• Journal of the Microelectronics and Packaging Society
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• v.17 no.2
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• pp.41-47
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• 2010

The effect of PCB and BGA pad designs was investigated on the mechanical property of Pb-free solder joints. The mechanical property of solder joint was tested by three different test methods of drop impact tests, bending impact test, and high speed shear test. Two kinds of pad design such as NSMD (Non-Solder Mask Defined) and SMD (Solder Mask Defined) were applied with the OSP finished Pb-free solder (Sn-3.0Ag-0.5Cu, Sn-1.2Ag-0.5Cu). in the drop impact test and bending impact test, the characterized lifetime showed the same tendency, and SMD design showed better mechanical property of solder joint than NSMD regardless of test method, which was due to the different crack path. The fracture crack on SMD pad was propagated along the intermetallic compound (IMC) layer of solder joint, while the fracture crack on NSMD pad propagated through upper edge of land which shields pattern. In the high speed shear test, pad lift occurred on the solder joint of NSMD. SMD/SMD combination of pad design consequently illustrated the best mechanical property of BGA/PCB solder joint, followed by SMD/NSMD, NSMD/SMD, and NSMD/NSMD.

• International Journal of Railway
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• v.2 no.2
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• pp.43-49
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• 2009

Wear and rolling contact fatigue (RCF) defects are most important causes of rail damage, and often interaction competitive at present railway track. Head check is one of rolling contact fatigue (RCF) defects, and generally occurs in mild circular curves and transition curves that are set at both ends of sharp circular curves. Wear tends to limit the crack growth of head checks by removing the material from the RCF surface. In order to clarify the conditions of the occurrence and growth of head checks, the authors measured the interacting forces between wheels and rails and the angle of attack of wheelset, and carried out contact analyses using the actual profile data of wheels and rails. The effects of the lateral force, the contact geometry, and the wear rate at rail gauge comer on the formation of head checks were also analyzed by using the worn profiles of actual wheels and rails and the data obtained by a track inspection car. Some specific range of wear rate at the gauge comer was identified as having close relation with occurrence of head checks.

• 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 B
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• v.31 no.3 s.258
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• pp.225-233
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• 2007

The growth of GaN on the patterned substances has proven favorable to achieve thick, crack-free GaN layers. In this paper, numerical modeling of transport and reaction of species is performed to estimate the growth rate of GaN from tile reaction of TMG(trimethly-gallium) and ammonia. GaN growth rate was estimated through the model analysis including the effect of species velocity, thermal convection and chemical reaction, and thermal condition for the uniform deposition was to be presented. The effect of shape and construction of microscopic pattern was also investigated using a simulator to perform surface analysis, and a review was done on the quantitative thickness and shape in making GaN layer on the pattern. Quantitative analysis was especially performed about the shape of reactor geometry, periodicity of pattern and flow conditions which decisively affect the quality of crystal growth. It was found that the conformal deposition could be obtained with the inclination of trench ${\Theta}>125^{\circ}$. The aspect ratio was sensitive to the void formation inside trench and the void located deep in trench with increased aspect ratio.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.6
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• pp.910-914
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• 2012

In constructing all kinds of equipment and steel structures, discontinuous areas such as weld defects formed in a welded structure tend to generate cracks that will result in damage. In this study, ATOS high-strength steel welding becomes important in butt welding where the tensile strength of the steel is over 80kg/$mm^2$. Structural discontinuities such as joints are more susceptible cracks in part due to their repeated loading and fatigue crack growth. The quality of parts produced depend or the shielded amounts of steel and on the skill of the welders in making strong welds. It is true that there are many factors that can be used to generate a lot of research in this area. However geometry and load conditions due to the combined effects with many issues could be solved through this study. Butt welding material at a plate thickness of 12t in ATOS 80 high-strength steel with a 4 pass, 20l/min, 24V/200A welder is good at making specimens with the quality shown in radiographic testing.

• Structural Engineering and Mechanics
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• v.23 no.2
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• pp.147-161
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• 2006

Recent developments in fractal theory suggest that fractal may provide a more realistic representation of characteristics of cementitious materials. In this paper, the roughness of fracture surfaces in cementitious material has been characterized by fractal theory. A systematic experimental investigation was carried out to examine the dependency of fracture parameters on the aggregate sizes as well as the loading rates. Three maximum aggregate sizes (4.76 mm, 12.7 mm, and 19.1 mm) and two loading rates (slow and fast loading rate) were used. A total of 25 compression tests and 25 tension tests were performed. All fracture parameters exhibited an increase, to varying degrees, when aggregates were added to the mortar matrix. The fracture surfaces of the specimens were digitized and analyzed. Results of the fractal analysis suggested that concrete fracture surfaces exhibit fractal characteristics, and the fractal geometry provide a useful tool for characterizing nonlinear fracture behavior of concrete. Fractal dimension D was monotonically increased as maximum aggregate sizes increase. A new fractal fracture model was developed which considers the size and shape of aggregate, and the crack paths in the constituent phases. Detailed analyses were given for four different types of fracture paths. The fractal fracture model can estimate fractal dimension for multiphase composites.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.365-368
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• 2006

RBSN Method, Rigid-Body-Spring Network Method, is a structural analysis method that overcomes the problems faced in FEM analysis of concrete or crack forming structures. In RBSN, irregular lattices are used to model structural components consisting of bulk material, curvilinear reinforcements, and their interfaces. Because reinforcements and their interfaces in the bulk material are freely positioned, meshing is irrespective of the geometry of the representing bulk material. In this paper, RBSN method of 3D is applied in simulating the pull-out test of FRP (Fiber Reinforced Polymer) embedded in concrete. The comparison of analysis results to experimental results shows that RBSN method simulates the shear-slip behavior very precisely. From the analysis results, 3D RBSN method is proven to be an effective and accurate analysis method for concrete structural analysis. Also, the results show that RBSN method can be a potential analysis method for concrete structures that can replace the current FEM analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.1 s.232
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• pp.107-114
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• 2005

In order to analyze the elastic-plastic fracture behavior of a structure, the fracture resistance curve of the material should be known first. The standard CT specimen was used to obtain the fracture resistance curves of a piping system. However, it is known that the fracture resistance curve by the standard CT specimen is very conservative to evaluate the integrity of a structure. Also the fracture resistance curve is effected by the specimen geometry and the dimensions because of the constraint effect. The objective of this paper is to be certain the conservativeness of the fracture resistance curve by the standard CT specimen and to provide an additional safety margin. For these, the fracture tests using a real pipe specimen and the standard CT specimen test were performed. A 4-point bending jig was manufactured for the pipe test and the direct current potential drop method was used to measure the crack extension and the length for the pipe test. Also finite element analyses were performed with a CT specimen and a pipe in order to prove the additional safety margin. From the result of tests and analyses of the pipe and the standard CT specimen, it was observed that the fracture analysis with the standard CT specimen is conservative and the additional safety margin was proved.

• Journal of the Korean Society of Safety
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• v.37 no.6
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• pp.81-88
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• 2022

It is necessary to better understand the effect of age-related degradation on the performance of reinforced concrete shear walls in nuclear power plants in order to ensure their structural safety in the event of earthquakes. Therefore, this paper studies seismic fragility of the typical shear wall in nuclear power plants under earthquake excitation Reinforced concrete shear wall is composed of wall, horizontal and vertical flanges. Due to characteristics of its geometry, it is difficult to predict the ultimate behavior of shear wall under earthquake excitation. In this study, for more realistic numerical simulation, the Latin Hyper-Cube (LHC) simulation technique was used to generate uncertain variables for the material properties of concrete shear walls. The effects of crack, characteristics of inelastic behavior of concrete, and loss of cross section were considered in the nonlinear finite element analysis. The effects of aging-related deterioration were investigated on the performance of reinforced concrete shear walls through analysis of undegraded concrete shear walls and degraded concrete shear walls. The resulting seismic fragility curves present the change of performance of concrete shear wall due to age-related degradation.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.1
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• pp.64-70
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• 2012

Two kinds of eddy current probes are mainly used to perform the steam generator tube integrity assesment in NPPs. The first one is the bobbin probe using for inspection of volumetric defect like a fretting wear. The second one is the rotating probe using for inspection of non-volumetric defect like a crack. The eddy current probe is one of the essential components which consist of the whole eddy current examination system, and provides a decisive data for the tube integrity in accordance with acceptance criteria described in specific procedures. The design of ECT probe is especially important to improve examination results because the quality of acquired ECT data is depended on the probe design characteristics, such as coil geometry, electrical properties, operation frequency. In this study, it is analyzed that the coil winding number of differential bobbin probe affects the electrical properties of the probe. Eddy current bobbin probes for the steam generator tubes in NPPs are designed and fabricated according to the results. Experiment shows that the change in coil winding number has much effects on the optimum inspection frequency determined by the tube geometry and material. Therefore, the coil winding number in bobbin probe is very important in the probe design. In this study, a basis of the coil winding number for the eddy current bobbin probe design for steam generator tubes in NPPs is established.