• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.227-232
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• 2001

In this research we made cement particle with the average size of 4 ${\mu}{\textrm}{m}$ which can penetrate even minor cracks based on the theory of J. K. Michel who reported particles can penetrate the crack of width up to 3 times of maximum particle size. The inorganic crack injection materials were produced by adding superplasticizer. Physical properties of hardened slurry with JIS molds were also tested at 3, 7 and 28 days and the adhesion properties of the slurry in various process conditions were also tested at 3, 7 and 28 days. The cracked specimens which were repaired with slurries produced at various conditions were tested after 3, 7 and 28 days curing in the air and split tensile strength properties were characterized.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.681-686
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• 2001

The purpose of this study is to provide the optimum mix design of concrete to be placed at the face slab concrete in CFRD(Concrete Faced Rockfill Dam) for pumped storage power plants. The basic performance tests including compressive strength, modulus of elasticity, flexural strength and the control properties of crack including plastic shrinkage, drying shrinkage were conducted for concrete using fly ash and polypropylene fiber. From this study, the fly ash concrete represented the better results in the aspects of basic performance, control properties of crack and economy than ordinary portland cement concrete. Especially the concrete mix design containing 20% of fly ash is recommended to be applied in the construction of the face slab concrete in CFRD for pumped storage power plants.

• 대한안전경영과학회:학술대회논문집
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• 대한안전경영과학회 2001년도 춘계학술대회
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• pp.179-184
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• 2001

The objective of this work is to develop the capability to analyze accurately the mixed-mode propagation of a crack in composite structures with elastic orthotropic material stiffness properties and anisotropic material strength characteristics. We employ the normal stress ratio theory to predict the direction of crack extension. It is shown that the angle of crack extension can be altered by the use of second order term in the series expansion is important for the accurate determination of crack growth direction.

• 콘크리트학회논문집
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• 제12권3호
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• pp.39-46
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• 2000

This study is to investigate the watertightness properties of waterproofing admixture mixed redispersible polymer and siliceous powder. Series I deals with change in micro-structure of mortar by waterproofing admixture according to the water/cement ratios of 0.5, 0.6, 0.7 and 0.8 Crystal growth in micro-structure was observed through SEM to estimate on the watertightness effect of it. SeriesII deals with watertightness properties of waterproofing admixture on water permeability coefficient, crack restoration capacity and carbonation depth. SeriesII deals with watertightness properties of waterproofing admixture on water permeability coefficient, crack restoration capacity and carbonation depth. The result of this study can be summarized as follows. 1) Fluidity of mortar and concrete was increased by adding waterproofing admixture. 2) From observation through SEM. Crystals grew larger and denser in micro-structure as fiberic crystalization. 3) Waterproofing admixture is good watertightness properties in a level of high water/cement ratios and long limit of time. 4) Crack restoration capacity was appeared and durability was progressed by waterproofing admixture.

• 콘크리트학회논문집
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• 제16권4호
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• pp.511-520
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• 2004

이 연구에서는 기존의 콘크리트 실험에서 평가된 파괴에너지를 수정 특이-파괴진행대 이론에 대해 해석하였다. 수정 특이-파괴진행대 이론은 균열성장에 대한 에너지해방률과 균열면의 파괴진행에 대한 균열면응력-균열폭 관계의 두 파괴특성을 필요로 한다. 해석결과 균열면응력-균열폭 관계는 시험편의 형상과 균열속도에 민감하지 않았다. 파괴진행대에서 파괴에너지율은 파괴진행대가 완전히 형성될 때까지 균열성장길이에 선형으로 증가하였으며, 이후에는 파괴에너지밀도로 일정한 값을 유지하였다. 변형에너지방출률은 시험편의 형상과 균열속도에 큰 변화를 보였으며, 균열속도에 대해서는 선형의 대수함수로 표현될 수 있다. 균열성장에 대한 변형에너지방출률의 변화는 다른 실험의 미세균열의 성장과 국부화 그리고 완전 파괴진행대의 형성에 대한 이론적인 근거를 보여준다.

• Elastomers and Composites
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• 제33권5호
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• pp.335-344
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• 1998

본 연구에서는 군용 전투차량 궤도 패드용으로 사용되는 고무 배합물의 내크랙성 향상을 위해 기계적 물성이 우수한 천연고무를 이용하여 크랙 개시 저항성 즉, 인열 에너지와 크랙성장 저항성인 크랙 성장 속도를 평가하였다. 내크랙성에 영향을 주는 인자는 여러 가지가 있으나, 본 실험에서는 주로 충전제인 카본블랙과 가교 시스템을 평가하였다. 본 연구결과 촉진제의 함량이 황의 함량과 동일 할 때 내크랙성이 가장 우수하였다. 또한 카본블랙은 보강성이 우수한 hard black의 일종인 ISAF (N220)가 강도 및 가공성에서 가장 우수한 것으로 평가되었으며 적정 함량은 50phr이었다.

• 한국정밀공학회지
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• 제12권11호
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• pp.36-44
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• 1995

When sliding a hard cylinder along the surface of glass, periodic surface cracks appear on the flat surface due to tensile stresses induced by the slider. These cracks propagate into the substrate and will affect the fracture properties of a body. Crack spacings and the directions of crack propagation into glass were calculated numerically by applying the finite element method and linear elastic fracture mechanics. The calculated crack spacings were in the range of the experimental results. Stress intensity factors and crack extension angles depended on the radius of slider and the load, and from these two factors the possible directions of crack propagation were calculated. The calculated propagation directions were in good agreement with real crack propagation.

• 한국기계가공학회지
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• 제2권4호
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• pp.67-72
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• 2003

In this study, to investigate the effects of 2-step shot peening at the surface of spring steel, crack growth tests are conducted on spring steel and shot peened specimens. And then the residual stresses and fractographs are examined. The crack growth equation that can describe the whole crack growth behavior is used to evaluate the experiment results. The results show that fatigue crack glows slowly in the shot peened specimen than in the unpeened. And in the case of the 2-step shot peened specimen the initial stress intensity factor range and the fracture toughness is higher than the unpeened specimen due to the compressive residual stress. Fractographs show that the compressive residual stress of the surface suppress the fatigue crack opening and consequently slow crack growth rates.

• Journal of Mechanical Science and Technology
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• 제18권3호
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• pp.419-431
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• 2004

The dynamic response of a cracked functionally graded piezoelectric material (FGPM) under transient anti-plane shear mechanical and in-plane electrical loads is investigated in the present paper. It is assumed that the electroelastic material properties of the FGPM vary smoothly in the form of an exponential function along the thickness of the strip. The analysis is conducted on the basis of the unified (or natural) crack boundary condition which is related to the ellipsoidal crack parameters. By using the Laplace and Fourier transforms, the problem is reduced to the solutions of Fredholm integral equations of the second kind. Numerical results for the stress intensity factor and crack sliding displacement are presented to show the influences of the elliptic crack parameters, the electric field, FGPM gradation, crack length, and electromechanical coupling coefficient.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.369-372
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• 2006

In this paper, analysis method of HPFRCC is proposed as predicting properties flexural behavior. For analyzing HPFRCC beam, properties of strain-hardening, multiple cracking, and crack spacing control are considered as non-homogeneous material properties of the beam. This paper focused on the deflection, maximum moment of the flexural beam, distribution of crack width with the monte carlo simulation.