• Tribology and Lubricants
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• 제22권2호
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• pp.93-98
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• 2006

The numerical analysis of the negative pressure porous gas bearings is presented. The pressure distribution is calculated using the finite difference method. The Reynolds equation and Darcy's equation are solved simultaneously. The air bearing stiffness and damping are evaluated using the perturbation method. Rectangular uniform grid is employed to model the bearing. The vacuum preloading is considered. The pressure in the vacuum pocket is assumed to be a constant negative pressure. The total load, stiffness, damping and flow rate are calculated fur several geometrical configurations and several values of negative pressure. It is found that too large vacuum pocket can result in negative total force.

• Structural Engineering and Mechanics
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• 제15권2호
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• pp.199-223
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• 2003

The formulation of a non-linear shear deformable shell element is presented for the solution of stability problems of stiffened plates and shells. The formulation of the geometrical stiffness presented here is exactly defined on the midsurface and is efficient for analyzing stability problems of thick plates and shells by incorporating bending moment and transverse shear resultant force. As a result of the explicit integration of the tangent stiffness matrix, this formulation is computationally very efficient in incremental nonlinear analysis. The element is free of both membrane and shear locking behaviour by using the assumed strain method such that the element performs very well in the thin shells. By using six degrees of freedom per node, the present element can model stiffened plate and shell structures. The formulation includes large displacement effects and elasto-plastic material behaviour. The material is assumed to be isotropic and elasto-plastic obeying Von Mises's yield condition and its associated flow rules. The results showed good agreement with references and computational efficiency.

• 대한의용생체공학회:의공학회지
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• 제40권5호
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• pp.158-164
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• 2019

The interbody fusion cage used to replace the degenerative intervertebral disc is largely composed of titanium-based biomaterials and biopolymer materials such as PEEK. Titanium is characterized by osseointergration and biocompatibility, but it is posed that the phenomenon such as subsidence can occur due to high elastic modulus versus bone. On the other hand, PEEK can control the elastic modulus in a similar to bone, but there is a problem that the osseointegration is limited. The purpose of this study was to implement titanium material's stiffness similar to that of bone by applying cellular structure, which is able to change the stiffness. For this purpose, the cellular structure A (BD, Body Diagonal Shape) and structure B (QP, Quadral Pod Shape) with porosity of 50%, 60%, 70% were proposed and the reinforcement structure was suggested for efficient strength reinforcement and the stiffness of each model was evaluated. As a result, the stiffness was reduced by 69~93% compared with Ti6Al4V ELI material, and the stiffness most similar to cortical bone is calculated with the deviation of about 12% in the BD model with 60% porosity. In this study, the interbody fusion cage made of Ti6Al4V ELI material with stiffness similar to cortical bone was implementing by applying cellular structure. Through this, it is considered that the limitation of the metal biomaterial by the high elastic modulus may be alleviated.

• 한국의류산업학회지
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• 제15권1호
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• pp.156-162
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• 2013

For the development of high quality textiles, silk fabrics were dyed repeatedly with persimmon juice by padding mangle. We evaluated the mechanical properties and hand value by Kawabata Evaluation system for dyed silk fabrics. The results obtained from this study were as follows. With the increase of repeating padding times of dyeing, the linearity load-extension curves of the silk fabrics were increased; however, the tensile resilience of fabrics decreased. The hysteresis values of shear force were increased without significant change of shear stiffness. The coefficient of friction values were also decreased and geometrical roughness values were increased. The silk fabrics dyed with persimmon juice had shown the thickness and weight grow as the number of padding increases. The hand values of silk fabrics which were classified into 6 items in the Kawabata Evaluation System, were evaluated as repeating times of dyeing with persimmon juice. The hand values of Koshi(stiffness) and Hari(anti-drape stiffness) were increased, whereas Shinayakasa (flexibility with soft feeling) and Fukurami(fullness and softness) were decreased by dyeing with persimmon juice. However there was no significant change in hand values according to repeating padding times of dyeing.

• Earthquakes and Structures
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• 제12권4호
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• pp.409-423
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• 2017

This paper proposes a quick and simplified method to describe masonry vaults in global seismic analyses of buildings. An equivalent macro-element constituted by a set of six trusses, two for each transverse, longitudinal and diagonal direction, is introduced. The equivalent trusses, whose stiffness is calculated by fully modeled vaults of different geometry, mechanical properties and boundary conditions, simulate the vault in both global analysis and local analysis, such as kinematic or rocking approaches. A parametric study was carried out to investigate the influence of geometrical characteristics and mechanical features on the equivalent stiffness values. The method was numerically validated by performing modal and transient analysis on a three naves-church in the elastic range. Vibration modes and displacement time-histories were compared showing satisfying agreement between the complete and the simplified models. This procedure is particularly useful in engineering practice because it allows to assess, in a simplified way, the effectiveness of strengthening interventions for reducing horizontal relative displacements between vault supports.

• 한국산학기술학회논문지
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• 제11권7호
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• pp.2661-2669
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• 2010

본 연구에서는 매트릭스가 손상된 적층복합판의 비선형 거동을 분석하기 위한 일차전단변형이론에 기초한 유한요소 정식을 유도하였다. Duan and Yao가 제안한 Matrix 균열의 강성 치환 방법을 적용하여 다방향 강성저하식을 구성하였다. 발생된 Matrix 균열은 탄성계수, 전단탄성계수 및 프아송비의 변화로 표현할 수 있으며, 이를 이용하여 판의 국부 강성 변화를 예측할 수 있다. 가정된 자연변형률 방법을 적용한 쉘요소를 이용하여 면내 및 전단잠김 현상이 발생하지 않았다. 적층복합판의 선형해석은 물론 비선형 해석결과들은 참고문헌의 결과들에 수렴되었다. 매트릭스가 손상된 적층복합판의 해석 결과들은 향후 연구에 비교자료로 활용될 수 있을 것이다.

• 한국강구조학회 논문집
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• 제21권5호
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• pp.483-492
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• 2009

소성영역에서 부재의 강성감소, 휨효과 및 잔류응력의 영향을 고려하면서 극한 한계상태에서 강골조의 거동을 평가하기 위해 개선 소성 힌지법을 이용하여 평면강골조의 비선형해석을 실시하고, 강접 및 반강접 평면강골조의 다양한 모델에 대한 수치해석을 통하여 거동을 평가하는데 목적이 있다. 그리고 상용프로그램을 이용한 해석결과를 이용하여 반강접율의 변화에 따른 골조의 거동을 분석한다.

• Structural Engineering and Mechanics
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• 제57권4호
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• pp.617-639
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• 2016

In this work, an analytical formulation based on both hyperbolic shear deformation theory and stress function, is presented to study the nonlinear post-buckling response of symmetric functionally graded plates supported by elastic foundations and subjected to in-plane compressive, thermal and thermo-mechanical loads. Elastic properties of material are based on sigmoid power law and varying across the thickness of the plate (S-FGM). In the present formulation, Von Karman nonlinearity and initial geometrical imperfection of plate are also taken into account. By utilizing Galerkin procedure, closed-form expressions of buckling loads and post-buckling equilibrium paths for simply supported plates are obtained. The effects of different parameters such as material and geometrical characteristics, temperature, boundary conditions, foundation stiffness and imperfection on the mechanical and thermal buckling and post-buckling loading capacity of the S-FGM plates are investigated.

• 한국의류산업학회지
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• 제6권5호
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• pp.660-666
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• 2004

This article describes the change of hand value of chitosan crosslinked cotton fabrics. The chitosan crosslinked cotton fabrics were manufactured by mercerizing process using epichlorohydrin(ECH) as crosslinkins agent, 2% aqueous acetic acid as a solvent of chitosan and ECH, and 20% aqueous sodium hydroxide as a mercerizing agent and crosslinking catalyst. Cotton fabrics were dipped in the mixed solution of chitosan and ECH, picked up by mangle, mercerized and crosslinked in NaOH solution, and finally wash and dry. Mechanical and physical properties of the chitosan crosslinked fabric were investigated using Kawabata Evaluation System(KES) and other instruments. Tensile energy and tensile strain were decreased with the increase of the concentration of chitosan. Tensile resilience, compression resilience bending rigidity, bending hysteresis, shear stiffness, shear hysteresis, coefficient of friction, geometrical roughness, compression linearity, compressional energy, and thickness were increased with the increase of the concentration of chitosan. On the other hand, bending rigidity, bending hysteresis, coefficient of friction, geometrical roughness, compressional resilience, and thickness were increased with the increase of the concentration of crosslinking agent(epichlorohydrin).

• Structural Engineering and Mechanics
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• 제20권4호
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• pp.477-493
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• 2005

In case of Mindlin plate, not only the bending deformation but also the shear behavior is allowed. While the bending and shear stiffness are given in the same order in terms of elastic modulus, they are in different order in case of plate thickness. Accordingly, bending and shear contributions have to be dealt with independently if the stochastic finite element analysis is performed on the Mindlin plate taking into account of the uncertain plate thickness. In this study, a formulation is suggested to give the response variability of Mindlin plate taking into account of the uncertainties in elastic modulus as well as in the thickness of plate, a geometrical parameter, and their correlation. The cubic function of thickness and the correlation between elastic modulus and thickness are incorporated into the formulation by means of the modified auto- and cross-correlation functions, which are constructed based on the general formula for n-th joint moment of random variables. To demonstrate the adequacy of the proposed formulation, a plate with various boundary conditions is taken as an example and the results are compared with those obtained by means of classical Monte Carlo simulation.