• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1013-1019
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• 2016

CFRP is the composite material manufactured by the hybrid resin on the basis of carbon fiber. As this material has the high specific strength and the light weight, it has been widely used at various fields. Particularly, the unidirectional carbon fiber can be applied with the layer angle. CFRP made with layer angle has the strength higher than with no layer angle. In this paper, the property of crack growth due to each layer angle was investigated on the crack propagation and fracture behavior of the CFRP compact tension specimen due to the change of layer angle. The value of maximum stress is shown to be decreased and the crack propagation is slowed down as the layer angle is increased. But the limit according to the layer angle is shown as the stress is increased again from the base point of the layer angle of $60^{\circ}$. This study result is thought to be utilized with the data which verify the probability of fatigue fracture when the defect inside the structure at using CFRP of mechanical structure happens.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.487-492
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• 2007

The enhancement of the service life of damaged or cracked structures is a major issue for researchers and engineers. The hierarchical void element with the integrals of Legend polynomials is used to characterize the fracture behavior of unpatched crack as well as repaired crack with bonded composite patches by computing the stress intensity factors and stress contours at the crack tip. The numerical approach is based on the v-version degenerate shell element including the theory of anisotropic laminated composites. Since the equivalent single layer approach is adopted in this study, the proposed element is necessary to represent a discontinuous crack part as a continuum body with zero stiffness of materials. Thus the aspect ratio of this element to represent the crack should be extremely slender. The sensitivity of numerical solution with respect to energy release rate, displacement and stress has been tested to show the robustness of hierarchical void element as the aspect ratio is increased up to 2000. The stiffness derivative method and displacement extrapolation method have been applied to calculate the stress intensity factors of Mode I problem.

• Journal of the Korean Ceramic Society
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• v.35 no.12
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• pp.1257-1265
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• 1998

Hertzian contact tests were used to investigate the evolution of fracturedamage in the coating layer as functions of contact load and coating thickness by studying crack patterns in porcelain on glass-infiltrated alumina bilayer system conceived to simulate the crown structure of a tooth. Cone cracks initiated at the coating top surface without delamination at interface and crack propagation to substrate. Preferentially the cracks made multi-cracks at the coating top surface rather than proceeding to interface. The cracks were highly stabilized with wide ranges between the loads to initiate first cracking and to cause final failure im-plying damage-tolerant capability. Finite element modelling was used to evaluate the stress distribution. Maximum tensile stress were responsible for the cracking at the coating layer and had a profound influence on the crack pattern and fracture damage in the layered structure materials.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.698-701
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• 2007

A top emission organic light emitting diode comprising of a triple anode on polycarbonate $film/TNATA/NPB/Alq_3:C545T/cathodes$ has been fabricated. The triple layer structure of Cr/Al/Cr allowed for fabrication of a crack-free anode and provided better higher work function than ITO anode.The anode showed compatibility with flexible plastic substrate and no crack was formed during bending test while ITO anode showed crack.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.707-710
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• 2004

This paper reported the results of mock-up test on mass concrete for transfer girder using setting time difference of super retarding agent(SRA). According to test results, two mock-up structures were made. Plain concrete without placing layer reached maximum temperature after 24hours since placement and caused surface hydration cracks at top section. However, concrete with placing layer reached maximum temperature after 72hours and surface temperature was higher than center temperature, which did not cause surface crack. After form removing, no crack was observed at side surface of plain concrete, while concrete using SRA at mid section had surface scaling and settling crack. According to coring results, concrete with placing layer had a penetration crack from top section to bottom section. Therefore, the setting time difference method to reduce hydration heat will have difficulty in applying the mass concrete for transfer girder.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.1
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• pp.112-117
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• 2016

For artificial ground greening construction without root-proofing layer, this research reviewed the effect on watertightness of asphalt waterproofing layer by plant roots penetration based on crack width, and crack penetrated roots. Experiment on concrete crack width was performed with three conditions such as 0.15, 0.30, and 0.45 mm, and all three conditions confirmed that all plant roots penetrations were made through crack area in 12 ~ 18 months. In addition, according to evaluation of effects on waterproofing layer by crack penetrated plant roots and in condition of 0.45 mm crack width, it indicated that penetration is made on asphalt waterproofing layer in 12 months due to roots penetration.

• Journal of the Korean Ceramic Society
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• v.39 no.5
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• pp.484-489
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• 2002

Hot-pressure sintered laminar composites with alumina/zirconia or mullite/zirconia as an outer layer and alumina/zircon (resulting in reaction-bonded mullite/zirconia during sintering) as an inner layer were fabricated by tape casting and lamination. Various forms of crack were observed in sintered laminar composites, these cracks included channel cracks in the outer layer, transverse cracks in the inner layer and interface cracks debonding interlayer. Based on detailed microscopic observations, the cracks were attributed to thermal expansion mismatch between the oxides consisting of the each layer. In particular, the interlayer and transverse cracks were confirmed in the laminates consisted of the mullite/zirconia system as the outer layers, however, those cracks were not observed in the alumina/zirconia system used. In addition, the crack propagation did not exhibit same behavior in the two kinds of outer layer when the indentation load was applied.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.322-327
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• 2000

This paper investigates the time-dependent crack growth in X20CrMoV 12 1 steel weld joints. Crack growth test are carried out $545^{\circ}C$ on side-grooved 1/2T CT specimens under static loads. A simulated material is produced for the intercritical HAZ, where fracture normally occurs. Constitutive properties are obtained for the simulated HAZ material as well as for the base metal and weld metal. Finite element analyses of crack growth are performed on the models with and without a HAZ layer, using the experimental crack length-time history. The inclusion of HAZ layer increase the load line velocities significantly. The crack growth rates are correlated reasonably well with $C^*$. The smallest crack size for the validity of $C^*$ is found much smaller than the ASTM crack initiation size for 1T CT specimen of creep ductile materials.

• 연구논문집
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• s.31
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• pp.127-133
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• 2001

In chromium electrodeposition, crack is inevitably accompanied by chromium layer. Behavior of crack formation and crack density were different from the plating conditions such as current density, temperature, waveform of applied current and so on. And cracks have an influence on the corrosion resistance of chromium deposit, because corrosion occurs through the network of cracks between deposit and substrate. Therefore, many researches have been achieved in order to remove the cracks in chromium deposit. Formation of double layers, Cr/Cr and Ni/Cr were investigated to increase corrosion resistance of chromium deposit in this study. As pretreatment prior to outer chromium coating, acid pickling and current control method were examined. Cracks in cross-section of each sample were observed with SEM and CASS(Copper modified acetic acid salt spray) test was performed to evaluate corrosion resistance. It was found that corrosion resistance of Cr/Cr and Ni/Cr double layers were superior to Cr or Ni single layer from the results of CASS test.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.12
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• pp.95-103
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• 2001

The buckling of an orthotropic layer bonded to an orthotropic half-space with an interface crack subjected to compressive load under plane strain is analyzed. General solution to the stability equations describing the buckling behavior of both the layer and the half-space is expressed in terms of displacement functions. The displacement functions are represented by the solution of Cauchy-type singular integral equations, which are numerically solved. Numerical results of the critical buckling loads are presented fur various geometric parameters and material properties of both the layer and half-space.