• Structural Engineering and Mechanics
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• 제24권4호
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• pp.447-461
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• 2006

Here, the axisymmetric free flexural vibrations and thermal stability behaviors of functionally graded spherical caps are investigated employing a three-noded axisymmetric curved shell element based on field consistency approach. The formulation is based on first-order shear deformation theory and it includes the in-plane and rotary inertia effects. The material properties are graded in the thickness direction according to the power-law distribution in terms of volume fractions of the constituents of the material. The effective material properties are evaluated using homogenization method. A detailed numerical study is carried out to bring out the effects of shell geometries, power law index of functionally graded material and base radius-to-thickness on the vibrations and buckling characteristics of spherical shells.

• Journal of Information Display
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• 제2권4호
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• pp.57-62
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• 2001

Green-emitting $Zn_2SiO_4$:Mn phosphor particles having a spherical shape and high luminescence intensities under VUV were prepared by spray pyrolysis process under severe preparation conditions. The type of precursor solutions affected the morphology and luminescence characteristics of the prepared particles. The particles prepared from the clear solution by laboratory-scale process had spherical shape and dense morphology, while the particles prepared from the severe preparation conditions had rough surface and collapsed structure. However, the particles prepared from the colloidal solution utilizing fumed silica were spherical in shape and filled morphology at the severe preparation conditions of high flow rate of carrier gas, high concentration of solution, and large reactor size. The prepared $Zn_2SiO_4$:Mn phosphor particles with complete spherical shape had higher photoluminescence intensity than that of the commercial product prepared by solid state reaction.

• Smart Structures and Systems
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• 제14권2호
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• pp.225-246
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• 2014

The present paper develops piezo-thermo-elastic analysis of a thick spherical shell for generalized functionally graded piezoelectric material. The assumed structure is loaded under thermal, electrical and mechanical loads. The mechanical, thermal and electrical properties are graded along the radial direction based on a power function with three different non homogenous indexes. Primarily, the non homogenous heat transfer equation is solved by applying the general boundary conditions, individually. Substitution of stress, strain, electrical displacement and material properties in equilibrium and Maxwell equations present two non homogenous differential equation of order two. The main objective of the present study is to improve the relations between mechanical and electrical loads in hollow spherical shells especially for functionally graded piezoelectric materials. The obtained results can evaluate the effect of every non homogenous parameter on the mechanical and electrical components.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
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• pp.1060-1062
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• 2002

Spherical and dense BAM phosphor particles were prepared by spray pyrolysis. The key idea of dense BAM particles is to lead gelation in droplets, which was successfully achieved by using the aluminum polycation as the precursor solution for the spray pyrolysis. The BAM phosphor particles prepared by spraying the aluminum polycation solution have completely spherical shape and dense structure. When directly applied to make phosphor film on the glass by the screen-printing method, the prepared spherical BAM phosphor particles showed better packing density and surface morphology than that of commercial one, which has irregular shape and large particle size. It was also found that the thermal degradation in the photoluminescence intensity for dense and spherical BAM particles was less than that of commercial one.

• 대한기계학회논문집A
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• 제33권12호
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• pp.1357-1365
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• 2009

In this study, we enhance the numerical approach of Lee et al.$^{(1)}$ to spherical indentation technique for property evaluation of hyper-elastic rubber. We first determine the friction coefficient between rubber and indenter in a practical viewpoint. We perform finite element numerical simulations for deeper indentation depth. An optimal data acquisition spot is selected, which features sufficiently large strain energy density and negligible frictional effect. We then improve two normalized functions mapping an indentation load vs. deflection curve into a strain energy density vs. first invariant curve, the latter of which in turn gives the Yeoh-model constants. The enhanced spherical indentation approach produces the rubber material properties with an average error of less than 3%.

• Structural Engineering and Mechanics
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• 제78권3호
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• pp.297-303
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• 2021

In this paper, a mathematical model is used to the evaluation of thermoelastic interactions in fiber-reinforced material with a spherical cavity. With the goal of establishing the generalized thermoelastic model with thermal relaxation time are exploited. inner surface of the spherical cavity is tractions free and loaded by the uniform step in temperature. The finite element scheme is used to get the problem numerical solutions. The numerical results have been discussed graphically to show the impacts of the presence and the absence of reinforcement.

• Elastomers and Composites
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• 제39권1호
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• pp.23-35
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• 2004

본 연구에서는 먼저 유한요소해석을 통해 주요 물성계수들이 압입시 하중-변위 곡선형상에 미치는 영향을 분석하였다. 또한 유한요소 압입해석을 통해 마찰계수의 영향으로 하중-변위 곡선, 시편하부의 단위부피당 변형에너지 및 변형률 주불변량이 바뀌지 않는 최적 압입깊이와 시편하부지점을 선정하였다. 이러한 관찰을 통해 하나의 요소에서 얻어지는 단위부피당 변형 에너지와 변형률 주불변량을 하중-변위 데이터와 모사 시킬 수 있는 무차원 함수를 얻을 수 있었으며, 이 과정에서 예측된 물성계수를 바탕으로 공칭응력-공칭변형률 곡선을 얻을 수 있었다.

• 소성∙가공
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• 제22권7호
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• pp.389-393
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• 2013

One of the most efficient designs for manufacturing LNG tank is the Moss spherical type because it has been validated through precise analyses with respect to reliability and construction safety by stress analysis. The Moss spherical tank is assembled with hundreds of Al thick plate patches that are deformed to curved shape at elevated temperature and welded together. It is essential to evaluate the amount of deflection in the Al5083 thick plate when the patch is transferred from the heating chamber to the forming die since the patch has a length of 12,000 mm and a thickness of 60 mm. Based on FE analysis results, a design procedure for minimizing deflection in Al5083 thick plate during transfer using a moving carrier is demonstrated in this paper.

• 한국압력기기공학회 논문집
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• 제15권1호
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• pp.8-17
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• 2019

Perforated plates are used for the steam generator tube-sheet and the Reactor Vessel Closure Head in the Nuclear Power Plant. The ASME code, Section III Appendix A-8000, addresses the analysis of perforated plates, however, this analysis is only limited to the flat plate with a triangular perforation pattern. Based on the concept of the effective elastic constants, simulation of flat and spherical perforated plates and their equivalent solid plates were carried out using Finite Element Analysis (FEA). The isotropic material properties of the perforated plate were replaced with anisotropic material properties of the equivalent solid plate and subjected to the same loading conditions. The generated curves of effective elastic constants vs ligament efficiency for the flat perforated plate were in agreement with the design curve provided by ASME code. With this result, a plate with spherical curvature having perforations can be conveniently analyzed with equivalent elastic modulus and equivalent Poisson's ratio.

• 한국전기전자재료학회논문지
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• 제26권10호
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• pp.726-730
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• 2013

In order to develop a high voltage insulation material, spherical silicas with two average particle sizes of 5 ${\mu}m$ and 20 ${\mu}m$ were mixed in different mixing ratios (1:0, 0.7:0.3, 0.5:0.5, 0.3:0.7, 0:1) and their total filling content was fixed at 65 wt%. In order to observe the dispersion of the spherical silicas and the interfacial morphology between silica and epoxy matrix, field emission scanning electron microscope (FE-SEM) was used. The electrical insulation breakdown strength was estimated in sphere-plate electrodes with different insulation thicknesses of 1, 2, and 3 mm. Electrical insulation breakdown strength decreased with increasing mixing ratio of 5/20 ${\mu}m$ and the thickness dependence of the breakdown strength was also observed. The tensile strength of the neat epoxy was 82.8 MPa as average value and its increased with decreasing particles size and that of epoxy/silica (2 ${\mu}m$) was 107 MPa, which was 130.8% higher value.