• Journal of the Microelectronics and Packaging Society
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• v.16 no.4
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• pp.9-15
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• 2009

Compared to the flip-chip process using solder bumps, Cu pillar bump technology can accomplish much finer pitch without compromising stand-off height. Flip-chip process with Cu pillar bumps can also be utilized in radio-frequency packages where large gap between a chip and a substrate as well as fine pitch interconnection is required. In this study, Cu pillars with and without Sn caps were electrodeposited and flip-chip-bonded together to form the Cu-Sn-Cu sandwiched joints. Contact resistances and die shear forces of the Cu-Sn-Cu sandwiched joints were evaluated with variation of the height of the Sn cap electrodeposited on the Cu pillar bump. The Cu-Sn-Cu sandwiched joints, formed with Cu pillar bumps of $25-{\mu}m$ diameter and $20-{\mu}m$ height, exhibited the gap distance of $44{\mu}m$ between the chip and the substrate and the average contact resistance of $14\;m{\Omega}$/bump without depending on the Sn cap height between 10 to $25\;{\mu}m$.

• Steel and Composite Structures
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• v.48 no.2
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• pp.207-233
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• 2023

Steel-concrete composite box girder bridges are widely used in the construction of highway and railway bridges both domestically and abroad due to their advantages of being light weight and having a large spanning ability and very large torsional rigidity. Composite box girder bridges exhibit the effects of shear lag, restrained torsion, distortion and interface bidirectional slip under various loads during operation. As one of the most commonly used calculation tools in bridge engineering analysis, one-dimensional models offer the advantages of high calculation efficiency and strong stability. Currently, research on the one-dimensional model of composite beams mainly focuses on simulating interface longitudinal slip and the shear lag effect. There are relatively few studies on the one-dimensional model which can consider the effects of restrained torsion, distortion and interface transverse slip. Additionally, there are few studies on vehicle-bridge integrated systems where a one-dimensional model is used as a tool that only considers the calculations of natural frequency, mode and moving load conditions to study the dynamic response of composite beams. Some scholars have established a dynamic analysis model of a coupled composite beam bridge-train system, but where the composite beam is only simulated using a Euler beam or Timoshenko beam. As a result, it is impossible to comprehensively consider multiple complex force effects, such as shear lag, restrained torsion, distortion and interface bidirectional slip of composite beams. In this paper, a 27 DOF vehicle rigid body model is used to simulate train operation. A two-node 26 DOF finite beam element with composed box beams considering the effects of shear lag, restrained torsion, distortion and interface bidirectional slip is proposed. The dynamic analysis model of the coupled composite box girder bridge-train system is constructed based on the wheel-rail contact relationship of vertical close-fitting and lateral linear creeping slip. Furthermore, the accuracy of the dynamic analysis model is verified via the measured dynamic response data of a practical composite box girder bridge. Finally, the dynamic analysis model is applied in order to study the influence of various mechanical effects on the dynamic performance of the vehicle-bridge system.

• Journal of the Korean Geotechnical Society
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• v.38 no.7
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• pp.49-62
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• 2022

The hollow modular concrete block reinforced foundation method is one of the ground reinforcement foundation methods that uses hexagonal honeycomb-shaped concrete blocks with mixed crushed rock to reinforce soft grounds. It then forms an artificial layered ground that increases bearing capacity and reduces settlement. The hollow modular honeycomb-shaped concrete block is a geometrically economical, stable structure that distributes forces in a balanced way. However, the behavioral characteristics of hollow modular concrete block reinforced foundations are not yet fully understood. In this study, a bearing capacity test is performed to analyze the reinforcement effectiveness of the hollow modular concrete block through the laboratory model tests. From the load-settlement curve, punching shear failure occurs under the unfilled sand condition (A-1-N). However, the filled sand condition (A-1-F) shows a linear curve without yielding, confirming the reinforcement effect is three times higher than that of unreinforced ground. The bearing capacity equation is proposed for the parts that have contact pressure under concrete, vertical stress of hollow blocks, and the inner skin friction force from horizontal stress by confining effect based on the schematic diagram of confining effect inside a hollow modular concrete block. As a result of calculating the bearing capacity, the percentage of load distribution for contact force on the area of concrete is about 65%, vertical force on the area of hollow is 16.5% and inner skin friction force of area of the inner wall is about 18.5%. When the surcharge load is applied to the concrete part, the vertical stress occurs on the area of the hollow part by confining effect first. Then, in the filled sand in the hollow where the horizontal direction is constrained, the inner skin friction force occurs by the horizontal stress on the inner wall of the hollow modular concrete block. The inner skin friction force suppresses the punching of the concrete part and reduces contact pressure.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.9
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• pp.13-19
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• 2018

Effects of multiwall carbon nanotube (MWCNT) type and flow type (shear and elongational flow) on the electrical conductivity of polycarbonate (PC)/ MWCNT nanocomposites were investigated. Two different MWCNTs produced a huge difference in electrical conductivity in an injection molded PC/MWCNT nanocomposite. It was observed that MWCNTs having a higher aspect ratio provide much lower electrical conductivity in injection molded PC/MWCNT nanocomposites while the conductivities of compression molded samples from two different MWCNTs were the same. We found that this is due to a difference in the deformability of the two MWCNTs. As the aspect ratio of the MWCNT increases, the orientation of MWCNT by the external force becomes easier and the conductive path diminishes. Consequently the conductivity of the nanocomposites decreases. Nanocomposite samples prepared at a higher extensional rate and shear rate showed lower electrical conductivity. This is also attributed to the flow induced orientation and reduced conductive path of the MWCNTs. The experimental results were discussed in relation to variation in the tube-tube contact due to the change of the MWCNT orientation.

• Journal of Welding and Joining
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• v.31 no.5
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• pp.54-58
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• 2013

Joint properties of vehicle ECU (Electric Control Unit) module which was manufactured by using Sn-Cu-Cr-Ca alloy were investigated. A new solder which has a middle melting temperature about $231^{\circ}C$ was fabricated as the type of 300um solder ball and paste type. The prototype modules were made by reflow process and measured spreadability, wettability shear strength and estimated interface reaction. The spreadability of the alloy was about 84% from the measurement of contact angle of the solder ball and the wetting force was measured 2mN. The average shear strength of the module which was manufactured by using the solder paste, was 1.9 $kg/mm^2$. Also, the thickness of IMC(intermetallic compound) was evaluated with various aging temperature and time in order to understand Cr effect on Sn-0.7Cu solder. $Cu_6Sn_5$ IMC was formed between Cu pad and the solder alloy and the average thickness of the $Cu_6Sn_5$ IMC was measured about 4um and it was about 50% of thickness of $Cu_6Sn_5$ IMC in Sn-0.7Cu. It is expected to have a positive effect on reliability of the solder joint.

• Geomechanics and Engineering
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• v.30 no.6
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• pp.525-538
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• 2022

This paper presents a more general model for T-shaped combined footings that support two columns aligned on a longitudinal axis and each column provides an axial load and two orthogonal moments. This model can be applied to the following conditions: (1) without restrictions on its sides, (2) a restricted side and (3) two opposite sides restricted. This model considers the linear soil pressure. The recently published works have been developed for a restricted side and for two opposite sides restricted by Luévanos-Rojas et al. (2018a, b). The current model considers the uniform pressure distribution because the position of the resultant force coincides with the center of gravity of the surface of the footing in contact with the soil in direction of the longitudinal axis where the columns are located. This paper shows three numerical examples. Example 1 is for a T-shaped combined footing with a limited side (one column is located on the property boundary). Example 2 is for a T-shaped combined footing with two limited opposite sides (the two columns are located on the property boundary). Example 3 is for a T-shaped combined footing with two limited opposite sides, one column is located in the center of the width of the upper flange (b₁/2=L₁), and other column is located at a distance half the width of the strip from the free end of the footing (b₂/2=b-L₁-L). The main advantage of this work over other works is that this model can be applied to T-shaped combined footings without restrictions on its sides, a restricted side and two opposite sides restricted. It also shows the deficiencies of the current model over the new model.

• Structural Engineering and Mechanics
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• v.43 no.4
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• pp.503-526
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• 2012

Pounding between closely located adjacent buildings is a serious issue of dense cities in the earthquake prone areas. Seismic responses of adjacent buildings subjected to earthquake induced pounding are numerically studied in this paper. The adjacent buildings are modeled as the lumped mass shear buildings subjected to earthquake acceleration and the pounding forces are modeled as the Kelvin contact force model. The Kelvin model is activated when the separation gap is closed and the buildings pound together. Characteristics of the Kelvin model are extensively explored and a new procedure is proposed to determine its stiffness. The developed model is solved numerically and a SDOF pounding case as well as a MDOF pounding case of multistory adjacent buildings are elaborated and discussed. Effects of different separation gaps, building heights and earthquake excitations on the seismic responses of adjacent buildings are obtained. Results show that the seismic responses of adjacent buildings are affected negatively by the pounding. More stories pound together and pounding is more intense if the separation gap is smaller. When the height of buildings differs significantly, the taller building is almost unaffected while the shorter building is affected detrimentally. Finally, the buildings should be analyzed case by case considering the potential earthquake excitation in the area.

• Steel and Composite Structures
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• v.13 no.4
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• pp.397-408
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• 2012

This paper describes the refined 3-D finite element (FE) modeling of composite frames composed of concrete-filled steel tubular (CFST) columns and steel-concrete composite beams based on the test to get a better understanding of the seismic behavior of the steel-concrete composite frames. A number of material nonlinearities and contact nonlinearities, as well as geometry nonlinearities, were taken into account. The elastoplastic behavior, as well as fracture and post-fracture behavior, of the FE models were in good agreement with those of the specimens. Besides, the beam and panel zone deformation of the analysis models fitted well with the corresponding deformation of the specimens. Parametric studies were conducted based on the refined finite elememt (FE) model. The analyzed parameters include slab width, slab thickness, shear connection degree and axial force ratio. The influences of these parameters, together with the presence of transverse beam, on the seismic behavior of the composite frame were studied. And some advices for the corresponding seismic design provisions of composite structures were proposed.

• Geomechanics and Engineering
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• v.7 no.6
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• pp.665-678
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• 2014

In discrete element modeling, 2D software has been widely used in order to gain further insights into the fundamental mechanisms with less computational time. The porosities used in 2D DEM studies should be determined with appropriate approaches based on 3D laboratory porosities. This paper summarizes the main approaches for converting porosities from 3D to 2D for DEM studies and theoretical evaluations show that none of the current approaches can be widely used in dealing with soil mechanical problems. Therefore, a parabolic equation and a criterion have been suggested for the determination of 2D porosities in this paper. Moreover, a case study has been used to validate that the 2D porosity obtained from the above suggestion to be rational with both the realistic contact force distribution in the specimen and the good agreement of the DEM simulation results of direct shear tests with the corresponding experimental data. Therefore, the parabolic equation and the criterion are suggested for the determination of 2D porosities in a wide range of polydisperse particle systems, especially in dealing with soil mechanical problems.

• Nuclear Engineering and Technology
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• v.54 no.1
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• pp.357-373
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• 2022

The high-temperature gas-cooled reactor pebble-bed module project is the first commercial Generation-IV NPP(Nuclear Power Plant) in China. A new joint is used for the vertical support of RPV(Reactor Pressure Vessel). The steel corbel is integrally embedded into the reactor-cabin wall through eight asymmetrically arranged pre-stressed high-strength bolts, achieving the different path transmission of shear force and moment. The vertical monotonic loading test of two specimens is conducted. The results show that the failure mode of the joint is bolt fracture. There is no prominent yield stage in the whole loading process. The stress of bolts is linearly distributed along the height of corbel at initial loading. As the load increases, the height of neutral axis of bolts gradually decreases. The upper and lower edges of the wall opening contact the corbel plate to restrict the rotation of the corbel. During the loading, the pre-stress of some bolts decreases. The increase of the pre-stress strength ratio of bolts has no noticeable effect on the structure stiffness, but it reduces the ultimate bearing capacity of the joint. A simplified calculation model for the elastic stage of the joint is established, and the estimation results are in good agreement with the experimental results.