• Journal of Mechanical Science and Technology
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• v.19 no.6
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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.

• Journal of Applied Reliability
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• v.9 no.1
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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.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2003.11a
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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.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.2
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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.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1996.04b
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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.

• Journal of Families and Better Life
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• v.21 no.4
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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.

• Journal of Applied Reliability
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• v.15 no.4
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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.

• Journal of Korean Academy of Nursing
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• v.29 no.5
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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.

• Journal of Drive and Control
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• v.14 no.1
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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.

• Journal of Engineering Education Research
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• v.11 no.4
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• pp.64-75
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• 2008

The purpose of the study was to verify reliability and validity of SDLRS instrument and to prove up possibility of usage as an evaluation method for evaluating life-long learning. Literature review and survey were used to accomplish objectives of the study. 218 students in department of mechanical engineering of A university at Gyunggi province were responded for SDLRS(Guglielmino, 1977) instrument. Data were analyzed using descriptive statistics, factor analysis, t-test, and ANOVA test. 58 items in original version instrument were converted to 23 items. There were 7 factors for assessing the self-directed learning readiness according to this measurement scale with a total variance of about 58%. The total reliability of the final 23 items was $\alpha$. The final 7 factors consisted of love for learning, openness for learning, self-perception, basic learning function and independence, acceptance of responsibility for learning, leadership and future directivity, and creativity and exploration. The result of SDLRS analysis according to individual background, there were significant statistically in the grade, period of employment in industry, entering graduate school or not, and GPA, but no significant statistically in sexual difference, employment in industry or not, final academic level of parent, and income level of the family. In the future, final instrument will be needed to check in the respect of correlation with another ability and skill influencing on life-long learning, and more study will be done for developing life-long learning.