• Journal of the Korean Geotechnical Society
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• v.16 no.1
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• pp.221-226
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• 2000

In this study, the characteristics of gas-water relative permeability curves in a single fractured-plate according to the various aperture size were analyzed by using the Hele-Shaw type glass plate model. The plate was made of glasses for the observation of the two-phase flow pattern, and seven cases were set up based on the aperture size in the range of field scale from 30 to $120\mum$. The experiment was conducted by steady-state method, and the water saturation was determined more accurately by the developed digital image process technique. The empirical equations of relative permeability to gas and water for single fractured-plate were correlated by using the aperture size which directly affects the two-phase flow pattern and critical saturation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.96-102
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• 1990

Cracks found in pressure vessels have been reported to be mostly semi-elliptic surface cracks. The fatigue crack growth behaviour of the surface cracks on pressure vessel materials, SPV 50Q and API 5A-K55, was studied with the consideration of the crack opening character. To determine the crack opening loads for the surface cracks, the displacement/strain were measured at three positions; the center and the side of the surface crack, the back face of the specimen using CMOD gauge and strain gauges. The experimental results showed that the crack opening load levels measured at the side of the surface crack were generally a little higher than those measured at the back face. As for the crack growth rates at the different parts of the surface crack, the experiments also showed that, if .DELTA.K$_{eff}$ is used, the exponent n of the Paris' law obtained were the same for the rear and the side parts of the surface cracks.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.19-26
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• 2014

Concrete guide rail and median barrier are an attached RC member, however they are vulnerable to cracking due to slip form construction and large surface of member. In this study, causes and pattern of cracking are analyzed through assessment and NDT (Non-Destructive Technique) evaluation for concrete guide rail and median barrier on highway structure. For this work, analysis on drying shrinkage and hydration heat are performed considering installation period, and plastic shrinkage is also analyzed considering their environmental conditions. From the evaluation, plastic settlement around steel location, drying/ plastic shrinkage, and aggregate segregation are inferred to be the main causes of cracking in the structures. The crack causes and patterns are schematized and techniques of crack-control are suggested. Furthermore concrete guide rail/ median barrier in the bridge on the sea are vulnerable to cracking at early age so that special attentions should be paid at the stages of material selection and construction.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.4
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• pp.352-357
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• 2008

The detection of micro cracks in materials at the early stage of fracture is important in many structural safety assurance problems. The nonlinear ultrasonic technique (NUT) has been considered as a positive method for this, since it is more sensitive to micro crack than conventional linear ultrasonic methods. The basic principle is that the waveform is distorted by nonlinear stress-displacement relationship on the crack interface when the ultrasonic wave transmits through, and resultantly higher order harmonics are generated. This phenomenon is called the contact acoustic nonlinearity (CAN). The purpose of this paper is to prove the applicability of CAN experimentally by detection of micro fatigue crack artificailly initiated in Aluminum specimen. For this, we prepared fatigue specimens of Al6061 material with V-notch to initiate the crack, and the amplitude of second order harmonic was measured by scanning along the crack direction. From the results, we could see that the harmonic amplitude had good correlation with COD and it can be used to detect the crack depth in more accurately than the common 6 dB drop echo method.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.21-22
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• 2009

This paper presents the results of an experimental study on flexural behavior and cracking process of concrete beams subjected to cycles of freezing and thawing after patch-repaired with strain-hardening cement composites (SHCCs). The SHCCs were reinforced with hybrid 0.75% PVA and 0.75% PE fibers. Experimental testing of concrete beams patch-repaired with SHCCs revealed that the SHCC patch-repair system without freeze thaw (FT) exposure showed average 3.31 times increased load carrying capacity and for beams exposed to 300 FT cycles, load carrying capacity increased up to 2.42 times. Cracking damage of SHCC patch-repaired beams mitigated compared to plain concrete beams but this trend decreased under FT exposure.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1583-1591
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• 1990

Life prediction and residual life prediction of structures of machines are one of the most strongly world wide needed problems as requirement in the stage of slowly developing economy which comes after rapidly and highly developing stage. For the purpose of statistical life prediction, fatigue test was conducted under the 4 stress levels, and for each stress level, about 20 specimens are used. The statistical properties of crack growth parameter m and C in the fatigue crack growth law of da/dN=C(.DELTA.K)sup m/, and the relationship between m and C, and the statistical distribution pattern of fatigue crack growth rate can be obtained by experimental results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.1
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• pp.87-95
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• 1989

The fatigue crack propagation of random short fiber SMC composite material was investigated. In macroscopic viewpoint, SMC composite material was treated as isotropic material and was analyzed in terms of conventional fracture mechanics. Experiments were conducted on mode I and mixed respectively and various loading level was applied to each mode. Fatigue crack growth can be explained in three steps and most of fatigue life is consumed in initial crack growth. In this experiments, power law, i.e, da/dN=C(C.DELTA.K)$^{m}$ , between fatigue crack growth rate and stress intensity factor range, was valid and the value of the exponent m is about 10, which is much higher than that of other metals. Fracture mechanism was also investigated by SEM fractographic study.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.5
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• pp.23-31
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• 2010

In this study, a shaking table test was performed for the evaluation of the failure capacity of an anchor foundation system in the case of an aged condition. For the shaking table test, three kinds of specimens were manufactured as follows: 1) a non-damaged anchor; 2) a specimen with cracks running through the anchor; and 3) a specimen with cracks along the expected corn-shape fracture away from the anchor. A dynamic characteristic was determined through a measurement of the frequency response function (FRF), and the seismic capacity was evaluated by using a shaking table test. Failure capacities were calculated using an acceleration response and it was compared with the anchor design code.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.5
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• pp.1-12
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• 2013

This study presents the evaluations of seismic performance and displacement ductility for two types of RC columns: existing RC column without SFM (Super Flexibility Membrane) and CSF (RC columns strengthened with SFM). After they are analyzed by the experiment as well as FEM, crack patterns and load-displacement curve of CSF by the former are shown to similar to those of CSF by the latter. The flexural cracks are dominant in CSF, whereas shear cracks in CNF (existing RC column without SFM). Displacement ductility of CSF is shown significantly to increase as well as ultimate displacement, compared to those of CNF. Therefore CSF can be replaced to CNF in order to increase the seismic performance and displacement ductility.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.2
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• pp.67-73
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• 2016

When assessing crack initiation of fiber reinforced concrete, usually tensile strength or flexural strength is becomes indicator, but also depend on the curing effect take place during the production of specimen. In general, after conducting concrete specimen is cured by water at temperature $20{\pm}3^{\circ}C$ in laboratory, and accomplished the assessment of strength, but most of concrete structure is kept in drying condition after moist curing through the prescribed period. However, unlike these trends that technological advances have been made, influence of the difference of curing method on crack strength is not yet clear. Therefore, in this study, it is examined on the effect of curing methods affecting the mechanical property of fiber reinforced concrete, especially crack strength.