• Journal of the Korean Society for Heat Treatment
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• v.17 no.6
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• pp.356-364
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• 2004

The hydrides in cladding affect the corrosion and tensile properties. In this study corrosion and tensile properties were evaluated with varying the hydrogen concentration. The charged hydrogen contents were ranged from 200 to 1000 ppm. The corrosion rate in water and LiOH solution increases with the hydrogen concentration. The hydride did not affect the corrosion mechanism in the pre-transition region, but in the post-transition region the corrosion rate was accelerated. Cladding E contained higher Niobium content was slowly accelerated compared with other claddings. The yield and ultimate strengths were independent on the hydrogen content. However, the total elongation decreased gradually with increasing the hydrogen content. SEM observation of fracture surface showed that an average of depth of voids decreased with increasing the hydrogen content and small secondary crack are observed.

• Nuclear Engineering and Technology
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• v.36 no.4
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• pp.327-337
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• 2004

It is commonly required that tubes with defects exceeding $40\%$ of wall thickness in depth should be plugged; however, this criterion is too conservative for some locations and for some types of defects. Many studies have been done with the aim of developing an alternative plugging criteria, and these studies have shown that steam generator tubes with a certain range of axial through-wall cracks could remain in service without any safety or reliability problems. However, these studies have been limited, thus far, to consideration of single cracked tubes, necessitating a study on multiple cracks, which are commonly found. A crack coalescence model applicable to steam generator tubes with two collinear axial through-wall cracks was proposed in the previous study. In this paper, the investigation is extended to the parallel axial cracks spaced in a circumferential direction, because parallel axial cracks are more frequently detected during in-service inspections than collinear axial cracks. Interaction effects between two parallel cracks are evaluated by performing elastic and elastic-plastic finite element analyses.

• Nuclear Engineering and Technology
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• v.42 no.5
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• pp.546-551
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• 2010

The objective of this research is to estimate the crack location and size of a carbon steel pipe by using a laser ultrasound guided wave for the wall thinning evaluation of an elbow. The wall thinning of the carbon steel pipe is one of the most serious problems in nuclear power plants, especially the wall thinning of the carbon steel elbow caused by Flow-Accelerated Corrosion (FAC). Therefore, a non-destructive inspection method of elbow is essential for the nuclear power plants to operate safely. The specimens used in this study were carbon steel elbows, which represented the main elements of real nuclear power plants. The shape of the wall thinning was an oval with a width of 120mm, a length of 80mm, and a depth of 5mm. The L(0,1) and L(0,2) modes variation of the ultrasound guided wave signal is obtained from the response of the laser generation/air-coupled detection ultrasonic hybrid system represent the characteristics of the defect. The trends of these characteristics and signal processing were used to estimate the size and location of wall thinning.

• Journal of Surface Science and Engineering
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• v.48 no.6
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• pp.354-359
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• 2015

Stainless steel has poor corrosion resistance in marine environment due to the breakdown of a passive film caused by chloride. It suffers electrochemical corrosion like pitting corrosion, crevice corrosion, and stress corrosion crack (SCC) in marine environment. In general, it indicates that the passive film of $Al_2O_3$ has better corrosion resistance than that of $Cr_2O_3$ in seawater. This paper investigated the damage behavior 304 stainless steel and hot-dip aluminized 304 stainless steel in seawater solution. Various electrochemical experiments were carried out including potential measurement, potentiodynaimic experiment, Tafel analysis and galvanostatic experiment. As a result of anodic polarization experiment, higher pitting damage depth was indicated at 304 stainless steel than hot-dip aluminized 304 stainless steel. In addition, relatively higher corrosion current density was shown at hot-dip aluminized stainless steel as a result of Tafel analysis.

• Magazine of the Korea Concrete Institute
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• v.5 no.4
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• pp.135-144
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• 1993

A fatigue analysis procedure for prestressed concrete composite girder bridges is established, which includes the time-dependent effects of component materials. The procedure can take into account the movement of neutral axis depth as crack develops and give quite good agreement with experimental results available. It is also assured that Korean Standard prestressed concrete composite girder has enough fatigue resistance. The procedure in this paper gives a way to express the fatigue capacity of prestressed concrete beams in the form of S-N curve, which can be utilized under variable amplitude fatigue load.

• Structural Engineering and Mechanics
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• v.39 no.2
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• pp.207-221
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• 2011

This paper aims to study the behavior of short reinforced concrete columns confined with external glass Fiber Reinforced Polymers (GFRP) sheets under eccentric loads. The experimental part of the study was achieved by testing 9 specimens under eccentric compression. Three eccentricity ratios corresponding to e/t = 0, 0.10, 0.50 in one direction of the column were used. Specimens were divided into three groups. The first group was the control one without confinement. The second group was fully wrapped with GFRP laminates before loading. The third group was wrapped under loading after reaching 75% of failure loads of the control specimens. The third group was investigated in order to represent the practical case of strengthening a loaded column with FRP laminates. All specimens were loaded until failure. The results show that GFRP laminates enhances both failure load and ductility response of eccentrically loaded column. Moreover, the study also illustrates the effect of confinement on the first crack load, lateral deformation, strain in reinforcement and failure pattern. Based on the analysis of the experimental results, a simple model has been proposed to predict the improvement of load carrying capacity under different eccentricity ratios. The predicted equation takes into consideration the eccentricity to cross section depth ratio, the ultimate strength of GFRP, the thickness of wrapping laminate, and the time of wrapping (before loading and under loading). A good correlation was obtained between experimental and analytical results.

• Computers and Concrete
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• v.24 no.6
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• pp.513-525
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• 2019

In this work, an experimental research has been performed on Steel Fiber-Steel Reinforced Concrete (SFSRC)specimens subjected to four-point bending tests to evaluate the feasibility of mutual replacement of steel fibers and conventional reinforcement through studying failure modes, load-deflection curves, stiffness of characteristic points, stiffness degradation curves and damage analysis. The variables considered in this experiment included steel fiber volume percentage with and without conventional reinforcements (stirrups or steel fibers) with shear span depth ratios of S/D=2.5 and 3.5. Experimental results revealed that increasing the volume percentage of steel fiber decreased the creation and propagation of shear and bond cracks, just like shortening the stirrups spacing. Higher crack resistance and suturing ability of steel fiber can improve the stability of its bearing capacity. Both steel fibers and stirrups improved the stiffness and damage resistance of specimens where stirrups played an essential role and therefore, the influence of steel fibers was greatly weakened. Increasing S/D ratio also weakened the effect of steel fibers. An equation was derived to calculate the bending stiffness of SFSRC specimens, which was used to determine mid span deflection; the accuracy of the proposed equation was proved by comparing predicted and experimental results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.451-460
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• 1989

This paper dealt with the effect of the ratios N2 to H2 gas on the corrosion fatigue failure behavior of ion-nitrided SM45C steel specimens. The specimens were water cooled after ion-nitriding at 500.deg. C for 3hrs in 5 Torr, 0.8N$_{2}$ and 0.5N$_{2}$ atmospheres. As the nitrogen concentration increases, the higher compressive residual stresses developed in the surface layer and the depth of nitrided layer increased, which in turn gave rise to increases in fatigue strength and corrosion fatigue life. In the region less than 1.5 * 10$^{5}$ cycles, fatigue failure initiated at the brittle nitrided case, whereas in the region higher than 1.5 * 10$^{5}$ cycles crack initiated from the non-metallic inclusions in the subsurface. The initiation of corrosion fatigue failure was mainly attributed to pitting of case hardened surface layer.

• KCI Concrete Journal
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• v.11 no.3
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• pp.5-17
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• 1999

In recent years. the concept of the modified compression field theory (MCFT) was develped and applied to the analysis of reinforced concrete beams subjected to shear, moment, and axial load. Although too complex for regular use in the shear design or beams. the procedure has value in its ability to provide a rational method of anlysis and design for reinforced concrete members. The objective of this paper is to review the MCFT and apply it for the prediction of the response and shear strength of reinforced concrete beams A Parametric analysis was Performed on a reinforced T-section concrete beam to evaluate and compare the effects of concrete strength. longitudinal reinforcement ratio shear reinforcement ratio, and shear span to depth ratio in two different approaches the MCFT and the ACI code. The analytical study showed that the concrete contribution to shear strength by the MCFT was higher than the one by the ACI code in beams without stirrups, while it was lower with stirrups. On the other hand. shear reinforcement contribution predicted by the MCFT was much higher than the one by the ACI code. This is because the inclination angle of shear crack is much smaller than 45$^{\circ}$assumed in the ACI code.

• Magazine of the Korea Concrete Institute
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• v.3 no.3
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• pp.141-148
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• 1991

Investigations on the behavior of steel fiber reinforced high strength concrete beams subjected to predominant shear are accomplished to determine their diagonal shear strength including ultimate shear strength. The par¬ameters varied were the fiber volume fraction(Vf) of the steel-fibers and shear span to depth ratio(a/d). The test result show that diagonal shear strength and ultimate shear strength are increased significantly due to crack arrest mechamsm. Predictive equations are suggested for evaluating the diagonal cracking strength and ultimate shear strength of the fiber reinforced high strength concrete beams.