• Proceedings of the Korean Geotechical Society Conference
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• 1993.06e
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• pp.56-81
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• 1993

• Proceedings of the Materials Research Society of Korea Conference
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• 1998.08a
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• pp.73-73
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• 1998

• Structural Engineering and Mechanics
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• v.82 no.3
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• pp.401-416
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• 2022

The aim of this study is to examine the frictionless double receding contact problem for two functionally graded (FG) layers pressed with a uniformly distributed load and resting on a homogeneous half plane (HP) using analytical and numerical methods. The FG layers are made of a non-homogeneous material with an isotropic stress-strain law with exponentially varying properties. It is assumed that the contact at the FG layers and FG layer-HP interface is frictionless. The body force of the FG layers and homogeneous HP are ignored in the study. Firstly, an analytical solution for the contact problem has been realized using the theory of elasticity and the Fourier integral transform techniques. Then, the problem modeled and two-dimensional analysis was carried out by using the ANSYS package program based on FEM. Numerical results for contact lengths and contact pressures between FG layers and FG layer-HP were provided for various dimensionless quantities including material inhomogeneity, distributed load width, the shear module ratio, and the heights of the FG layers for both methods. The results obtained using FEM were compared with the results found using the analytical formulation. It was found that the results obtained from analytical formulation were in perfect agreement with the FEM study.

• Korean Journal of Metals and Materials
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• v.47 no.3
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• pp.202-208
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• 2009

The effects of aging time on the microstructure and shear strength of the Low Temperature Co-fired Ceramic (LTCC)/Ag pad/Electroless Nickel Immersion Gold (ENIG)/BGA solder joints were investigated through isothermal aging at $150^{\circ}C$ for 1000 h with conventional Sn-37Pb and Sn-3Ag-0.5Cu. $Ni_3Sn_4$ intermetallic compound (IMC) layers was formed at the interface between Sn-37Pb solder and LTCC substrate as-reflowed state, while $(Ni,Cu)_3Sn_4$ IMC layer was formed between Sn-3Ag-0.5Cu solder and LTCC substrate. Additional $(Cu,Ni)_6Sn_5$ layer was found at the interface between the $(Ni,Cu)_3Sn_4$ layer and Sn-3Ag-0.5Cu solder after aging at $150^{\circ}C$ for 500 h. Thickness of the IMC layers increased and coarsened with increasing aging time. Shear strength of both solder joints increased with increasing aging time. Failure mode of BGA solder joints with LTCC substrate after shear testing revealed that shear strength of the joints depended on the adhesion between Ag metallization and LTCC. Fracture mechanism of Sn-37Pb solder joint was a mixture of ductile and pad lift, while that of Sn-3Ag-0.5Cu solder joint was a mixture of ductile and brittle $(Ni,Cu)_3Sn_4$ IMC fracture morphology. Failure mechanisms of LTCC/Ag pad/ENIG/BGA solder joints were also interpreted by finite element analyses.

• Restorative Dentistry and Endodontics
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• v.19 no.1
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• pp.45-63
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• 1994

128 freshly extracted human molars were used to study the interaction between dentinal smear layer removal with various agents, and the shear bond strength of a light cured glass ionomer cement to dentin. It was proposed that the removal of smear layers using acidic cleaners followed by incorporation of Fe mordant with dentin could enhanced the infiltration of monomer component in light curing glass ionomer cement and resulted in a high bond strength. For the first treatment process for removal of smear layers on the surfaces of dentin, 50 % citric acid, 10% maleic acid and 10 % phosphoric acid were used, and for the second treatment process, 15% ferric chloride, 6.8% ferric oxalate or 30% potassium oxalate were used. Distilled water was used as a control. After double sequential treatment on dentin, a light curing glass ionomer cement was bonded to dentin. After being immersed in water at 31'C for 24 hours, shear bond strengths were measured Instron testing machine(Model No.4202, USA). Surface changes were also observed using SEM (Hitachi, S-2300, Japan) after treatment process with each agents. The following conclusions were drawn : 1. Dentin surface cleaned with maleic acid and treated with ferric oxalate showed the highest bond strength with light curing glass ionomer cement. 2. Bond strengths of glass ionomer cement to dentin treated with maleic acid or citric acid were the highest, and that treated with phosphoric acid showed the lowest. 3. The effect of ferric oxalate on shear bond strength to dentin was always higher than that of ferric chloride. 4. The smear layers were clearly removed and the orifices of dentinal tubules were opened widely by the citric acid, maleic acid and phosphoric acid. 5. The orifices of dentinal tubules opened after using the first solution were closed with the treatment of ferric chloride. 6. The precipitate like crystals were formed on dentin surfaces and tubules, but a significant decrease in bond strength of glass ionomer cement to dentin surface treated with potassium oxalate.

• Structural Engineering and Mechanics
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• v.69 no.1
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• pp.11-20
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• 2019

The biaxial failure mechanism of transversally bedding concrete layers was numerically simulated using a sophisticated two-dimensional discrete element method (DEM) implemented in the particle flow code (PFC2D). This numerical modelling code was first calibrated by uniaxial compression and Brazilian testing results to ensure the conformity of the simulated numerical model's response. Secondly, 21 rectangular models with dimension of $54mm{\times}108mm$ were built. Each model contains two transversely bedding layers. The first bedding layer has low mechanical properties, less than mechanical properties of intact material, and second bedding layer has high mechanical properties, more than mechanical properties of intact material. The angle of first bedding layer, with weak mechanical properties, related to loading direction was $0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, $75^{\circ}$ and $90^{\circ}$ while the angle of second layer, with high mechanical properties, related to loading direction was $90^{\circ}$, $105^{\circ}$, $120^{\circ}$, $135^{\circ}$, $150^{\circ}$, $160^{\circ}$ and $180^{\circ}$. Is to be note that the angle between bedding layer was $90^{\circ}$ in all bedding configurations. Also, three different pairs of the thickness were chosen in models, i.e., 5 mm/10 mm, 10 mm/10 mm and 20 mm/10 mm. The result shows that in all configurations, shear cracks develop between the weaker bedding layers. Shear cracks angel related to normal load change from $0^{\circ}$ to $90^{\circ}$ with increment of $15^{\circ}$. Numbers of shear cracks are constant by increasing the bedding thickness. It's to be noted that in some configuration, tensile cracks develop through the intact area of material model. There is not any failure in direction of bedding plane interface with higher strength.

• Steel and Composite Structures
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• v.21 no.2
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• pp.373-394
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• 2016

The postbuckling behavior of laminated composite plates and shells, subjected to various shear loadings, is presented, using a modified 8-ANS method. The finite element, based on a modified first-order shear deformation theory, is further improved by the combined use of assumed natural strain method. We analyze the influence of the shell element with the various location and number of enhanced membrane and shear interpolation. Using the assumed natural strain method with proper interpolation functions, the present shell element generates neither membrane nor shear locking behavior even when full integration is used in the formulation. The effects of various types of lay-ups, materials and number of layers on initial buckling and postbuckling response of the laminated composite plates and shells for various shear loading have been discussed. In addition, the effect of direction of shear load on the postbuckling behavior is studied. Numerical results and comparisons of the present results with those found in the literature for typical benchmark problems involving symmetric cross-ply laminated composites are found to be excellent and show the validity of the developed finite element model. The study is relevant to the simulation of barrels, pipes, wing surfaces, aircrafts, rockets and missile structures subjected to intense complex loading.

• Earthquakes and Structures
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• v.22 no.4
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• pp.355-372
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• 2022

The study is part of an experimental program on full-scale Un-Reinforced Masonry (URM) wall panels strengthened with Textile reinforced mortars (TRM). Eight brick walls (two with and five without central opening), were tested under the diagonal tension (shear) test method in order to investigate the strengthening system effectiveness on the in-plane behaviour of the walls. All the URM panels consist of the innovative components, named "Orthoblock K300 bricks" with vertical holes and a thin layer mortar. Both of them have great capacity and easy application and can be constructed much more rapidly than the traditional bricks and mortars, increasing productivity, as well as the compressive strength of the masonry walls. Several parameters pertaining to the in-plane shear behaviour of the retrofitted panels were investigated, including shear capacity, failure modes, the number of layers of the external TRM jacket, and the existence of the central opening of the wall. For both the control and retrofitted panels, the experimental shear capacity and failure mode were compared with the predictions of existing prediction models (ACI 2013, TA 2000, Triantafillou 1998, Triantafillou 2016, CNR 2018, CNR 2013, Eurocode 6, Eurocode 8, Thomoglou et al. 2020). The experimental work allowed an evaluation of the shear performance in the case of the bidirectional textile (TRM) system applied on the URM walls. The results have shown that some analytical models present a better accuracy in predicting the shear resistance of all the strengthened masonry walls with TRM systems which can be used in design guidelines for reliable predictions.

• Earthquakes and Structures
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• v.23 no.3
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• pp.297-313
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• 2022

Composite steel plate shear wall (CSPSW) is a relatively novel structural system proposed to improve the performance of steel plate shear walls by adding one or two layers of concrete walls to the infill plate. In addition, the buckling of the infill steel plate has a significant negative effect on the shear strength and energy dissipation capacity of the overall systems. Accordingly, in this study, using the finite element (FE) method, the performance and behavior of composite steel shear walls using T-shaped stiffeners to prevent buckling of the infill steel plate and increase the capacity of CSPSW systems have been investigated. In this paper, after modeling composite steel plate shear walls with and without steel plates with finite element methods and calibration the models with experimental results, effects of parameters such as several stiffeners, vertical, horizontal, diagonal, and a combination of T-shaped stiffeners located in the composite wall have been investigated on the ultimate capacity, web-plate buckling, von-Mises stress, and failure modes. The results showed that the arrangement of stiffeners has no significant effect on the capacity and performance of the CSPSW so that the use of vertical or horizontal stiffeners did not have a significant effect on the capacity and performance of the CSPSW. On the other hand, the use of diagonal hardeners has potentially affected the performance of CSPSWs, increasing the capacity of steel shear walls by up to 25%.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1997.10a
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• pp.133-140
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• 1997

Based on the Green's function technique, an analytical approach is developed to examine the surface wave screening effectiveness of composite wave barriers. The composite barrier consists of a high velocity layer sandwiched between two thin layers of low shear velocity materials. The high velocity layer is represented by differential matrix operators which relate the wave fields on each side of the layer. The low velocity layers are modeled by non-rigid contact conditions which allow partial sliding at the interfaces. Screening ratio of barriers with various combination of material, geometric, and non-rigidness parameters are compared and discussed in some detail.