• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 추계학술대회 논문집
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• pp.475-476
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• 2009

• International Journal of Concrete Structures and Materials
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• 제11권2호
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• pp.215-228
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• 2017

A new approach for measuring the specific fracture energy of concrete denoted modified disk-shaped compact tension (MDCT) test is presented. The procedure is based on previous ideas regarding the use of compact tension specimens for studying the fracture behavior of concrete but implies significant modifications of the specimen morphology in order to avoid premature failures (such as the breakage of concrete around the pulling load holes). The manufacturing and test performance is improved and simplified, enhancing the reliability of the material characterization. MDCT specimens are particularly suitable when fracture properties of already casted concrete structures are required. To evaluate the applicability of the MDCT test to estimate the size-independent specific fracture energy of concrete ($G_F$),the interaction between the fracture process zone of concrete andthe boundary of theMDCTspecimens at the end of the test is properly analyzed. Further, the experimental results of $G_F$ obtained by MDCT tests for normal- and high-strength self-compacting concrete mixes are compared with those obtained using the well-established three-point bending test. The procedure proposed furnishes promising results, and the $G_F$ values obtained are reliable enough for the specimen size range studied in this work.

• 대한기계학회논문집A
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• 제29권8호
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• pp.1118-1122
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• 2005

The direct current potential drop (DCPD) method and the unloading compliance (UC) method with a crack opening displacement gauge were applied simultaneously to the Zr-2.5Nb curved compact tension (CCT) specimens to determine which of the two methods can precisely determine the crack initiation point and hence the crack length for evaluation of their fracture toughness. The DCPD method detected the crack initiation at a smaller load-line displacement compared to the UC method. As a verification, a direct observation of the fracture surfaces on the curved compact tension specimens was made on the CCT specimens experiencing either 0.8 to 1.0 mm load line displacement or various loads from $50\%\;to\;80\%$ of the maximum peak load, or $P_{max}$. The DCPD method is concluded to be more precise in determining the crack initiation and fracture toughness, J in Zr-2.5Nb CCT specimens than the UC method.

• Journal of Mechanical Science and Technology
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• 제17권6호
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• pp.796-804
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• 2003

The use of fracture mechanics has traditionally concentrated on crack growth under an opening mechanism. However, many service failures occur from cracks subjected to mixed-mode loading. Hence, it is necessary to evaluate the fatigue behavior under mixed-mode loading. Under mixed-mode loading, not only the fatigue crack propagation rate is of importance, but also the crack propagation direction. In modified range 0.3$\leq$a/W$\leq$0.5, the stress intensity factors (SIFs) of mode I and mode II for the compact tension shear (CTS) specimen were calculated by using elastic finite element analysis. The propagation behavior of the fatigue cracks of cold rolled stainless steels (STS304) under mixed-mode conditions was evaluated by using K$\_$I/ and $_{4}$ (SIFs of mode I and mode II). The maximum tangential stress (MTS) criterion and stress intensity factor were applied to predict the crack propagation direction and the propagation behavior of fatigue cracks.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.487-490
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• 2004

In this paper, we investigated the characteristics of initiation and propagation behavior for fatigue crack observed by changing various shapes of initial crack and magnitudes of loading in modified compact tension shear(CTS) specimen subjected to shear loading. In the low-loading condition, the secondary fatigue crack was created in the notch root due to friction on the pre-crack face grew to a main crack. In the high-loading condition, fatigue crack under shear loading propagated branching from the pre-crack tip. Influenced by the shear loading condition, fatigue crack propagation retardation appeared in the initial propagation region due to the reduction of crack driving force and friction on crack face. In both cases, however, fatigue cracks grew in tensile mode type. The propagation path of fatigue crack under the Mode II loading was 70 degree angle from the initial crack regardless of its shape and load magnitude.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.119-124
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• 2003

In this study, retardation behavior of fatigue crack under single overloading of the mixed mode I+II state was experimentally investigated. To produce single overload in the mixed mode I+II state, the compact tension shear (CTS) specimen and loading device were used. The propagation tests for fatigue crack were performed under mode I loading overloading afterwards. We examined the observed deformation aspects, variation of fatigue life and crack propagation rate, and the aspects of retardation behavior from tests. The retardation effect of mixed-mode single overload on fatigue crack propagation behavior was smaller than that of mode I single overload. It has been confirmed that the retardation behavior did not immediately appear and the retardation length was short when the component of mixed-mode overload was changed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.302-307
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• 2004

This paper reviewed characteristics of fatigue crack behavior observed by changing various shapes of initial crack and magnitudes of loading in compact tension shear(CTS) specimen subjected to shear loading. In the high-loading condition, fatigue crack under shear loading propagated branching from the pre-crack tip. Meanwhile, the secondary fatigue crack in the low-loading condition which was created in the notch root due to friction on the pre-crack face grew to a main crack. Influenced by the mode II loading condition, fatigue crack propagation retardation appeared in the initial propagation region due to the reduction of crack driving force and friction on crack face. In both cases, however, fatigue cracks grew in tensile mode type. Propagation path of fatigue crack under the shear loading was 70 degree angle from the initial crack regardless of its shape and load magnitude.

• 대한기계학회논문집A
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• 제20권11호
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• pp.3498-3506
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• 1996

A loading device to be used in fracture experiment is presented. It's loading angle can be adjusted from $-45^{\circ}$ to $105^{\circ}$ at intervals of $15^{\circ}$ for a CTS ( compact tension-shear) specimen, so that it is to be useful to measure mixed mode toughness. The equations to give the $K_ I$, $K_ I1$ and J-integral for the experiment are evluated though finite elemetn analysis in which the loading procedure is simulated and the behaviors of the specimen such as load-displacement curve are estimated. In the course of the evaluation the values $K_ I$, $K_ I1$ and J-integral calculated through recentrly released numerical methods are employed as the reference ones.

• Nuclear Engineering and Technology
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• 제19권3호
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• pp.169-179
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• 1987

소형시험편(1/2"T)을 이용, 균열진전량 및 J계산식에 따른 재료의 J-R (J-T) 곡선의 변화를 조사하여 신뢰성있는 J-R(J-T) 곡선을 구하기 위한 실험 및 해석방법을 고찰하였다. 시험은 국내 원자력발전소 압력용기감시 시험에 포함되어 있는 파괴인성시편과 꼭같이 SA 533 Grade 3, Class1 재료로 제작한 1/2"T, C-T 시편을 이용, Single Specimen Unloading Compliance Technique으로 수행하였다. 시험 및 해석결과 Ernst의 Deformation theory J (JD)식을 이용하여 초기 Uncracked ligament (be)의 25～30%까지 균열을 진전시켜 구한 J-R(J-T) 곡선이 대형시편의 결과와 가장 유사한 값을 나타내었다. 한편 Ernst의 Modified J (JM)식에 의한 J-R (J-T) 곡선은 Deformation theory J(JD)에 의한 J-R(J-T) 곡선보다 다소 높은 Instability 예측점을 얻을 수 있기 때문에 실제 압력용기 안전성 해석시에는 가동률향상 및 수명연장 측면에서 Modified J의 사용은 고려되어야 할 것이다.되어야 할 것이다.

• 대한기계학회논문집A
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• 제40권6호
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• pp.531-537
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• 2016

기계 혹은 구조물의 파손 및 파괴는 소재의 내부에 존재하는 결함에서 발생하는 크랙에 의한 것이다. 이러한 크랙들은 밀집하여 존재하는 경우가 많기 때문에 크랙의 진전 및 성장특성들을 고려하지 않으면 안 된다. 이에 따라 본 연구에서는 표준 CT 시험편 내부의 크랙 및 구멍의 위치에 따른 파괴특성을 고찰하였으며, 표준CT 시험편에 편심된 집중하중을 가하였을 때, 시험편 내 크랙 주변의 구멍의 존재유무 및 위치에 따른 파괴역학적 거동에 대하여 규명하였다. 연구 결과로서 Model 3(크랙 주변에 구멍이 한 개 존재하는 시험편 모델로서 크랙의 끝부분과 구멍 간의 거리 가로방향으로 2mm의 경우)가 최대 변형량, 최대 응력 및 최대 변형 에너지, 모두 가장 크게 나타났으며, 모든 시험편 모델들이 시험편 내부의 크랙과 구멍의 거리가 가까울수록 최대 응력이 커지는 경향을 보였다. 또한 구멍의 개수와는 별개로 시험편 내부의 크랙 가까이에 구멍이 존재할 때 크랙 가까이에서 최대 응력은 커지는 경향이 나타나는 것을 알 수 있었으며, 이러한 본 연구 결과를 토대로 기계 혹은 기계 구조물 내부에 구멍을 뚫는다면, 시험편에 발생하는 파괴 응력의 값을 줄임으로써 파손이나 고장이 일어나는 것을 방지할 수 있을 것으로 사료된다.