• Title/Summary/Keyword: Crack Retardation

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Correlation between Overload Retardation and Hardening Exponent (과부하로 인한 균열지연과 변형경화지수와의 상호관계)

  • Sang-Chul,Kim;Jin-Man,Jeong;Moon-Sik,Han
    • Bulletin of the Society of Naval Architects of Korea
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    • v.26 no.2
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    • pp.41-48
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    • 1989
  • This paper investigates the relationship between strain hardening exponents(n) of various marine materials and fatigue crack retardation effect after applying single overload. Using the four different sheet materials, following results are obtained. (1) The fatigue crack propagation rate after applying single overload was retarded and the effects of this retardation were closely related to the strain hardening exponent. (2) The larger the strain hardening exponents were, the more were the fatigue crack retardation effects after applying single overload. (3) The considerable crack closure with the applying of a overload was observed in matrals with large strain hardening exponent. When n is smaller than 0.1, the fatigue crack retardation effects are negligible. On the contrary, when n is larger than 0.2 the fatigue crack retardation effects are significant.

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An investigation of the behavior in the corner crack propagation of Al-Alloy by the plane bending fatigue (평면 굽힘 피로하중에 의한 알루미늄 합금재의 모서리 균열 전파거동에 관한 연구)

  • 김영식;김영종
    • Journal of Advanced Marine Engineering and Technology
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    • v.8 no.1
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    • pp.49-63
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    • 1984
  • The 5086-H116 Al-Alloy plate specimens having an edge through-thickness notch were investigated to find out the characteristics of the corner crack propagation by the plane bending fatigue. The experiments were also carried out in order to clarify the change of the corner crack propagation behaviour due to the various materials and their thicknesses. In addition, the retardation effect of overload on the corner crack propagation was quantatively studied. Main results obtained are as follows; 1. In the case of estimating the crack propagation rate of the corner crack, it is more reasonable to consider the growth rate of fracture surface area than that of crack length. 2. The shape of the corner crack growing in the plane plate under the bending fatigue can be estimated. 3. The crack propagation rate increases with the increasing of the thickness and the decreasing of the Young's modulus of materials. 4. Regardless of a thickness and kind of materials of specimen, the characteristics of the corner crack propagation can be concluded. 5. The retardation effect of overload is distinct in the corner crack propagation.

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The Use of Compliance to Investigate Fatigue Crack Retardation by Cover Plates and Stop Hole Expansion (컴프라이언스를 이용한 보강판재와 균열선단 구멍확장의 피로균열 진전 지연효과 규명)

  • 한문식
    • Transactions of the Korean Society of Automotive Engineers
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    • v.9 no.4
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    • pp.204-213
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    • 2001
  • This paper develops the compliance approach to the problem of load sharing between a cracked plate and a cover plate used to bridge the crack. The theory is validated by using calculated stress intensity factors for the covered and uncovered cases and by using stop hole method to reduce experimentally observed growth rates to a common base. Calculations are then made on the effect of cover plate width on fatigue crack retardation in order to demonstrate the predictive capability of the technique.

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An evaluation of Fatigue Crack Propagation Behaviors on Cyclic Overload Test (반복과대하중에 의한 피로파괴거동의 고찰)

  • 김용수;신근하;강동명;김병석
    • Journal of the Korean Society of Safety
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    • v.7 no.2
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    • pp.47-56
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    • 1992
  • The retardation effect of fatigue crack propagation after cyclic overloading seems to be affected by strain hardening exponent. Namely, for the material with high values of n, the delay effect is found to be severe. We proposed a modified crack retardation equation which may apply the retardation of fatigue crack growth after a cyclic overloading, as (da/dN)'$_{cyc}$=($\mu$n+λ)B $\Delta$ $K^{q}$ /[(1- $R_{eff}$) $K_{cf}$$\Delta$K]. where, $R_{eff}$ is effective stress ratio [=( $K_{min}$-K, os)/( $K_{max}$$K_{res}$)] The constants $\mu$=-0.5 and λ=0.6, and the values are found to be identical for materials such as aluminum (A 1060), steel (SS 34), brass ( $B_{s}$ SIB) and stainless steel (SUS 304) used in this investigation. (SUS 304) used in this investigation.ation.n.n.

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A Study on Corrosion Fatigue Crack Propagation Behaviors due to a Single Overload in 6063-T5 Aluminum Alloy (6063-T5 알미늄 합금의 단일과대하중에 의한 부식피로균열진전거동에 관한 연구)

  • 강동명;우창기;이하성
    • Journal of the Korean Society of Safety
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    • v.12 no.3
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    • pp.38-44
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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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Improvement to Crack Retardation Models Using ″Interactive Zone Concept″

  • Lee, Ouk-Sub;Chen, Zhi-Wei
    • International Journal of Precision Engineering and Manufacturing
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    • v.3 no.4
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    • pp.72-77
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    • 2002
  • The load interaction effect can be best illustrated by the phenomenon of overload retardation. Some prediction methods for retardation are reviewed and the problems discussed in the present paper. The so-called under-load effect much of the retardation disappears if a very low level minimum stress follows the overload, is also of importance for a prediction model to work properly under random load spectrum. The concept of Interactive Zone (IZ) fully considering reversed plasticity during unloading was discussed. This IZ concept can be combined with existing models to derive some improved models that can naturally take account of the under-load effect. Some simulations by IZ improved models for test under complex load sequences including multiple overloads and both over/under loads are compared with test results. It is seen that the improvement by IZ concept greatly enhanced the ability of existing models to accommodate complex load interaction effects.

Assessment of Fatigue Crack Propagation Considering the Redistribution of Residual Stress due to Overload

  • Jang, Chang-Doo;Leem, Hyo-Kwan;Choi, Yeoung-Dal;Bang, Jun-Kee;So, Ha-Young
    • Journal of Ship and Ocean Technology
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    • v.11 no.2
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    • pp.26-33
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    • 2007
  • For the assessment of the retardation of fatigue crack propagation behavior due to overload, new FE analysis algorithms considering compressive residual stress redistribution near crack tip was proposed in this paper. The size of plastic zone near crack tip was obtained by elasto-plastic analysis and it was compared with Irwin's equation. The amount of residual stress redistribution was assessed by subsequent elasto-plastic analysis, and the difference of residual stress distributions between constant amplitude load and overload was obtained. In the analysis of fatigue crack propagation, the applied SIF range was evaluated by ASTM E647, and the effect of residual stresses on crack propagation was considered using the effective SIF concept. The test results of crack propagations were compared with the predicted data obtained by the analysis.

단일 과대하중에의한 크랙지연 거동에 관한 연구

  • 송삼홍;권윤기
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1993.04b
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    • pp.328-332
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    • 1993
  • Single overload tests are carried out for SS41. Specimens are used hollow type and solid type that stress condition prevail plane stress and plane strain at surface crack. According to the crack initiation and propagation period, single overload applies to three regime and overload ratios change into 1.5, 2.0. Crack retardation zones at initation range aren't different in both specimens respectively, however at propagation range come into large scale in hollow specimen. Delayed load cycles come into large scale in solid type. And the more the overload ratio increase, the larger the retardation zone increase but the magnitude doesn't exactly equal to the expected from the overload ratio.

Fatigue Crack Growth of Welded-Structural Steel under Simple-Variable Loading (단순변동하중(單純變動荷重)을 받는 용접구조용강(鎔接構造用鋼)의 피로균열성장(疲勞龜裂成長))

  • Chang, Dong Il;Bak, Yong Gul;Lee, Bong Hak
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.7 no.4
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    • pp.103-113
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    • 1987
  • Fatigue tests using a single-peak loading and a two-step loading were carried out to examine the fatigue crack growth behaviar and to find the appropriate analysis method. C-T specimens were made using structural steel SWS58 for the tests. From this, just after a single-peak loading acceleration effect was occured and after some times retardation effect was found. And eminent retardation effect was found after High-Low two-step loading. The transition effect of crack growth due to this variable loading was occured owing to the residual stress and the plastic zone size at the crack tip. And the behaviors of these are well explained by Elber's Crack Closure Model. Also I could find that the Wheeler's Retardation Model is a simple and appropriate theory among analysis methods of fatigue crack growth under the variable loading.

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Crack Growth Retardation Behavior in Aluminium 2024-T3 Alclad Alloy by Pre-Indentation (예비압입에 의한 알루미늄 2024-T3 알클래드 합금의 균열성장 지연거동)

  • 황정선;조환기
    • Journal of the Korea Institute of Military Science and Technology
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    • v.4 no.2
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    • pp.42-51
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    • 2001
  • The effects of pre-indentation technique are presented for A12024-T3 Alclad alloy using as skin material for aircraft fuselage and wing. Indentations were applied to specimens to be placed on the presumed path of fatigue crack growth before fatigue tests. Tension-tension fatigue tests were conducted on the edge cracked specimens in the L-T orientation. Test results were analyzed to investigate the effectiveness of pre-indentation with the variation of specimen's thickness, position of indentation and applied maximum stress. Fatigue crack retardation by pre-indentation is well recognized in the various conditions.

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