• 한국해양공학회지
• /
• 제15권2호
• /
• pp.94-98
• /
• 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.

• 한국안전학회지
• /
• 제23권5호
• /
• pp.105-110
• /
• 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.

• 대한인간공학회지
• /
• 제36권4호
• /
• pp.293-303
• /
• 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.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2000년도 춘계학술대회논문집
• /
• pp.1790-1795
• /
• 2000

송전선로에 새로운 Spacer damper를 설계하는데 이 논문의 목적이며, 이 설계되는 새로운 Spacer damper는 매우 중요한 특징과 장점을 가지고 있다. 또한, 최근 Spacer damper의 문제가 프랑스, 일본 등 다른 나라에서도 자동화 시스템과 함께 많이 발전되어 왔다. 개발된 Spacer damper외 설치는 특별한 기기없이 설치가능하며, 최근 자동 클램핑 장치 이용한 Spacer damper가 도입되어 피로 파괴와 미풍진동에 매우 효과적임이 입증되었고 보수유지가 거의 필요없으므로 경제성도 높으나 고가의 수입가격으로 인해 국산화의 필요성이 절실하다.

• 한국해양공학회지
• /
• 제11권3호
• /
• pp.29-38
• /
• 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.

• 한국기계가공학회지
• /
• 제19권6호
• /
• pp.9-16
• /
• 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.

• 한국철도학회논문집
• /
• 제12권3호
• /
• pp.396-404
• /
• 2009

고속열차의 개발과 함께 구름접촉피로에 의한 레일의 피로균열 및 피로파괴에 대한 연구를 통해 주행안정성을 확보할 수 있는 방안 마련이 필요하다. 따라서 본 연구에서는 Eisenmann의 근사계산식(실용식)을 이용하여 속도, 차륜반경, 궤도지지강성, 침목간격, 축중, 궤도품질에 따른 레일내부 발생응력을 검토하였다. 또한, 유한요소해석을 통해 초기균열의 길이 및 각도, 온도에 따라 레일두부에서 발생하는 전단응력을 검토하여 모드별 응력확대계수를 도출하였다. 이로써 고속철도 레일의 피로수명에 영향을 미치는 주요인자들을 확인하였다.

• 대한기계학회논문집A
• /
• 제35권10호
• /
• pp.1281-1289
• /
• 2011

본 논문에서는 소형풍력발전시스템 블레이드 제작에 사용되는 복합재료의 피로수명 데이터에 대한 통계적 해석을 위하여 다양한 확률분포 모델의 적합성에 대한 연구를 수행하였다. 이를 위하여 삼축 유리섬유강화 복합재료를 대상으로 0$^{\circ}C$, 45$^{\circ}C$ 및 90$^{\circ}C$ 의 하중방향에 대한 인장시험을 실시하였다. 또한 상기의 하중방향에 대하여 4 수준의 피로응력준에서의 피로시험을 수행하였다. 이를 통하여 획득한 피로수명 데이터를 대상으로 1) 전체 적합성, 2) 끝단 적합성 및 3) 피로물리 일치성의 기준을 이용하여 2 모수 Weibull, 3 모수 Weibull, 정규 및 대수정규분포의 적합성을 평가하였다. 또한 피로수명의 분산에 대한 하중방향 및 피로응력의 영향 역시 검토하였다.

• The Journal of Korean Physical Therapy
• /
• 제16권4호
• /
• pp.23-37
• /
• 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.

• 대한물리의학회지
• /
• 제17권1호
• /
• pp.31-39
• /
• 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.