• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.5
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• pp.532-537
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• 2004

FEF(Focused Electromagnetic Field) technique was newly developed that is based on the induction principle exciting electromagnetic field. The technique consists of an induction wire and a sensor for detecting electromagnetic field, and is applied in a non-contact mode. In this study, the technique was applied to the evaluation of EDM slits in some conductive materials - aluminum alloy, stainless steel and Inconel alloy. The voltage in the non-defect region is depended upon the measurement lift-off. The voltage signals on defects are measured with peak values, and the peak values changed with the depth of defects. The voltage distributions for all conductive materials are the same trend.

• International Journal of Concrete Structures and Materials
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• v.7 no.1
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• pp.79-93
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• 2013

One of the biggest problems affecting bridges is the transverse cracking and deterioration of concrete bridge decks. The causes of early age cracking are primarily attributed to plastic shrinkage, temperature effects, autogenous shrinkage, and drying shrinkage. The cracks can be influenced by material characteristics, casting sequence, formwork, climate conditions, geometry, and time dependent factors. The cracking of bridge decks not only creates unsightly aesthetic condition but also greatly reduces durability. It leads to a loss of functionality, loss of stiffness, and ultimately loss of structural safety. This investigation consists of field, laboratory, and analytical phases. The experimental and field testing investigate the early age transverse cracking of bridge decks and evaluate the use of sealant materials. The research identifies suitable materials, for crack sealing, with an ability to span cracks of various widths and to achieve performance criteria such as penetration depth, bond strength, and elongation. This paper also analytically examines the effect of a wide range of parameters on the development of cracking such as the number of spans, the span length, girder spacing, deck thickness, concrete compressive strength, dead load, hydration, temperature, shrinkage, and creep. The importance of each parameter is identified and then evaluated. Also, the AASHTO Standard Specification limits liveload deflections to L/800 for ordinary bridges and L/1000 for bridges in urban areas that are subject to pedestrian use. The deflection is found to be an important parameter to affect cracking. A set of recommendations to limit the transverse deck cracks in bridge decks is also presented.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.10
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• pp.1869-1876
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• 1992

The effect of particle property on FOD(foreign object damage) and strength degradation in structural ceramics especially, silicon carbide was investigated by accelerating a spherical particle having different material and different size. The damage induced showed significant differences in their patterns with increase of impact velocity. Also percussion cone was formed at the back part of specimen when particle size became large and its impact velocity exceeded a critical value. The extent of ring cracks was linearly related to particle size, however the impact of steel particle produced larger ring cracks than that of SiC particle. Increasing impact velocity the residual strength showed different degradation behaviors according to particle and its size. In the region the impact site represents nearly elastic deformation behavior, the residual strength was dependent upon the depth of cone crack regardless of particle size. However in elastic- plastic deformation region, the radial cracks led to rapid drop in residual strength.

• Proceedings of the KWS Conference
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• 1998.10a
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• pp.288-291
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• 1998

Inconel 600 alloy is used as the material of nuclear steam generator tubing because of its mechanical properties, formability, and corrosion properties. According to reports, the life time of nuclear power plants decreases because of the pitting, intergranular attack, primary water stress corrosion cracking(PWSCC), and intergranular stress corrosion cracking(IGSCC), and denting in the steam generator. The SCC test is very important because of SCC appears in various environment such as solutions, materials, and stress. The C-Rig specimen was made of the steam generator welded sleeve repairing by the pulsed Nd:YAG laser. In the corrosion invironment, corrosion solutions are Primary Water, Caustic, and Sulfate solution and corrosion time is 1624-4877hr. The permitted stress is 30-60ksi.In this C-Ring SCC test is the relationship between corrosion depth, crack and corrosion environment is evaluated. SCC was happens in Sulfate and Corrosion solution but doesn't happen in Primary Water. The corrosion time and stress is very affected by the severely environment of Sulfate or Caustic solution. The microstructure observation indicates that SCC causes interganular failure in the grain boundary of vertical direction.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.879-884
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• 2001

The use of recycled-aggregate concrete is increasing faster than the development of appropriate design recommendations. In addition, recycled-aggregate and higher compressive strengths are two of the most desired characteristics to improve the use of concrete as a construction material. The paper reports limited experimental data on the shear capacity of high-strength recycled aggregate concrete beams. Ten beams were tested to determine their diagonal cracking and ultimate shear capacities. The variable in the test program were concrete strength(300, 500 and 700kgf/$cm^{2}$), and shear span/depth ratio (a/d : 2.0, 3.0 and 4.0). Test results indicate that the ACI Building code prediction of Eq.(11-3) and (11-5) for high-strength recycled aggregate concretes are unconservative for all beams (with concrete strength 300, 500 and 700kgf/$cm^{2}$, a/d ratios 2.0, 3.0 and 4.0). But Zsutty Equation for high-strength recycled aggregate concretes is conservative for all beams. The results of the experimental investigation on the cracking patterns for beams show that the angle that the critical inclined crack makes with the horizontal axis decreases with increasing a/d.

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.161-168
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• 1998

Increase of traffic volume in recent years results in deterioration of the bridge slab, which is directly subjected ot vehicle loads. Where extensive repair is necessary, replacement or enhancement of load carrying capacity using full depth precast concrete deck is often the most practical solution. Precast deck system has transverse joints between adjacent precast decks. Vertical shear forces occur when a vehicle wheel load is carried by precast decks and the joints are used to transfer the load to an adjacent deck. Effective load transfer between precast decks is critical for integral behavior. Finite element analysis and tests were run on the proposed femal-to-female type joint. 18 joint specimens were tested to investigate the effects of angle. D/H, and confining stress under static load. Results indicate joint with angle of 60$^{\circ}$ and D/H of 1/4 shows the improved load carrying capacity on crack. It is effective in protecting the cracking of joints to keep the joint in compression using confining stress.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1993.10a
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• pp.1230-1242
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• 1993

In a case of mushroom (Lentinus Edodes L.) , visual features are crucial for grading and the quantitative evaluation of the growth state. The extracted quantitative visual features can be used as a performance index for the drying process control or used for the automatic sorting and grading task. First, primary external features of the front and back sides of mushroom were analyzed. And computer vision based algorithm were developed for the extraction and measurement of those features. An automatic thresholding algorithm , which is the combined type of the window extension and maximum depth finding was developed. Freeman's chain coding was modified by gradually expanding the mask size from 3X3 to 9X9 to preserve the boundary connectivity. According to the side of mushroom determined from the automatic recognition algorithm size thickness, overall shape, and skin texture such as pattern, color (lightness) ,membrane state, and crack were quantified and measured. A portion of t e stalk was also identified and automatically removed , while reconstructing a new boundary using the Overhauser curve formulation . Algorithms applied and developed were coded using MS_C language Ver, 6.0, PC VISION Plus library functions, and VGA graphic function as a menu driven way.

• Structural Engineering and Mechanics
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• v.66 no.4
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• pp.423-438
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• 2018

This pioneer study focuses on finite element modeling and numerical modeling of three types of Reinforced Concrete Haunched Beams (RCHBs). Firstly, twenty RCHBs, consisting of three types, and four prismatic beams which had been tested experimentally were modeled via a nonlinear finite element method (NFEM) based software named as, ATENA. The modeling results were compared with experimental results including load capacity, deflection, crack pattern and mode of failure. The comparison showed a good agreement between the results and thus the model used can be effectively used for further studies of RCHB with high accuracy. Afterwards, new mechanism modes and design code equations were proposed to improve the shear design equation of ACI-318 and to predict the critical effective depth. These equations are the first comprehensive formulas in the literature involving all types of RCHBs. The statistical analysis showed the superiority of the proposed equation to their predecessors where the correlation coefficient, $R^2$ was found to be 0.89 for the proposed equation. Moreover, the new equation was validated using parametric and reliability analyses. The parametric analysis of both experimental and predicted results shows that the inclination angle and the compressive strength were the most influential parameters on the shear strength. The reliability analysis indicates that the accuracy of the new formulation is significantly higher as compared to available design equations and its reliability index is within acceptable limits.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.5
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• pp.553-561
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• 2015

In this study, the performance assessment criterion for reasonable maintenance of shield TBM tunnel was presented. The performance assessment items such as crack, leakage, breakage, spalling, exfoliation/detachment, efflorescence, quality condition, exposure of steel, carbonation, faulting step, bolts condition, drainage condition, ground condition, contact section condition and conduit condition were selected by analyzing domestic and foreign performance assessment criterions and investigating segment lining deterioration cases through the site investigation and in-depth inspection analysis result on the shield TBM tunnel. In addition, the reasonable weight using AHP (Analytic Hierarchy Process) were estimated.

• Proceeding of KASS Symposium
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• 2008.05a
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• pp.70-73
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• 2008

Because the inclination and crack of stone pagoda structure are caused by the depth difference of soft soil ground and ground subsidence in weak zone, a long-term conservation of stone pagoda structure is difficult. But it is insufficient to analyze the behavior of stone pagoda structure considering soft soil ground in our country. Therefore, we find the structural effect happening in stone pagoda structure by analyzing mechanically a specific of soft soil ground and carry out structural analysis and structural modelling of stone pagoda structure that considers soft soil ground by discrete element method.