• Title/Summary/Keyword: 유효 응력확대계수

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A Study on Fracture Characteristics of Woven Carbon Fiber Reinforced Composite Material (직물탄소 섬유강화 복합재료의 파괴특성에 관한 연구)

  • 김광수;김상태
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.3
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    • pp.497-505
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    • 1992
  • 본 연구에서는 최근에 개발된 직물 탄소섬유강화 복합재료의 파괴인성치를 정 량적으로 결정하고 파괴거동을 조사하고자 한다. 본 연구의 목적은 이 재료에 선형 탄성파괴역학의 적용여부를 알아보고, R곡선을 이용하여 균열의 생성점 및 불안정 파 괴점의 파괴인성치를 정확히 구하며, 주사형 전자현미경을 통해 파단면 및 균열 성장 시점을 관찰하여 파괴거동을 조사하는데 있다.

Crack growth behavior of fatigue surface crack initiated from a small surface defect (작은 表面缺陷에서 發생.成長하는 表面疲勞균열의 成長特性에 관한 硏究)

  • 서창민;권오헌;이정주
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.2
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    • pp.191-197
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    • 1987
  • It has been well known that the fracture mechanics can be applied to large through crack growth. But the growth rate of small surface cracks initiated from a small defect under rotary bending fatigue tests can not be treated as a function of stress intensity factor range. In this paper, to investigate the growth behavior of surface small fatigue cracks in the view-point of both fracture mechanics and strength of materials, the fatigue test has been carried out on two kinds of plain carbon steels with a small surface defect. Applying the concept of the cyclic strain intensity factor range .DELTA. $K_{\epsilon}$/$_{t}$ to the analysis of small surface fatigue crack growth, it is found that the relationship between cyclic strain intensity factor range and crack growth rate shows linear relation on logarithmic coordinates regardless of defect sizes and two kinds of carbon steels.s.s.

Finite Element Simulation of Fatigue Crack Growth: Determination of Exponent m in Paris Law (피로균열성장의 유한요소 시뮬레이션: Paris 법칙의 지수 m의 결정)

  • Chu, Seok-Jae;Liu, Cong-Hao
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.7
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    • pp.713-721
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    • 2012
  • The finite element simulations of fatigue crack growth are carried out. Using only the mechanical properties usually obtained from the tensile test as input data, we attempted to predict the fatigue crack growth behavior. The critical crack opening displacement is determined by monitoring the change in displacements at the node close to the crack tip. Crack growth is simulated by debonding the crack tip node. The exponent in the Paris law was determined and compared to the published exponent. Plotting with respect to the effective stress intensity factor range yielded more consistent results.

Short Crack Analysis by Fatigue Crack Opening Behavior (피로균열개구거동을 이용한 짧은균열의 거동 분석)

  • Song, Sam-Hong;Lee, Kyeong-Ro
    • Journal of the Korean Society for Precision Engineering
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    • v.14 no.4
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    • pp.136-144
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    • 1997
  • The characteristics of fatigue crack growth subject to out-of-plane bending fatigue are studied in terms of crack opening behavior by using pre-cracked smooth specimens. Crack opening stress is measured by an elastic compliance method which may precisely and continuously provide many date using strain gages during experiment. The results of the short crack and the long crack arranged by crack closure concept show that the effective stress gange ratio of short crack is grester than that of long crack, and ano- malous growth behavior of short crack may be elucidated by the variation of crack opening stress. When the variation of fatigue crack growth rate is arranged versus effective stress intensity factor range. Iinear relation is held also for the short crack. It shows that growth behavior of short crack can be quantitatively represent- ed by the fracture mechanics parameter using effective stress intensity factor range.

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A Study on the Fatigue Crack Growth Behavior in Welding Residual Stress Field(I) (용접잔류응력장에서의 피로균열 성장거동에 관한 연구(I))

  • 최용식;김영진;우흥식
    • Journal of the Korean Society of Safety
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    • v.5 no.1
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    • pp.19-29
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    • 1990
  • The objective of this paper is to investigate the effect of residual stresses on the $\Delta$K$\sub$th/ and fatigue crack growth behavior of butt weldments. For this purpose, transverse butt sutmerged arc welding was performed on SM50A steel plate and CT(compact tension) specimens which loading direction is perpendicular to weld bead were selected. Welding residual stresses distribution on the specimen was determined by hole drilling method. The case of crack located parallel to weld bead, the states of as weld and PWHT, $\Delta$K$\sub$th/ of specimens(HAZ, weld zone) was higher than that of the base metal probably because of the compressive residual stresses of crack tip. In low $\Delta$K region, it is estimated that the effects of residual stresses for da/dN are great. In region II, the da/dN of weldments in as weld state was lower than that of the base metal. Though da/dN of Weldments in PWHT state was similar to that of the base metal. The constant of power law, m in two states consisted with the base metal. Therefore , it is estimated that the value of m is not affected by residual stresses. Fatigue crack growth behavior of weldments consisted with the base metal considering the effective stress intensity factor range($\Delta$K$\sub$eff/) included the effect of initial residual stress(Kres). Thus, we can predict the fatigue crack growth behavior of weldment by knowing the distribution of initial residual stress at the crack tip.

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Redistribution of Welding Residual Stress and its Effects on Fatigue Crack Propagation (피로균열이 진전할 때 용접잔류응력의 재분포와 그 영향)

  • 이용복;조남익
    • Journal of Welding and Joining
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    • v.13 no.4
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    • pp.155-162
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    • 1995
  • Redistribution of residual stress and its effects during fatigue crack propagates from tensile residual stress region in weldment are investigated. Tests are performed by using welded CCT specimens of structual rolling steel (SS400) and it makes fatigue crack propagate from tensile residual stress region. For this study tension-tension loading type is selected by external loading condition and magnetizing stress indicator is used correctly to measure redistribution of residual stress according to fatigue crack growth and number of loading cycles. From this result, it is proved that redistribution of residual stress is mainly consist of residual stress released by fatigue crack growth. When fatigue crack propagates from tensile residual stress region residual stress are redistributed and it makes fatigue crack growth rate largely increase. Fatigue crack growth rate is low in case of redistributed residual stress compare with initial distributed residual stress.

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A study of Fatigue Crack Growth Behavior and Crack Closure in 5083-O Aluminum Alloy (5083-0 알루미늄合金의 疲勞균열進展 擧動과 균열닫힘에 관한 硏究)

  • 박영조;김정규;김일현
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.10 no.2
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    • pp.208-214
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    • 1986
  • To establish the evaluation of the fatigue crack growth behavior in 5083-O aluminum alloy, constant load-amplitude fatigue crack growth tests were carried out under the small scale yielding conditions. Crack length and closure of this material were measured by the compliance method using a clip-on gage. The main results obtained as follows: The fatigue crack growth rate against stress intensity factor range .DELTA.K exhibits the trilinear form with two transitions at the growth rate 5.5*10$^{-6}$ and 5.5*10$^{-5}$ mm/cycle, in the so-caled Region II. The trilinear form appears still in the plot of growth rate versus effective stress intensity factor range .DELTA. $K_{eff}$. Stress ratio R affects the relationship of crack growth rates versus .DELTA.K but does not affect the reation of crack growth rate versus .DELTA. $K_{eff}$. The experimental results indicate that the effective stress intensity range ratio U depends on the maximum stress intensity factor $K_{max}$, but not on the stress ratio R.o R.R.

Fracture Characteristics of Concrete at Early Ages (초기재령 콘크리트의 파괴 특성)

  • Lee, Yun;Kim, Jin-Keun
    • Journal of the Korea Concrete Institute
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    • v.14 no.1
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    • pp.58-66
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    • 2002
  • The objective of this study is to examine the fracture characteristics of concrete at early ages such as critical stress intensity factor, critical crack-tip opening displacement, fracture energy, and bilinear softening curve based on the concepts of the effective-elastic crack model and the cohesive crack model. A wedge splitting test for Mode I was performed on cubic wedge specimens with a notch at the edge. By taking various strengths and ages, load-crack mouth opening displacement curves were obtained, and the results were analyzed by linear elastic fracture mechanics and the finite element method. The results from the test and analysis showed that critical stress intensity factor and fracture energy increased, and critical crack-tip opening displacement decreased with concrete ages from 1 day to 28 days. By numerical analysis four parameters of bilinear softening curve from 1 day to 28 days were obtained. The obtained fracture parameters and bilinear softening curves at early ages may be used as a fracture criterion and an input data for finite element analysis of concrete at early ages.

A Study on Evaluation of Crack Opening Point in Fatigue Crack Propagation Course ( I );Measurement of Crack Opening Point by Experiment (피로크랙 진전과정에서의 크랙열림점 평가에 관한 연구(I))

  • 최병기;윤한용;박창언;정태권
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.3
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    • pp.924-930
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    • 1991
  • 본 연구에서는 크립게이지와 스트레인게이지를 사용하여 정확한 크랙 열림점 의 값을 제시하고져 한다.

Behaviour of Fatigue Crack Propagation under Mixed Mode(I+II) with variation of Crack Length (혼합모드(I+II)하에서 균열길이 변화에 따른 피로균열 전파 거동)

  • Jeong, Eui-Hyo;Hur, Bang-Soo;Kwon, Yun-Ki;Oh, Taek-Yul
    • Proceedings of the KSME Conference
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    • 2000.04a
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    • pp.182-187
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    • 2000
  • The application of fracture mechanics have traditionally concentrated on cracks leaded by tensile stresses, and growing under an opening or mode I mechanism. However, many cases of failures occur from growth of cracks subjected to mixed mode loading. Several criteria have been proposed regarding the crack growth direction under mixed mode loadings. This paper is aimed at prediction of fatigue crack growth behaviour under mixed mode(I+II) in two dimensional branched type precrack. In this paper, the maximum tangential stress(MTS) criterion was used to predict crack growth direction. Not only experiment but also finite element analysis(FEA) was carried out. The theoretical predictions were compared with experimental results in this paper

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