• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 봄 학술발표회 논문집
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• pp.91-96
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• 1994

The growth and propagation of microcracks existed in concrete cause failure of concrete. This is called "damage". The concepts of two principles, equivalent strain principle and equivalent energy principle, are reviewed and compared in the case of uniaxial compressior to concrete. The damage evolution law and constitutive equation are derived by using the Helmholz free energy and the dissipation potential by means of the thermodynamic principles.rinciples.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 춘계학술대회 논문집
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• pp.167-174
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• 1994

The creep behavior and creep fracture of alumina at high temperature were investigated under four point flexural test. The steady-state creep behavior was observed at low bending stress and the primary creep until fracture was observed at high bending stress. The loading history of bending stress did not affect on the steady-stated creep rate. Intergranular fracture was dominant for fracture of alumina at room and high temperature. However, transgranular fracture was dominant on creep fracture of alumina under high temperature by nuclueation and growth of microcracks due to residual flaws or cavities in the material.

• 한국농공학회:학술대회논문집
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• 한국농공학회 2001년도 학술발표회 발표논문집
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• pp.193-197
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• 2001

The growth in concrete structures repair has prompted major efforts to develop high early strength concrete. The internal or external restraint of thermal shrinkage movements could thus generate tensile stresses in concrete structures if it is used rapid setting repair concrete. Restrained shrinkage and thermal stresses could produce microcracks in concrete which increase its permeability and accelerate its long-term deterioration under weathering and load effects. This study aims at evaluation and increase of the engineering properties of high early strength concrete using regulated set cement.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.643-647
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• 2003

Power plant Piping operating at elevated temperature often fails prematurely by the growth of microcracks under creep conditions. Therefore, the life assessment of high temperature components that contain cracks is an important technological problem. The mechanisms of crack growth in simple metals and alloys have been investigated using both mechanical and microstructural approaches. In this study, life prediction accounting for creep, crack growth and thermal stress is analyzed.

• 한국세라믹학회지
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• 제31권5호
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• pp.543-551
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• 1994

The creep behavior and creep fracture of sintered alumina at high temperature were investigated under four point flexural test. Steady-state creep behavior was observed at low bending stress and primary creep until fracture was observed at hish bending stress. The loading history of bending stress did not affect on steady-state creep rate. Intergranular fracture was dominant for fracture of alumina at room and high temperature. However, transgranular fracture was dominant on creep of alumina under high temperature by nucleation and growth of microcracks due to residual flaws or cavities in the material.

• Structural Engineering and Mechanics
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• 제4권6호
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• pp.631-644
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• 1996

Geomaterials such as soil and rock are composed of discrete elements of microstructures with different grains and microcracks. The studies of these microstructures are of increasing interest in geophysics and geotechnical engineering relating to underground space development We first show experimental results undertaken for direct observation of microcrack initiation and propagation by using a newly developed experimental system, and next a homogenization method for treating a viscoelastic behavior of a polycrystalline rock.

• 한국세라믹학회지
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• 제24권1호
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• pp.56-62
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• 1987

Tetragonal phase PZT ceramics with a tetragonality of c/a=1.027 to 1.041 were sintered at 1275$^{\circ}C$ for one hour. And the directionality of domain arrangement, microstructure, dielectric and aging properties were investigated. With increasing tetragonality, the directionality of domain arrangement of 180$^{\circ}$-domain on the surface is smaller than that in the internal part of specimens. Dielectric constants after poling are increased due to the increased internal energy or decreased due to the microcracks created by poling.

• 한국표면공학회지
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• 제21권1호
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• pp.19-27
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• 1988

The principe and practice of pulse plating, and prospect in the future on pulse plating are reviewed. Some of the advantages of pulse pulse plating are detailed as compared with DC plating. The advantages of pulse plating are summarized as follows: 1)smooth and fine grained deposits 2) reduction in hydrogen embrittlement of deposits 3) reduction of residual stress and microcracks in the deposit 4) improvement of physical properties 5) uniform alloy composition through the deposit thinkness 6) improved thrower and adhesion.

• 화약ㆍ발파
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• 제21권4호
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• pp.23-35
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• 2003

본 연구에서는 남원지역 화강암을 대상으로 각 방향에 따른 물성간의 상관관계와 역학적 이방성을 규명하고자 하였다. 화강암의 수평, 수직축의 방향별 물성치는 일축압축강도 및 압열인장강도와 선형관계를 나타내었으며, 초음파 속도 측정 결과 수직방향은 나머지 두 수평방향 보다 약 10∼15% 정도 빠르게 나타났다. 이러한 속도 차이의 원인은 주로 암석 내에 존재하는 미세균열의 발달형태에 따르는 것으로 판단되며, 이는 현미경관찰 결과와 매우 일치함을 알 수 있었다. 점하중시험에 의한 점하중강도지수(Is(50)) 측정결과, 화강암의 경우 일축압축강도와 점하중강도지수의 비는 18∼20에 해당하는 것으로 나타났다. 일축압축강도와 점하중강도지수. 슈미트해머 반발치. 압열인장강도와 좋은 상관관계를 나타내었으며, 이중 점하중강도지수가 가장 높은 상관관계를 보였다. 이로부터 알 수 있듯이 점하중 강도지수가 일축압축강도를 추정하는데 가장 유효한 도구임을 확인할 수 있었다.

• 터널과지하공간
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• 제26권4호
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• pp.327-337
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• 2016

본 연구에서는 화강암 내부의 미세균열 분포에 따른 이방성이 수압파쇄실험 결과에 미치는 영향을 평가하였다. 압력증가율을 일정하게 설정하여 수압파쇄실험을 수행한 결과, 원주방향(주입정 방향과 직교)으로 리프트면이 분포한 시료의 파쇄압력이 가장 낮게 측정되었고, 이는 미세균열의 밀도가 높기 때문이다. 수압파쇄실험과정에서 시료 내부의 변화가 발생하는 주입압력의 크기와 유체 주입속도의 변화 또한 결방향에 따라 분포한 미세균열의 밀도와 관계가 있는 것으로 판단된다. 유체주입속도를 일정하게 설정하여 수압파쇄실험을 수행하였을 경우, 상대적으로 미세균열의 밀도가 높은 리프트면이 원주방향으로 분포된 시료에서 주입압력증가율이 낮게 나타났고, 유체가 침투될 수 있는 균열망이 상대적으로 적게 형성된 그레인면 및 하드웨이면이 원주방향으로 분포된 시료에서는 압력증가율이 높게 나타났다. X-ray CT 촬영을 통해 시료 내부에 생성된 균열의 방향을 확인한 결과, 대부분의 시료에서 리프트면 혹은 그레인면과 평행한 방향으로 균열이 생성된 것을 확인하였고, 이는 암석 내에 상대적으로 미세균열의 밀도가 높아서 분리성이 크기 때문이다.