• Nuclear Engineering and Technology
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• 제34권5호
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• pp.433-435
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• 2002

The relation between sintered densities and porosities in UO$_2$ pellets is investigated. The open porosity decreases linearly up to about 95% T.D.,(theoretical density) as the sintered density increases whereas, above 96% T.D., sintered UO$_2$ pellets do not have any open pores. The fraction of open porosity to the total porosity also decreases linearly as the sintered density increases, though the slope is lower than that of open porosity and, above 95% T.D., the fraction decreases rapidly to approach a zero.

• Coupled systems mechanics
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• 제6권4호
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• pp.399-415
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• 2017

This paper deals with the nonlinear static deflections of functionally graded (FG) porous under thermal effect. Material properties vary in both position-dependent and temperature-dependent. The considered nonlinear problem is solved by using Total Lagrangian finite element method within two-dimensional (2-D) continuum model in the Newton-Raphson iteration method. In numerical examples, the effects of material distribution, porosity parameters, temperature rising on the nonlinear large deflections of FG beams are presented and discussed with porosity effects. Also, the effects of the different porosity models on the FG beams are investigated in temperature rising.

• 한국결정성장학회지
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• 제32권2호
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• pp.51-54
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• 2022

연료전지에 사용되는 귀금속 전류집전체의 물성은 소재 기공도에 크게 영향을 받는다. 따라서 소재 기공도를 제어 위한 다양한 노력들이 진행되어왔다. 이중 많이 사용되는 전략으로 재료 열처리 시 기공형성제를 첨가하는 것이다. 기존의 기공형성제는 3차원 구조체였다. 본 연구에서는 차별화 전략으로 Ag 전류집전체의 기공도를 높이기 위해 2차원 구조 나노시트를 소결방지제로 첨가하였다. 실제로 나노시트 첨가에 의해 소결밀도가 감소되는 것을 보여주었다. 2차원 소재로는 초나노 두께(~ 1 nm)를 갖는 RuO₂ 나노시트가 이용되었다.

• Structural Engineering and Mechanics
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• 제77권2호
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• pp.217-229
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• 2021

The effect of distribution shape of porosity using a quasi-3D theory for free vibration analysis of FG microbeams is studied analytically in the present paper. The microbeams are simply-supported and nonhomogeneous, with power function variation of Young's modulus along their thickness. The modified coupled stress theory is utilized to consolidate size dependency of microbeam. Both even and uneven distribution shape of porosity are considered and the effective properties of porous FG microbeams are defined by theoretical formula with an additional term of porosity. The equation of motion is obtained through Hamilton's principle, however, Navier type solution method is used to obtain frequencies. The influences played by many parameters are also investigated.

• Steel and Composite Structures
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• 제24권5호
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• pp.579-589
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• 2017

The objective of this work is to analyze post-buckling of functionally graded (FG) beams with porosity effect under compression load. Material properties of the beam change in the thickness direction according to power-law distributions with different porosity models. It is known that post-buckling problems are geometrically nonlinear problems. In the nonlinear kinematic model of the beam, total Lagrangian finite element model of two dimensional (2-D) continuum is used in conjunction with the Newton-Raphson method. In the study, the effects of material distribution, porosity parameters, compression loads on the post-buckling behavior of FG beams are investigated and discussed with porosity effects. Also, the effects of the different porosity models on the FG beams are investigated in post-buckling case.

• Geomechanics and Engineering
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• 제35권4호
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• pp.367-383
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• 2023

The present paper examines the natural frequency responses of the bi-directional (n_x-n_y, n_y-n_z and n_z-n_x) and multidirectional (n_x-n_y-n_z) functionally graded (FG) plate and curved structures with and without porosity. The even and uneven kind of porosity pattern are considered to observe the influence of porosity type and porosity index. The numerical findings have been obtained using a higher order shear deformation theory (HSDT) based isometric finite element (FE) approach generated in a MATLAB platform. According to the convergence and validation investigation, the proposed HSDT based FE model is adequate to predict free vibrational responses of multidirectional porous FG plates and curved structures. Further a parametric analysis is carried out by taking various design parameters into account. The free vibrational behavior of bidirectional (2D) and multidirectional (3D) perfect-imperfect FGM structure is examined against various power law index, support conditions, aspect, and thickness ratio, and for the curvature of curved structures. The results indicate that the maximum non-dimensional fundamental frequency (NFF) value is observed in perfect FGM plates and curved structures compared to porous FGM plates and curved structures and it is maximum for FGM plates and curved structures with uneven kind of porosity than even porosity.

• Smart Structures and Systems
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• 제26권2호
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• pp.147-156
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• 2020

This numerical study demonstrates the porosity conditions and the intensity of the interactions with the aggressive agents. It is established that the density as well as the elastic modulus are correlated to ultrasonic velocity The following investigation assessed the effects of cement grade and porosity on tensile strength, flexural and compressive of Ultra High Performance Concrete (UHPC) as a numerical model in PLAXIS 2d Software. Initially, the existing strength-porosity equations were investigated. Furthermore, comparisons of the proposed equations with the existing models suggested the high accuracy of the proposed equations in predicting, cement grade concrete strength. The outcome obtained showed a ductile failure when un-corroded reinforced concrete demonstrates several bending-induced cracks transfer to the steel reinforcement. Moreover, the outcome also showed a brittle failure when wider but fewer transverse cracks occurred under bending loads. Sustained loading as well as initial pre-cracked condition during the corrosion development have shown to have significant impact on the corrosion behavior of concrete properties. Moreover, greater porosity was generally associated with lower compressive, flexural, and tensile strength. Higher cement grade, on the other hand, resulted in lower reduction in concrete strength. This finding highlighted the critical role of cement strength grade in determining the mechanical properties of concrete.

• Geomechanics and Engineering
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• 제7권6호
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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.

• Geomechanics and Engineering
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• 제24권1호
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• pp.91-103
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• 2021

This paper concerns with forced dynamic response of thick functionally graded (FG) beam resting on viscoelastic foundation including porosity impacts. The dynamic point load is proposed to be triangle point loads in time domain. In current analysis the beam is assumed to be thick, therefore, the two-dimensional plane stress constitutive equation is proposed to govern the stress-strain relationship through the thickness. The porosity and void included in constituent is described by three different distribution models through the beam thickness. The governing equations are obtained by using Lagrange's equations and solved by finite element method. In frame of finite element analysis, twelve-node 2D plane element is exploited to discretize the space domain of beam. In the solution of the dynamic problem, Newmark average acceleration method is used. In the numerical results, effects of porosity coefficient, porosity distribution and foundation parameters on the dynamic responses of functionally graded viscoelastic beam are presented and discussed. The current model is efficient in many applications used porous FGM, such as aerospace, nuclear, power plane sheller, and marine structures.

• 한국세라믹학회지
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• 제53권1호
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• pp.13-17
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• 2016

It is highlighted that increasing the adsorbent surface area on volumetric basis is very important in providing an easy access for gas molecules. Fine particles around $3{\mu}m$ of soft-burned dolomite kiln dust (SB-DKD) were hydrated to wet slurry samples by ball mill process and then placed in a chamber to use spray dryer method. Spherical granules with particle size distribution of $50{\sim}60{\mu}m$ were prepared under the experimental condition with or without addition of a pore-forming agent. The relationship between bead size of the pore-forming agent and size of SB-DKD particles is the most significant factor in preparation of spherical granules with a high porosity. Whereas addition of smaller beads than SB-DKD resulted in almost no change in the surface porosity of spherical granules, addition of larger beads than SB-DKD contributed to obtaining of the particles with both 15 times larger average pore volume and 1 order of magnitude larger porosity. It is considered that spherical granules with improved $N_2$ gas adsorption ability may also be utilized for other atmospheric gas adsorption.