• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.11a
• /
• pp.227-232
• /
• 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.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.11a
• /
• pp.681-686
• /
• 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.

• Proceedings of the Safety Management and Science Conference
• /
• 2001.05a
• /
• pp.179-184
• /
• 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.

• Journal of the Korea Concrete Institute
• /
• v.12 no.3
• /
• pp.39-46
• /
• 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.

• Journal of the Korea Concrete Institute
• /
• v.16 no.4 s.82
• /
• pp.511-520
• /
• 2004

The fracture energy evaluated from the previous experimental results can be simulated by using the modified singular fracture process zone (S-FPZ) model. The fracture model has two fracture properties of strain energy release rate for crack extension and crack close stress versus crack width relationship $f_{ccs}$ ( w ) for fracture process zone (FPZ) development. The $f_{ccs}$( w ) relationship is not sensitive to specimen geometry and crack velocity. The fracture energy rate in the FPZ increases linearly with crack extension until the FPZ is fully developed. The fracture criterion of the strain energy release rate depends on specimen geometry and crack velocity as a function of crack extension. The variation of strain energy release rate with crack extension can explain theoretically the micro-cracking, micro-crack localization and full development of the FPZ in concrete.

• Elastomers and Composites
• /
• v.33 no.5
• /
• pp.335-344
• /
• 1998

In this study, the tearing energy and the rate of crack propagation of natural rubber (NR) compounds were evaluated to improve the crack resistance of tank-track pads. Although the factors affecting the crack resistance properties of NR compounds are various in this experiment, the effects of filler(carbon black) and the crosslinking system were evaluated. When the amount of accelerator is equal to that of sulfur( eg. efficient vulcanization), the compound shows the most excellent in the aged mechanical properties and the crack resistance properties. The ISAF carbon black(CB) having a good reinforcing characteristics was better than any other CB grades in physical properties and processablity. The optimum content was 50phr.

• Journal of the Korean Society for Precision Engineering
• /
• v.12 no.11
• /
• pp.36-44
• /
• 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.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.2 no.4
• /
• pp.67-72
• /
• 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
• /
• v.18 no.3
• /
• pp.419-431
• /
• 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.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2006.05b
• /
• pp.369-372
• /
• 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.