• Journal of Welding and Joining
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• 제17권2호
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• pp.36-43
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• 1999

The effect of microstructure on the fracture toughness of multi pass weld metal has been investigated. The micromechanisms of fracture process are identified by in-situ scanning electron microscopy(SEM) fracture observation using single edge notched specimen. The notches of the in-situ fracture specimens were carefully located such that the ends of the notches were in the as-deposited top bead and the reheated weld metal respectively. The observation of in-situ fracture process for as-deposited top bead indicated that as strains are applied, microcracks are formed at the interfaces between soft proeutectoid ferrite and acicular ferrite under relatively low stress intensity factor. Then, the microcracks propagate easily along the proeutectoid ferrite phase, leading to final fracture. These findings suggest that proeutectoid ferrite plays an important role in reducing the toughness of the weld metal. On the other hand, reheated regions showed that the microcrack initiated at the notch tip grows along the localized shear bands under relatively high stress intensity factor, confirming that reheated area showing momogeneous and fine microstructure would be beneficial to the fracture resistance of weld metal.

• Geomechanics and Engineering
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• 제18권6호
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• pp.585-594
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• 2019

In-situ leaching could be one of the promising mining methods to extract the minerals from deep fractured rock mass. Constrained by the low permeability at depth, however, the performance does not meet the expectation. In fact, the rock mass permeability mainly depends on the pre-existing natural fractures and therefore play a crucial role in in-situ leaching performance. More importantly, fractures have various characteristics, such as aperture, persistence, and density, which have diverse contributions to the promising method. Hence, it is necessary to study the variation of fluid rate versus fracture parameters to enhance in-situ leaching performance. Firstly, the subsurface fractures from the depth of 1500m to 2500m were mapped using the discrete fracture network (DFN) in this paper, and then the numerical model was calibrated at a particular case. On this basis, the fluid flow through fractured rock mass with various fracture characteristics was analyzed. The simulation results showed that with the increase of Fisher' K value, which determine the fracture orientation, the flow rate firstly decreased and then increased. Subsequently, as another critical factor affecting the fluid flow in natural fractures, the fracture transmissivity has a direct relationship with the flow rate. Sensitive study shows that natural fracture characteristics play a critical role in in-situ leaching performance.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2001년도 총회 및 춘계학술발표회
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• pp.73-76
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• 2001

We have simulated the effect of fracture characteristics on reduction of effective permeability of the fractured rocks due to in-situ bacteria growth. A nutrient is injected continuously for growth of in-situ bacteria. We used a power law for fracture length distribution and a fBm for fracture aperture spatial distribution. The results show that in-situ bacteria growth reduces the Permeability hyperbolically, but the porosity of backbone fracture does not change significantly. It shows that reduction of the permeability proceeds at faster speed for smaller value of length exponent(a) and for larger value of Hurst exponent(H). The fracture length distribution has stronger effect on speed of reduction than the aperture spatial distribution. The time needed to reduce permeability is inversely proportional to the hydraulic gradient.

• 대한금속재료학회지
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• 제48권7호
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• pp.683-689
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• 2010

In this study, FeAl based intermetallic matrix composites reinforced with in-situ synthesized TiC particles were fabricated by an in-situ liquid mixing process. The microstructures, mechanical properties and fracture behaviors of the in-situ liquid mixing processed composite were investigated and compared with the vacuum suction casting processed composite. The results showed that the in-situ formed TiC particles exhibited fine and uniform dispersion in the liquid mixing processed composite, while significant grain boundary clustering and coarsening of TiC particles were obtained by the vacuum suction process. It was also shown in both types of composites that the hardness and bending strength were increased with the increase of the TiC volume fractions. Through the study of fractography in the bending test, it was considered that the TiC particles prohibited brittle intergranular fracture of FeAl intermetallic matrix by crack deflections. Because of the uniformly distributed fine TiC particles, the bending strength of the liquid mixing processed composite was superior to that of the casting processed composite.

• Composites Research
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• 제13권3호
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• pp.48-57
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• 2000

앞 동반논문의 이론에서 기술된 기재위에 입혀진 코팅크랙킹의 파괴역학 분석을 4점 굴곡시험을 이용하여 실증하였다. 파괴역학 접근에 의해서 코팅의 다중크랙킹을 예측하여 코팅층에서 새로운 크랙이 생길 때의 변위에너지 방출량(G)을 구하였다. 여러 건조시간과 건조온도의 변화에 따른 금속 및 고분자 기재위에 입혀진 코팅의 변위에 대한 코팅 크랙밀도의 실험데이타가 in-situ 코팅의 파괴인성 값을 구하기 위해 사용되었다. 건조온도가 올라가고 건조시간이 길어짐에 따라 $G_c$는 감소하였다. 본 논문은 코팅의 파괴인성 평가에 있어 4점 굴곡시험이 얼마나 유용한지를 보여주며 in-situ 코팅인성을 구하는 방법을 제시하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 춘계학술발표대회 논문집
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• pp.67-70
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• 2000

Mechanical properties of (10%$AI_20_3{\cdot}SiO_2$+5%Ni)/Al hybrid composites fabricated by the reaction squeeze casting were compared with those of (15%$AI_20_3{\cdot}SiO_2$)/Al composites. Intermetallic compound formed by reaction between molten aluminum and reinforcing powder was uniformly distributed in the Al matrix. These intermetallic compounds were identified as $Al_3$NI using EDS and X-ray diffraction analysis. Microhardness and flexural strength of hybrid composites were higher than that of (15%$AI_20_3{\cdot}SiO_2$)/Al Composite. In-Situ fracture tests were Conducted on (15%$AI_20_3{\cdot}SiO_2$)/Al Composites and (10%$AI_20_3{\cdot}SiO_2$+5%Ni)/Al hybrid composites to identify the microfracture process. It was identified from the in-situ fracture test of (10%$AI_20_3{\cdot}SiO_2$+5%Ni)/Al composites, microcracks were initiated mainly at the short fiber / matrix interfaces. As the loading was continued, the crack propagated mainly along the separated interfacial regions and the well developed shear bands. It was identified from the in-situ fracture test of (10%$AI_20_3{\cdot}SiO_2$+5%Ni)/Al hybrid composites, microcracks were initiated mainly by the short fiber/matrix interfacial debonding. The crack proceeded mainly through the intermetallic compound clusters

• Geomechanics and Engineering
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• 제7권4호
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• pp.403-430
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• 2014

Shale gas formations exhibit strong mechanical and strength anisotropies. Thus, it is necessary to study the effect of anisotropy on the hydraulic fracture initiation pressure. The calculation model for the in-situ stress of the bedding formation is improved according to the effective stress theory. An analytical model of the stresses around wellbore in shale gas reservoirs, in consideration of stratum dip direction, dip angle, and in-situ stress azimuth, has been built. Besides, this work established a calculation model for the stress around the perforation holes. In combination with the tensile failure criterion, a prediction model for the hydraulic fracture initiation pressure in the shale gas reservoirs is put forward. The error between the prediction result and the measured value for the shale gas reservoir in the southern Sichuan Province is only 3.5%. Specifically, effects of factors including elasticity modulus, Poisson's ratio, in-situ stress ratio, tensile strength, perforation angle (the angle between perforation direction and the maximum principal stress) of anisotropic formations on hydraulic fracture initiation pressure have been investigated. The perforation angle has the largest effect on the fracture initiation pressure, followed by the in-situ stress ratio, ratio of tensile strength to pore pressure, and the anisotropy ratio of elasticity moduli as the last. The effect of the anisotropy ratio of the Poisson's ratio on the fracture initiation pressure can be ignored. This study provides a reference for the hydraulic fracturing design in shale gas wells.

• Geomechanics and Engineering
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• 제7권3호
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• pp.233-246
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• 2014

Estimation of fracture initiation pressure is one of the most difficult technical challenges in hydraulic fracturing treatment of vertical or horizontal oil wells. In this study, the influence of in-situ stresses and pore pressure values on fracture initiation pressure and its profile in vertical and horizontal oil wells in a normal stress regime have been investigated. Cohesive elements with traction-separation law (XFEM-based cohesive law) are used for simulating the fracturing process in a fluid-solid coupling finite element model. The maximum nominal stress criterion is selected for initiation of damage in the cohesive elements. The stress intensity factors are verified for both XFEM-based cohesive law and analytical solution to show the validation of the cohesive law in fracture modeling where the compared results are in a very good agreement with less than 1% error. The results showed that, generally by increasing the difference between the maximum and minimum horizontal stress, the fracture pressure and its profile has been strongly changed in the vertical wells. Also, it's been clearly observed that in a horizontal well drilled in the direction of minimum horizontal stress, the values of fracture pressure have been significantly affected by the difference between overburden pressure and maximum horizontal stress. Additionally, increasing pore pressure from under-pressure regime to over-pressure state has made a considerable fall on fracture pressure in both vertical and horizontal oil wells.

• 터널과지하공간
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• 제32권1호
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• pp.1-19
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• 2022

본고에서는 수압파쇄를 이용한 초기응력 측정결과의 정밀도 제고 방안으로 최근 제안된 일본 지반공학회 표준시험법 개정안의 검토 결과를 수록하였다. 개정안에서는 수압파쇄에 의해 형성된 암석 균열 표면의 거칠기와 잔류 간극을 고려한 균열재개압력의 수정식을 제안하였다. 또한, 수압파쇄시스템 컴플라이언스가 초기응력 추정 결과에 미치는 영향을 파악하고 주변 암반의 탄성계수가 클수록 수압파쇄시스템 컴플라이언스가 충분히 낮아야함을 보였다.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 1999년도 제2회 학술발표회
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• pp.156-175
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• 1999

물리검층은 최근에 토목지반조사분야에 대한 활용성이 증가하고 있다. 이것은 물리 검층이 시추공 내에서 분해능 높은 다양한 원위치 물성정보를 제공할 수 있는 장점이 있기 때문이다. 현재 토목지반조사분야에서 적용되고 있는 것은 주로 암상구분, 파쇄대 인식과 동탄성계수의 산출, 지하수흐름검층 등이다. 이와 관련하여 최근에 활용성이 증가하는 물리검층법에 대한 소개와 지반조사와 관련한 물리검층 사례, 그리고 완전파형음파검층에 의한 탄성파 속도와 암반분류와 관계에 대한 사례를 소개한다.