• International Journal of Reliability and Applications
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• 제15권2호
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• pp.85-98
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• 2014

Accelerated life testing (ALT) is a well famous technique in life testing and reliability studies, this is particularly used to induce so high stress leading to failure of the highly reliable units quickly under stipulated duration of time. The step-stress ALT is one of the systematic experimental strategy of ALT applied to fail the units in steps. In this article we focus on two important issues (i) necessity of life tests at higher steps with relevant causes (ii) to develop a new optimum test plan for 3-step SSALT under the modified cumulative exposure model proposed by Khamis and Higgins (1998). It is assumed that the lifetime of test units follows Rayleigh distribution and its scale parameter at constant stress level is assumed to be a log-linear function of the stress. The maximum likelihood estimates of the parameters involved in the step-stress ALT model are obtained. A simulation study is performed for numerical investigation of the proposed new optimum plan 3-step, step-stress ALT. The necessity of the life test units at 3-step step-stress is also numerically examined in comparison to simple step-stress setup.

• Elastomers and Composites
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• 제37권2호
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• pp.107-114
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• 2002

청정실(Clean room)에 사용되는 환기팬용 모터의 방진고무부품의 수명을 예측하기 위해서 가속 열 노화 시험을 수행하였다. 방진고무부품은 EPDM으로 만들었다. 노화 수명을 판단하기 위한 한계점을 20%의 압축 영구 줄음률로 하여 절대 온도의 역수 값으로 아레니우스 선도를 유도하였다. 아레니우스 관계식으로부터 방진고무부품의 다양한 온도에서의 수명과 활성화에너지를 구하였다. 그리고 수명을 판단하는데 있어 상당한 시간을 대체할 수 있는 가속 시험법을 설계하였다. 또한 방진고무부품에 첨가되는 노화 방지제가 수명에 미치는 영향을 알아보았다.

• Tribology and Lubricants
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• 제31권2호
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• pp.35-41
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• 2015

A water-pump located in the cooling area of a car circulates cooling water. A particular bearing element, known as a water-pump bearing, installed in the rotating part carries the entire load. The failure of this water-pump bearing has a direct impact on the failure of the automobile engine, and so securing its reliability is crucial. Several researchers have examined the design principles of the water-pump bearing, but there are no reports on the life characteristic of the bearing yet. Herein, we report the construction of test equipment to reproduce the spalling of the roller contact, which is the main failure mode of the chosen water-pump bearing. We chose the radial load as an accelerated stress factor and validated the failure mode by monitoring the surface defects. We conducted the accelerated life test after determining the accelerated stress level through a combination of finite element analysis and a preliminary test. In the life tests, we used an accelerometer to perform failure diagnosis. In the last stage of this study, we present a statistical reliability analysis. Thus, we fully estimated the shape parameter of the water-pump bearing, accelerating level on the load , and the lifetime (MTTF and B₁₀ life) under real use conditions, and finally proposed an interval estimation value considering the uncertainty of the estimated value.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1491-1492
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• 2008

This paper investigates life test of LED lighting module using accelerated life test method. Pooly designed LED lighting systems can experience a short life. By knowing the relationship between life and heat, LED system manufacturers can design and build long-lasting systems. In this study, various white LED from several other manufacturer were subjected to life tests at LED lated temperatures for prediction to life of LED lighting systems. Results show that the different LED products have various optical characteristic and different life values.

• 한국신뢰성학회지:신뢰성응용연구
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• 제6권1호
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• pp.37-50
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• 2006

The accelerated life tests of the catalytic gas sensor were performed at three different gas concentration conditions. From the test data, the power-Weibull model was estimated and the acceleration factor between test condition 25%LEL(Lowe Explosive Limit) and use condition 5%LEL was about 3 according to this acceleration model. Using this acceleration factor, life test specification for qualifying that B10 lifetime of the catalytic gas sensor meets the goal lifetime (5 years) was designed.

• 마이크로전자및패키징학회지
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• 제15권2호
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• pp.55-61
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• 2008

본 논문은 블루투스 모듈의 구조 및 솔더접합부에 대한 신뢰성 평가에 국한된 기존의 방법을 확장하여 정량적인 신뢰성 평가를 수행한 결과를 나타낸다. Field 환경조건에서의 정량적인 신뢰성 평가를 위해, 온도 싸이클링(temperature/thermal cycling)에서의 온도차를 가속스트레스로 선정하여 가속수명시험을 실시하였다. 가속수명시험을 통해 구한 고장시간 데이터들을 이용하여 수명분포 매개변수들을 추정하고 코핀-만슨(Coffin-Manson) 모델을 이용하였다. 가속수명시험을 수행한 결과, 블루투스 모듈의 고장모드는 Open, 고장메커니즘은 크랙(Crack)과 박리(Delamination)였다. Field에서 수거한 고장품들의 고장모드와 고장메커니즘이 가속수명시험을 통해 재현되었다. 또한 본 논문에서 블루투스 모듈이 Field에서 받을 수 있는 온도 싸이클링에서의 다양한 온도차에 대한 정량적인 수명을 예측할 수 있는 방법이 제시되었다. 제안된 방법을 이용하여 온도차 $70^{\circ}C$를 받고 있는 블루투스 모듈의 $B_{10}$ 수명은 약 4년으로 추정되었다.

• 한국지반신소재학회논문집
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• 제17권4호
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• pp.213-224
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• 2018

본 연구에서는 접힘홈이 형성된 띠형 섬유보강재를 대상으로, 보강재 종류 및 크리프시험 방법에 따른 크리프특성을 분석하고 크리프 감소계수를 평가하기 위하여 인장강도가 다른 6종류의 띠형 섬유보강재(인장강도 15kN, 25kN, 35kN, 50kN, 70kN, 90kN)에 대한 가속 크리프시험(SIM)을 수행하였다. 또한, 특히 활용 빈도가 높은 인장강도 25kN인 띠형 섬유보강재에 대해서는 장기 크리프시험을 동시에 수행하여 가속 크리프시험 결과와 비교, 분석하였다. 분석 결과, 보강재의 설계수명이 증가할수록 크리프 감소계수가 증가하고, 동일한 소재와 제조방법을 사용한 띠형 섬유보강재는 인장강도가 서로 다르더라도 설계수명에 따라 거의 유사한 크리프 감소계수값을 보여주며, 장기 및 가속 크리프시험 데이터를 모두 사용한 경우의 크리프 감소계수는 장기 크리프시험 데이터만 사용한 경우보다 설계수명 50년~100년을 고려하면 크리프 감소계수가 5.9%~7.1% 정도 작게 평가됨을 알 수 있었다.

• 한국신뢰성학회지:신뢰성응용연구
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• 제9권4호
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• pp.291-302
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• 2009

Accelerated and field degradation tests are performed for reliability assessment of an anticorrosive paint for steel structures. Test data were analyzed to obtain the degradation model and the life time distributions of the paint. A power law degradation model and lognormal performance distribution were used to predict the lifetime of the anticorrosive paint and the method of finding an acceleration factor is provided.

• International Journal of Reliability and Applications
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• 제15권2호
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• pp.125-150
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• 2014

Accelerated life tests (ALTs) are extensively used to determine the reliability of a product in a short period of time. Test units are subject to elevated stresses which yield quick failures. ALT can be carried out using constant-stress, step-stress, progressive-stress, cyclic-stress or random-stress loading and their various combinations. An ALT with linearly increasing stress is ramp-stress test. Much of the previous work on planning ALTs has focused on constant-stress, step-stress, ramp-stress schemes and their various combinations where the stress is generally increased. This paper presents an optimal design of ramp soak-stress ALT model which is based on the principle of Thermal cycling. Thermal cycling involves applying high and low temperatures repeatedly over time. The optimal plan consists in finding out relevant experimental variables, namely, stress rates and stress rate change points, by minimizing variance of reliability function with pre-specified mission time under normal operating conditions. The Burr type XII life distribution and time-censored data have been used for the purpose. Burr type XII life distribution has been found appropriate for accelerated life testing experiments. The method developed has been explained using a numerical example and sensitivity analysis carried out.

• Journal of Welding and Joining
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• 제28권1호
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• pp.77-85
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• 2010

Stainless steel sheets are widely used as the structure material for the railroad cars and the commercial vehicles. These kinds structures used stainless steel sheets are commonly fabricated by using the gas welding. Gas welding is very important and useful technology in fabrication of a railroad car and vehicles structure.However fatigue strength of the gas welded joints is considerably lower than parent metal due to stress concentration at the weld, fatigue strength evaluation of gas welded joints are very important to evaluate the reliability and durability of railroad cars and to establish a criterion of long life fatigue design. In this paper, $({\Delta}{\sigma}_a)_R-N_f$ curve were obtained by fatigue tests. Using these results, the accelerated life test(ALT) was conducted. From the experimental results, an acceleration model was derived and acceleration factors are estimated. So it is intended to obtain the useful information for the fatigue lifetime of plug and ring gas welded joints and data analysis by statistic reliability method, to save time and cost, and to develop optimum accelerated life prediction plans.