대등(對等)고장률을 활용한 직 · 병렬구조 시스템의 신뢰도할당 구도

조경환 한국신뢰성학회 2016 한국신뢰성학회 학술대회논문집 Vol.2016 No.11

The purpose of this paper is to present a modified reliability allocation scheme of a series-parallel system based on that of a series system. Equivalent failure rate is derived as mean failure rate as failure rate of a redundant system is time-varying. We can get constant failure rate that produces the same value of reliability as that of redundant system when time interval is fixed. It means that reliability can be converted to constant failure rate by means of equivalent failure rate. Target failure rate is used in general instead of target reliability via equivalent failure rate. Target failure rate of a series-parallel system can be allocated into those of subsystems including both series and parallel subsystems. Mathematical equations are suggested to figure out target failure rates of parallel subsystems when a target reliability of a series-parallel system is given.

골유착성 치과 임플란트의 성공률에 대한 임상적 연구

김영석,이동근,민승기,이준,문철 대한악안면성형재건외과학회 2002 Maxillofacial Plastic Reconstructive Surgery Vol.24 No.2

The purpose of this study is to review the prognosis of the endosteal osseointegrated dental implants placed in the total and partial edentulous area of mandible and maxilla and to suspect the possible causes leading to failure. 301 osseointegrated dental implants that had been inserted between 1992 thru 2000 were followed up for over one year (average follow up : three years) in function. Medical records and radiographs included CT were evaluated and analyzed by the overall success rate, gender and age factor, general disease, implant fixture length and diameter, surface status of implant, bone density, and the stage of removal. Chi squire test was used statistically. Of the 301 osseointegrated dental implants, 18 dental implants (6.0%) were removed and cumulative survival rate was 94%. No significant difference in the failure rate were found between male (5.4%) and female (6.5%). The failure rate were 8.0% in the fifties, 7.3% in the forties, 5.2% in the thirties, 4.6% in the sixties. Patients who had systemic disease were highly related with failure rate (25%), and cumulative survival rate was 75%. Success rate was the highest in the premolar area than anterior and molar area (p<0.05). The failure rate was highest in the D4 bone (12.5%). High failure rate was found in the wide diameter implant (9.7%) and 7∼9㎜ short implant (12.5%). No significant difference in the failure rate were found between implant surface condition. Stages of removal were pre-prosthetic (16 implants) and post-prosthetic (2 implanrs) stage. The failure rate in the conventional technique was 5.1%, 19.1% in the GBR, 10% in the sinus lifting. Marginal bone resorption around the implants were found 0.15㎜ in the 3 months. 0.4㎜ in the 6 months. 0.71㎜ in the 1 year, 0.9㎜ in the 2 years and 1.06㎜ in the 3 years.

야전운용제원에 기반한 공군 OO유도탄 고장률 예측에 관한 연구

박천규,마정목 한국산학기술학회 2020 한국산학기술학회논문지 Vol.21 No.7

The one-shot weapon system is destroyed after only one mission. So, the system requires high reliability. Guided missiles are one-shot weapon systems that have to be analyzed by storage reliability since they spend most of their life in storage. The analysis results depend on the model and the ratio of correct censored data. This study was conducted to propose a method to more accurately predict the future failure rate of Air force guided missiles. In the proposed method, the failure rate is predicted by both MTTF (Mean Time To Failure) and MTBF (Mean Time Between Failure) models and the model with a smaller error from the real failure rate is selected. Next, with the selected model, the ratio of correct censored data is selected to minimize the error between the predicted failure rate and the real failure rate. Based on real field data, the comparative result is determined and the result shows that the proposed sampling rate can predict the future failure rate more accurately. 일회성 무기체계는 대기 상태로 있다가 단 한 번의 임무를 수행한 이 후 폐기되는 특성에 따라 높은 신뢰도를 요구받는다. 유도탄은 일회성 무기체계로써 특성상 저장 상태로 수명의 대부분을 보내고, 임무수행을 위한 운용시간은 짧기때문에 임무성공률이 아닌 저장 신뢰도로 분석해야 한다. 유도탄의 신뢰도를 분석할 때에 어떠한 방법을 사용하는지에 따라 그 결과는 달라질 수 있으며, 고장자료와 함께 포함되는 우측 관측중단자료의 비율에 따라서도 차이가 발생할 수 있다. 본 연구는 공군의 OO유도탄을 대상으로 미래의 고장률을 보다 정확하게 예측하기 위한 방법을 제시하고자 작성하였다. 제시하는 방법은 먼저 평균 고장시간(MTTF: Mean Time To Failure, 이하 MTTF)을 적용한 모델과 고장간 평균시간(MTBF: Mean Time Between Failure, 이하 MTBF)을 적용한 모델로 고장률을 예측하고, 두 모델 중 실제 고장률과 차이가 작은 모델을 선택한다. 선택한 모델로 고장자료와 함께 포함되는 우측 관측중단자료의 비율을 달리하여 고장률을 예측하고, 실제 고장률과의 차이가 최소화되는 비율을 찾는다. 실제 자료를 바탕으로 제안한 비율과 현재 검사 비율의 비교를 통해 제안한 비율이 미래 고장률을 예측하기에 더 적합함을 보였다.

PC 사용 환경에 기반한 2.5 인치 하드 디스크의 수명주기 예측에 대한 연구

조의현(Euy-Hyun Cho),박정규(Jeong-Kyu Park),이민우(Min-woo Lee),권순무(Soon-Mu Kwon) 한국디지털콘텐츠학회 2014 한국디지털콘텐츠학회논문지 Vol.15 No.2

The mass storage of data and the importance of storage capacity lately has emerged. In this paper, we suggest the new method which estimate life cycle from acceleration life test about 2.5 inch hard disk driver as mass storage, which minimize the difference between real market annual failure rate and estimated failure rate. we obtain market transfer capacity per hours from returned 2.5inch hard disk drives about 309 numbers and accelerating transfer capacity per hours from acceleration life test. we calculate acceleration factor about duty cycle and estimate annual failure rate from failure rate and acceleration factors: temperature acceleration factor, duty cycle acceleration factor, the transfer capacity per hour represent the 93.4 % of user is 5.8 GB/hour, the transfer capacity per hour from acceleration life test is 81.4 GB/hour. the acceleration factor of duty cycle is 14.1. annual failure rate is stabilized at market one year after, annual failure rate is between 0.3 and 0.378. estimated annual failure rate is 0.4, so it is matched at 75~94 % between estimate annual failure rate and market annual failure rate. This study influence the estimate method of annual failure rate by the result of acceleration life cycle of manufacture.

The Effect of Usage and Storing Conditions on John Deere 3140 Tractor Failures in Khouzestan Province, Iran

Afsharnia, Fatemeh,Marzban, Afshin Korean Society for Agricultural Machinery 2017 바이오시스템공학 Vol.42 No.2

The use of tractors to carry out agricultural work has played an important role in mechanizing the agricultural sector. A repairable mechanical system (such as an agricultural tractor) is subject to deterioration or failure. In this study, a regression model was used to predict the failure rate of a John Deere 3140 tractor. The machine failure pattern was carefully studied, and key factors affecting the failure rate were identified in five regions of the Khouzestan province. Through a questionnaire, data was obtained from farm records. This data was grouped into six sub-groups, according to the annual use hours (AUH) and the manner in which the tractors were stored. Results showed that AUH and storage policies affected failure rate slightly. With an increase in the age of the tractors, the failure rate in the tractors used for 1050-2000 hours annually and stored outdoors was higher than those used for 200-1000 hours annually and stored in sheds. When the tractors were of the same age, the slope of the curve in the 200-1000 annual use hours increased gradually and then rapidly, but failure rate in the 1050-2000 annual use hours was high from the beginning, and subsequent increase in this value was almost uniform. As a result, it can be said that with an increase in the annual use hours, the failure and breakdown rate in John Deere 3140 tractors rapidly increases, but maintenance conditions only slightly affect the failure and breakdown rate.

고장률이 시간 구간별로 다른 경우의 신뢰도

전태보(Jeon Tae Bo) 강원대학교 산업기술연구소 2007 産業技術硏究 Vol.27 No.1

Failure rate serves as a pivotal role in reliability study. Of all, the constant failure rate is the most popularly used in field exercises. In reality, however, the electrical and electronic parts’ life is represented by not only the constant failure rate but the decreasing and/or increasing failure rates. Explicit consideration and incorporation of them into the model development may yield more desirable results. In this study, we built a reliability model for failure rates varying over time intervals and derived well known measures such as probability density function, reliability function, mean life, moments, and mission time. We then evaluated mean life with consideration of the first-year multiplier and compared the results those with constant failure rate. The results given in the study may provide a reference applying for practical decision making.

고장률이 시간 구간별로 다른 경우의 신뢰도

전태보 江原大學校 産業技術硏究所 2007 産業技術硏究 Vol.27 No.B

Failure rate serves as a pivotal role in reliability study. Of all, the constant failure rate is the most popularly used in field exercises. In reality, however, the electrical and electronic parts' life is represented by not only the constant failure rate but the decreasing and/or increasing failure rates. Explicit consideration and incorporation of them into the model development may yield more desirable results. In this study, we built a reliability model for failure rates varying over time intervals and derived well known measures such as probability density function, reliability function, mean life, moments, and mission time. We then evaluated mean life with consideration of the first-year multiplier and compared the results those with constant failure rate. The results given in the study may provide a reference applying for practical decision making.

신뢰도 배분기법을 이용한 야전 고장률 결측값 추정

이재원,김의준,이서현,임재학 한국신뢰성학회 2024 신뢰성응용연구 Vol.24 No.1

Purpose: It is crucial to gather failure data from field operations of weapon systems and provide reliable information, such as component failure rates. However, missing data often occurs during this process, resulting in some components having missing failure rate values. This study proposes a method for estimating missing values in field failure rates using reliability allocation techniques. Methods: We examined various reliability allocation methods, including the equal, ARINC, feasibility of objective, AGREE, and comprehensive reliability allocation methods. In this study, we specifically apply the equal and ARINC allocation methods, which are deemed suitable for the situation addressed. The estimation process for missing failure rate values involves two steps: utilizing reliability allocation techniques to calculate initial estimates and then refining these estimates through a fine-tuning process. Results: Applying the method proposed in this study to estimate the missing failure rate values of components in the K2 tank, the results indicate that the ARINC allocation method outperforms the equal allocation method. Conclusion: The proposed estimation method offers an alternative solution for addressing information resulting from omitted failure records in field operations. It is also expected to be applied in the development of a failure rate databook. Furthermore, with additional factor information required for reliability allocation, other allocation methods could be applied.

The Effect of Usage and Storing Conditions on John Deere 3140 Tractor Failures in Khouzestan Province, Iran

( Fatemeh Afsharnia ),( Afshin Marzban ) 한국농업기계학회 2017 바이오시스템공학 Vol.42 No.2

The use of tractors to carry out agricultural work has played an important role in mechanizing the agricultural sector. A repairable mechanical system (such as an agricultural tractor) is subject to deterioration or failure. In this study, a regression model was used to predict the failure rate of a John Deere 3140 tractor. The machine failure pattern was carefully studied, and key factors affecting the failure rate were identified in five regions of the Khouzestan province. Through a questionnaire, data was obtained from farm records. This data was grouped into six sub-groups, according to the annual use hours (AUH) and the manner in which the tractors were stored. Results showed that AUH and storage policies affected failure rate slightly. With an increase in the age of the tractors, the failure rate in the tractors used for 1050-2000 hours annually and stored outdoors was higher than those used for 200-1000 hours annually and stored in sheds. When the tractors were of the same age, the slope of the curve in the 200-1000 annual use hours increased gradually and then rapidly, but failure rate in the 1050-2000 annual use hours was high from the beginning, and subsequent increase in this value was almost uniform. As a result, it can be said that with an increase in the annual use hours, the failure and breakdown rate in John Deere 3140 tractors rapidly increases, but maintenance conditions only slightly affect the failure and breakdown rate.

Influence of dynamic loading on failure behavior of spot welded automotive steel sheets

Noh, Wooram,Koh, Youngwoo,Chung, Kwansoo,Song, Jung-Han,Lee, Myoung-Gyu Elsevier 2018 International journal of mechanical sciences Vol.144 No.-

<P><B>Abstract</B></P> <P>Dynamic failure of the spot welded automotive steel sheets, similar and dissimilar combinations of TRIP980 and GMW2 sheets, was analyzed with finite element (FE) simulations. The strain rate-sensitivity of the base sheets was considered to investigate the influence of dynamic loading on failure behavior of the welded sheets. Mechanical properties were first identified under the quasi-static loading as the reference condition. Hardening behavior and fracture criterion were identified by numerical inverse method applied to the standard tensile test and a miniature tensile test for the base sheet and the weld nugget, respectively. Moreover, strain rate-sensitivities of the base sheets were inversely characterized as a function of strain and strain rate. Dynamic lap-shear and coach-peel coupon tests were performed to evaluate the dynamic failure behavior of the welded sheets. Peak strength, failure mode and load-displacement curves of the coupon tests were predicted with the FE simulations. The combined experimental and numerical approach showed that the strain rate-sensitivity of the base sheet played a key role on determination of failure characteristics in coupon tests.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Dynamic failure behavior of the spot welded automotive sheets was modeled based on coupled experiment and FE simulations. </LI> <LI> Strain rate-sensitive mechanical properties of the constituent zones in the welded joints were characterized and modeled. </LI> <LI> An in-depth FE analysis was provided to predict and to analyze the effect of the rate-sensitivity on failure behavior of welds. </LI> <LI> The proposed modeling approach could provide good predictions for the performance of welded coupons and fracture modes. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>