• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.1
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• pp.125-134
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• 1989

Pseudo-random load waves for fatigue testing were generated by personal computer simulation and preliminary study was performed on the growth behavior of surface fatigue crack under random ladings. The closure behavior and growth rates of surface fatigue crack were significantly influenced by the characteristics of random waves. It was also found that the growth rates of surface fatigue crack under random loadings could not be always described by the effective stress intensity factor based on the concept of crack closure.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1647-1650
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• 2003

The Objective of this work was to design Surface Antenna Structure (SAS) and investigate fatigue behavior of SAS that was asymmetric sandwich structure. This term, SAS, indicates that structural surface becomes antenna. Constituent materials were selected considering electrical properties, dielectric constant and tangent loss as well as mechanical properties. For the antenna performance, SSFIP elements inserted into structural layers were designed for satellite communication at a resonant frequency of 12.5 GHz and final demonstration article was 16${\times}$8 array antenna. From electrical measurements, it was shown that antenna performances were in good agreement with design requirements. In cyclic 4-point bending, flexure behavior was investigated by static and fatigue test. Fatigue lift curve of SAS was obtained. The fatigue load was determined experimentally at a 0.75(1.875kN) load level. SAS concept is the first serious attempt at integration for both antenna and composite engineers and promises innovative future communication technology.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.60-64
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• 2001

In this paper, the tension-compression fatigue test method and the fatigue life characteristics of carbon fabric/epoxy laminate coupon are presented. To avoid the buckling during the compression, a proper design for the test coupons is essential. The critical buckling loads for the coupons are calculated by assuming the coupons as columns under two types of fixed conditions. The first is that both ends of each coupon are perfectly clamped, the second is that both ends of each coupon are simply supported. The strain-load curves are obtained by compressing the representative coupons, on each surface of which a strain gage is attached. The buckling loads obtained from the tests are all between the two calculated critical buckling loads. All the coupons are broken by the compression during the fatigue tests. It is estimated to be the reason that the fatigue load causes delamination before the eventual failure of each coupon, and sequentially the micro-buckling in the delaminated region drives each coupon into fatigue failure during the compression. The S-N curve, the fatigue life characteristics of carbon fabric/epoxy is obtained.

• Journal of the Korean Society for Railway
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• v.9 no.6 s.37
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• pp.695-700
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• 2006

This study investigates the effects of the material properties and the fatigue behavior in the SM490A material specimens due to the low-temperature atmosphere. In the fatigue behavior, the low-temperature affects the fatigue life. As the temperature get low, the fatigue limit increase, also As the yield strength and the tensile strength increase, the impact absorbed energy decrease. The difference of fatigue lift represents to normal distribution and it is larger between the room temperature and the low temperature, but in the result of the cumulative density function, the effect of temperature is not too large on it.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.108-111
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• 2003

The Objective of this work was to design Surface Antenna Structure (SAS) and investigate fatigue behavior of SAS that was asymmetric sandwich structure. This term, SAS, indicates that structural surface becomes antenna. Constituent materials were selected considering electrical properties, dielectric constant and tangent loss as well as mechanical properties. For the antenna performance, SSFIP elements inserted into structural layers were designed for satellite communication at a resonant frequency of 12.5 GHz and final demonstration article was $16\;{\times}\;8$ array antenna. From electrical measurements, it was shown that antenna performances were in good agreement with design requirements. In cyclic 4-point bending, flexure behavior was investigated by static and fatigue test. Fatigue life curve of SAS was obtained. The fatigue load was determined experimentally at a 0.75(1.875kN) load level. SAS concept is the first serious attempt at integration for both antenna and composite engineers and promises innovative future communication technology.

• Korean Journal of Health Education and Promotion
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• v.24 no.2
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• pp.29-44
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• 2007

Objectives: The administrative employees of government were analyzed on their levels of fatigue symptoms to reveal the various factors related to them. Methods: The self-administered questionnaires were performed, during the period between Dec. 5th, 2005 and Jan. 31st, 2006, to 1,005 individuals in the service of general administration located in Daejeon Metropolitan City. The survey items included subjects' socio-demographic and job-related characteristics, health-related behavior, degree of job demand, job autonomy, social support in work, type A behavior pattern, locus of control, sense of self-esteem, and degree of fatigue. The study results were analyzed and the authors came to the following major findings, by univariate and multiple regression analysis with degree of fatigue dependent variables and other variables independent. Results and Conclusions: The study results indicated that the level of fatigue symptoms is so complicatedly influenced by variable factors as well as job-related characteristics such as socio-demographic characteristics, rank in work, or job career, to a greater extent, by job specifications and personality traits(type A) like whether performing health-related behavior or not, job demand, job autonomy, social support in work, or sense of self-esteem. Thus the effective strategy for stress reduction among governmental employees requires additional programs focusing on innovated job specifications and managed personality trait.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.4
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• pp.1241-1250
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• 1996

The characteristics of fatigue cumulative damage and fatigue life of 8-harness satin woven CFRP composites with a circular hole under constant amplitude and 2-level block loading are estimated by Stochastic Makov chain model. It is found in this study that the fatigue damage accumulation behavior is very random and the fatigue damage is accumulated as two regions under constant amplitude fatigue loading. In constant amplitude fatigue loading the predicted mean number of cycles to a specified damage state by Markov chain model shows a good agreement with the test result. The predicted distribution of the fatigue cumulative damage by Markov chain model is similar to the test result. The fatigue life predictions under 2-level block loading by Markov chain model revised are good fitted to the test result more than by 2-parameter Weibull distribution function using percent failure rule.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.1
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• pp.83-90
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• 2004

In this study, CT specimens were prepared from spring steel(SUP9) processed shot peening which was room temperature and low temperature experiment. And we got the following characteristics from fatigue crack growth test carried out in the environment of room temperature and low temperature at $25^{\circ}C$, $-30^{\circ}C$, $-50^{\circ}C$, $-70^{\circ}C$,$-100^{\circ}C$, and $-150^{\circ}C$, in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range ΔKth in the early stage of fatigue crack growth (Region I)was increased but stress intensity factor range ΔK in the stable of fatigue crack growth (Region II) was decreased in proportion to decrease temperature. It is assumed that the fatigue resistance characteristics and fracture strength at low temperature and high temperature is considerably higher than that of room temperature in the early stage and stable of fatigue crack growth region.

• Journal of The Korean Society of Integrative Medicine
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• v.10 no.3
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• pp.53-62
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• 2022

Purpose : This research is a descriptive study that aimed to identify the levels of health promotion behaviors, fatigue, and depression of nursing students and confirm the effect of health promotion behaviors on fatigue and depression. Methods : Data were collected from September 27 to October 15, 2021 through survey questionnaires on 178 nursing students of 2 universities in G-do who voluntarily agreed to participate. The collected data were analyzed using SPSS 23.0, the general characteristics of nursing students were analyzed by frequency and percentage, and the levels of their health promotion behaviors, fatigue, and depression of nursing students was analyzed by mean and standard deviation. The relationship among the health promotion behaviors, fatigue, and depression was analyzed by Pearson's Correlation Coefficient. Multiple regression analysis was performed for the effects of health promotion behaviors on fatigue and depression of nursing students. Results : The nursing students' health promotion behaviors averaged 2.25±.43 points out of 5, and for each sub-factor, interpersonal relationship was the highest at 2.66±.49 points and physical activity was the lowest at 2.01±.60 points. Fatigue was 4.89±1.02 points out of 7 and depression was 10.52±9.10 points out of 63. A statistically significant correlation was found among health promotion behaviors, fatigue, and depression. Health promotion behaviors that significantly affected fatigue were stress management (𝛽=-.263, p=.004) and physical activity (𝛽=-.208, p=.026), which showed 35 % explanatory power on fatigue. Health promotion behaviors that significantly affected depression were spiritual growth (𝛽=-.342, p=.002), and physical activity (𝛽=-.231, p=.016), which showed 31 % explanatory power for depression. Conclusion : This study is meaningful in that it provided basic data to develop an effective health promotion behavior program to prevent and manage nursing students' fatigue and depression, by identifying and analyzing the sub-factors of health promotion behaviors affecting their fatigue and depression.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2008.04a
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• pp.50-55
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• 2008

In order to investigate and estimate the cause of fatigue crack occurred to curved girder bridge that is used during 20 years, in this study, filed tests to obtain the characteristic of stress hysteresis were performed under the real traffic flows. From these test results, we analyzed the cause of fatigue crack for various fatigue crack patterns. Also, the characteristic of structural behavior for the curved girder bridge were examined from the FE analysis. In addition, to retrofit various fatigue cracks occurred in the bridge, FE analyses considering the characteristics of crack patterns were performed and retrofitting methods were suggested.