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스프링강 표면 내구수명 향상을 위한 온간 피닝 공정의 유한요소 해석
이상욱(Sangwook Lee),김재연(Jaeyeon Kim),박재원(Jaiwon Park),변재원(Jaiwon Byeon) 한국신뢰성학회 2018 신뢰성응용연구 Vol.18 No.1
Purpose: Numerical and experimental study was performed to evaluate the effect of peening temperature on the residual compressive stress distribution and magnitude of residual compressive stress at the material surface. Methods: A compressive air-propelled warm peening equipment was designed and manufactured for warm peening test. Results: 3D dynamic finite element (FE) model of the warm peening test was proposed and validity of the proposed FE model was verified by comparing the predicted residual stresses with the measured residual stresses in the open literature. Maximum warm peening temperature and a proper peening time were investigated with the proposed FE model. Conclusion: Compressive residual stress increased remarkably with peening temperature increased. But, peening temperature is greater than 350℃, the effect of peening temperature disappeared. Therefore, maximum peening temperature possibly applicable for warm peening industry might be 350℃ and peening time is 45s.
적외선 열화상 이미지 컨트라스트 파라미터를 이용한 결함 크기의 비파괴 평가
최정영(Jungyoung Choi),최수용(Sooyoung Choi),김재연(Jaeyeon Kim),유기태(Kitae Yoo),박재원(Jaiwon Park),현창용(Hyunchang Yong),변재원(Jaiwon Byeon) 한국신뢰성학회 2018 신뢰성응용연구 Vol.18 No.1
Purpose: In this study, the defect quantification of thin metal plate was evaluated by using lock-in infrared thermography. Methods: A STS304 standard specimens, which had the artificial-defects of different size, were used. The focal distance between the infrared camera and the specimen was set to 500mm, and the distance between the lump and the specimen was set to 200mm. One halogen lamp with a maximum capacity of 1kW was used, and phase-lock infrared thermal images with a frequency of 1Hz were captured and analyzed. Result: Objectively quantified data values were obtained by analyzing the contrast ratio and signal-to-noise ratio. Conclusion: The possibility of defect diagnosis for thin metal plate was confirmed by using the lock-in infrared thermography technique.
전기화학분극법에 의한 리튬 이온 전지의 열적 기계적 손상 평가
김재연(Jaeyeon Kim),유기태(Kitae Yoo),왕택립(Zeli Wang),임미나(Mina Lim),조소연(Soyeon Cho),김동오(Dongo Kim),이명훈(Myounghun Lee),변재원(Jaiwon Byeon) 한국신뢰성학회 2019 신뢰성응용연구 Vol.19 No.1
Purpose: Health and safety of lithium ion batteries have become important issue due to increasing reports on explosion and firing accident during use. In this research, mechanical and thermal damages of a lithium ion battery were evaluated by applying alternative current electrochemical impedance spectroscopy. Methods: Nyquist plot was obtained for the isothermally exposed batteries to 85℃, 100℃ and 120℃ as well as mechanically twisted and bended lithium polymer batteries, respectively. Ohmic, SEI (secondary electrolytic interface), and charge transfer resistance were extracted and compared among them. Results: Nyquist plot of both thermally exposed and mechanically deformed batteries were observed to shift toward high resistance region. SEI resistance value increased with thermal exposure, which is attributed to the decomposition reaction of lithium salt over 60℃. For the mechanically deformed battery, Ohmic resistance increased, while little change in SEI resistance was observed. Conclusion: SEI resistance and Ohmic resistance value extracted from the Nyquist plot can be applied as a state-of-health monitoring indicator of the lithium ion batteries used under thermal exposure or mechanical deformation condition, respectively.