• Title, Summary, Keyword: Fatigue

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The Influence of the Small Circular Hole Defect on the Fatigue Crack Propagation Behavior in Aluminum Alloys (알루미늄 합금재의 피로크랙 전파거동에 미치는 미소원공결함)

  • Kim, G.H.;Lee, H.Y.
    • Journal of the Korean Society of Marine Engineering
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    • v.32 no.6
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    • pp.834-840
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    • 2008
  • We carried out fatigue testing with materials of aluminum alloyC7075-T6, 2024-T4) by rotary bending fatigue tester. We investigated fatigue limit, fatigue crack initiation, fatigue crack propagation behavior and possibility of fatigue life prediction to the different small circular hole defect. The summarized result are as follows; Fatigue limit of the smooth specimens were related tensile strength and yield strength. In case of more large applied stress and small circular hole crack defect, the fatigue crack was grown rapidly. The fatigue crack propagation behavior proceed at according to inclusion. Fatigue crack propagation ratio appeared instability and retardation phenomenon in the first half of fatigue life but appeared stability and replied in the latter half. On other hand, this experimental data of the materials are appeared fatigue life predictability.

Development of Integrated Fatigue Strength Assessment System (피로강도평가를 위한 통합 전산 시스템의 개발)

  • Park, Jun-Hyeop;Song, Ji-Ho
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.2
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    • pp.264-274
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    • 2001
  • An integrated fatigue strength assessment system was computerized. The system developed consists of 9 modules: user interface, cycle counting, load history construction, data searching, fatigue properties estimation, fatigue data analysis, true stress and strain analysis, expert system for crack initiation life prediction, fatigue crack initiation and propagation life prediction. Fatigue strength database also was included in this system. The fatigue expert system helps a beginner to predict a fatigue crack initiation life in fatigue strength assessment. The expert system module in this system is developed on the personal computer by using C language and UNiK, an expert system developing tool. To evaluate the system, the results of test under variable loading of SAE and failure data from a field were analyzed. The evaluation show that the system provided fatigue life prediction within 3-scatter band and gave reasonable predictions. To get more accurate predictions of fatigue life without fatigue properties, we recommend utilizing the system along with the fatigue strength database.

A study on the Fatigue Life Prediction Method of the Spot-welded Lap Joint (점용접이음재의 피로수명 예측기법에 관한 연구)

  • 손일선;배동호
    • Transactions of the Korean Society of Automotive Engineers
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    • v.8 no.3
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    • pp.110-118
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    • 2000
  • For reasonable fatigue design and estimation of fatigue durability considered fatigue strength and stiffness of the automotive body structure, many fatigue data must be insured according to the shapes, materials, and welding conditions of the spot welded lap joints. However, because it is actually difficult problem, there is need to establish a new method to be able to predict its fatigue life without any additional fatigue tests. Therefore, In order to improve such problems, in this study, the maximum stress function presenting the $\delta\sigma_{1max}―\delta P$ relation was defined form the relation between $\delta\sigma_{1max}-N_f$ and ${\delta}P-N_f$. By using the fatigue data on the IB type spot-welded lap joints previously obtained from the fatigue test results, fatigue life of the spot-welded lap joint previously obtained from the fatigue test results, fatigue life of the spot-welded lap joint having a certain dimension was tried to predict without any additional fatigue tests. And, its result was verified by ${\delta}P-$N_f$ curves. Obtained conclusion are as follows, 1) a maximum stress function considered the relation of the maximum principal stress, fatigue load, and the effects of geometrical factors of the IB type spot-welded lap joint was suggested. 2) the fatigue life predicted by the maximum principal stress function and the relation of $\delta\sigma_{1max}-N_f$ was well agreed with the fatigue life obtained through the actual fatigue test result. 3) the fatigue life of the IB type spot-welded lap joint having a certain dimension is able to be predicted without any additional fatigue tests from the fatigue life prediction method by the maximum principal stress function.

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Fatigue Assessment Model of Corroded RC Beams Strengthened with Prestressed CFRP Sheets

  • Song, Li;Hou, Jian
    • International Journal of Concrete Structures and Materials
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    • v.11 no.2
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    • pp.247-259
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    • 2017
  • This paper presents a fatigue assessment model that was developed for corroded reinforced concrete (RC) beams strengthened using prestressed carbon fiber-reinforced polymer (CFRP) sheets. The proposed model considers the fatigue properties of the constituent materials as well as the section equilibrium. The model provides a rational approach that can be used to explicitly assess the failure mode, fatigue life, fatigue strength, stiffness, and post-fatigue ultimate capacity of corroded beams strengthened with prestressed CFRP. A parametric analysis demonstrated that the controlling factor for the fatigue behavior of the beams is the fatigue behavior of the corroded steel bars. Strengthening with one layer of non-prestressed CFRP sheets restored the fatigue behavior of beams with rebar at a low corrosion degree to the level of the uncorroded beams, while strengthening with 20- and 30%-prestressed CFRP sheets restored the fatigue behavior of the beams with medium and high corrosion degrees, respectively, to the values of the uncorroded beams. Under cyclic fatigue loading, the factors for the strengthening design of corroded RC beams fall in the order of stiffness, fatigue life, fatigue strength, and ultimate capacity.

A Study on Application of Fatigue Risk Management System for Pilot to Fly Longer Hours (장시간 체공 항공기 조종사의 피로위험관리 적용 연구)

  • Kim, Dae Ho;Lee, Jang Ryong
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.27 no.2
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    • pp.47-53
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    • 2019
  • The development of the aviation industry and the changes in the military operation mission environment are demanding more long - distance operation (long - time flight), and such a flying environment is a risk factor for fatigue - related accidents. For the aviation related organizations such as ICAO and FAA, fatigue risk management system (FRMS) are applied along with flight time restriction regulations to prevent fatigue related accidents. The most important process in FRMS is fatigue risk management. Fatigue risk management systematically manages fatigue through scientific fatigue risk data collection and fatigue risk assessment. The purpose of this study is to applicate the assessment of scientific fatigue risk management to pilots of airplanes engaged in long flight. We reviewed the current state of risk management and FRMS through previous research. We also developed fatigue risk management indicators and examined the validity of internationally recognized fatigue risk data collection methods and fatigue risk assessment tools. There are 134 mission (flight) data used for development. In order to verify the indicators, the fatigue risk score between the items was assigned through pair-wise comparison. In addition, the verify test results were normalized.

A Study on Fatigue Crack Growth Parameters for Fatigue Life Assessment based on Fracture Mechanics (파괴역학 기반 피로 수명 평가를 위한 피로 균열 진전 파라미터에 관한 연구)

  • Kim, Hyeon-Su;Park, Tae-Jong;Lee, Dong-Ju;Shin, Sang-Beom;Kim, Myung-Hyun
    • Journal of Welding and Joining
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    • v.35 no.1
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    • pp.61-67
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    • 2017
  • Recent studies on the fatigue assessment of high strength steel weld based on the fracture mechanics have frequently raised the problems related to the conservatism in the fatigue crack growth rate specified in the relevant design code. The purpose of this study is to evaluate the effect of the fatigue crack growth parameter on the fatigue life for the low carbon steel weld. In order to do it, the fatigue tests with the constant stress ratio were performed to evaluate the fatigue crack growth rate in the butt weld of SM490. And the fatigue crack growth parameters of the weld were evaluated in accordance with ASTM E647. From the comparative fatigue assessment results, it was found that the fatigue crack growth rate specified in the relevant design code was too conservative to estimate the residual fatigue life of welded structure. So, in order to get the more reliable results, it was recommended that the fatigue life estimation based on the fracture mechanics be performed with the fatigue crack growth parameter specified by test.

Fatigue and Fatigue-Regulation Behaviors of Undergraduates in Courses Related to Public Health and Undergraduates in Courses not Related to Public Health (보건계열 대학생과 비보건계열 대학생의 피로와 피로조절행위)

  • Choi, Jung
    • Journal of Korean Academy of Fundamentals of Nursing
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    • v.16 no.1
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    • pp.83-91
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    • 2009
  • Purpose: The purpose of this study was to compare fatigue and fatigue-regulation behaviors in undergraduates courses related to public health (group A) and undergraduates in courses not related to public health (group B). Method: Using a structured questionnaire, data were collected from 236 undergraduates. Descriptive statistics, Pearson correlation coefficient, t-test with SAS package were used for data analysis, Results: There was a statistically significant difference between group A and group B in t-test comparison by group for fatigue, and all subcategories of fatigue and fatigue-regulation behaviors. The frequency of fatigue-regulation behavior of group A was 12.23 and the mean for total efficiency of fatigue-regulation behavior was 2.17, while the frequency of fatigue-regulation behavior for group B was 10.47 and the mean for total efficiency of fatigue-regulation behavior was 1.75. Finally, total fatigue and all subcategories of fatigue were positively related to fatigue-regulation behaviors. Conclusion: It is necessary to develop an intervention program for regulating fatigue in undergraduates courses related to public health.

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The Fatigue Behavior of Laser Weldment in Heterogeneous Materials (이종재료 레이저 용접부의 피로거동)

  • 권응관;오택열;곽대순;이종재
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.759-764
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    • 1997
  • In this study, Fatigue behavior of laser weldment in heterogeneous materials was investigated. Fatigue strength test and fatigue crack propagation test were performed for specimens with laser weldment in heterogeneous materials, and hardness test was performed. From the fatigue strength test. it was observed that the difference of strength between heterogeneous materials had eflect on crack initiation position and fatigue limit. From the fatigue crack propagation test. it was observed that fatigue behavior of laser weldment in heterogeneous materials is different from that in same materials. The difference of strength between heterogeneous materials and laser weldment had effect on fatigue crack propagation rate.

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Assessment of fatigue damage in 5% chrome cold rolling work roll (5% 크롬 냉간 압연용 작업롤의 피로손상 평가에 대한 연구)

  • Kwak, G.J.;Kim, K.S.;Lee, S.W.;Yeo, W.K.;Park, Y.C.
    • Proceedings of the KSME Conference
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    • pp.316-321
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    • 2000
  • The role of fatigue on the surface damage of 5% chrome cold milling work roll is evaluated. Uniaxial and torsional fatigue tests are carried out, and the baseline data for fatigue life evaluation are established. An appropriate multiaxial fatigue parameter is developed from the fatigue data. Fatigue tests are also performed under compressive mean stresses, and a mean stress model is formulated. A computer program is developed to assess the interaction of fatigue and grinding of the roll. The fatigue damage is computed for selected servicing conditions. It is found that the fatigue damage can be an important issue when the effect of mean stress is ignored, however the fatigue damage is negligibly small when the effect of mean stress including the residual stresses currently used is fully accounted. The result indicates that spalling due to the growth of thermal shock cracks is more important than fatigue damage in roll surface failure.

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Fatigue Characteristics of Non Load-Carrying Fillet Welded Joints According to Post-Processing (용접후처리에 따른 하중비전달형 필렛용접부의 피로특성)

  • Hong, Sung-Wook
    • Journal of the Korean Society of Safety
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    • v.25 no.6
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    • pp.161-168
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    • 2010
  • A series of fatigue tests have been performed on the non-load carrying fillet welded joints in order to quantitatively assess the fatigue characteristics due to the grindings and TIG(Tungsten Inert Gas) welding treatments. From the results of fatigue tests, it has been shown that the fatigue strengths at $2{\times}106$ load cycles were improved in the case of the grinding sand TIG welding treatments, and we could know that it is satisfying fatigue strength prescribed in fatigue design standard in general. Besides, from the results of fracture mechanics approaches, the geometric shape correction factors were the most dominant factors in the initial fatigue crack growth, but as the fatigue crack develops, the finite plate correction factor were became the most dominant factor, and the fatigue life on non-load carrying fillet welded joints could be relatively exactly estimated by using the relations between fatigue crack growth rate and stress intensity factor obtained from finite element analysis and existing proposed formulae.