeds in the presence of the assembly clearance of the cross joint. In addition, cracks in the rubber cover are caused by the deterioration of the intermetallic rubber surface. Through this failure mechanism analysis, severe durability factors were selected and accelerated durability tests were conducted. In this paper, the final limit life of universal joints can be evaluated through accelerated endurance tests. Furthermore, the endurance life of the product before the change and the endurance life of the product after the change are compared to prove the improvement effect through design changes.

The reliability of the lifting system has to be ensured so that heavy cargo is handled safely during loading and unloading. Therefore, the accelerated life test was performed on the lifting bow shackle, which is highly affected by the main failure mode, among the components of the lifting system. Besides, an efficient inspection method was suggested for the preventive maintenance of the bow shackles. The acceleration index and acceleration coefficient of the bow shackles were calculated by using the life data of them. The guaranteed life data of the bow shackle can be used to predict the useful life in industries related to lifting work.

제품 개발기간의 단축속도가 빨라지는 현 시점과 제품의 부품 시험을 통한 개발 과 정은 현실적인 한계에 부딪히고 있다. 이러한 문제점을 해결하기 위해 지금 까지는 가 속수명시험(Accelerated Life Test)법을 개발·적용해 왔다. 그러나 제품의 사용조건이 가혹해 짐으로써 온도를 이용한 가속시험을 적용하기에는 한계가 있다. HALT는 급격한 온도변화와 6축 진동을 시료에 전달할 수 있는 장비로써 위의 조 건을 충족시킬 수 있다.[5] 그러므로 본 연구에서는 부품과 재료의 신뢰도 정보를 신속 하게 얻을 수 있는 HALT의 국내외 연구 동향과 적용 현황을 비교 분석 뿐만 아니라 HALT와 HASS의 효과적인 활용방안을 모색하고자 한다.[2]

As information-oriented industry has been developed and electronic devices has come to be smaller, lighter, multifunctional, and high speed, the components used to the devices need to be much high density and should have find pattern due to high integration. Also, diverse reliability problems happen as user environment is getting harsher. For this reasons, establishing and securing products and components reliability comes to key factor in company's competitiveness. It makes accelerated test important to check product reliability in fast way. Out of fine pattern failure modes, failure of Electrochemical Migration(ECM) is kind of degradation of insulation resistance by electro-chemical reaction, which it comes to be accelerated by biased voltage in high temperature and high humidity environment. In this thesis, the accelerated life test for failure caused by ECM on fine pattern substrate, 20/20μm pattern width/space applied by Semi Additive Process, was performed, and through this test, the investigation of failure mechanism and the life-time prediction evaluation under actual user environment was implemented. The result of accelerated test has been compared and estimated with life distribution and life stress relatively by using Minitab software and its acceleration rate was also tested. Through estimated weibull distribution, B10 life has been estimated under 95% confidence level of failure data happened in each test conditions. And the life in actual usage environment has been predicted by using generalized Eyring model considering temperature and humidity by developing Arrhenius reaction rate theory, and acceleration factors by test conditions have been calculated.

Light emitting diode(LED) plays important role in illumination applications such as general lighting, automotive, and outdoor lights due to their high reliability and energy saving elements. The long lifetime is one of the main advantages of LED and thus, the Accelerated Life T(ALT) is used to help achieving the target life time. This paper presents the investigation of ALT models and failures for LED in recent literatures. LED reliability improvement technologies will be discussed finally.

Organic light emitting diode(OLED) has been developed fast from 1963 when electric light emitting phenomenon was discovered. PMOLED(passive matrix OLED) is producted earlier than AMOLED(active matrix OLED). PMOLED is mainly mounted at sub display, but AMOLED is mounted at main display. Nowadays AMOLED is expanded to PMP(portable multimedia players), navigation and TV market. Even thought OLED's market is opening to many applications, OLED's life is worried until now. If we know about OLED's real life, we need time to test so much time over 20,000hrs. Realistically, there is difficult to test such as long time with products from the information-technology sector having a short life cycle. In this paper, we study about OLED's accelerated test to reduce life test by current. We can design OLED's accelerated life model by the result of test. The model consists of design variables like ratio of light emitting, organic material structure, condition of aging, etc. In conclusion, this model can be applied to study about organic material, machine and manufacturing process etc, and also it's possible to develop a method of manufacturing process & materials, so we need to study on the subject of this paper continuously.

There has been much research on the reliability and durability of the product life cycle using accelerated life test(ALT), accelerated stress test(AST) and accelerated stress audit(ASA) in the industry. Most of these systems use vibration induced by acceleration and deceleration. The device used for these kinds of research should have wide-band exciting frequency ranges to find the weak mode of the product. In this paper, platform of ALT based on the Stewart platform is controlled by using pneumatic actuators. Pneumatic actuators use motion and impact in this paper to cause wide-band exciting frequency. The change in frequency and pressure in the six cylinders is used to control the level of exciting vibration. Many control strategies are tested to improve the performance and one of the best control algorithms is suggested.

This paper presents the log likelihood function for integrated models for ALT such as exponential-general Eyring, Weibull-temperature and specific heat, lognormal-temperature and specific heat. Additionally this paper estimates the system reliability and mean time to failure(MTTF) for series, parallel, k of n, and standby system using ALT linkage parameter. Lastly this study designs three variable reliability acceptance sampling(RAS) plans such as type I, II censored test, sequential test by the use of integrated models for ALT.

This paper is to present linkage parameter to integrate statistical models and physical models for accelerated life test. Statistical models represent the relationship of probability distribution and life. Physical models show the relationship of life and stress. Moreover, this study proposes the four steps for construction of integrated models for accelerated life test using linkage parameter. Finally, this paper develops new integrated models such as extreme value distribution-general Eyring, linearly increasing failure rate function-general Eyring, etc., and estimates various reliability measures.

Recently, there are many researches that are performed for increasing reliability about product life cycle using ALT(Accelerated Life Test), AST(Accelerated Stress Test) and ASA(Accelerated Stress Audit) in the industry. The test of this research needs a device that has wide-band frequency vibration. But most test devices such as HALT only show the good response of high frequency area. In this research, the platform of ALT was developed based on Stewart Platform using pneumatic Actuators. Pneumatic Actuators represent response of wide-band frequency by motion and mpact. Cylinders of Stewart Platform is operated based on frequency and pressure. This research shows system characteristic of Platform to develop the control algorithm of accelerated life test platform in future research.

염해에 노출된 콘크리트 구조물의 내구수명을 정량적으로 평가하기 위해서는 사용 배합을 통하여 확산계수를 평가하고 이를 이용한 염화물 침투 해석이 필요하다. 본 연구에서는 비말대에 노출된 콘크리트 구조물에 대하여 촉진 확산계수를 NT BUILD 492 및 ASTM 1202를 통하여 평가하였으며, 기존의 연구를 이용하여 겉보기 확산계수를 도출하였다. 사용배합의 특성과 가장 보수적인 조건인 임계 염화물량과 표면 염화물량을 고려하였으며, Life 365 ver.2 프로그램을 이용하여 외벽 및 기둥구조의 내구수명을 평가하였다. 10년 및 15년의 Built-up period의 변화에 대해서는 내구수명은 큰 차이를 보이지 않았으며. 슬래그를 사용한 두 개의 배합에서는 높은 시간의존성 지수와 낮은 초기 염화물 확산계수로 인해 75년 이상의 높은 내구수명이 확보되었다.

The lifetime of the electrode is one of the most important factors on the stability of the electrode. Since the lifetime of the DSA (Dimensionally stable anode) electrode is long, an accelerated lifetime test is required to reduce the test time. Beacuse there is no basis or standard method for accelerated lifetime testing, many researchers use different methods. Therefore, there is a need for basis and methods for accelerated lifetime testing that other researchers can follow. We designed a reactor system for accelerated lifetime testing and planned specific methods. Reactor system was circulating batch reactor. Reactor volume and cooling water tank were 12.5 L and 100 L, respectively. Electrode size was 2 cm x 3 cm (real electrolysis area, 5 cm2). In order to maintain the harsh conditions, accelerated lifetime test was carried out in a high current density (0.6 A/cm2) and low electrolyte concentration (NaCl, 0.068 mol/L). Maintaining a constant temperature was an important operation parameter for exact accelerated lifetime test. As the accelerated lifetime test progressed, the active component of electrode surface was consumed and desorption occurred. At the point of 5 V rise, corrosion of the surface of the base material(titanium) also started.

유용성감초추출물(oil soluble licorice extract)은 미백에 효능이 있는 원료로서, 미백 효과가 최적으로 유지되는 유통기한을 알아야 할 필요가 있다. 실온 상태에서의 화장품 유통기한을 측정하는 것이 제품의 개발 기간에 비해 상대적으로 길기 때문에 가혹 조건하에서의 성분 변화 실험을 통해 실제 유통기한을 예측하고자 하였다. 이를 위해 유용성감초추출물의 수명과 가속 온도 스트레스와의 관계를 아레니우스식에 의해 분석하였다. 가속 온도 스트레스 설정 시 화장품 제형이 변하지 않는 온도 범위 내인 50, 55 및 60 로 설정하였고, 이 구간 내에서 일정 스트레스 부과 방식을 설정하여 실험을 수행하였다. 본 연구에서 화장품 중 유용성감초추출물의 수명은 초기함량의 10 %가 감소되는 시간으로 정의하였으며, 각 온도에서의 유용성감초추출물의 수명은 50 에서 580 h, 55 에서 319 h, 60 에서 166 h로 측정되었다. 실험 결과값을 아레니우스 모델에 적용하여 유용성감초추출물의 수명과 온도 사이의 수명 관계식[log(수명) = - 35.0243 + 1.15322 × (11604.83/온도)]을 도출하였고, 이 식에 의해 25 에서 유용성감초추출물의 수명은 26 개월로 예측할 수 있었다. 예측 결과는 유용성감초추출물을 실온에서 측정한 결과로 검증하였으며 95 % 신뢰수준에서 수명 예측값과 실제값은 유의하지 않았다. 이 연구 방법은 주름 및 미백개선용 기능성 화장품들의 유통기한을 빠르고 정확하게 예측하는데 기여할 것으로 기대된다.