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윤서현,최병철,신기항,남기우 한국산업융합학회 2023 한국산업융합학회 논문집 Vol.26 No.2
The subway is one of the most common and important means of transportation in modern society. In order to use the subway safely, tracks are necessary, but trains are prone to derailment and collisions. In order for the train to run safely on the track, the fishplate that connects the line connection is used. The damaged railway was a fishplate for connecting subway lines used for 11 years, and damage analysis and countermeasures were presented. Beach marks were observed on both fracture surfaces, and striations appeared at the range of crack propagation. The damaged part is Cr carbide, which has a higher hardness than the base metal, and is judged to be embrittled and destroyed by fatigue. The SM50C fishplate was subjected to a cyclic stress of about 59% of the upper limit of tensile-compression fatigue limit, but inclusions were the cause of failure. In order to prevent fatigue failure of the SM50C steel fishplate, the occurrence of inclusions should be minimized and processed to have a homogeneous structure when manufacturing the fishplate. In addition, compressive residual stress is given through surface modification such as peening to control crack generation. It is necessary to minimize the change in shape that can become a stress concentration part along with accurate fastening of the bolt, and to design the stress distribution to be as uniform as possible.
한국 간호사의 건강연구에서 야간근무 노출 평가에 대한 고찰
윤서현,강충원,기도형,김현주 한국산업보건학회 2018 한국산업보건학회지 Vol.28 No.4
Objective: Shift work including night work is known to be harmful to the health of nurses. This study was conducted in order to systematically review the academic literature on the health effects of working time patterns, including shift work or night work, among Korean nurses and propose a research direction for the future. Methods: We searched online academic databases to find relevant papers in domestic and international journals using the keyword terms ‘shift work’, ‘night work’, ‘night shift’, ‘work shift’, ‘nurse’, and ‘Korea’, and reviewed a total of 36 articles. Results: As a result of this literature review, more than half of the articles were found to investigate the health effects between shiftwork and non-shiftwork nurses. A few studies considered the shift type(n=6), frequency of night shift(n=4), and shiftwork duration(n=3) as working time patterns. These studies focused mainly on mental health(n=18) or sleep(n=15). Conclusions: Based on the review results obtained from this study, it is necessary to assess working time patterns of Korean nurses using a variety of variables including night-work-related factors, and various health outcomes should be examined considering the confounder.
Failure Analysis and Countermeasures of SCM435 High-Tension Bolt of Three-Step Injection Mold
윤서현,남기우 한국산업융합학회 2020 한국산업융합학회 논문집 Vol.23 No.4
When injection mold is repeatedly used for mass production, fatigue phenomenon due to cyclic stress may occur. The surface and interior of structure might be damaged due to cyclic stress or strain. The objective of this study was to analyze failure of SCM435 high-tension bolts connecting upper and lower parts of a three-stage injection molding machine. These bolts have to undergo an accurate heat treatment to prevent the formation of chromium carbide and the action of dynamic stresses. Bolts were fractured by cyclic bending stress in the observation of ratchet marks and beach marks. Damaged specimen showed an acicular microstructure. Impurity was observed. Chromium carbide was observed near the crack origin. Both shape parameters of the Vickers hardness were similar. However, the scale parameter of the damaged specimen was about 20% smaller than that of the as-received specimen. Much degradation occurred in the damaged specimen. Bolts should undergo an accurate heat treatment to prevent the formation of chromium carbide. They must prevent the action of dynamic stresses. Bolts need accurate tightening and accuracy of heat treatment and screws need compression residual stress due to peening.