• Title, Summary, Keyword: 피로도

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기계부품의 피로파괴사례 및 방지대책

  • 김재곤
    • Journal of the KSME
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    • v.29 no.2
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    • pp.118-124
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    • 1989
  • 피로파괴의 발생원인을 살펴보면 다음과 같이 4가지로 구별된다. (1) 설계불량 (2) 가공불량 (3) 소재불량 (4) 부적절한 사용 그러나 현재 기계설계시 일반적으로 형상계수 및 충격계수를 포함한 안전율을 여유있게 고려하기 때문에 피로강도가 간접적으로 설계시 반영되어 피로파괴는 주로 가공이나 원소재 불량 및 사용상의 부주의에 의한 경우가 대부분이다. 즉 기계가공 도중에 노치가 유입되어 응력집중을 발생시키거나, 규정된 표면처리 혹은 열처리가 이루어지지 못해서 재료의 피로강도가 저하한 경우가 많으며, 소재 역시 비금속 개재물이 다량 함유되어 있거나 열처리 특성이 조악한 소재가 사용되어 요구되는 강도를 확보하지 못한 경우도 많다. 그 반면 사용자 측에서도 설계강도를 무시한 과부하를 인가하거나, 부식환경 혹은 고온에서 사용하여 피로파괴를 촉진시키는 경우도 있으므로 사용자도 설계조건을 인식하여 그 한계를 넘지 않도록 해야 한다. 피로파괴는 단순한 원인에 의한 경우가 적고 복잡한 여러 형상이 중첩되는 경우가 많기 때문에 해석하기 어려운 경우가 많다. 결국 피로 파괴의 방지는 피로강도를 저하시킬 수 있는 요인들을 종합하여 설계단계에서부터 최종 사용단계까지 지속적인 관리에 의해서만 달성 될 수 있다.

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Experimental Fatigue Characteristics of Composite Bridge Deck of Hollow Section (중공단면 복합소재 교량 바닥판의 실험적 피로특성 분석)

  • Lee, Sung-Woo;Hong, Kee-Jeung
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.19 no.4
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    • pp.337-345
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    • 2006
  • In this study, to evaluate fatigue characteristics of developed composite bridge deck, compression fatigue test at girder support and flexural fatigue test for the 2.8m-long flexural test model were carried out. For the test specimen, DB 24 truck load was applied up to 2,000,000 cycles. In the compression fatigue test, behavior at deck tube and its bonded connection were evaluated. In the flexural fatigue test, deck behavior at mid-span and girder connection were evaluated.

Fatigue Crack Growth Analysis of Steel Deckplates Under Bending Stress (휨응력을 받는 바닥강판의 피로균열진전해석)

  • Choi, Jun Hyeok;Kyung, Kab Soo;Choi, Dong Ho;Chang, Dong Il
    • Journal of Korean Society of Steel Construction
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    • v.11 no.4
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    • pp.409-416
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    • 1999
  • The fatigue crack growth analysis based on the fracture mechanics is useful to the estimation of the fatigue life on welded structures under cyclic loading. The analysis procedure in fatigue crack growth under uniform axial loading is applicable to bending fatigue problem as well. The intent of the present study is to show the procedure for calculating the fatigue crack propagation lifetimes of deckplates under bending stress and to explain the crack growth rates for the two dimensional crack problems. It is shown that the fatigue crack grows at a decreasing rate and the fatigue life depends on the initial crack length and the crack shape. The numerically predicted crack growth agree with the experimental data.

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A Study on the Effect of Disparity-based Asymmetrical Filtering on Visual Fatigue in the Binocular Stereoscopic Video (변이 기반 비대칭 필터링의 양안식 스테레오 비디오에서의 시각피로에 미치는 영향 고찰)

  • Um Gi Mun;Ahn Chunghyun;Lee Soo-In
    • Proceedings of the Korean Society of Broadcast Engineers Conference
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    • pp.149-152
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    • 2003
  • 기존의 양안식 스테레오 디스플레이 시스템은 장면 내에 매우 큰 변이를 가지는 물체가 존재 할 경우에 시각피로를 유발하여 오랜 시간동안 시청하기가 어렵게 된다. 본 논문에서는 변이 기반 비대칭 필터링 기법을 제안하고, 이 기법의 시각 피로도에 미치는 영향을 주관적 평가를 통하여 고찰하며, 아울러 교차변이(crossed disparity) 및 비교차변이(uncrossed disparity)에 따른 시각 피로도에 미치는 영향의 변화 또한 고찰하였다. 실험 결과, 변이기반 비대칭 필터링은 시각 피로의 측면에서는 비교차변이만 존재하는 영상의 경우에는 원래의 스테레오 영상에 비해 큰 영향이 없거나, 오히려 필터링 수준에 따라 오히려 시각적 피로가 심하게 되는 결과를 나타내었다. 또한 교차변이의 경우에는 시파피로가 필터링 수준을 높임에 따라 조금씩 시각피로가 개선되는 결과를 나타내었다. 따라서, 비대칭 필터링에 의한 시각피로의 개선효과는 스테레오 영상 내 변이 종류와 그 크기, 시청자의 주시전 등 여러 요인에 따라 달라질 수 있음을 앞 수 있었다.

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Fatigue Strength Evaluation of Bogie Frame of Urban Maglev Train (도시형 자기부상열차 대차 프레임의 피로강도 평가)

  • Han, Jeong Woo;Kim, Heung Sub;Bang, Je Sung;Song, See Yeob
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.37 no.7
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    • pp.945-951
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    • 2013
  • This study evaluated the fatigue strength of the bogie frame of an urban maglev train through fatigue analysis, cumulative damage, and fatigue tests based on a proposed fatigue evaluation method. The results of FEM analysis in which various load combinations were adopted showed that all data were under the fatigue limit of a butt welded joint made of A6005 in a Goodman diagram. The cumulative fatigue damage was calculated at the highest level from a bolt connecting the area of the electromagnetic pole in the casting block; however, the total sum was evaluated as D=0.808 based on $1{\times}10^7$ cycles, which indicates that it did not exceed the failure criteria. In addition, the results of the fatigue testshowed that there was no crack at any position in the bogie frame, which corresponded to the results of fatigue analyses.

Fatigue Life Estimation of Induction-Hardened Drive Shaft Under Twisting Loads (비틀림 하중을 받는 고주파열처리 드라이브 차축의 피로수명 평가)

  • Kim, Tae Young;Kim, Tae An;Han, Seung Ho
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.41 no.6
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    • pp.567-573
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    • 2017
  • The drive shaft of passenger vehicle has an important role in transmitting the torque between the power train system and the wheels. Torsional fatigue failures occur generally in the connection parts of the spline edge of the drive shaft, when there is significant fatigue damage under repeated twisting loads. A heat treatment, an induction hardening process, has been adopted to increase the torsional strength as well as the fatigue life of the drive shaft. However, it is still unclear how the extension of the induction hardening process in a used material relates to its shear-strain fatigue life range. In this study, a shear-strain controlled torsional-fatigue test with a specially designed specimen was conducted by an electro-dynamic torsional fatigue test machine. A finite element analysis of the drive shaft was carried out using the results obtained by the fatigue experiment. The estimated fatigue life was verified through a twisting load test of the real drive shaft in a test rig.

The Effects of Emotional Labor on Fatigue Scale of Private Security Guards in Regular Exercise (시큐리티 요원의 규칙적인 운동참여 활동이 감정노동과 피로도에 미치는 영향)

  • Kim, Eui-Young
    • Korean Security Journal
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    • no.62
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    • pp.205-221
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    • 2020
  • The purpose of this study was to examine the effects of emotional labor on fatigue in regular private participation of sports workers, and to provide basic data to improve the welfare and working environment of private security guards, the core of private security industry. The survey response of 260 private security guards was used as the final analysis data, and the following conclusions were drawn through statistical tests of factor analysis, t-test, correlation analysis, and multiple regression analysis using the SPSS Windows 18.0 statistical program. First, the private security guards who regularly participate in sports showed lower sub-variability of fatigue, physical, exhaustion, and nervous system fatigue than private security guards who did not participate in sports. Second, it was found that fatigue was lower as the inner variables became higher, and that as the surface behavior became higher, the fatigue factor was lower. In conclusion, regular exercise participation can reduce emotional labor and improve fatigue of civil security personnel.

Fatigue Behavior of Composites with different Fiber Orientation (섬유 방향에 따른 복합재 피로특성에 관한 연구)

  • Kang, Tae-Young;An, Hyo-Seong;Chun, Heoung-Jae;Park, Jong-Chan
    • Composites Research
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    • v.34 no.2
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    • pp.77-81
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    • 2021
  • Due to the high specific strength and stiffness of the composite materials, the composite materials have been extensively used in various industries. In particular, carbon fiber reinforced composites are widely used in many mechanical structures. In addition, since carbon fiber reinforced composites have anisotropic properties, to understand the fatigue behavior of composites with different fiber orientation is very important for the efficient structural design. Therefore, in this paper, the effect fiber orientation on the fatigue life of composite materials was experimentally evaluated. For this purpose, tensile and fatigue tests were performed on the off-axis specimens (0°, 10°, 30°, 45°, 60°, 90°) of the composite materials. As a result of the fatigue tests, the fatigue strength of the composites decreased significantly as the fatigue strength slightly deviated from 0 degrees. On the other hand, the more deviated, the less decreased. This is because the role of supporting the load of fibers decreased as the stacking angle increased. In addition, the fatigue behavior was analyzed by introducing a fatigue strength ratio (Ψ) that eliminates the fiber orientation dependence of the off-axis fatigue behaviors on the unidirectional composites. The off-axis fatigue S-N lines can be reduced to a single line regardless of the fiber orientation by using the fatigue strength ratio (Ψ). Using the fatigue Ψ-N line, it is possible to extract back to any off-axis fatigue S-N lines of the composites with different fiber orientations.

지혜 깊어지는 건강: 40대를 지켜라 -휴식을 취해도 풀리지 않는 만성피로증후군

  • Choe, Se-Hui
    • 건강소식
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    • v.35 no.3
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    • pp.18-20
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    • 2011
  • 피로(疲勞)의 사전적 의미는 과로로 인해 정신이나 몸이 지쳐 힘든 상태를 말한다. 과도한 업무나 스트레스, 수면부족, 지나친 음주 등으로 인해 신체 리듬이 깨지면 피곤함을 쉽게 느끼게 된다. 대부분 충분한 휴식을 취하면 피곤함이 덜어지는데 휴식을 취해도 1개월 이상 피로가 계속되면 지속성(prolonged)피로, 6개월 이상 지속되면 만성(chronic)피로를 분류된다.

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