• Title/Summary/Keyword: 균열지연

Search Result 160, Processing Time 0.025 seconds

An Experimental Study on the Factors that Affect Fatigue Crack Growth Retardation Behavior in S45C Steel (S45C 강의 피로균열전파 지연거동의 영향인자에 관한 실험적 연구)

  • Kim, Seon-Jin;An, Seok-Hwan
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.25 no.3
    • /
    • pp.470-477
    • /
    • 2001
  • Constant ΔK fatigue crack growth tests were performed by applying an intermediate multiple overload for S45C steel. The purpose of the present study is to investigate effects of specimen thickness at various baseline stress intensity factor range levels (ΔK(sub)b), overload application position (a/W) and overload application frequency (OL(sub)HZ) on fatigue crack growth retardation behavior. The principal results are summarized as follows. The amount of retardation for a given ΔK(sub)b level is increased with increasing the baseline stress intensity factor range level for all specimen thickness. The normalized minimum crack growth rate is increased with increasing the specimen thickness, except for ΔK=45MPa√m. The retardation cycle is decreased with increasing a/W and increased with OL(sub)HZ.

An Experimental Study on the Factors that Affect Fatigue Crack Growth Retardation Behavior in SM45C Steel (SM45C 강의 피로균열전파 지연거동에 미치는 영향인자에 관한 실험적 연구)

  • Kim, Seon-Jin;Kim, Jong-Hoon;Ahn, Seok-Hwan
    • Proceedings of the KSME Conference
    • /
    • 2000.04a
    • /
    • pp.55-60
    • /
    • 2000
  • Constant ${\Delta}K$ fatigue crack growth tests were performed applying an intermediate multiple overload for SM45C steel. The purpose of the present study is to investigate the effects of specimen thickness at various baseline stress intensity levels$({\Delta}K_b)$, overload application frequency(a/W) and overload application frequency$(OL_{HZ})$ on fatigue crack growth retardation behavior. The principal results are summarized as follows. The amount of retardation for a given ${\Delta}K_b$ level is increased with increasing the baseline stress intensity level in all specimen thickness. The normalized minimum crack growth rate is increased with increasing the specimen thickness, except for ${\Delta}K=45MPa \sqrt m$. The retardation cycle is decreased with increasing the overload application position and increased with the overload application frequency.

  • PDF

Residual Stress Redistribution and Fatigue Behavior in Weldment (용접재의 잔류응력 재분포와 피로거동)

  • 이용복;정진성
    • Journal of Welding and Joining
    • /
    • v.15 no.3
    • /
    • pp.20-28
    • /
    • 1997
  • 용접부에는 많은 취약조건들이 존재하며 파괴의 주 원인이 되고 있어 이들에 대한 많은 연구가 진행되고 있다. 따라서, 현재 용접재료, 용접 조건 및 용접방법 등 을 개선함으로써 여러 방면에서 좋은 결과를 얻고 있다. 그러나 아직도 용접시의 열소 성변형과 구속조건에 따라 분포하는 잔류응력에 의한 피로균열거동에 대한 연구는 정확한 잔류응력 측정의 어려움으로 미흡한 상태이다. 특히 잔류응력의 측정기술과 반복하중에 의한 피로균열 진전시 잔류응력의 이완 등은 이들을 해석하는데 많은 어 려움을 주고 있다. 용접시 높은 열에 의한 재료의 팽창과 냉각시의 수축변형은 용접 부재에 인장 및 압축 잔류응력을 유발시키고, 인장잔류응력은 균열 진전될 때 잔류 응력은 오히려 균열을 지연시키기도 한다. 또한 잔류응력장에서 피로 균열이 진전될 때 잔류응력은 일반적으로 작용하중의 크기와 반복 수 그리고 균열 진전 등으로 인하 여 이완되고 재분포된다. 본 해설에서는 용접재의 피로거동중에 발생하는 잔류응력의 재분포 현상을 하중의 범위, 하중 반복수, 균열 진전의 영향으로 구분하여 각각의 영향에 대해서 기술하고자 한다.

  • PDF

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
    • /
    • v.7 no.4
    • /
    • pp.103-113
    • /
    • 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.

  • PDF

Effect of specimen thickness on fatigue crack growth and retardation behavior of 7075-T73 aluminum alloy (7075-T73 알루미늄 합금의 피로균열진전거동 및 지연현상에 미치는 두께의 영향)

  • 김정규;박병훈;류석현
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.13 no.4
    • /
    • pp.670-679
    • /
    • 1989
  • The constant amplitude loading and 100% single overloading fatigue studies of domestic high tensile 7075-T73 aluminum alloy were performed to exmine the effect of specimen thickness and its mechanisms on fatigue crack growth behavior. The stage II fatigue crack growth rates tend to increase with decreasing specimen thickness under constant amplitude loading condition and this has relation with stress intensity factors and plastic zone size. The amount of retardation by an overload increased with decreasing specimen thickness when the crack depth and baseline stress intensity factors were constant. The crack depth is one of major factors which affect retardation phenomena by an overload and the amount of retardation increase with decreasing the crack depth. Its main mechanisms are crack closure and decreasing of K at the crack tip by branching and deflection of crack. And they are affected by near surface more severely than central portion of specimen.

A Study on the Effect of the Overload Ratio on the Fatigue Crack Growth Retardation (과대하중비가 균열성장지연에 미치는 영향에 관한 연구)

  • Kim, Kyung-Su;Kim, Sung-Chan;Shim, Chun-Sik;Park, Jin-Young;Cho, Hyung-Min
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
    • /
    • 2003.05a
    • /
    • pp.306-311
    • /
    • 2003
  • A growing fatigue crack is known to be retarded on application of an overload cycle. The retardation may be characterized by the total number of cycles involved during retardation and the retarded crack length. The overload ratio plays an important role to influence the retardation behavior. The objective of the present investigation is to study the effect of different overload ratio on the retardation behavior. For DENT(double edge notched tension) specimens and ESET(eccentrically-loaded single edge crack tension) specimens, fatigue crack growth tests are conducted under cyclic constant-amplitude loading including a single tensile overloading with different overload ratios. The proposed crack retardation model predicts crack growth retardation due to a single tensile overloading. The predictions are put into comparison with the experimental results to confirm the reliability of this model.

  • PDF

A Fracture Mechanic's Study for Crack Growth Retardation Phenomenon using Effective Plastic Zone Concept (균열성장 지연현상에 대한 유효 소성역 개념을 사용한 파괴역학적 연구)

  • Kang, Yong-Goo;Lee, Tae-Won;Park, Chang-Yong
    • Journal of the Korean Society of Manufacturing Process Engineers
    • /
    • v.14 no.2
    • /
    • pp.112-120
    • /
    • 2015
  • In this study, the growth rate of surface cracks (da/dN) during the retardation period was analyzed in terms of effective stress intensity factor range(${\Delta}K_{eff}^*$) obtained by using the proposed effective plastic zone concept. Effective stress intensity factors obtained by using the effective plastic zone concept were smaller than those obtained by using Willenborg analysis. On the growth rate of surface cracks analyzed by ${\Delta}K$, the dependence of overload stress levels appears. On the growth rate by ${\Delta}K_{eff}$ obtained by Willenborg analysis, there is a linear relationship with two different slops between da/dN and ${\Delta}K_{eff}$. However, on the growth rate by ${\Delta}K_{eff}^*$ obtained by the proposed effective plastic zone concept, there is a linear relationship between da/dN and ${\Delta}K_{eff}^*$ that coincides with the results of constant amplitude loading.

Prediction of Crack Growth in 2124-7851 Al-Alloy Under Flight-Simulation Loading (비행하중하에서 2124-T851 알루미늄합금의 피로균열진전 예측)

  • Sim, Dong-Seok;Hwang, Don-Yeong;Kim, Jeong-Gyu
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.26 no.8
    • /
    • pp.1487-1494
    • /
    • 2002
  • In this study, to propose the prediction method of the crack growth under flight-simulation loading, crack growth tests are conducted on 2124-7851 aluminum alloy specimens. The prediction of crack growth under flight-simulation loading is performed by the stochastic crack growth model which was developed in previous study. First of all, to reduce the complex load history into a number of constant amplitude events, rainflow counting is applied to the flight-simulation loading wave. The crack growth, then, is predicted by the stochastic crack growth model that can describe the load interaction effect as well as the variability in crack growth process. The material constants required in this model are obtained from crack growth tests under constant amplitude loading and single tensile overload. The curves predicted by the proposed model well describe the crack growth behavior under flight-simulation loading and agree with experimental data. In addition, this model well predicts the variability of fatigue lives.

Influence of overload on the fatigue crack growth retardation and the statistical variation (강의 피로균열지연거동에 미치는 과대하중의 영향과 통계적 변동에 관한 연구)

  • 김선진;남기우;김종훈;이창용;박은희;서상하
    • Journal of Ocean Engineering and Technology
    • /
    • v.11 no.3
    • /
    • pp.76-88
    • /
    • 1997
  • Constant .DELTA.K fatigue crack growth rate experiments were performed by applying an intermediate single and multiple overload for structural steel, SM45C. The purpose of the present study is to investigate the influence of multiple overloads at various stress intensity factor ranges and the effect of statistical variability of crack retardation behavior. The normalized delayed load cycle, delayed crack length and the minimum crack growth rate are increased with increasing baseline stress intensity factor range when the overload ratio and the number of overload application were constant. The crack retardation under low baseline stress intensity factor range increases by increasing the number of overload application, but the minimum crack growth rate decreases by increasing the number of overload application. A strong linear correlation exists between the minimum crack growth rate and the number of overload applications. And, it was observed that the variability in the crack growth retardation behavior are presented, the probability distribution functions of delayed load cycle, delayed crack length and crack growth life are 2-parameter Weibull. The coefficient of variation of delayed load cycle and delayed crack length for the number of 10 overload applications data are 14.8 and 9.2%, respectively.

  • PDF

Crack Growth Retardation Effect and Metallographic Observation of Aluminum Alloy Plate with Pre-Indentation (예비압입에 의한 알루미늄 합금 판재의 균열성장 지연효과 및 금속조직 변화)

  • 황정선;조환기;윤용인
    • Journal of the Korea Institute of Military Science and Technology
    • /
    • v.6 no.4
    • /
    • pp.73-79
    • /
    • 2003
  • Fatigue test is conducted to see the effect of pre-indentation on the fatigue crack retardation of Al5052-H18 plate. Metallographic observation is introduced to deduce the relationship between fatigue crack retardation and fracture appearance with indentation. The grain size of the specimen becomes smaller with the increase of indentation force and the plastic zone is formed with the decrease of grain size. The fatigue striations are appeared densely as the Indentation force becomes higher. Metallographic observation and fatigue test results show that the indentation force has the limited value in improving fatigue crack retardation. Important point to retard the fatigue crack growth is that the crack growth path should pass through the indented area.