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혼합모드(Ⅰ+Ⅱ)하에서 각도와 균열길이 변화를 갖는 피로균열 전파 거동
정의효,허방수,권윤기,오택열 韓國工作機械學會 2000 한국생산제조학회지 Vol.9 No.5
The applications of fracture mechanics have traditionally concentrated on cracks loaded by tensile stresses, and growing under an opening or mode I mechanism. However, many cases of failures occur from growth of cracks subjected to mixed mode loading. Several criteria have been proposed regarding the crack growth direction under mixed mode loadings. This paper is aimed at investigation of fatigue crack growth behaviour under mixed mode(I+II) with variation of angle and pre-crack length in two dimensional branched type precrack. Especially the direction of fatigue crack propagation was predict-ed and effective stress intensity factor was calculated by finite element analysis(FEA). In this paper, the maximum tangen-tial stress(MTS) criterion was used to predict crack growth direction. Not only experiment but also finite element analysis was carried out and the theoretical predictions were compared with experimental results.
정의효(Ui-Hyo Jeong),형재필(Jae-Phil Hyung),임성용(Seong-Yong Lim),임홍우(Hong-Woo Lim),장중순(Joong-Soon Jang) 한국신뢰성학회 2014 신뢰성응용연구 Vol.14 No.3
Electrodeless lamp is famous for its long life. But its reliability is dependent not only on electrodes but also on materials and structures. To evaluate end product’s reliability, we studied high temperature durability by 60℃, 75 ℃ and 90 ℃ temperature tests, and predicted failure times by an exponential model through regression analysis. However, the test showed that temperature does not affect degradation of electrodeless lamps. Their luminous outputs degrade during the early time of the test (till 250 hours) and then converge to a saturation points. Also, ‘410nm ~ 530nm’ spectrum degrades more than other spectra.
정의효(Uihyo Jeong),임홍우(Hongwoo Lim),형재필(Jaephil Hyung),정창욱(Changuk Jung),조정하(Jeongha Cho),장중순(Joongsoon Jang) 한국신뢰성학회 2018 신뢰성응용연구 Vol.18 No.1
Purpose: To propose improved method for normalization, compare to the de facto international standard which is IESNA TM-21 or conventional normalization methods. Methods: Firstly, we analysed conventional methods and specified the problem of normalization method which is based on first measured data. Secondly, we proposed our approach which is based on the design specification. Lastly, we studied a real degradation data which is conducted for 15,000 hours. Conclusion: Proposed normalization method is better approach because it can reflect real data and design specification, and reduce distortion when analysing degradation data. Also, It is appliable to other long-life reliability items.
고분자캐패시터에 대한 충방전 조건에서의 온도에 따른 정전용량감소 특성 연구
정의효(Ui-Hyo Jeong),임홍우(Hong-Woo Lim),형재필(Jae-Phil Hyung),고민지(Min-Ji Ko),정창욱(Chang-Uk Jung),조정하(Jeong-Ha Cho),장중순(Joong-Soon Jang) 한국신뢰성학회 2017 신뢰성응용연구 Vol.17 No.1
Purpose: Polymer capacitors are known to have very high reliability as compared with liquid electrolytic capacitors, but their capacity has been reported to decrease in charge and discharge at low temperature. The purpose of this study to clarify these characteristics. Methods: In order to clarify these characteristics, charging-discharging tests were carried out for 200 hours with three different capacities and at 5 different temperature from 5℃ to 100℃. Results: As a result of the test, it was confirmed that the capacity of the polymer capacitor was decreased with higher capacity and lower temperature. Conclusion: Such a failure phenomenon was caused by the shrinkage and expansion characteristics of the polymer used therein, it is presumed that this failure phenomenon is due to the complex pore structure made by etching.