• Title, Summary, Keyword: Fatigue

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A Probabilistic Analysis for Fatigue Cumulative Damage and Fatigue Life in CFRP Composites Containing a Circular Hole (원공을 가진 CFRP 복합재료의 피로누적손상 및 피로수명에 대한 확률적 해석)

  • 김정규;김도식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.8
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    • pp.1915-1926
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    • 1995
  • The Fatigue characteristics of 8-harness satin woven CFRP composites with a circular hole are experimentally investigated under constant amplitude tension-tension loading. It is found in this study that the fatigue damage accumulation behavior is very random and history-independent, and the fatigue cumulative damage is linearly related with the mean number of cycles to a specified damage state. From these results, it is known that the fatigue characteristics of CFRP composites satisfy the basic assumptions of Markov chain theory and the parameter of Markov chain model can be determined only by mean and variance of fatigue lives. The predicted distribution of the fatigue cumulative damage using Markov chain model shows a good agreement with the test results. For the fatigue life distribution, Markov chain model makes similar accuracy to 2-parameter Weibull distribution function.

A Study on Optimal Spot-weld Layout Design of the Shock Tower Structure Considering Fatigue Life under Random Vibration Load (불규칙 진동하중을 받는 쇽 타워의 피로수명을 고려한 점용접 위치 최적설계)

  • Lee, Yong-Hoon;Lee, Seung-Yoon;Bae, Bok-Soo;Yim, Hong-Jae
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.538-543
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    • 2011
  • In this paper, optimal spot weld layout design of the shock tower structure is performed for increasing fatigue life of spot weld and fatigue life of shock tower simultaneously. To predict the fatigue life, linear static analysis is conducted then fatigue analysis is performed by applying random vibration load. To optimize the spot weld layout, design variables that have an effect on spot weld fatigue life are selected. Based on the DOE table, spot weld fatigue analysis is conducted. Finally, response surface model is made from fatigue analysis results and optimized spot weld layout model which increases fatigue life of sport weld and fatigue life of shock tower is determined.

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Influencing Factors on Fatigue of Middle Aged Women (중년여성의 피로에 영향을 미치는 요인)

  • Chang, Hae-Kyung
    • Korean Journal of Adult Nursing
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    • v.22 no.6
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    • pp.634-643
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    • 2010
  • Purpose: The purpose of this study was to identify the reported factors influencing fatigue of middle aged women. Methods: Two hundred seven middle aged women between 40 and 59 years of age were recruited from five areas in Korea from March 1, 2010, to April 20, 2010. Data were collected by self-reported questionnaires. Data analysis was done using SPSS/WIN 15.0 program for descriptive statistics, Pearson correlation coefficients and stepwise multiple regression. Results: The average score of fatigue was $2.34{\pm}0.40$. There were significant differences in reported fatigue according to economic status and health status. The reported fatigue was significantly correlated with somatic attribution, psychological attribution, normalizing attribution, depression, marital adjustment, stress, and social support. The major factors that affect fatigue in middle aged women were stress, depression, and normalizing attribution, which explained 32.3% of fatigue. Conclusion: The findings can reduce the fatigue by controlling stress and depression. Additionally, this study can understand the attribution of fatigue in middle aged women. More studies are needed to identify other variables that influence on the fatigue of middle aged women.

Improvement of Fatigue Limit in Spheroidal Graphite Cast Iron with High Strength and Toughness (고강도·고인성 구상흑연주철의 피로한도의 개선)

  • Kim, M.G.;Kim, J.H.
    • Journal of the Korean Society for Heat Treatment
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    • v.12 no.1
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    • pp.40-46
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    • 1999
  • Rotary bending fatigue tests were carried out to investigate the improvement of fatigue limit in annealed and austempered spheroidal graphite cast iron. Main results obtained are as follows. (1) The tensile strength(hardness) of Series C is higher than that of Series B, and fatigue limits are 245MPa in Series C, 230MPa in Series B and 195MPa in Series A, respectively. (2) The fatigue limits of Series B and Series A are mainly governed by the resistance to fatigue crack initiation. Whereas, the fatigue limit of Series C is governed by the resistance to fatigue crack initiation and growth. The defect size and the resistance to crack initiation and growth should be considered to clarify the fatigue properties in spheroidal graphite cast iron. (3) Improvement of fatigue limit by half-austempering is more reasonable than that of full-austempering treatment in multi defective materials as spheroidal graphite cast iron.

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A Study on Fatigue Characteristics of Domestic Low-Relaxation PS Strands (국산 저이완 PS 강연선의 피로특성에 관한 연구)

  • 변근주;송하원;박상순;노병철
    • Journal of the Korea Concrete Institute
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    • v.11 no.6
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    • pp.113-119
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    • 1999
  • Fatigue failure is a phenomenon such that structures under cyclic service load is failed by sudden brittle manner. Therefore, in order to obtain structures safety against the fatigue failure during their service lifes, fatigue characteristics should be considered for design and analysis of the structures. As stress range of prestressed (PS) tendons, which governs fatigus characteristic of prestressed concrete (PSC) structures, increases with increased use of partial prestressig, it is more necessary to consider fatigue characteristics of PS tendons. In this paper, direct-tension fatigue experiments with special specimen-setting devices are carried out to obtain fatigue characteristics of domestic low relaxation PS strands having different diameters and PS strands connected with coupler. Then, allowable stress range of fatigue for PSC beams using low relaxation strands are presented for the fatigue examination of prestressed concrete beams applied cyclic loading.

The Development of Fatigue Load Spectrum and Fatigue Analysis for the Tilt Rotor UAV (틸트 로터 무인항공기의 피로하중 스펙트럼 생성 및 피로해석)

  • Im, Jong-Bin;Park, Young-Chul;Park, Jung-Sun;Lee, Jeong-Jin
    • Proceedings of the KSME Conference
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    • pp.654-659
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    • 2007
  • In this paper, the fatigue load spectrum for tilt rotor UAV is developed and fatigue analysis is achieved for flaperon joint. Tilt rotor UAV has two modes which are helicopter mode when UAV is taking off and landing and fixed wing mode when UAV is cruising. To make fatigue load spectrum, FELIX for helicopter mode and TWIST for fixed wing mode are used. And Fatigue analysis of flaperon joint is achieved using fatigue load spectrum we obtained. When S-N test data are analyzed, we use the Kriging meta model to get probability S-N curve for whole range of material life. The result which is life of flaperon joint obtained by suggested fatigue analysis procedure in this paper is compared with that obtained by MSC/Fatigue.

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The Prediction of Rolling Contact Fatigue of Wheels for a Korea High Speed Train (한국형 고속철도 차량의 차륜의 구름접촉 피로 예측)

  • Choi Jeong Heum;Han Dong-Chul;Kim Ki-Hwan
    • Proceedings of the KSR Conference
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    • pp.1109-1114
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    • 2005
  • The rolling contact fatigue of wheels for high speed trains is a matter of increasing importance. The wheel damages from fatigue crack makes noise up and safety down. RCF-casued accidents cause traffic congestion and economical costs as well as personal injuries. In this study, we examine the rolling contact fatigue of wheels for power car running at 300km/h. Using the results of multi-body dynamic analysis and the proposed procedure of Ekberg, we calculate the fatigue index of surface-initiated fatigue, subsurface-initiated fatigue and fatigue initiated at deep material defects. As a result. the fatigue index shows us whether fatigue will appear and in which form. In addition, we present Shakedown map on surface-initiated fatigue.

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A Study on Fatigue Damage Modeling Using Neural Networks

  • Lee Dong-Woo;Hong Soon-Hyeok;Cho Seok-Swoo;Joo Won-Sik
    • Journal of Mechanical Science and Technology
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    • v.19 no.7
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    • pp.1393-1404
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    • 2005
  • Fatigue crack growth and life have been estimated based on established empirical equations. In this paper, an alternative method using artificial neural network (ANN) -based model developed to predict fatigue damages simultaneously. To learn and generalize the ANN, fatigue crack growth rate and life data were built up using in-plane bending fatigue test results. Single fracture mechanical parameter or nondestructive parameter can't predict fatigue damage accurately but multiple fracture mechanical parameters or nondestructive parameters can. Existing fatigue damage modeling used this merit but limited real-time damage monitoring. Therefore, this study shows fatigue damage model using backpropagation neural networks on the basis of X -ray half breadth ratio B / $B_o$, fractal dimension $D_f$ and fracture mechanical parameters can estimate fatigue crack growth rate da/ dN and cycle ratio N / $N_f$ at the same time within engineering limit error ($5\%$).

Fatigue Properties of Copper Foil and the Evolution of Surface Roughness

  • Oh, Chung-Seog;Bae, Jong-Sung;Lee, Hak-Joo
    • International Journal of Precision Engineering and Manufacturing
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    • v.9 no.4
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    • pp.57-62
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    • 2008
  • The aim of this investigation was to extract the fatigue properties at the designated fatigue life of copper foil and observe the mean stress and stress amplitude effects on both the fatigue life and the corresponding surface morphology. Tensile tests were performed to determine the baseline monotonic material properties of the proportional limit and ultimate tensile strength. Constant amplitude fatigue tests were carried out using a feedback-controlled fatigue testing machine. The mean stress and the stress amplitude were changed to obtain the complete nominal stress-life curves. An atomic force microscope was utilized to observe the relationship between the fatigue damage and the corresponding changes in surface morphology. A Basquin's exponent of-0.071 was obtained through the fatigue tests. An endurance limit of 122 MPa was inferred from a Haigh diagram. The specimen surface became rougher as the number of fatigue cycles increased, and there was a close relationship between the fatigue damage and the surface roughness evolution.

Estimation of Probability Distribution of Fatigue Lives in Crank Throw Forged Steel (크랭크스로 단조강의 피로수명의 확률분포 추정)

  • Kim, Seon-Jin;Ahn, Seok-Hwan
    • Journal of Power System Engineering
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    • v.20 no.3
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    • pp.29-35
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    • 2016
  • Because of the severe service environment of the large marine vessel, the fatigue strength and its evaluation play an important role in design and maintenance of marine crankshaft. The aim of this work is to investigate the probability distribution of fatigue lives in crank throw forged steel and to develop the methodology for estimation of the probabilistic design fatigue strength. Detailed studies were performed on the constant amplitude axial loading fatigue test. The experiments were controlled by stress ratio of -1 and 15Hz frequency for each stress level. The considerable variability of fatigue life was observed in each stress level under rigidly controlled constant fatigue testing conditions. The fatigue life of crank throw forged steel was well followed the log-normal and Weibull distribution. In addition, it can be used for the estimation of probabilistic design fatigue strength by using the proposed methodology.