• 한국기계가공학회지
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• 제11권4호
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• pp.82-89
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• 2012

In order to clarify the effect of overload on crack growth behaviors, fatigue tests for overload were carried out for round plain specimens of SM45C steel. In the experiment, typical semi-elliptical crack shape was found and further crack growth behaviors were tested. Using three types of single overload fatigue tests, Crack growth retardation phenomenon were examined. The growth rate of surface crack(da/dN) during retardation period was analyzed in terms of ${\Delta}K$ and ${\Delta}K_{eff}$. On the growth rate of surface crack analyzed by ${\Delta}K$, the dependence of overload stress levels appears. However, on the growth rate by ${\Delta}K_{eff}$ obtained by Willenborg analysis, there is a liner relationship between da/dN and ${\Delta}K_{eff}$ with narrow scatter band.

• 한국기계가공학회지
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• 제11권5호
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• pp.13-20
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• 2012

In order to clarify the effect of overload on crack growth behaviors, fatigue tests for overload were carried out for round plain specimens of SM45C steel. In the experiment, typical semi-elliptical crack shape was found and further crack growth behaviors were tested. Using three types of single overload fatigue tests, Crack growth retardation phenomenon were examined. The growth rate of surface crack(da/dN) during retardation period was analyzed in terms of ${\Delta}K$ and ${\Delta}K_{eff}$. On the growth rate of surface crack analyzed by ${\Delta}K$, the dependence of overload stress levels appears. However, on the growth rate by ${\Delta}K_{eff}$ obtained by Willenborg analysis, there is a non-liner relationship between da/dN and ${\Delta}K_{eff}$ with narrow scatter band.

• 대한기계학회논문집
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• 제16권9호
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• pp.1605-1614
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• 1992

본 연구에서는 고장력 7075-T73 알루미늄합금에 대하여 변동하중의 기보파형 인 단일과대하중과 고-저(high-low) 블럭하중하의 지연거동에 미치는 과대하중비 %O.L., 기준응력확대계수범위 .DELTA. $K_{b}$ 및 무차원 균열깊이 a/W의 영향을 규명하였 으며, 또한 Wheeler모델의 수정에 의한 예측피로수명을 실험치와 함께 검토하였다.다.

• 한국기계가공학회지
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• 제12권5호
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• pp.42-49
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• 2013

In this study, in order to analyze the crack retardation behaviors, effective plastic zone concept was proposed. By use of the proposed concept, crack retardation period, compressive residual stress and variation of effective plastic zone shapes were obtained. The results were compared with those of Willenborg model. Retardation period, compressive residual stress and effective plastic zone size obtained by using effective plastic zone concept were larger then the results obtained by using Willenborg analysis. Effective stress intensity factors obtained by using effective plastic zone concept were smaller then the results obtained by using Willenborg analysis.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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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.

• 한국안전학회지
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• 제12권3호
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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.

• Journal of the Korean Academy of Child and Adolescent Psychiatry
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• 제7권2호
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• pp.258-266
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• 1996

자해 행동은 정신지체, 자폐증 등의 발달 장애와 Lesch-Nyhan 증후군 등의 선천성 유전 질환에서 흔히 나타나는 문제 행동으로 실제 임상에서 이런 자해 행동은 아동과 가족에게 커다란 스트레스가 되고 아동의 사회 적응에 주된 문제가 되기도 한다. 본 저자는 과거에는 전혀 자해 행동을 보이지 않다가 발열, 발진 등의 신체 질환과 동시에 갑자기 심한 자해 행동을 보여 얼굴과 사지에 성형외과적 수술이 필요할 정도로 심각한 손상을 받았으나 전반적인 신체상황이 호전되고 항정신병 약물을 투여한 상황에서 완전히 자해 행동이 사라진 증례를 문헌 고찰과 함께 보고하려고 한다.

• 한국안전학회지
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• 제7권2호
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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.

• 한국분말재료학회지
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• 제19권2호
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• pp.127-133
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• 2012

The sintering behaviors and process parameters of some compounds (carbides, oxides, sulfides, borides) were investigated experimentally. These compounds were successfully consolidated and showed high densities. Some unique phenomena such as retardation of grain growth, suppression of thermal decomposition and maintenance of initial non-equilibrium phases, were observed by the proper control of process in spark sintering.

• 대한토목학회논문집
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• 제7권4호
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• pp.103-113
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• 1987

본(本) 연구(硏究)는 단순변동하중하(單純變動荷重下)에서의 피로균열성장거동(疲勞龜裂成長擧動)을 고찰하고 해석방법(解析方法)을 구하고자, 용접구조용강(鎔接構造用鋼) SWS 58을 사용하여 CT 시험편을 제작하고 간단한 하중모델을 설정(設定)하여 피로실험(疲勞實驗)을 행했다. 그 결과 단일과하중작용직후(單一過荷重作用直後)에는 가속효과(加速效果)가 경미(輕微)하게 발생하였으며 그후 상당한 지연효과(遲延效果)가 발생했다. 2단중복하중하(段重復荷重下)에서는 low-high인 경우 약간의 가속효과(加速效果)가 발생하나 high-low인 경우는 상당한 지연효과(遲延效果)가 발생했다. 이러한 하중변화(荷重變化)에 따른 균열성장율(龜裂成長率)(da/dN)은 균열선단(龜裂先端)의 잔류응력(殘留應力)과 소성영역(塑性領域)으로 인한 상호영향(相互影響)때문이며, 이러한 미시적(微視的) 균열성장거동(龜裂成長擧動)은 Elber의 crack closure model로 잘 설명(說明)될 수 있으나 피로균열성장해석방법(疲勞龜裂成長解析方法)으로는 불충분(不充分)하다. 반면 변동하중하(變動荷重下)에서의 피로균열성장해석방법(疲勞龜裂成長解析方法) 중(中) Wheeler의 retardation model은 간편하면서도 적합한 이론임을 알 수 있었다.