• Journal of Mechanical Science and Technology
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• 제19권6호
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• pp.1229-1242
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• 2005

When natural rubber is used for a long period of time, it becomes aged; it usually becomes hardened and loses its damping capability. This aging process affects not only the material property but also the (fatigue) life of natural rubber. In this paper the aging effects on the material property and the fatigue life were experimentally investigated. In addition, several fatigue life prediction equations for natural rubber were proposed. In order to investigate the aging effects on the material property, the load-stretch ratio curves were plotted from the results of the tensile test, the compression test and the simple shear test for virgin and heat-aged rubber specimens. Rubber specimens were heat-aged in an oven at a temperature ranging from $50^{\circ}C$ to $90^{\circ}C$ for a period ranging from 2 days to 16 days. In order to investigate the aging effects on the fatigue life, fatigue tests were conducted for differently heat-aged hourglass-shaped and simple shear specimens. Moreover, finite element simulations were conducted for the specimens to calculate physical quantities occurring in the specimens such as the maximum value of the effective stress, the strain energy density, the first invariant of the Cauchy-Green deformation tensor and the maximum principal nominal strain. Then, four fatigue life prediction equations based on one of the physical quantities could be obtained by fitting the equations to the test data. Finally, the fatigue life of a rubber bush used in an automobile was predicted by using the prediction equations, and it was compared with the test data of the bush to evaluate the reliability of those equations.

• 한국신뢰성학회지:신뢰성응용연구
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• 제9권1호
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• pp.37-45
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• 2009

Recently mechanical watt-hour meters are being replaced by electronic watt-hour meters. The replacement period of mechanical watt-hour meters is 7 years. This period is based on long term historical data. The replacement period of electronic watt-meters is also 7 years. This period is determined using the replacement period of mechanical watt-hour meters. However lifetime of mechanical watt-hour meters is different from the lifetime of electronic meters. In order to determine desirable replacement period of electronic watt-hour meters, accelerated life tests of major components in electronic watt-hour meters were performed. The test results showed that LCD was the component which had the shortest lifetime. In this paper, lifetime of electronic watt-hour meters manufactured by 3 company was estimated and life test standard for LCD was developed.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.129-138
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• 2003

Rolling bearings are classified one of the most important machine elements. The various function of bearings are greatly influenced by grease, and higher performance of rolling bearing greases is required in improve bearing lubrication. Three urea/ether oil greases with identical composition were synthesized to compare the performance of these greases according to the thickener content of grease. The typical grease physical properties were investigated. And life test of these greases was conducted by FE-9 grease life tester. The characteristics of the greases before and after life test were investigated using FT-IR, microscope, OIT and TAN meter. Large differences in the grease performance depending on the content of the thickener were observed. The grease with higher content of the hickener showed higher performance such as long life time and low TAN value. After preliminary test, twelve greases were synthesized and evaluated the performance of dropping point and OIT, then optimized two greases were selected by SSRED (Six Sigma Robust Engineering Design) using dropping point and OIT data. Characteristics of the optimized two greases were on the same level with estimated value. The optimized grease by means of OIT value showed longer grease life in comparison with optimized grease by dropping point. However two greases showed higher performance than typical urea/ether oil.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권2호
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• pp.69-75
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• 2005

In order to improve the reliability of high voltage rotating machines and mold transformers, it is necessary to understand the breakdown mechanism and life assessment of the high voltage winding parts. Especially the on-line PD test provides the ability to monitor effects, such as slot discharge, internal discharge, and end-winding discharge without interrupting the electrical machines, this method has been proven the major testing technology. Capacitive couplers have been the most widely used sensors for the on-line partial discharge detection in rotating machines nowadays. This paper deals with the electrical characteristics and long-term reliability of a ceramic coupler(CC), which can be easily mounted into high voltage input terminal part, has been developed and tested to continuously measure PD activity during operating condition. This paper presents electrical characteristics (dielectric loss angle, capacitance, PD inception level, breakdown voltage, and frequency response bandwidth) and long-term life test result of the developed 6.6 kV class on-line ceramic coupling sensor. It was found that this sensor had good electrical characteristics to detect PD activity during the operating condition with its detection frequency band is between several and several tens MHz. Also, the voltage life of the 6.6kV class ceramic coupler was calculated over 60 years.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1996년도 제24회 춘계학술대회
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• pp.35-40
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• 1996

Friction and wear behavior of MoS$_{2}$ bonded films were evaluated at a Block-on-Ring typed tribo-tester, and their properties were compared with those of Falex tester in terms of the wear life of the films. Test results showed that friction and wear properties were significantly affected by the test methods of different contact configuration, and the wear life at a Block-on-Ring type tribo-tester was mostly governed by the resin binder. To obtain long wear life of the films, various combinations of solid-resin-content ratio and chemical resin modification were attempted and evaluated. Adhesion properties of resin binders were also measured and compared by using a scratch tester.

• 가정과삶의질연구
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• 제21권4호
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• pp.1-10
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• 2003

This paper compares the time perspective between Korean and American college students and examines the difference of it according to gender and social status of them. The subject of this study were 385 Korean students and 385 American counterparts. The data were collected by survey with questionnaires and analyzed by SPSS program for the frequency, percentile, mean, standard deviation, t-test, one-way ANOVA and Duncan test. The results indicate that American students have more long-term personal direction than Korean counterparts and the effects of gender and social status are different in Korea and America. Korean students showed no difference according to these two variables but female America students indicate more long-term personal direction than male students and the time perspectives were different according to social status in America.

• 한국신뢰성학회지:신뢰성응용연구
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• 제15권4호
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• pp.270-275
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• 2015

Purpose : UHMWPE (Ultra-high-molecular-weight-polyethylene) is one of the most widely used material in knife protection clothes because of high strength, elasticity, and light weight. The purpose of this study is to develop the accelerated life test method and predict the lifetime for the knife protection fabric composed by UHMWPE. Methods : In this study, degradation characteristics of UHMWPE fibers and knife protection fabric for cut resistance were evaluated under the hydrolysis and photo-degradation conditions. It was found out that the degradation rate of retained tensile strength was more significant in the photo-degradation than hydrolysis. Therefore, the failure time was determined as the time that the retained tensile strength in photo-degradation is less than 50%. Considering an acceleration factor for irradiance and exposure time, the lifetime was predicted from the calculated failure time. Results : As a result of the accelerated life test, the $B_{10}$ lifetime of knife protection fabric composed by UHMWPE fibers is estimated as 2.8 years for a 90% statistical confidence level. Conclusion: Since the lifetime is predicted by the view-point of radiant exposure in this study, there is a possibility that the estimated lifetime may differ from the actual lifetime. However, it is considered as an useful methodology to estimate the long-term lifetime of knife protection fabrics.

• 대한간호학회지
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• 제29권5호
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• pp.1103-1112
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• 1999

In the last few years, psychiatric nurse practitioners have shown a growing an interest in community psychosocial rehabilitation, caring for chronic psychiatric patients as case manager in South Korea. The purpose of this study was to evaluate the effectiveness of a community psychiatric rehabilitation nursing program on self-care activity and quality of life and to suggest this program as an effective nursing intervention in a group of chronic home-based psychiatric patients in a poor town. A nonequivalent control group, pretest-posttest design was used. Of the twenty women that started the program, sixteen finished it. The data were analyzed by the Wilcoxon Rank Sum Test. The program included the process of case management which consisted of four phases: the first was an active case finding and pre-test, the second was home visiting and contacted by phone. the third was group activity therapy of 12 sessions, and the fourth phase was terminal and post-test. The effects of the program were assessed by quality of life and self-care activity. The quality of life and the self-care activity, especially, area of nutrition. elimination, dressing. leisure activity, and follow-up clinic visiting showed greater improvement than those of the control group. The results of this study suggest that this program was effective in improving the quality of life of chronic home-based psychiatric patients.

• 드라이브 ㆍ 컨트롤
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• 제14권1호
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• pp.29-34
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• 2017

This study analyzed a life test method for a power take-off (PTO) gearbox. An engine transfers mechanical power (rotation and torque) to a hydraulic pump through a PTO Gearbox with one input shaft and three output shafts. PTO gear box durability under high loads over long time periods was tested using dynamometers. In order to reflect the rated operating conditions, power must be distributed to each output shaft, and experiments were conducted under various conditions to verify the characteristics of the distributed power. An accelerated life test was designed using speed and torque as acceleration factors. Also, efficiency tests were conducted under various load conditions. Also, a lubrication oil composition analysis was performed to analyze gearbox wear status.

• 공학교육연구
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• 제11권4호
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• pp.64-75
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• 2008

본 연구는 평생학습 능력의 중심 개념인 자기주도학습의 측정을 위한 자기주도학습 준비도 검사도구(SDLRS)의 신뢰도, 타당도를 검증하여, 공학교육의 프로그램 학습성과 항목 중 평생학습 능력의 평가도구로서의 활용 가능성을 제시하고자 한다. 이를 위한 구체적인 연구목표는 다음과 같다. 즉, 자기주도학습 준비도 검사도구의 신뢰도와 타당도를 검증하고 공과대학 학생들의 개인 변인에 따른 자기주도학습 준비도의 차이를 검증하는 것이다. 연구의 목적을 달성하기 위해 문헌연구와 조사연구를 수행하였는데, 평생학습과 자기주도학습에 대한 문헌연구를 토대로 Gugliemino(1977)의 자기주도학습 준비도 검사도구를 이용하여 경기도 소재 A대학의 기계공학 전공 학생들 218명을 대상으로 조사연구를 수행하였다. 검사도구는 5점 척도로 구성되어 있으며 수집된 자료는 기술통계, 요인분석, t검증, ANOVA에 의한 F검증 등의 분석 방법이 이용되었다. 58개의 원검사 도구는 7차례에 걸친 요인분석 결과 23개 문항으로 압축되었다. 또한 학습에 대한 사랑, 학습에 대한 개방성, 자아개념, 기본학습기능과 독립성, 학습에 대한 책임수용, 주도성과 미래지향성, 독창성과 탐구적 특성의 7개 요인으로 재구조화되었으며 전체 변량의 약 58%를 설명하였으며 Cronbach $\alpha$값은 .8332이었다. 개인적 배경에 따른 자기주도학습 준비도 분석 결과 학년, 산업체 근무기간, 대학원 진학계획, 학점에 대해서는 통계적으로 유의한 차이가 있었으나, 성별, 산업체 근무여부, 부모의 학력, 가구의 소득 수준에 따라서는 통계적으로 유의한 차이가 없는 것으로 나타났다. 이상과 같은 연구를 기초로 하여 향후에는 보다 많은 모집단을 대상으로 연구를 수행함으로써 연구결과를 검증해 볼 필요가 있다. 또한, 다양한 검사도구의 적용을 통해 검사도구간의 상관관계 및 평생학습에 영향을 주는 능력과의 상관관계에 대한 후속연구를 수행함으로써 평생학습 능력을 향상시킬 수 있는 방안에 대한 연구를 보다 체계적으로 수행해야 할 것이다.