• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.116-121
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• 2000

During the operation, fatigue failures and cracks of duct plate due to excessive duct vibration occurred in the fan-duct systems of fossil fueled boilers. We measured static pressure variation(pressure pulsation) in the outlet, and also measured vibration at the outlet duct of a centrifugal fan. It was found that strong pressure Pulsation caused by the inlet vortex occurred in inlet vane of centrifugal fan in the middle range of vane opening. Thus, excessive duct vibration is caused by strong pressure pulsation. In this paper, it is shown that the frequency and amplitude of pressure pulsation depend mainly on vane opening and are compared with duct vibration. Also, effective solution for reducing pressure pulsation and vibration are presented.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.82-87
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• 2000

During the operation, fatigue failures and cracks of duct plate due to excessive duct vibration occurred in the fan-duct systems of fossil fueled boilers. We measured static pressure variation(pressure pulsation) in the outlet, and also measured vibration at the outlet duct of a centrifugal fan. It was found that strong pressure pulsation caused by the inlet vortex occurred in inlet vane of centrifugal fan in the middle range of vane opening. Thus, excessive duct vibration is caused by strong pressure pulsation. In this paper, it is shown that the frequency and amplitude of pressure pulsation depend mainly on vane opening and are compared with duct vibration. Also, effective solution for reducing pressure pulsation and vibration are presented.

• Proceedings of the KSR Conference
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• 2001.05a
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• pp.193-199
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• 2001

In this study, the carbody design of the rubber tired AGT(Automated Guide-way Transit System) under development by KRRI was numerically analysed to evaluate its structural strength according to the standard specifications for Korean LRT (Light Rail Transit). The numerical results showed that the detail design of the carbody was strong enough to satisfy the specifications with respect to the axial compression strength, the vertical strength and the vertical stiffness(natural frequency). However, the carbody design had some problems on the fatigue strength by twist loadings. So, it was recommended that the carbody design should be modified to improve the twisting strength by reinforcing the front end structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1347-1353
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• 2011

Friction stir welding (FSW) method has extensively been used in manufacturing methods because of the several advantages over conventional welding methods, such as better mechanical properties, reduced occurrence of joining defects, high material saving, and low production time, etc. The aim of this paper is to review the optimal FSW conditions using the previous experimental results and is to investigate the fatigue crack growth rate in three different zones, WM, HAZ and BM for FSWed Al7075-T651 aluminum plates. As far as our experiments are concerned, the optimal conditions are obtained as rotation speed, 800rpm and travelling speed, 0.5mm/sec. The fatigue crack growth rate showed strong dependency on three different zones WM, HAZ and BM, and crack driving force.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.4
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• pp.345-351
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• 2010

The oblique incidence technique for ultrasonic nonlinear characterization was studied in stainless steel 316L alloy subjected to high cycle fatigue. A dog-bone plate specimen was prepared to make different faitgue-driven deformation at each position where the stress concentration could occur in the middle of specimen. In addition to the normal transmission technique, the oblique incidence technique which is newly suggested in this study, was used to measure ultrasonic nonlinear parameter. The fatigued specimen shows higher ultrasonic nonlinear parameter than the virgin specimen for both techniques. Ultrasonic nonlinear parameter highly increases in the middle of test specimen where the stress concentration existes. Relative nonlinear parameter has strong correlation with fatigue damage. Consequently, the oblique incidence technique with longitudinal wave can be potential to characterize high cycle fatigue damage.

• Elastomers and Composites
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• v.20 no.3
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• pp.189-204
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• 1985

The purpose of this study is to examine the dynamic properties, especially the damping and fatigue properites, of NR vulcanizates and to find out the vulcanizate which can be used as damping materials in industry. The results of this study can be summarized as follows: 1. In the ODR test, the S-2 vulcanizate was the fastest one in terms of having reached to optimum cure times($t_{90}$) and, with the same formula, when 50phr of HAF carbon black loaded, the shortest optimum cure times has shown. 2. The S - 2 vulcanizate was the best than the others in the physical properties. In aging properties, however, the E - 1 vulcanizate appeared to be better than the other vulcanizates. 3. The results of the RDS test for the NR vulcanization system under the condition of 0.1% strain amplitude and 1 Hz frequency showed no connection between Tg and the the nature of the crosslinking system, but 50phr loading of HAF carbon black increased Tg. The damping values of vulcanizates in the elastic region showed a strong relations the damping values and the crosslinking system. The S - 2 vulcanizate with higher crosslink density had lower damping values than other vulcanizates, and furthermore, the SH - 2 vulcanizates with 50phr loading of HAF carbon black increased the damping values. 4. The Goodrich Flexometer test showed that the heat buildup for the gum NR vulcanizates was less than for those which contained 50phr of HAF carbon black. In particular, the fatigue life of the vulcanizate with lower damping values appeared to be longer than that of the vulcanizates with higher damping values. In the fatigue test, the increasment of the loading or the temperature, applied to the vulcanizates, appeared to be shorten their fatigue life.

• Restorative Dentistry and Endodontics
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• v.29 no.3
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• pp.267-272
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• 2004

The purpose of this in vitro study was to evaluate the effect of surface defects and cross-sectional configuration of NiTi rotary files on the fatigue life under cyclic loading. Three NiTi rotary files ($K3^{TM},{\;}ProFile^{\circledR},{\;}and{\;}HERO{\;}642^{\circledR}$) with ＃30/.04 taper were evaluated. Each rotary file was divided into 2 subgroups : control (no surface defects) and experimental group (artificial surface defects), A total of six groups of each 10 were tested. The NiTi rotary files were rotated at 300rpm using the apparatus which simulated curved canal (40 degree of curvature) until they fracture. The number of cycles to fracture was calculated and the fractured surfaces were observed with a scanning electron microscope. The data were analyzed statistically. The results showed that experimental groups with surface defects had lower number of cycles to fracture than control group but there was only a statistical significance between control and experimental group in the $K3^{TM}$ (p<0.05), There was no strong correlation between the cross-sectional configuration area and fracture resistance under experimental conditions. Several of fractured files demonstrated characteristic patterns of brittle fracture consistent with the propagation of pre-existing cracks. This data indicate that surface defects of NiTi rotary files may significantly decrease fatigue life and it may be one possible factor for early fracture of NiTi rotary files in clinical practice.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.10
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• pp.4917-4926
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• 2012

This study was designed to assess the factor of influence to occupational stress who work in the field of firefighters and questionnaire was uesd to analyse the stress scores and find the primary factors influence to occupational stress. The number of respondents were 408 who received the refresher training and period of investigation was august 2011 through october 2011. A structured questionnaire was employed to evaluate the participants' socio-demographics, job-related factors, health-related behaviors, occupational stress, reaction factor (fatigue, job satisfaction) and buffer factor (social support). Occupational stress and fatigue were assessed using the Korean Occupational Stress Scale-Short Form (KOSS-SF) and the Multidimensional Fatigue Scale (MFS), respectively. The analysis showed that we found a strong correlation between fatigue, job satisfaction and occupational stress. Occupational stress was associated with an increased risk of fatigue and decreased the job satisfaction. In the multiple regression analysis(stepwise), main factor that influence to occupational stress were job satisfaction, gender, age, processing number for a day, exercise. In logistic regression analyses, a higher occupational stress was associated with higher odds of fatigue(High) and the odds was down by 15.0% after adjustment for job satisfaction, gender, age, processing number for a day, exercise. Thus, a job satisfaction promote program for the reduction of occupational stress and the promotion of firefighters's health is strongly recommended.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.3
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• pp.333-340
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• 2004

The use of the othotropic steel deck is steadily increased due to the advance of the technology in the steel bridges which recently have been longer. But the othotropic steel deck bridge is the structure that is very fragile to the fatigue, especially, the fatigue crack at the cross of the longitudinal rib and transversal rib is one of the biggest problems that othotropic steel deck bridges have. The causes of these fatigue cracks come from the secondary stress on out-plane behavior of transversal rib. In this study, we conducted the experiment to find the optimal details to improve fatigue strength on intersection between longitudinal rib and transversal rib in the othotropic steel deck bridge through numerical analysis using the experiment of the fatigue in the 3-dimensional real structure and program LUSAS. As a result of study, it is showed that the details of the korean standard section attached with a curved bulkhead plate is the most profitable. And, it is indicated that the stress which is generated when the reform improved section by parametic study can be reduced by about 50% at most or more. Along with the reduced stress and the longer interval between transversal ribs(G=400), the decreased steel amount by 4% and the shortened welding length by 34% make it possible to produce the othotropic steel deck bridge which is strong against fatigue.

• Journal of dental hygiene science
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• v.14 no.2
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• pp.256-263
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• 2014

The purpose of this study was to examine the relationship among burnout, compassion fatigue, compassion satisfaction and social support of clinical dental hygienists. The subjects in the study were 313 dental hygienist who were randomly selected in dental clinic and hospital, which were located in Daejeon, South and North Chungcheong province. Data were gathered using structured questionnaires from June 17 to July 31, 2013. The major findings of the study were as follows: 1. As for burnout by general characteristics, there were statistically significant difference according to age, marital status, clinical career, agency work type and job position. 2. The relationship of burnout and other variables was analyzed, and compassion fatigue had a significant positive effect on burnout, and compassion satisfaction and social support had negative effects on burnout. 3. As a result of analyzing which variables affected burnout, it's found that burnout were under the influence of agency work type, compassion fatigue, compassion satisfaction and social support. These variables made a 56.9% prediction of burnout. These findings provide strong empirical evidence for the importance of compassion fatigue, compassion satisfaction and social support in explaining burnout of clinical dental hygienists. Therefore, the effective human resource management programs should be developed to consideration with the dental hygienist work environment and the quality of service.