• Title, Summary, Keyword: Fatigue

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A Study on Application of Fatigue Correction Factor for Environmental Fatigue Evaluation of Pressurizer Surge Line (가압기 밀림관 환경피로평가를 위한 피로보정계수 적용에 관한 연구)

  • Yang, Jun-Seog;Park, Chi-Yong;Kang, Seon-Ye
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.33 no.10
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    • pp.1151-1157
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    • 2009
  • Nuclear power plants applying for the continued operation over design life are required to address the effects of reactor water environment in fatigue design requirement of the ASME Code. Reactor water environmental effects are generally evaluated by calculating fatigue correction factors on fatigue usage. This paper describes the application for pressurizer surge line of environmental fatigue correction factors and the strain rate impact in the application. From this paper, the environmental fatigue correction factors resulted from the assumption of a step change in temperature are especially compared with those calculated from the data measured during plant startup. As a conclusion of this paper, the design transient conditions applied to the fatigue design may be conservative in case of the environmental fatigue evaluation.

The Degree of Fatigue According to Subjective Recognition in Middle - Aged Women - (중년여성의 피로인지여부에 따른 피로 정도)

  • Shin, Eun-Ju
    • Journal of Oriental Neuropsychiatry
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    • v.14 no.2
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    • pp.107-115
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    • 2003
  • This study was conducted to investigate the subjective degree of fatigue, the degree of fatigue depending on analysis of MMPI and SDNN in middle-aged women. Data were collected from 51 patients, registered at Oriental Medicine Hospital in J-city and K-city respectively. The instrument used in this study were the Multidimensional Assessment of Fatigue developed by Belza(1995) and revised by Jung & Kim(1999) and the Minnesota Multiphasic Personality Inventory(MMPI) and Standard Deviation of Normal to Normal(SDNN). The collected data were analyzed by SPSS/WIN 9.0 program using frequencies, percentage, mean, standard deviation, t-test. The degree of fatigue in middle-aged women: the average score 30.61 out of the total score 40. Subdivision of fatigue scores: common fatigue degree 7.71, distress due to fatigue 7.67, degree of daily activity fatigue 7.43, and fatigue frequency in the previous week 7.84. The degree of fatigue according to subjective recognition was shown significant difference(t=6.707, p=.000).: group of recognition (33.58), group of ignorance (23.47). The degree of fatigue according to MMPI was shown significant difference. : In the group of recognition, scales of Hs, D, Hy, Pt were higher. The degree of fatigue according to SDNN was shown significant difference (T=-4.062, P=.000). : group of recognition (33.47ms), group of ignorance (45.70ms). The total fatigue score and scales of Hs, D, Hy in MMPI was correlated positively (r=.576; r=.466; r=.518), and total fatigue score and SDNN was correlated negatively (r=-.576). Conclusively fatigue is one of difficult problems in middle-aged women. Therefore it is necessary to develope some nursing intervention for reducing fatigue in its early stages.

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A Preliminary Study on Fatigue Strength of High Toughness Thermoplastic Composite Material AS4/PEEK (고인성 열가소성 복합재료 AS4/PEEK의 피로강도에 관한 기초적 검토)

  • Song, Ji-Ho;Gang, Jae-Yun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.4
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    • pp.1055-1064
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    • 2000
  • First, various specimen geometries, namely, coupon type, waisted type and dog-bone type, were examined to determine appropriate fatigue specimen of thermoplastic composite material AS4/PEEK and the n, fatigue strength of smooth and notched specimens of AS4/PEEK [-45/0/+45/90]2s was investigated. Fatigue tests were performed under load controlled condition at a stress ratio of 0. 1 at a frequency of 5Hz. Stiffness degradation of specimens with fatigue cycling was monitored using an automated unloading compliance technique. The waisted type specimen is found appropriate for smooth fatigue specimen geometry of AS4/PEEK. As for the effect of stress concentration, it is found that fatigue strength is higher for a 2mm-diameter hole notched specimen than a 5mm-diameter one. Fatigue notch factor decreases with the increase of fatigue life. These results are far different from the trend of fatigue strength of metallic materials. The stiffness variation of smooth specimen was only 4% at maximum until final fracture. On the other hand, the stiffness of hole notched specimen was reduced by 45% at maximum. Notched fatigue strength was compared between thermoplastic composite AS4/PEEK and thermosetting composite Graphite/Epoxy. In long-life fatigue (>104), the AS4/PEEK composite shows superior fatigue strength, but in short-life fatigue, the fatigue strength of the Graphite/Epoxy composite is nearly equal or somewhat higher than that of the AS4/PEEK composite.

Thermal-Mechanical and Low Cycle Fatigue Characteristics of 12Cr Heat Resisting Steel with Hold Time Effects (유지시간 효과를 고려한 12Cr 내열강의 열피로 및 저주기 피로 특성)

  • Ha, J.S.;Koh, S.K.;Ong, J.W.
    • Transactions of the Korean Society of Automotive Engineers
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    • v.3 no.1
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    • pp.1-12
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    • 1995
  • Isothermal and thermal-mechanical fatigue characteristics of 12Cr heat resisting steel used for high temperature applications were investigated including hold time effects. Isothermal low cycle fatigue test at $600^{\circ}C$ and in-phase, out-of-phase thermal-mechanical fatigue test at 350 to $600^{\circ}C$ were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. Regardless of thermal-mechanical and isothermal fatigue tests, cyclic softening behavior was observed and much more pronounced in the thermal-mechanical fatigue tests with hold times due to the stress relaxation during the hold time. The phase difference between temperature and strain in thermal-mechanical fatigue tests resulted in significantly shorter fatigue life for out-of-phase compared to in-phase. The differences in fatigue lives were dependent upon the magnitudes of plastic strain ranges and mean stresses. During the hold time in the strain-controlled fatigue tests, the increase in the plastic strain range and the stress relaxation were observed. It appeared that the increase in plastic strain range per cycle and the introduction of creep damage made important contributions to the reduction of thermal-mechanical fatigue life with hold time, and the life reduction tendency was more remarkable in the in-phase than in the out-of-phase thermal-mechanical fatigue. Isothermal fatigue tests performed under the combination of fast and slow strain rates at $600^{\circ}C$ showed that the fatigue life decreased as the strain rate and frequency decreased,especially for the low strain ranges.

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Women's Level of Fatigue after Delivery (산부의 피로정도에 관한 연구)

  • Kim, Sun-Hee
    • Korean Parent-Child Health Journal
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    • v.4 no.1
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    • pp.1-18
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    • 2001
  • Fatigue after delivery affect women's birth experience and interrupt the process of labor. Finally woman cannot have a positive birth result and will experience a postpartum fatigue. But researches about fatigue during the labor are lacked. Nurse help adapting a mother's role, bonding with new baby, recovering after birth, and improving woman's quality of life through decreasing fatigue during the labor and intercepting a continued postpartum fatigue. So it is very important that measuring a fatigue and confirming relationships between fatigue and factors affecting fatigue. The purpose of this study was measuring the level of fatigue within 4hours after delivery and identifing factors affecting fatigue. The ultimate goal was to contribute to improving a birth experience and adapting after birth through decreasing the level of fatigue and interventions. The data was collected for this study at the hospital of two universities and the third hospital in Seoul from Aug. 15. to Nov. 10. 2000. The subjects were 106 of mothers who deliveried a normal newborn and were tested within four hours after birth. The instruments were The Visual Analogue Scale for fatigue, The State Anxiety Inventory, and The Labor Support Inventory. The data were analyzed by using percentage, mean, SD, t-test, ANOVA, Pearson correlation. The results of this study were as follows; (1) The level of fatigue during the labor was 61.48point. (2) The deferences according to general and obstetric character affecting fatigue founded that there were Significant differences according to job(t=2.659, p=0.009), and the type of delivery(t=-2.035, p=0.044). (3) The deferences according to factors affecting fatigue revealed that there was significant difference according to quality of sleep(F=2.935, p=0.037). The significant fatigue and the fatigue after delivery was anxiety(r=0.343, p=0.000). The above findings indicate that the level of fatigue during the labor is higher than during pregnancy and postpartum. Woman having a job, delivering by vacuum was more fatigued. The level of fatigue according to a quality of sleep was significant difference. The poor quality of sleep, higher level of fatigue. And the more anxiety after delivery, the more fatigue. So, the variable nursing interventions for lessening the level of fatigue through appling the situation for rest, relaxation during the labor to reserve energy, and decreasing anxiety should be provided for mothers.

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Fatigue Strength Improvement and Fatigue Characteristics by TIG-Dressing on Weld Bead Toes (용접지단부 TIG처리에 의한 피로강도향상 및 피로특성)

  • Jung, Young Hwa;Kim, Ik Gyeom;Nam, Wang Hyone;Chang, Dong Huy
    • Journal of Industrial Technology
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    • v.20 no.A
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    • pp.169-178
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    • 2000
  • The 4-point bending tests have been performed In order to estimate the effect of TIG-dressing on fatigue strength and fatigue characteristics quantitatively for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue tests, fatigue strengths of as-welded specimens have satisfied the grade of fatigue strength prescribed in specifications of korea, AASHTO and JSSC. Fatigue strength at 2 million cycles of TIG-dressing specimens have increased compared with as-welded specimens. As the result of beachmark tests, fatigue cracks occurred at several points, where the radius of curvature and flank angle in the weld bead toes were low, and grew as semi-elliptical cracks, then approached to fracture. As a result of finite element analysis, stress concentration factor in weld bead toes has closely related to the flank angle and radius of curvature, and between these, the radius of curvature has more largely affected in stress concentration factor than flank angle. As a result of fracture mechanics approaches, the crack correction factor of test specimens has largely affected on stress gradient correction factor in case a/t is below 0.4. From the relations between stress intensity factor range estimated from FEM analysis and fatigue crack growth rate, fatigue life has been correctly calculated.

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Improvement of Fatigue Strength by Spot Heating for Out-of-plane Gusset (국부가열을 이용한 면외거셋의 피로강도 향상)

  • Jung, Young-Hwa;Nam, Wang-Hyone;Chang, Dong-Huy
    • Journal of Industrial Technology
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    • v.21 no.B
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    • pp.213-222
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    • 2001
  • In the study, the fatigue strength improvement and mechanism have been estimated by the Spot-Heating treatment on welded bead toes. For this, web-gusset specimens were made without residual stresses and the others with residual stresses imposed by Spot-Heating. The 4-point bending tests were performed in order to estimate the effect of spot-heating on fatigue strength and fatigue characteristics quantitatively for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue test, fatigue strength of As-Welded specimen for non load-carrying fillet welded joints subjected to pure bending has satisfied the grade of fatigue prescribed in specifications of korea, AASHTO and JSSC. As compare with As-Welded specimen and Spot-Heating specimen have increased about 20% for the fatigue strength at $7.7{\times}10^6$ cycles. The Spot-Heating by reformation of the residual stress on welded bead toes has greatly affected the fatigue crack propagation life, but has slightly affected the fatigue crack initiation life.

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The Influence of Grain Size on the Fatigue Crack Propagation Behavior in the Low Carbon Steel (SM26C) (저탄소강재(SM25C)의 피로크랙 전파거동에 미치는 결정립 크기의 영향)

  • 김건호
    • Journal of Advanced Marine Engineering and Technology
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    • v.26 no.1
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    • pp.76-82
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    • 2002
  • In this study, the rotary bending fatigue test was carried out with low carbon steel(SM25C). The specimens were heat-treated in order to change the grain size, and investigated items are fatigue limit, small crack initiation, fatigue crack propagation behavior and possibility of fatigue life prediction according to the different grain size. The summarized result are as follows ; Fatigue limit of the smooth specimen was dependent upon the grain size. The fatigue crack initiation of the small grain size specimen was delayed more than that of the large grain size specimen. And the small cracks of small grain size specimen were distributed in the narrow region of the main crack circumference contrary to the large grain size specimen. The main crack was grown along the grain boundary having co-alliance with small cracks. The experiment material has quantitatively disclosed the possibility of fatigue life prediction because the fatigue crack propagation behavior is dependent upon the grain size.

Fatigue Life Evaluation of Notched Shaft Using Local Strain Approach (국부변형률방법을 이용한 노치를 지닌 축의 피로수명평가)

  • 고승기;김영일;이학주;김완두;이상록
    • Transactions of the Korean Society of Automotive Engineers
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    • v.4 no.2
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    • pp.80-89
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    • 1996
  • Fatigue life of a notched shaft was evaluated in order to estimate the durability and integrity of the notched shaft in design stage. Cumulative fatigue dama- ge analysis was performed using local strain approach based on the assumption that the fatigue life of a notched component is approximately same as that of a smooth specimen is subjected to the same strain at the notched component. In this paper, shafts with different notch root radius of 1, 2㎜ resulting in different values of stress concentration factors were tested under||rotating bending fatigue loading condition. Theoretical stress concentration factor for each notch type was calculated using finite element method. Fatigue life prediction program, FALIPS, written in C language was developed using the strain-life curve, and the local strain approach integrating Neuber's rule, cyclic stress-strain, and hysteresis loop equations. The fatigue life evaluated using the fatigue notch factor obtained from the experimentally determined fatigue strength showed very large scattering with nonconservatism, but the fatigue notch factors derived from the stress concentration factors and Peterson's equation reduced the considerablely accurate fatigue life evaluation within a factor of three.

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The fatigue analysis using cumulative damage rule (Miner's rule) for the welding areas of carbody structure (누적손상법(Miner's rule)을 이용한 철도차량 차체 용접부의 피로평가)

  • Kim, Kwang-Woo;Park, Geun-Soo;Park, Hyung-Soon
    • Proceedings of the KSR Conference
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    • pp.30-34
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    • 2007
  • Structural integrity of railway vehicles should last for a long period against various and continuous fatigue loadings, and the carbody structures of railway vehicle are manufactured by applying multiform welding types for each material. Since the most of cracks are occurred and proceeded at the vicinity of welding area during the lifetime of carbody structure, the fatigue strength evaluation for welding area of carbody structure should have been carried out. Rotem Company has evaluated lifetime and fatigue strength of carbody structure according to the fatigue analysis based on the international standard and/or inner-official regulation. This study introduces the fatigue analysis method that we have evaluated and calculated the damages for the welding areas of carbody structure under various fatigue loading conditions using cumulative fatigue damage rule(Miner's rule) to verify whether the cumulative damage does exceed unity. This study contains the fatigue test of specimens to derive stress-life relations(S-N curve), sub-modeling analysis and the calculation of cumulative damages under fatigue loading. The fatigue analysis verifies the welding area shall be capable of withstanding under fatigue loading, identifies how critical area shall be selected and presents the principles to be used for design verification.

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