• 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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Repair of Fatigue Damage of Coped Stringers in Railway Truss Bridge (트러스 철도교에서 피로손상이 발생한 절취된 세로보의 보강방법)

  • Kim, Ki-Du;Jeon, Jun-Chang;Hwang, Yoon-Koog;Chang, Dong-Il
    • Journal of Korean Society of Steel Construction
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    • v.8 no.4
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    • pp.95-103
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    • 1996
  • 단순 전단연결 구조를 가진 강철도교의 세로보 단부의 절취부위에서 많은 피로균열이 발견되었으며, 이러한 부위의 피로균열은 피로손상의 전형적인 예이다. 피로균열을 가진 세로보 절취부위의 보강방법을 연구하기 위하여 가로보 및 세로보의 상부 플랜지에 인장판을 부착한 경우와 부착하지 않은 경우로 구분하여 피로실험을 수행하였다. 피로실험에 사용된 하중은 현장에서 측정된 실동응력을 기초하여 빈도해석을 통해 산정하였다. 피로실험 결과, 인장판으로 보강한 모멘트 저항 연결구조상세가 철도교에서 균열성장을 효과적으로 정지시킬 수 있는 것으로 판명되었으며, 피로손상을 가진 절취부위의 보강방법으로 제시될 수 있을 것으로 사료된다.

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선체구조물의 피로강도 해석기법

  • 송재영;신찬호
    • Computational Structural Engineering
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    • v.10 no.3
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    • pp.7-14
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    • 1997
  • 본 고에서는 설계자가 초기 설계시 적용할 수 있는 간이피로해석방법에 대하여 기술하였으며, 특히 선체의 각 구조상세에 대하여 산정된 응력집중계수를 이용하여 피로수명을 쉽게 평가할 수 있는 집중응력방법을 정립하였다. 이 집중응력방법을 사용하면 모든 구조상세에 대하여 한개의 S-N 선도를 적용하게 되므로 일관성 있는 피로상도해석을 수행할 수 있다. 또한 피로수명에 큰 영향을 미치는 파랑하중은 설계조건에 주어진 선급규칙에 따라 계산되어진다. 선체구조의 피로강도평가 기술은 계측, 실험, 해석 및 경험을 포함하는 광범위하고 포괄적이면서 정밀함을 요구하는 종합기술이지만 여기에는 많은 불확실성이 내포되어 있다. 따라서 이를 구명하고 모든 선체구조에 적용할 수 있는 신뢰성 있는 피로강도 평가기술을 개발하기 위하여는 실선계측을 통한 피로하중규명 선체구조에 적용할 수 있는 피로강도 Data base개발, 균열진전해석 등 많은 과제에 대한 집중적인 연구가 계속 수행되어야 한다.

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A Study on the Measuring EMG Signal Using Two-Dimensional images of the Fatigue analysis (2차원 영상을 이용한 근전도신호의 피로도 해석에 관한연구)

  • Kang, Byung-Jong;Lee, Young-Seock
    • Proceedings of the KAIS Fall Conference
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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.

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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.

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.

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 Strength of In-plane Welded Attachments (면내 거셋 용접연결부의 피로강도)

  • Bae, Doobyong
    • Journal of Korean Society of Steel Construction
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    • v.15 no.6
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    • pp.629-637
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    • 2003
  • This s paper presented the results of the three phases of fatigue tests to determine the fatigue strength of in-plane welded gusset joints, which are the most common details inevitably existing in the region of high stress range. A total of 57 fatigue specimens with varying thickness and strengths were made and tensile fatigue tests performed. One full-scale beam fatigue test was also performed. The validity of the fatigue strength of those details in the specification was confirmed, with the effects of thickness of flanges and welded attachments, length of attachments, and strength of applied steel examined. The characteristics of crack initiation and propagation were also observed. The test result was evaluated by comparing it with other test data and fatigue criteria of other countries. To determine the degree of stress concentration in the weld toe depending on geometric configuration such as attachment length and transition radius, analyses were performed. Compared to the present specification, analytical results indicate the need to revise and subdivide the detail categories.

Comparison and Review of Fatigue Design Criteria by the Structural Analysis of Steel Truss Bridges (강재 트러스교의 해석에 의한 피로설계기준 비교 및 검토)

  • Kim, Sang-Seog;Jung, Hie-Young
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.7 no.3
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    • pp.241-249
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    • 2003
  • The service life of steel bridges can be assured only when their strength, serviceability and fatigue safety are fulfilled. However, at the present time, the continuous research for fatigue of steel bridges is desperately required since not much research work has been done so far. In this study, a guideline on the fatigue design is suggested for the practical purpose in order to establish the long-term safety of steel bridges against fatigue. The continuous steel truss bridge was analyzed for the cumulative reversals of the actual traffic, stress ranges and fatigue strength. From the results, the domestic fatigue design procedure was found to be fairly overestimated in comparison to the design code of other foreign countries. Therefore, it is necessary to review the current fatigue design specifications and have the new and rationalized design criteria in the future domestic fatigue design guidance.