• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.7
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• pp.2159-2166
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• 1996

The stochastic properties of variation in fatigue crack growth are important in reliability and stability of structures. In this study,the stochastic model for the variation of fatigue crack growth rate was proposed in consideration of nonhomogeneity of materials. For this model, experiments were ocnducted on 7075-T6 aluminum alloy under the constant stress intensity factor range. The variation of fatigue crack growth rate was expressed by random variables Z and r based on the variation of material coefficients C and m in the paris-Erodogan's equation. The distribution of fatigue life with respect to the stress intensity factor range was evaluated by the stochastic Markov chain model based on the Paris-Erdogan's equation. The merit of proposed model is that only a small number of test are required to determine this this function, and fatigue crack growth life is easily predicted at the given stress intensity factor range.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1453-1460
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• 2002

Creep-fatigue crack growth models have been proposed employing $(C_t)_{avg}$ as a crack tip parameter characterizing the time-dependent crack growth. The basic assumptions made in these previous models were ideal creep reversal conditions such as no creep reversal and complete creep reversal condition. Due to this assumption, the applicability of the models was limited since they did not consider partial creep reversal condition which is usually observed in many engineering metals at high temperature. In this paper the creep reversal parameter, Temperature;$C_R$, which was defined by Grover, is critically evaluated to quantity the extent of partial creep reversal at the crack tip. This approach does not rely on any simplifying assumptions regarding the extent of the amount of creep reversal during the unloading part of a trapezoidal fatigue cycles. It is shown that the $(C_t)_{avg}$ value calculated for 9Cr steel agrees well with the experimentally measured one. It is argued that the extent of improvement is not significant when the result is compared with that of the conventional model which has an assumption of full creep reversal behavior.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.629-640
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• 2016

This study was conducted to investigate the influence of job stress, fatigue symptoms and job satisfaction on turnover intention among dental hygienists. Overall, 516 dental hygienists who work in dental clinics were surveyed using a standardized self-administered questionnaire from April 1 to June 30, 2015. Mean turnover intention was compared to each independent variable tested by t-tests and ANOVA, correlation among turnover intention, job stress, fatigue symptoms and job satisfaction was calculated by Pearson's correlation coefficient, and covariance structure analysis was used to evaluate whether turnover intention was associated with job stress, fatigue symptoms and job satisfaction. Turnover intention was significantly higher among subjects with higher job stress and fatigue, as well as those with lower job satisfaction. Additionally, turnover intention was significantly positively correlated with job stress and fatigue symptoms, while turnover intention was negatively correlated with job satisfaction. Covariance structure analysis revealed job stress had a greater impact on turnover intention than fatigue and job satisfaction, high job stress and fatigue, the lower the job satisfaction showed that the effect of increasing the turnover intention. Overall, these results indicate that turnover intention of dental hygienists are more heavily influenced by job satisfaction and job stress than fatigue. Therefore, efforts are needed to reduce job stress and fatigue, as well as to improve job satisfaction to reduce the degree of turnover intention among dental hygienists.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.4
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• pp.1759-1768
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• 2012

The present study was intended to measure the level of fatigue symptoms among nurses working for a university hospital and to reveal its related factors. The self-administered questionnaires were given to 450 nurses during the period from October 1st to 31st, 2010. As a results, the level of fatigue symptoms were 75.1% in normal group, and the high-risk group 24.9%. The level of fatigue symptoms reflected in job stress contents were higher as job demand was higher, and the autonomy of job and the supervisor support was lower. In correlations, fatigue symptoms were found to be in a positive correlation with job demand, whereas in negative correlation with autonomy of job and supervisor support. The adjusted odds ratio of fatigue symptoms on job demand were significantly increased in the high risk group than in low group, but autonomy of job. were significantly decreased in the high risk group than in low group. In conclusion, the study results indicated that the level of fatigue symptoms is independently influenced by job stress contents.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.5
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• pp.2156-2169
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• 2012

This study was performed to find out the relationship between farmer's syndrome and self-conscious fatigue symptoms in farmers of suburban area. The questionnaire was prepared to survey the socio-demographic characteristics, health-related behaviors, farming activities, farmer's syndrome, and self-conscious fatigue symptoms of the farmers, and the survey was carried out from April 1 to June 30, 2011 by interviewing 296 farmers residing suburban area of Daejeon city. As a results, the ratio of farmers who had positive farmer's syndrome, doubtful syndrome, and no syndrome were 34.1%, 47.6%, and 18.2%, respectively. The farmer's syndrome was positively correlated with the self-conscious fatigue symptoms, and farmers with self-conscious fatigue symptoms in high risk group were at higher risk of having farmer's syndrome. The results of hierarchic multiple regression analysis indicated that sex, education, health, and self-conscious fatigue symptom were correlated with the farmer's syndrome. Among the affective factors variables, independently self-conscious fatigue symptom was the most influential. As a conclusion, the occurrence of farmer's syndrome was influenced by the socio-demographic characteristics, health-related behaviors, and self-conscious fatigue symptoms of the farmers. Especially, self-conscious fatigue symptom was independently influenced the occurrence of farmer's syndrome.

• Journal of Korean Society of Steel Construction
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• v.20 no.5
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• pp.625-632
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• 2008

In the companion paper (Model Development), an analytical model estimating the available rotation capacity of fully restrained beam-column connections in special steel moment-resisting frames was proposed. In this paper, two limit states were considered as the connection rotation capacity criteria: (i) strength degradation failure when the strength falls below the nominal plastic strength due to the local buckling of the beam's cross-section and (ii) low-cycle fatigue fracture caused by plastic strain accumulation at the buckled flange after only a few cycles of high-amplitude deformation. A series of analyses are conducted using the proposed model with two limit states under monotonic and cyclic loadings. Beam section geometric parameters, such as flange and web slenderness ratios, varied over the practical ranges of H-shapedbeams to observe their effect on the rotation capacity and low-cycle fatigue life of pre-qualified WUF-W connections.

• Clean Technology
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• v.18 no.4
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• pp.347-354
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• 2012

In this study, simulation works have been performed for the $CO_2$ removal process contained in the DME production process using NMP (N-methyl-2-pyrrolidone) as a solvent. PRO/II with PROVISION release 9.1 at Invensys was used as a chemical process simulator and NRTL activity coefficient model with Henry's law option and Soave-Redlich-Kwong equation of state were used for thermodynamic models. For the determination of the binary interaction parameters in NRTL model, regression works have been performed to match the experimental thermodynamic data. Optimal feed tray location which minimizes the reboiler heat duty was determined.

• Composites Research
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• v.36 no.1
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• pp.16-24
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• 2023

This paper presents a multi-scale progressive fatigue damage model incorporating the model for interfacial debonding between fibers and matrix. The micromechanics model for the progressive interface debonding was adopted, which defined the four different interface phases: (1) perfectly bonded fibers; (2) mild imperfect interface; (3) severe imperfect interface; and (4) completely debonded fibers. As the number of cycles increases, the progressive transition from the perfectly bonded state to the completely debonded fiber state occurs. Eshelby's tensor for each imperfect state is calculated by the linear spring model for a damaged interface, and effective elastic properties are obtained using the multi-phase homogenization method. The fatigue damage evolution formulas for fiber, matrix and interface were proposed to demonstrate the fatigue behavior of CFRP laminates under cyclic loading. The material parameters for the fiber/matrix fatigue damage were characterized using the chaotic firefly algorithm. The model was implemented into the UMAT subroutine of ABAQUS, and successfully validated with flat-bar UD laminate specimens ([0]₈,[90]₈, [30]₁₆) of AS4/3501-6 graphite/epoxy composite.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.351-359
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• 2017

This study examined emotional labor, fatigue, and musculoskeletal pain in hospital nurses. The study sample included 235 hospital nurses. The data were collected by questionnaire and analyzed with descriptive statistics, t-test, ANOVA, Scheffe test, Pearson's correlation coefficients, and multiple regression.The average emotional labor score was 3.27, and of fatigue was 2.04. The musculoskeletal pain score was 4.43. Emotional labor and fatigue are significantly positively associated with musculoskeletal pain(r=.180, p=.006; r=.278, p<.001). Emotional labor was positively associated with the degree of fatigue(r=.353, p<.001). The significant predictors of musculoskeletal pain for nurses were physical fatigue(${\beta}=.324$, p<.001) and gender(female)(${\beta}=.171$, p=.009), explaining 13.7% of the variance in musculoskeletal pain(F=16.271, p<.001). The results suggest that engaging in emotional labor related to nursing tasks increases the risks of fatigue and musculoskeletal pain. Therefore, it is important to develop a management program to relieve the emotional labor, fatigue, and prevent musculoskeletal pain for clinical nurses.

• Magazine of the Korea Concrete Institute
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• v.9 no.3
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• pp.127-135
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• 1997

In this study, the wedge splitting tcst (WST) was carried out for the fatigue wack growth behavior of concrete. Selected test variables were concrete compressive strength of 28, 60 and 118 MI%, and stress ratio with 2 levels (6. 13%). In oder to make the designed stress ratio, the maximum and thr minimum fatigue loading level were 75-85% and 5- 10% of ultimate static load, respectively. Fatigue testing was preceded by crack mout.h opening displacement (CMOI)) compliance calibration tcst, and then the fatigue crack growth was computed by crack lcngth vs. (lMOI) compliance relations acquisited by the CMOD compliance calibration technique. To evaluate thc validity of CMOD compliancc calibration techniquc, the crack length p~mlicted by this method was cornpard with the crack length by linear elastic fracture mechanics(LEFIbl) and dyeing test. On the basis of the experimental results, a LRFhl-based c.mpirica1 model for f'at,igue crack growth rate(da/dN-AKI relationships) was presented. The fat,igut. crack growth ratc increased with the strength of concwtc. It appcars that t.he da/tiN-AKI relationships was influenced by stress ratio, however, the effect is diminished with an increase of strength. The comparisons between CblOl) compliance calibration technique anti the other. methods gave the validity of' ('MOD compliance calibration technique for the LZXT.