• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.1
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• pp.35-40
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• 2019

The objective of this paper is to identify the fatigue properties of carbon-fiber composite which is widely applied for the development of aircraft structures and obtain data for full-scale fatigue test. The durability and damage tolerance evaluation of composite structures is achieved by fatigue tests and parameters such as fatigue life factor and load enhancement factor. The specimens are made with carbon-fiber/epoxy UD tape and fabric prepreg. Fatigue tests are performed with several stress ratios and lay-up patterns. The Weibull shape parameters are analyzed by Sendeckyj model and individual fatigue lives with Weibull distribution. And the fatigue life factor and load enhancement factor considering reliability are evaluated.

• Journal of Aerospace System Engineering
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• v.14 no.6
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• pp.58-67
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• 2020

In this study, finite element fatigue analysis combined with a fatigue correlation factor is proposed to predict the bending fatigue life of a gear in an electro-mechanical aircraft actuator. First, stress-life curves are obtained for the gear material via a round bar fatigue test. Subsequently, stochastic stress-life (P-S-N) curves are derived for 50% and 1% failure probabilities, separately. The curves are applied to the fatigue analysis model of a single gear tooth, and the effect of the fatigue correction factor is analyzed. The analytical P-S-N curves reflecting the fatigue correction factor matched the experimental data. This shows that the analytical fatigue life is reliable and that the analysis technique is effective.

• Journal of the Korean Ceramic Society
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• v.30 no.3
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• pp.229-235
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• 1993

Thermal history and thermal stress of alumina specimen, which occured from thermal shock process, were calculated by finite difference method. Stress intensity factor and crack growth in cyclic thermal fatigue were calculated from single thermal shock temperature history and thermal stress. Cyclic thermal life were estimated by bending strength after cyclic thermal shock under critical thermal shock temperature. Calculated stress intensity factor was compared with real experimental thermal fatigue life of specimen. Fatigue life until critical stress intensity factor and real experimental result were comparable.

• Journal of Welding and Joining
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• v.6 no.1
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• pp.28-34
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• 1988

The fatigue test was carried out to evaluate the fatigue characteristics of the accelerated cooled (ACC) TMCP steel and its welded joint. From this study, it was confirmed that ACC TMCP steel has higher fatigue strength than conventional steels. After welding, however, the fatigue strength of ACC TMCP steel was deteriorated associated with HAZ softening when weld reinforcement was removed. On the other hand, with weld reinforcement, there is no effect of HAZ softening on the fatigue strength of welded joint because it is strongly dependant on the detail weld geometry i.e., stress concentration factor. Accordingly the fatigue strength of actual welded joint increases with decreasing the stress concentration factor of welded joint, regardless of HAZ softening.

• Journal of the Korean Society of Safety
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• v.15 no.3
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• pp.1-6
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• 2000

In fatigue crack growth test, it is important not only to analyze characteristics of fatigue crack growth but also to determine the threshold stress intensity factor, ${\Delta}K_{th}$. which is the threshold value of fatigue crack growth. Linear regression analysis using fatigue test data near the threshold is suggested to determine the ${\Delta}K_{th}$ in the standard test method but the ${\Delta}K_{th}$ can be affected by a fitting method. And there are some limitations on the linear regression analysis in the case of small number of test data near the threshold. The objective of this study is to investigate differences of the ${\Delta}K_{th}$ due to regression analysis method and to evaluate the relative error range of the ${\Delta}K_{th}$ in same fatigue crack growth test data.

• Korean Journal of Adult Nursing
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• v.17 no.3
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• pp.435-443
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• 2005

Purpose: This study investigated the degree of fatigue of hemodialysis patients, and finds the relationship between fatigue and self-efficacy, family support, and sleep factor. Also, this study was purposed to provide fundamental data to help set up a nursing plan and intervention for recovery and mitigation of hemodialysis patient's fatigue. Method: The subjects in this study were patients treated as hemodialysis patients in Kwangjoo City. Data, subjects are 143 patients. Fatigue was measured using Lee's scale(1991), Self-efficacy using Kim's scale(1995), and Family support using Kim's scale(1993). For the analysis of collected data, Cronbach alpha, descriptive statistics, t-test, ANOVA, Pearson's correlation coefficient, Stepwise multiple regression were used for statistical analysis by SPSSwin(version 11.0) program. Result: Fatigue degree of hemodialysis patients averaged 4.22. Among 143 hemodialysis patients, 70.63% patients answered that they had felt fatigue as noted in this study. The weariest time was after hemodialysis for 21.0% patients. There was significant difference according to the diagnosis period. The patients who were diagnosed over one year had felt more fatigue than ones who were diagnosed within one year. Fatigue was significantly associated with self-efficacy, family support, and sleep factor. Self-efficacy could explain 14.6% of fatigue. Conclusion: The fatigue degree relates with all, self-efficacy, family support, and sleep factor. Especially, it is affected by self-efficacy among them. Thus, the program should be developed to mitigate fatigue as the self-efficacy of hemodialysis is enhanced.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.6
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• pp.551-556
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• 2012

Fatigue is known to detrimentally affect a person's performance. Also, fatigue may reduce effectiveness and efficiency of marine officers and crew members. The purpose of this research is to understand on the status of the marine officers' fatigue. In this study, we carried out the questionnaire survey which is related to the marine officers' fatigue factors such as work, sleep and rest hour or period, sleepiness, casual factor, fatigue symptom, etc. The questionnaire contained 25 questions and it was distributed among 1,033 marine officers(deck officers 607 and engineers 426). The results of this survey show that marine officers' fatigue is a casual factor in marine accidents such as collisions, groundings and there was a fatigue difference between deck officers and engineers.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.10
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• pp.1151-1157
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• 2009

Nuclear power plants applying for the continued operation over design life are required to address the effects of reactor water environment in fatigue design requirement of the ASME Code. Reactor water environmental effects are generally evaluated by calculating fatigue correction factors on fatigue usage. This paper describes the application for pressurizer surge line of environmental fatigue correction factors and the strain rate impact in the application. From this paper, the environmental fatigue correction factors resulted from the assumption of a step change in temperature are especially compared with those calculated from the data measured during plant startup. As a conclusion of this paper, the design transient conditions applied to the fatigue design may be conservative in case of the environmental fatigue evaluation.

• 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.

• Journal of Ocean Engineering and Technology
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• v.5 no.1
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• pp.97-105
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• 1991

In this paper, the fatigue strength and the fatigue crack propagation behaviors of the round bar specimens which were spirally built up by welding and subsequently hardened by quenching were investigated. The material used was SF60 which was whdely employed in mechanical components, especially shafts. Fatigue tests were conducted at the fully reversed condition(R=-1) and axial and load control in the room temperature ahd air environment. The experimental results were expressed by both the range of stress intensity factor ($\Delta{K}$) and the effective range of stress intensity factor ($\Delta{K}_{eff}$). It was clarified that applying of quenching after the building up welding process improved the fatigue strength and the gatigue crack propagation property in the low range of $\Delta{K}$ of the built up round bar specimen.