• Title/Summary/Keyword: fatigue behaviors

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A Study of the Effect of Stress Waveform on the Behavior of High Temp. Fatigue Crack Propagation Using J Parameters (J파라미터를 이용한 고온피로균열전파 거동에 미치는 응력파형 영향의 연구)

  • Hur, Chung-Weon;Park, Won-Jo
    • Journal of the Korean Society of Safety
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    • v.15 no.2
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    • pp.8-12
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    • 2000
  • The fatigue crack propagation tests were performed in triangular and holding-time stress waveforms at $650^{\circ}C$. The behavior of fatigue crack propagation was investigated according to waveform. The analysis of high temperature fatigue crack propagation by the stress intensity factor range ${\Delta}K$, elastic fracture mechanics parameter, was not available. The behaviors of high temperature fatigue crack propagation by the J-integral(${\Delta}J_f$, J' and ${\Delta}J_c$), elasto-plastic fracture mechanics parameter, were investigated in a number of stress waveforms. The fast-fast waveform exhibited cycle-dependent(fatigue type), the slow-fast and the hold time with 500sec waveforms appear to be time-dependent(creep type) and the fast-slow and the hold time with 5, 25sec waveforms exhibited conbined behavior of both types(fatigue-creep conbined type).

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Investigation of Bending Fatigue Behaviors of Thermal Butt Fusion in Safety Class III High-Density Polyethylene Buried Piping in Nuclear Power Plants (원전 안전 3등급 고밀도 폴리에틸렌 매설 배관 맞대기 열 융착부의 굽힘 피로특성 평가)

  • Kim, Jong Sung;Lee, Young Ju;Oh, Young Jin
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.11 no.2
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    • pp.40-44
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    • 2015
  • The fatigue behavior of thermal butt fusion in safety class III high-density polyethylene (HDPE) buried piping for nuclear power plants was investigated using load-controlled bending fatigue on four-point bend test specimens. Based on the results, the presence of thermal butt fusion beads was confirmed to reduce the fatigue lifetime in the low- and medium-cycle fatigue regions while having a negligible effect in the high-cycle fatigue regions.

A Study on Corrosion Fatigye Crack Propagation Behaviors due to a Single Overload (단일과대하중하의 부식피로균열진전거동에 관한 연구)

  • 강동명;이하성;우창기
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1997.04a
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    • pp.481-485
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    • 1997
  • 6063-T5 alloys are tested in laboratory air, water and 3% NaCl solution to investigate the effects of corrosive environment on the retardation behavior through single overload fatigue test. Also, the fatigue crack propagation and the crack closure behavior are studied. The results obtained in this experimental study are summarized as follows: 1) Behaviors of fatigue crack growth retardation are observed in water and 3% NaCl solution as they do in air. The number of delay cycles and the size of affected region by single overload decrease greatly in water and 3% NaCl compared with those in air. 2) In fractographic results, the overload marking by single overload appear remarkably in air, but indistinctly in water and 3% NaCl solution. 3) The effect of crack closure on crack propagation is most remarkable in the beginning of crack propagation. With crack propagation, the crack closure level and its effect decrease greatly.

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Thermo-Mechanical Fatigue Crack Propagation Behaviors of 1.5Cr-0.67Mo-0.33V Alloy (1.5Cr-0.67Mo-0.33V강의 열피로 크랙전파 거동)

  • 송삼홍;강명수
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.9
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    • pp.2133-2141
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    • 1995
  • The thermo-mechanical fatigue tests were performed on the specimens extracted from 1.5Cr-0. 67Mo-0.33V alloy. The characteristics of thermo-mechanical fatigue crack propagation were examined and reviewed in view of fracture mechanics. The results obtained from the present study are summarized as follows : (1) The propagation characteristics of isothermal low-cycle fatigue crack are dominated by .DELTA.J$_{f}$ in case of PP waveform, and .DELTA.J$_{c}$ in case of CP waveform. (II)The propagation characteristics of thermo-mechanical fatigue crack are dominated by .DELTA.J$_{c}$ for in-phase case, and by .DELTA.J$_{c}$ for out-of-phase. The present results were in good agreement with the equation of propagation law for isothermal low-cycle fatigue crack in case of thermo-mechanical fatigue.tigue.e.

The Studies on the Occurrence & Countermeasures of Industrial Fatigue (산업피로의 발생과 대책에 관한 연구)

  • 신현재;안병준
    • Journal of Korean Society of Industrial and Systems Engineering
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    • v.6 no.8
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    • pp.41-48
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    • 1983
  • On the studies of the occurrence & countermeasures of industrial fatigue, the authors obtained the following results in the prevention & recovery of the industrial fatigue. Do not overtime work. To remove the unnecessary behaviors movement. To decide the standard amounts of work. Take a rest property in the procedures of work. Adjust & Arrange the work environments. Take a sufficient mutvition calories. Have plenty in reserve worktime. Set up modernizing machinery. To pay living wages.

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A Study on Corrosion Fatigue Properties of Welded Joints for TMCP High Strength Steels (TMCP 고장력강 용접부의 부식도영 특성에 관한 연구)

  • 이택순;이휘원;김영철
    • Journal of Ocean Engineering and Technology
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    • v.10 no.3
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    • pp.14-23
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    • 1996
  • The corrosion fatigue test were carried out to evaluate the fatigue characteristics of accelerated cooled (ACC) TMCP high tensile strength steels and weld joint with high heat input by one side one run submerged are welding. In this paper, the fatigue crack growth behaviors were investigated with the center crack tension specimen of base metal and heat affected zone in substitute sea water and air, respectively Main results obtained are sunnarized as follows: 1. The fatigue crack growth rates in sea water faster than those in air environment for the different heat input values, crack growth rate of base metal is very fast and effect of heat input is not remarkable. 2. In HAZ (82kJ/cm, 116kJ/cm), the crack branching phenomena were observed in both air and sea water environment, 3. In SEM observation, the corrosion effect on base metal was larger than that on HAZ in corrosion environment.

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Fatigue characteristics of $Pb(Zr,Ti)O_3$ capacitors on donor doping

  • Yang, Bee Lyong
    • Journal of the Korean Society for Heat Treatment
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    • v.15 no.3
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    • pp.113-117
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    • 2002
  • Fatigue characteristics of ferroelectric $Pb(Zr,Ti)O_3$ (PZT) based capacitors through donor doping is reported in this paper. La substitution up to 10% were carried out to study systematically the fatigue behaviors of epitaxial ferroelectric capacitors grown on Si using $(Ti_{0.9}Al_{0.1})N/Pt$ conducting barrier composite. Ferroelectric capacitors substituted with 10% La show sufficient low voltage switched polarization and fatigue free performance. Systematic decrease in the tetragonality of the ferroelectric phase (i.e., c/a ratio) results in the corresponding reduction in coercive voltage, sufficient remnant polarization at 1.5-3V, and good fatigue property.

Crack Opening Behavior of Perpetrated Crack Under Fatigue Load

  • Nam, Ki-Woo;Ahn, Seok-Hwan
    • Journal of Mechanical Science and Technology
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    • v.16 no.1
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    • pp.24-31
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    • 2002
  • The leak-before-break (LBB) behaviors of a structural component under high and low fatigue loads are an important problem in nuclear power plants, liquid nitrogen gas tankers and chemical plants. This paper is an experimental study to evaluate the crack opening behavior after penetration for plate and pipe specimens. Crack opening displacement after penetration under low fatigue load could be satisfactorily determined at the center of the plate thickness regardless of the specimen size. In the case of high fatigue load, it is shown that the crack opening displacement at the center of a penetrated crack carl be derived using the gross stress, $\sigma$/sug G/, and the front surface crack length, a$\_$s/, together with the back surface crack length, a$\_$b/.

Fatigue Crack Growth Behavior of Short fiber/Particle Hybrid Metal Matrix Composites (단섬유/입자 혼합 금속복합재료의 피로균열진전 거동)

  • Oh K.H.;Jang J. H.;Han K. S.
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2004.04a
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    • pp.219-222
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    • 2004
  • The effects of short fiber and particle hybrid reinforcement on fatigue crack propagation behaviors in aluminum matrix composites have been investigated. Single and hybrid reinforced 6061 aluminum containing same 20 $Al_2O_3\;volume\%$ with four different constituent ratios of short fibers and particles were prepared by squeeze casting method and tested to check the near-threshold and stable crack growth behavior. The fatigue threshold of the composites increased with portion of particle contents and showed the improved crack resistance especially in low stress intensity range. Addition of particle instead of short fiber also increased fracture toughness due to increase of inter-reinforcement distance. These increase in both fatigue threshold and fracture toughness eventually affected the fatigue crack growth behavior such that the crack growth curve shift low to high stress intensity factor value. Overall experimental results were shown that particle reinforcement was enhanced the fatigue crack resistance over the whole stress intensity factor range.

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An Experimental Study on the Fatigue Behavior and Stress Interaction of Arbitrarily Located Defects (II) (For Variable Loads and Distances between Defects) (불규칙하게 분포된 미소결함사이의 응력간섭 및 피로균열 거동에 대한 실험적 연구 (II) (결함간의 거리 및 하중변화를 중심으로))

  • Song, Sam-Hong;Bae, Jun-Su;Choe, Byeong-Ho
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.1
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    • pp.201-212
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    • 2001
  • If defects are located far apart, fatigue cracks are independently initiated from them and gradually approach other cracks so that the fatigue life becomes influenced by the crack growth behavior of those interacting cracks. In this study, the effect of the stress interaction between defects on the fatigue crack propagation behavior is investigated experimentally and these results are verified by finite element method. In addition, fatigue crack propagation behaviors under micro hole interaction field are studied.

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