• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.79-84
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• 2000

Crack closure and growth behavior of physically short fatigue cracks under random loading are Investigated by performing narrow- and wide-band random loading tests for various stress ratios. Artificially prepared two-dimensional, short through-thickness cracks are used. The closure behavior of short cracks under random loading is discussed, comparing with that of short cracks under constant-amplitude loading and also that of long cracks under random loading. Irrespective of random loading spectrum or block length, the crack opening load of short cracks is much lower under random loading than under constant-amplitude loading corresponding to the largest load cycle in a random load history, contrary to the behavior of long cracks that the crack opening load under random loading is nearly the same as or slightly higher than constant-amplitude results. This result indicates that the largest load cycle in a random load history has an effect to enhance crack opening of short cracks.

• 한국안전학회지
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• 제9권1호
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• pp.161-164
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• 1994

Computer aided unloading elastic compliance method was employed to measure the closure and the length of short cracks. The most significant factor that influences the fatigue growth behavior of short cracks is the crack closure Phenomenon. dc/dN-$\Delta$ $K_{eff}$ relationships of short cracks are found to coincide well with the corresponding long crack relationships. Non-propagating behavior of short cracks at notch root can be predicted from the crack opening SIF of short cracks, $K_{op}$ , and the growth equation of long cracks in Region I and II.n Region I and II.I.

• 한국안전학회지
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• 제8권1호
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• pp.54-58
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• 1993

The fatigue growth behavior of short cracks were studied various load ratios. Computer-aided unloading elastic compliance method was employed to measure the closure and the length of short cracks. In the dc/dN-$\Delta$K relationships. the decreasing behavior of the growth rate of short cracks is due to the decrease of crack opening ratio with increasing crack length. Irrespective of load ratio. the growth rate of short cracks can be well decribed in terms of the effective stress intensity factor range $\Delta$K$_{eff}$, which is calculated on the base of crack closure. dc/dN-$\Delta$K$_{eff}$ relationships of short cracks are found to coincide well with the corresponding long crack relationships. accordingly. the growth rate of short cracks can be predicted using that of long cracks.ort cracks can be predicted using that of long cracks.cks.

• 한국안전학회지
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• 제8권4호
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• pp.47-53
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• 1993

The growth of short cracks can be well described in terms of the effective stress intensity factor range, which is calculated on the base of crack closure. The relation between the crack opening SIF and crack length is determined from the experimental results. The crack opening SIF of short cracks, Kop, can be predicted from the crack opening SIF at threshold of long crack, Kop.L. The growth rate of short cracks at notch root can be predicted from the crack opening SIF of short cracks, Kop, and the growth equation of long cracks in region II.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.141-146
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• 2000

Crack closure and growth behavior of physically short fatigue cracks under random loading are investigated by performing narrow- and wide-band random loading tests for various stress ratios. The importance of the crack closure phenomenon is examined by predicting the growth lives of short cracks using obtained crack opening behavior. Artificially prepared two-dimensional, short through-thickness cracks are used. The crack opening load of short cracks is much lower under random loading than under constant-amplitude loading corresponding to the largest load cycle in a random load history. This result indicates that the largest load cycle in a random load history has an effect to enhance crack opening of short cracks. Most of the life prediction ratios are within the factor of 2 scatter band except several data at very short crack sizes, indicating that crack growth predictions based on the measured crack opening data are excellent. From the results obtained in this study, it can be concluded that crack closure is the primary factor governing fatigue crack growth of short cracks under random loading as well as under constant-amplitude loading.

• 한국정밀공학회지
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• 제7권4호
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• pp.55-64
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• 1990

The fatigue crack growth behavior of physically-short cracks(0.2${\Delta}K$ with $da/dN<1{\times}10^{-7}m/cycle$. The transition crack lengths where similtude with ${\Delta}K$ existed was between 1 and 2mm. The effective stress intensity factor range based on COD measurements gave better correlation between the physically-short and long cracks. Thus it can be considered that the crack closure effect is one of the main factors which causes the differences between these two cracks.

• 비파괴검사학회지
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• 제27권1호
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• pp.38-47
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• 2007

항공기 구조를 모사하여 일련의 리벳구멍을 갖는 AA2024-T3 박판 구조를 대상으로 음향방출(AE)을 이용하여 피로균열을 탐지하고, 표면초음파(SAW)를 이용하여 균열길이를 측정하였다. 누적 AE 발생수 곡선은 단균열(short crack)의 발생과 성장에 따라 일정한 간격을 두고 급격히 증가하는 계단식 형태로 나타났으나 피로균열의 성장은 지수함수적인 증가를 보였다. SAW를 이용한 균열길이 측정은 균열길이가 다른 13개의 균열에 대하여 실시하였고, 측정된 데이터를 이동식 현미경으로 측정한 결과와 비교하였다. 그 결과 1 mm 이하의 단균열의 크기를 표면초음파 방법으로 측정하는 것은 거의 불가능하였으나, 1 mm 이상의 균열에서는 비교적 높은 신뢰도로 균열길이 측정이 가능함을 확인함으로써 실용적인 측면에서 이 방법이 유효하게 사용될 수 있는 영역이 존재함을 알 수 있었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.467-468
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• 2010

염소이온 침투에 의한 콘크리트의 내구성 저하를 고찰하기 위하여 빠른 시간 내에 염소이온의 침투성을 추정할 수 있는 실험 방법론 및 이론적 해석방법이 다수 제안되었으며 이를 고려한 콘크리트의 내구성 설계 시스템의 개발은 활발히 연구되어 왔다. 그러나, 실제 환경에서 공용 중인 대다수의 콘크리트 구조물에는 환경, 하중 조건, 재료 및 시공 상의 이유로 균열이 존재함에도 불구하고, 대부분의 연구들이 비균열된 콘크리트를 대상으로 염소이온 확산계수의 추정 및 염소이온 프로파일의 예측 등에 집중되었다. 그래서 본 연구에서는 콘크리트의 미세균열이 염소이온 침투에 미치는 영향을 고찰하기 위한 연구의 일환으로 장, 단기 침투 실험결과를 고찰하고 이를 토대로 해석기법 개발의 전략을 수립하고자 한다.

• Earthquakes and Structures
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• 제16권6호
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• pp.727-741
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• 2019

A reinforced concrete water tank is a typical functional liquid storage structure and cracks are the greatest threat to the liquid storage structure. Tanks are readily cracked due to seismic activity, thereby leading to the leakage of the stored liquid and a loss of function. In order to study the effect of cracks on liquid storage tanks, self-healing and leakage tests for bending cracks and through cracks in the walls of a reinforced concrete water tank were conducted. Material performance tests were also performed. The self-healing performance of bending cracks in a lentic environment and through cracks in a lotic environment were tested, thereby the self-healing width of bending micro-cracks in the lentic environment in the short term were determined. The through cracks had the capacity for self-healing in the lotic environment was found. The leakage characteristics of the bending cracks and through cracks were tested with the actual water head on the crack. The effects on liquid leakage of the width of bending cracks, the depth of the compression zone, and the acting head were determined. The relationships between the leakage rate and time with the height of the water head were analyzed. Based on the tests, the relationships between the crack characteristics and self-healing as well as the leakage were obtained. Thereby the references for water tank structure design and grading earthquake damage were provided.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.136-137
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• 2006

Crack initiation and short crack propagation was studied on the polished notched surfaces of Cr-Mo prealloy sintered steels with 7.35 $g.cm^{-3}$ sintered density. An ultrasonic resonance test system operating in push-pull mode at 20 kHz and R=-1 was used. It showed that crack initiation took place in several places, small cracks growing oriented to the local pore structure rather than to stress orientation. Their growth rate is markedly higher than the corresponding one of long cracks. Finally, several microcracks join to form a dominant crack.