• Title/Summary/Keyword: Fatigue Break

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Numerical Simulation of Fatigue Growth of Multiple Surface Crack under Fatigue Load (피로 하중하에서의 복수표면크랙진전에 관한 수치시뮬레이션)

  • 한문식
    • Transactions of the Korean Society of Automotive Engineers
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    • v.10 no.6
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    • pp.133-141
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    • 2002
  • This paper describes a versatile finite element technique which has been used to investigate wide range of structural defects of practical importance. The procedure automatically remeshes the three-dimensional finite element model during the stages of crack growth. Problems include the surface cracks in leak-before-break situations, the shape development of multiple surface defects.

Analysis of Workload of the Domestic Coastal Ship Duty Officer to Prevent Marine Accidents (해양사고 예방을 위한 국내 연안선 항해당직자의 업무 부하 분석)

  • Yang, Young Hoon;Kim, Hongtae;Jang, Junhyuk
    • Journal of the Ergonomics Society of Korea
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    • v.36 no.5
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    • pp.579-587
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    • 2017
  • Objective: The purpose of this study is to measure the workload of Korea coastal ship crew members, to investigate whether they are following work-break time regulations and to identify the main causes of their workload. Background: According to the US Coast Guard, about 33% of human casualties are reported to be due to fatigue, and 30% of marine casualties reported by the British Marine Accident Investigation Agency (MAIB) are attributed to crew fatigue. But the coastal ship are not managed for business hours and breaks despite the harsh environment. Method: The workload of duty crew members on the 100 domestic coastal vessels was measured. It was also investigated whether they are following domestic and international work-break time regulations. Finally, the marine accidents resulted from the fatigue of the crew was analyzed. Results: As a result of workload analysis, the workload on the 42~62% of the vessels exceeded the standard of working time on the related regulation. The workload increased with the number of inbound and outbound ports. Especially, in the system where there are two seafarers, the workload exceeded the working time requirement. As a result of the marine accidents analysis on 100 vessels, it was found that collision and grounding occurred due to fatigue, workload and drowsiness in 7 marine accidents out of 30 marine accidents. Conclusion: It is necessary for the shipping companies to introduce an operation management manual for the management of the crews' workload and reasonable crew arrangement. It is also required for crew members to easily record work times and for shipping companies to manage the record. It would be possible to prevent many marine accidents by providing adequate rest to the crews and flexibly adjusting their working hours. Application: The results of this study can be used as fundamental data to manage crews' fatigue and to make job management manuals.

Effects of Health Behaviors on Perceived Physical and Psychological Job Stress Among Korean Manufacturing Workers (제조업 근로자의 건강행위와 직무로 인한 스트레스 자각증상의 관련성)

  • 박경옥;김인석;오영아
    • Korean Journal of Health Education and Promotion
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    • v.21 no.3
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    • pp.195-211
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    • 2004
  • Stress is a primary health promotion issue in worksite research because psychological distress is closely related not only to workers' health status but also to their job performance. This study identified the significant health behaviors affecting workers' job-related stress in Korean manufacturing industry with the national survey data conducted by the Korean Occupational Safety and Health Agency in 2003. A total of 7,818 factory workers in 1,562 manufacturing companies participated in the Korean nation-wide occupational health survey and 3,390 workers answered that they had any stressors in their workplace among the 7,818 workers finally participated in the analysis. Participants were selected by the stratified proportional sampling process by manufacturing industry classification, company size, and company locations (8 metropolitan and 8 non-metropolitan regions) in Korea. Trained interviewers visited the target companies and interviewed the factory workers randomly selected in each company. Smoking, drinking, weight control, exercise, sleeping, break time at work, and perceived fatigue were included in the health behavior construct. Stress symptoms was consisted of physical and psychological stress with 8 items. All survey responses were anonymously coded into the SPSS statistical program and testified using stepwise multiple regression analysis. Male workers were 73.5% and the 30s were 40.0% among the age groups. The married and the high school graduate were majority with 52.1% and 61.8% each. Current smokers were 44.7% and More than 50% of the participants drank alcohol sometimes. No exercise group was 59.3% and the participants who dissatisfied with their daily sleeping hours were 43.5%. In t-test and analysis of variance, the significant general characteristics associated with physical and psychological job stress were young age (p<0.001), single marital status (p<0.001), and short working period at the present company (p<0.001). The health behaviors related to physical job stress were current smoking, weight change during the past one year (p<0.001), weight control effort (p<0.001), exercise (p<0.001), daily sleeping dissatisfaction (p<0.001), break time, and perceived fatigue (p<0.001). All 10 health behavior factors were significantly associated with psychological job stress (p<0.05). Weight change, weight control effort, exercise, daily sleeping dissatisfaction, little break at work, and high perceived fatigue were significant factors affecting job stress. Daily sleeping dissatisfaction, little break at work, little exercise, weight change for the past one year and young age were selected as the significant health behavior and general factors affecting physical job stress symptoms in stepwise multiple regression analysis. The five factors explained 18.9% of the physical stress score variance. Six factors were selected as the significant health behaviors affecting psychological job stress: daily sleeping dissatisfaction, little exercise, frequent drinking alcohol, high perceived fatigue, little break at work, and little weight control effort. The six factors explained 10.6% of the psychological stress score variance.

Crack Opening Behavior of Perpetrated Crack Under Fatigue Load

  • Nam, Ki-Woo;Ahn, Seok-Hwan
    • Journal of Mechanical Science and Technology
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    • v.16 no.1
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    • pp.24-31
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    • 2002
  • The leak-before-break (LBB) behaviors of a structural component under high and low fatigue loads are an important problem in nuclear power plants, liquid nitrogen gas tankers and chemical plants. This paper is an experimental study to evaluate the crack opening behavior after penetration for plate and pipe specimens. Crack opening displacement after penetration under low fatigue load could be satisfactorily determined at the center of the plate thickness regardless of the specimen size. In the case of high fatigue load, it is shown that the crack opening displacement at the center of a penetrated crack carl be derived using the gross stress, $\sigma$/sug G/, and the front surface crack length, a$\_$s/, together with the back surface crack length, a$\_$b/.

A Study on the Short Break Time on VDT Work using EMG (근전도를 이용한 VDT 작업시 짧은 휴식시간에 관한 연구)

  • Kim, Yu-Chang;Lee, Jun-Pal
    • Journal of the Ergonomics Society of Korea
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    • v.26 no.4
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    • pp.41-47
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    • 2007
  • This paper suggested the best work conditions including short break time and the number of mouse clicks on the computer work for the prevention of MSDs on VDT work. Fatigue measures included EMG based parameters. The short break time conditions are grouped into 7, 15, and 30 seconds after every work for 10 min and the number of mouse clicks are divided into 10, 20, and 30 clicks/min. The result of the ANOVA of the shift value of %MVC(Maximum Voluntary Contraction) showed the following: 1) There was a considerable difference as regards to the break time except the number of mouse clicks on the upper trapezius muscle(p$<$0.05). The best conditions were shown in 15 sec after every 10 min and 30 clicks/min. 2) There were considerable differences as regards to the number of mouse clicks except the break time on the extensor digitorum muscle and extensor carpi ulnaris muscle(p$<$0.05). The best conditions were shown in 7 sec after every 10min and 10 clicks/min.

Study on Fatigue Behavior of Carbon Fiber Reinforced Polyimide Composites (탄소섬유강화 복합적층판의 피로특성에 관한 연구)

  • 이창수;황운봉;한경섭;윤병일
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.1
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    • pp.49-60
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    • 1991
  • Fatigue behavior of carbon fiber reinforced polyimide composite materials was studied experimentally and analytically. The physical variables, such as cyclic displacements and hysteresis loop energy were observed during fatigue tests. Fatigue life of the investigated [0/90]$_{2S}$ laminates was predicted by H'||'&'||'H models which was proposed based on the fatigue modulus and resultant strain. The predicted fatigue life by H'||'&'||'H curves was reasonably close to the experimental data. Fractography study shows that fatigue failure mechanism of [0/90]$_{2S}$ laminated composite materials involves failure break, matrix tearing and fiber-matrix debonding as well as delamination of layers.

Effects of Sleep and Fatigue on Soldiers Health Promoting Behaviors in Korean Army (육군 병사의 수면과 피로가 건강증진행위에 미치는 영향)

  • Hong, Eunji;Choi-Kwon, Smi
    • Korean Journal of Adult Nursing
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    • v.28 no.1
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    • pp.106-115
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    • 2016
  • Purpose: This study aimed to investigate sleep, fatigue, and the level of health promoting behaviors in Korean army soldiers. The factors influencing on health promoting behaviors of soldiers were also identified. Methods: A cross-sectional descriptive survey design was used. Data was collected from 269 soldiers in four military units of Korea in July 2015. Verran and Snyder-Halpern Sleep Scale, Fatigue Severity Scale, and Health Promoting Lifestyle Profile-II were used. Results: The health promoting behaviors were significantly different by perceived health status (p<.001) and presence of fatigue (p<.001). There were significant correlations between quality of sleep, fatigue, and health promoting behaviors of the subjects. In a multiple linear regression analysis, the level of health promoting behaviors were lower in the subjects with high level of fatigue (p<.001) and with fair perceived health status (p=.003). Conclusion: In order to increase health promoting behaviors of soldiers, it takes into account of soldiers' fatigue and perceived health status. Environmental arrangement for soldiers for the break time is needed urgently to decrease their fatigue as well as to improve their sleep quality.

Effect of Graston Technique on Fatigue Recovery after High-Intensity Exercise of the Quadriceps Femoris

  • Son, Ho-Hee
    • Journal of the Korean Society of Physical Medicine
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    • v.13 no.4
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    • pp.9-17
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    • 2018
  • PURPOSE: This study was conducted to compare the effects of the Graston-based massage method and microcurrent application on muscle fatigue after causing muscle fatigue of the quadriceps femoris by applying high-intensity exercise. METHODS: Study subjects (56 healthy subjects in their 20s) were randomized into a microcurrent group (MG), Graston group (GG), and control group (CG). To induce fatigue of the quadriceps femoris, the subjects performed squats 100 times without a break within about 5 minutes. Muscle fatigue was measured immediately after performing squats and 15 minutes after intervention. To measure muscle fatigue, surface electromyogram (EMG) was used to obtain and compare the median frequency. Microcurrent or Graston massage was applied to their quadriceps muscles 15 minutes after performing the squats. RESULTS: Muscle fatigue increased significantly in the vastus lateralis before and after intervention in the Graston group (p<.05), while no significant difference was observed in the rectus femoris and vastus medialis (p>.05). There were also no significant differences in the microcurrent group or the control group. CONCLUSION: Both the microcurrent group and Graston group showed a tendency for increasing median frequency values compared to the control group, but there was no significant difference except in the vastus lateralis treated with the Graston technique. Although there was no significant difference, the Graston technique could be utilized to reduce the occurrence of DOMS by preventing muscle fatigue in clinical practice or sports medicine.

Characteristics of Elastic Waves Generated by Fatigue Crack Penetration and Growth in an Aluminum Plate

  • Ahn, Seok-Hwan;Nam, Ki-Woo
    • Journal of Mechanical Science and Technology
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    • v.17 no.11
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    • pp.1599-1607
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    • 2003
  • The characteristics of elastic waves emanated from crack initiation in 6061 aluminum alloy subjected to fatigue loading are investigated through experiments. The objective of the study is to determine the differences in the properties of the signals generated from fatigue test and also to examine if the sources of the waves could be identified from the temporal and spectral characteristics of the acoustic emission (AE) waveforms. The signals are recorded using nonresonant, flat, broadband transducers attached to the surface of the alloy specimens. The time dependence and power spectra of the signals recorded during the tests were examined and classified according to their special features. Six distinct types of signals were observed. The waveforms and their power spectra were found to be dependent on the crack propagation stage and the type of fracture associated with the signals. The potential application of the approach in health monitoring of structural components using a network of surface mounted broadband sensors is discussed.

The Fatigue Behavior by Variety of Crack Length of Surface Cracked Plate with Stress Concentration Part (응력집중부를 갖는 표면균열재의 균열길이 변화에 따른 피로거동)

  • 남기우;김선진
    • Journal of Ocean Engineering and Technology
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    • v.9 no.1
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    • pp.83-91
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    • 1995
  • Surface defects in structural members are apt to be origins of fatigue cracks growth, which may cause serious failure of whole structures. Most structure has a part where stress concentrates such as welded joints, corner parts, etc. And then, analysis on crack growth and penetration from these defects, therefore, is one of the most important subjects for the reliability of LBB design. The present paper has performed an experimental and analysis on the fatigue crack propagation by variety in crack length of surface cracked plate with stress concentration part. The crack growth behavior can be explained quantitatively by using Newman-Raju equation and the stress partitioning method proposed by ASME B&P Code Sec. XI. The stress concentration factor $K_t$ has affected on the crack growth. The crack growth after penetration depends upon the initial front side crack length.

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