• The Journal of the Convergence on Culture Technology
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• v.6 no.3
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• pp.347-352
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• 2020

In this study, the variation of track impact factor according to the spring stiffness change rate of sleeper resilience pad was analyzed based on field measurements. In addition, the correlation between field measurement results and 7 million fatigue test results was verified. The fatigue effect diagram of the sleeper resilience pads was presented considering the nonlinear deterioration characteristics of the sleeper resilience pads used for the STEDEF track. Based on the field measurement results, the nonlinear characteristics of the track impact factor for the spring stiffness change rate over 30% of sleeper resilience pad on the track impact factor-track support stiffness diagram were analyzed to be consistent with the fatigue test results.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.444-450
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• 2010

In the present study, the microscopic degradation of copper and copper alloy subjected to cyclic deformation has been evaluated by the electrical resistivity measurement using the DC four terminal potential method. The copper (Cu) and copper alloy (Cu-35Zn), whose stacking fault energy is much different each other, were cyclically deformed to investigate the response of the electrical resistivity to different dislocation substructures. Dislocation cell substructure was developed in the Cu, while the planar array of dislocation structure was developed in the Cu-35Zn alloy increasing dislocation density with fatigue cycles. The electrical resistivity increased rapidly in the initial stage of fatigue deformation in both materials. Moreover, after the fatigue test it increased by about 7 % for the Cu and 6.5 % for the Cu-35Zn alloy, respectively. From these consistent results, it may be concluded that the dislocation cell structure responds to the electrical resistivity more sensitively than the planar array dislocation structure evolved during cyclic fatigue.

• The Journal of Korean Physical Therapy
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• v.27 no.4
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• pp.207-213
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• 2015

Purpose: The aim of the current study was to investigate EMG activity on dynamic balance of subjects with functional lumbar instability following fatigue of low back. Methods: The subjects (24 university students) were divided into 2 groups; functional lumbar instability group (6 males and 6 females) and lumbar stable group (7 males and 5 females) who could complete a questionnaire and undergo a prone instability test. All participants were evaluated for distribution of muscle activity using the TeleMyo DTSTM system. Dynamic balance was tested by Y balance test. This study was conducted for measurement of EMG activity on dynamic balance with the difference between FLIG and control group following muscle fatigue. Results: The functional lumbar instability group (FLIG) showed a significantly lower YBT score (%) of anterior, posterolateral direction on Y-balance test (YBT) in dynamic balance than the lumbar stable group (LSG) (p<0.05). The FLIG was significantly lower than the LSG in anterior direction in EMG activity(%) of MF, RA, ES, GMX, GME, RF, and posteromedial direction in EMG activity(%) of IO, ES and then posterolateral direction in EMG activity(%) of IO, ES in dynamic balance (p<0.05). There was significant correlation of MF, RA, and GMX in anterior reach direction (p<0.05) and ES, GME (p<0.01) and IO, ES in posteromedial reach direction (p<0.05) and EO, ES, GMX in posterolateral reach direction (p<0.05) there was positive correlation. Conclusion: This study showed that FLIG effected EMG activity by dynamic balance following muscle fatigue. Further study is needed for measurement of various ages and work with lumbar instability for clinical application.

• Journal of Convergence for Information Technology
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• v.8 no.2
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• pp.67-75
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• 2018

We sought to develop a multi-dimensional tool for measuring and understanding nurse fatigue. The participants were 301 nurses working in four hospitals in Seoul, South Korea. Basic items were developed after a preliminary literature review, and content validity was verified by a group of experts. The first 52 items from which the fatigue measurement tool was to be developed were tested for construct validity and were reduced via factor analysis to 31 items. Following a confirmatory factor analysis, the items were further reduced to 23 items in three categories: physical, mental, and emotional. A confirmatory factor analysis found the items to be adequate. The fatigue scale was found to have high construct validity and reliability. This scale is expected to serve as a preliminary data-gathering tool to assess the level of nurse fatigue and to develop interventions to alleviate it.

• Journal of muscle and joint health
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• v.15 no.1
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• pp.53-61
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• 2008

Purpose: The purpose of this study was to observe the changes of the pain, fatigue, perceived health status, disability in ADL, and depression after Tai Chi for arthritis. Method: The subjects were 19 osteoarthritis women enrolled at one primary health care post. They have agreed to participate in this study, and participated in the 12-week Tai Chi program from Dec. 2006 to Mar. 2007, and all the measurement processes in right after, 2 months later, and 4 months later after Tai Chi program. The measurement tools of this study were all self-reported questionnaires such as Numerical Rating Scale (0-100) for pain, fatigue, and perceived health status, Korean-WOMAC (Western Ontario and McMaster University Osteoarthritis) Index for joint stiffness, Korean Health Assessment Questionnaire, and CES-Depression scale. Results: The repeated measure ANOVA revealed the significant differences on pain among the right after, 2 months later, and 4 months later the program. Especially 2 months later after program, pain was significantly increased than right after by t-test. There were no significant differences on fatigue, perceived health status, disability in ADL, and depression. Conclusion: Pain was increased after Tai Chi for arthritis program, but fatigue, perceived health status, disability in ADL, and depression were not changed until 4 months after Tai Chi program.

• Journal of Ocean Engineering and Technology
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• v.5 no.2
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• pp.76-84
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• 1991

본 연구는 피로수명 평가를 위한 새로운 파괴역학적 parameter의 확립에 관한 연구이다. 실질적으로 피로파괴가 일어나는 피로 균열선단의 국소영역에서 변형분포를 미소원형격자측정법을 이용하여 실험적으로 명확히 밝혀내었다. 그리고 이 결과를 기초로 하여 국소피로 변형율장을 대표할 수 있는 피로변형율 확대계수 $\Delta$A를 제안하였다. 또한 새로운 parameter $\Delta$A의 유효성을 여러 피로조건에서 검토한 결과, 균열선단 국소 영역에서 피로 변형율 확대계수 $\Delta$A에 의하여 피로 균열전파 속도평가를 일의적으로 나타낼 수 있음을 확인하였다.

• Journal of Ocean Engineering and Technology
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• v.17 no.1
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• pp.47-54
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• 2003

In this study, the residual stress and the acoustic emission Charactreistics from fatigue crack propagation were investigated, bused on the welded material of STS316L. The residual stress of welding locations could be evaluated by ultrasonic parameters, such as L$_{CR}$ wave velocity and L$_{CR}$ wave frequency； the residual stress between base metal and weld metal was evaluated. In the fatigue tests, three types of signals were observed, regardless of specimen condition, base metal, and weld metal. Based on NDE analysis of AE signals by the time-frequency analysis method, it should also be possible to evaluate, in real-time, the crack propagation and final fracture process, resulting from various damages and defects in welded structural members.

• Proceedings of the KAIS Fall Conference
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• 2009.12a
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• pp.1010-1013
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• 2009

In this paper we propose the measurement of muscle fatigue using STFT(short time fourier transfom). The proposed method is time-frequency representation of muscle activity. We suggest that the proposed method can replace the classical muscle fatigue monitoring method using the median frequency.

• Journal of the Korean Society for Heat Treatment
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• v.8 no.4
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• pp.326-332
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• 1995

Using natural frequency measurement method, which is one of NDT method, natural frequency of the hot-rolled mild steel plate(specimen) under fatigue loading was measured. Between the degradation of the specimen under fatigue loading and the variation of the natural frequency of the specimen was investigated. As a result, the degradation of the specimen was described and monitored as variation of natural frequency of specimen. The natural frequency of specimen decreased gradually under fatigue loading. This means the variation of material properties of specimen. Especially. It means the variation of Young's modulus of specimen.

• Journal of Ocean Engineering and Technology
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• v.19 no.4 s.65
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• pp.21-27
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• 2005

Large welded structures, including ships and offshore structures, are normally in operation under cyclic fatigue loadings. These structures include many geometric discontinuities, as well as material discontinuities due to weld joints. The fatigue strength at these hot spots is very important for the structural performance. In the past, various Non Destructive Evaluation (NDE) techniques have been developed to detect fatigue cracks and to estimate their location and size. However, an important limitation of most of the existing NDE methods is that they are off line; the normal operation of the structure has to be interrupted, and the device often has to be disassembled. This study explores the development of a structural health monitoring system, with a special interest in applying the technique to welded structural members in ship and offshore structures. In particular, the impedance based structural health monitoring technique that employs the coupling effect of piezoceramic (PZT) materials and structures is investigated.