• Journal of Ocean Engineering and Technology
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• v.15 no.2
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• pp.94-98
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• 2001

fatigue life and nondestructive evaluation were examined experimentally using surface crack specimen and compact tension specimen of 5083 aluminium alloy. Acoustic emission signals emanated during failure of aluminum alloys has been the subject of numerous investigations. Possible sources of AE during deformation have been suggested as the dislocations, fracture of brittle particles and debonding of these particles from the alloy matrix. Fatigue life and penetration behavior of long surface crack can be evaluated quantitatively using K values proposed by authors. The influence of stress ratio on the frequency characteristics of AE signals were investigated.

• Journal of the Korean Society of Safety
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• v.23 no.5
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• pp.105-110
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• 2008

This study focused on the decreased effect of the work load on using the lower extremity supporter in kneeling posture. Fatigue measures included subjective discomfort ratings through the use of the Borg's CR-10 scale based parameters. The resting period and work method were considered as independent variables. The break time conditions are grouped into 10 seconds after work for 1 min and not exist break time. The method of work conditions are divided into four types. There are kneeling with the lower extremity supporter, kneeling with the knee protector, just kneeling and squatting. The result of the ANOVA of the shift value of subjective discomfort showed the followings: 1) There were differences as regards to the method of the work, the break time and the part of body($p{\leq}0.05$). 2) The lower extremity supporter showed the least subjective discomfort in other part of body except the upper leg.

• Journal of the Ergonomics Society of Korea
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• v.36 no.4
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• pp.293-303
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• 2017

Objective: This study aims to evaluate visual discomfort and visual fatigue caused by watching HMD and smartphones by conducting both subjective and objective measure. Background: With the rapid development of mobile Head-Mounted Display (HMD), the problem of visual discomfort and visual fatigue caused by watching Virtual Reality (VR) contents became a crucial concern for consumers and manufacturers, especially given that the casing of mobile HMD keeps the phone at a specified distance from the lenses that is close to the eyes. Method: Two smartphones were chosen for a preliminary study: LG G5 and Galaxy S7. As for a main study, iPhone 6S and Galaxy S7 were used. After being exposed to the selected clips, participants were asked to answer Simulator Sickness Questionnaire (SSQ) and went through optometric tests that measure tear break-up time, spherical equivalent, and contrast sensitivity. Results: The subjective assessments indicate that HMD causes more visual discomfort compared to watching a smartphone. Furthermore, the experimental result confirms that watching a HMD causes more eye dryness compared to smartphones. Conclusion: The result of the study compared visual discomfort and visual fatigue of two different displays, HMD and smartphone, and confirmed that watching HMD causes more visual discomfort and visual fatigue. Application: Ultimately, this study could help manufacturers understand the strengths and weaknesses of different display forms, providing guidance for an effective application of HMD.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1790-1795
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• 2000

The purpose of this papery is to introduce a new spacer damper's design for the bundle transmission lines network. It has the design, the main characteristics and advantage of this new kind of spacer damper. To reply to this problems, France, Japan and other countries had developed through many years a spacer damper with an automatic system. While the automatic clamping device are free of maintenance such as fatigue Break and aeolian vibration, imported price are so high. Now it is necessary to design, manufacture and certificate these automatic clamping device spacer damper.

• Journal of Ocean Engineering and Technology
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• v.11 no.3
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• pp.29-38
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• 1997

Crack penetration behavior by fatigue crack propagation and measurements of AE before-and-after crack penetration were examined using SS41 steel plate. Experimental crack shape of SU type was in good agreement with calculated shape rather than S type. Crack propagation behavior on the front surface appears not to change markedly after penetration. However, crack growth on the back surface appears to accelerate as reported by author. As a crack propagates, AE occurred heavily just before penetration. Then, it decreases and crack is penetrating. A transition from plane strain to plane stress was observed by fractographic study. At this time, separation of fracture surface was shown which affects AE occurrence.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.6
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• pp.9-16
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• 2020

This study aims to assess the effects of specimen thickness (ST) on fatigue crack growth in the early stages of crack propagation and near failure in magnesium alloys. The analysis of variance (ANOVA) method was adopted because fatigue crack propagation in magnesium alloys exhibits statistical behavior. The equality of variance test and residual diagnostics were performed on the grown cracks to confirm the validity of ANOVA by verifying the normal distribution and mutual independence of the residuals and their homoscedasticity. ANOVA confirmed that ST heavily impacts crack growth; i.e., when ST is smaller, cracks grow faster in the early crack propagation stage and break more quickly before the formation of larger cracks. We found that ST significantly affects fatigue crack growth in the early crack propagation stage and near the failure stage in magnesium alloys. The regression model was also used to predict crack formation near the failure stage.

• Journal of the Korean Society for Railway
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• v.12 no.3
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• pp.396-404
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• 2009

With developing the next generation high speed railway, there need to be plans to make sure of running safety though researchs on the crack and break of rail by rolling contact fatigue. Therefore, this study performed the parametric analysis effecting on the fatigue life of rail using simplified equations. It analyzed the internal stress of rail according to the track quality, train velocity, wheel radius, track stiffness, sleeper space, wheel load. For the more, via the finite element method, it analyzed shear force on the rail head which could be changed by the early length of crack, angle of crack and temperature. As a result, this study continued the main parameter effecting on the fatigue life of rail.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1281-1289
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• 2011

This paper deals with several statistical distribution functions for the analysis of fatigue life data of composite laminates for small wind-turbine blades. A series of tensile tests was performed on triaxial glass/epoxy laminates for loading directions of $0^{\circ}$, $45^{\circ}$, and $90^{\circ}$. Then, fatigue tests were carried out to determine the fatigue life at the aforementioned loading directions and the fatigue stresses at four levels. Two-parameter Weibull, three-parameter Weibull, normal, and log-normal distributions were used to fit the fatigue life data of the triaxial composite laminates. The three-parameter Weibull distribution most accurately described the fatigue life data measured experimentally for all the cases considered. Furthermore, the variation of fatigue life was simultaneously affected by the loading direction and fatigue stress level.

• The Journal of Korean Physical Therapy
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• v.16 no.4
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• pp.23-37
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• 2004

Fibromyalgia syndrome(FMS) is a chronic pain disorder of unknown etiology characterized by widespread musculoskeletal aches and pains, stiffness, and general fatigue, disturbed sleep and sleepiness. Frequently misdiagnosed, FMS is often confused with myofascial pain syndrome, polymyalgia rheumatica, polymyositis, hypothyroidism, metastatic carcinoma, rheumatoid arthritis (RA), juvenile rheumatoid arthritis, chronic fatigue syndrome, or systemic lupus erythematosus, any of which may occur concomitantly with FMS. The management of FMS often begins with a thorough examination and a diagnosis from a physician who is formally trained in tender-point/trigger-point recognition. An initial diagnosis provides reassurance to the patient and often reduces the anxiety and depression patterns associated with FMS. The most common goals in the management of FMS are (1) to break the pain cycle, (2) to restore sleep patterns, and (3) to increase functional activity levels. Because FMS is a multifactorial syndrome, it is likely that the best treatment will encompass multiple strategies. Medication with analgesics and antidepressants and also physiotherapy, are often prescribed and give some relief. The other most effective intervention for long-term management of FS to date is physical exercise. Physical therapists can instruct patients in the use of heat at home (moist hot packs, heating pads, whirlpools, warm showers or baths, and hot pads) to increase local blood flow and to decrease muscle spasm and tension. Also instruct patients in the proper use of cold modalities (ice packs, ice massage, and cool baths) to anesthetize localized areas of pain (tender points) and break the pain cycle. Massage and tender-point massage also may promote muscle relaxation. To date, the two most important interventions for the long-term management of FS are patient education and physical exercise. Lately, is handling FMS and Chronic Fatigue syndrome(CFS) together, becuase FMS and CFS are poorly understood disorders that share similar demographic and clinical characteristics. Because of the clinical similarities between both disorders it was suggested that they share a common pathophysiological mechanism, namely, central nervous system dysfunction.

• Journal of the Korean Society of Physical Medicine
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• v.17 no.1
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• pp.31-39
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• 2022

PURPOSE: This study examined the changes in the blood fatigue variables caused by isokinetic and isotonic exercise training. METHODS: Ten healthy adult males with at least one year of athletic experience participated. The participants performed the isokinetic circuit exercise program first, followed by an isotonic circuit exercise program. A two-hour break was allowed between the isokinetic circuit exercise program and the isotonic circuit exercise program. The circuit exercise program consisted of four items (Squat, Deadlift, Shoulder press, and Bench press). The blood samples were analyzed for the LDH, CPK, and Cortisol levels. RESULTS: The LDH level in the isokinetic group was significantly different from the isotonic group. In particular, the change in LDH level in the isokinetic group was 33.30% lower than that of the isotonic group. The serum CPK level of the isokinetic group showed a 10.03% lower decrease than the isotonic group, but the difference was not significant. The Cortisol level was relatively unchanged in the isotonic group, but it decreased in the isokinetic group. On the other hand, the Cortisol level did not show a significant difference between the two groups. CONCLUSION: The isokinetic group showed alleviation of the three indices, unlike the isotonic group. Further studies associated with the changes in blood fatigue variables through various exercise programs and exercise intensity will be needed.