• 대한금속재료학회지
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• 제48권7호
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• pp.625-629
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• 2010

This study investigates the effects of porosity on the thermal stability and the thermal shock resistance of a porous nozzle used for blowing an inert gas. The samples of $Al_2O_3-SiO_2-ZrO_2$ system, which had the apparent porosity of 16~30% and bulk density of $2.6{\sim}3.2g/cm^3$, were prepared by adding different graphite contents (5, 10, 20 wt%) as a pore-forming agent. The thermal shock test was conducted at ${\Delta}T=500$, 1000, and $1400^{\circ}C$ also and the thermal stability was also carried out at 1550, 1600, and $1650^{\circ}C$ for 5 hrs. The specimen contained 10 wt% graphite had uniform pore size distribution, whereas the specimen with 20 wt% graphite showed non-uniform pore size distribution. As a result of thermal shock test, the specimen containing 10 wt% graphite appears to have higher mechanical strength than the other specimens (5, 20 wt% graphite). Both the 5 wt% and 20 wt% graphite specimens developed a non-uniform pore size distribution and cracks that were generated by intensive thermal stress.

• 한국공간구조학회:학술대회논문집
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• 한국공간구조학회 2006년도 춘계 학술발표회 논문집 제3권1호(통권3호)
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• pp.91-101
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• 2006

We have conducted the study about the shelter effect against the wind by using the wind fence with various porosities and the measured distance from the wind fence, in three different types of it ; (Circle wind fence, Vertical wind fence, Horizontal wind fence) The shelter effect and turbulence characteristics of the selected wind barrier is throughly investigated by wind tunnel test. flow characteristics of velocities and turbulences behind wind fence were measured using hot-wire anemometer. we characterize the turbulence behind the wind fence by varying the porosity of 0 %, 20 %, 40%, and 60%, and the distances from the wind fence from 1 H to 9 H with maintaining the uniform flow velocity of 6 m/s. In addition, we investigated the overall characterization of the wind fence by measuring total of twenty eight points on the wind fence, which forms the lattice structure on it with seven points in lateral direction and four points in vertical direction. The results of analysis from the circle wind fence indicate that the degree of the turbulence is lowered and the velocity of the wind is decreased when the porosity of 40 % are used at the distance from 3 H to 9 H. On the other hand, the vertical, horizontal wind fence with the porosity of 20% is more advantageous at the distance of 2 H to 9 H. For the effectiveness of the wind fence depending on the position, the center part is the greatest and it decreases at the edges with 10 % to 30 % less than that of at the center.

• Structural Engineering and Mechanics
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• 제72권4호
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• pp.513-524
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• 2019

The present article deals with thermal buckling of functionally graded plates with porosity and resting on elastic foundation. The basic formulation is based on quasi 3D theory. The present theory contains only four unknowns and also accommodates the thickness stretching effect. Porosity-dependent material coefficients of the plate are compositionally graded throughout the thickness according to a modified micromechanical model. Different patterns of porosity distributions are considered. The thermal loads are assumed to be uniform, linear and non-linear temperature rises through the thickness direction. The plate is assumed to be simply supported on all edges. Various numerical examples are given to check the accuracy and reliability of the present solution, in which both the present results and those reported in the literature are provided. In addition, several numerous new results for thick FG plates with porosity are also presented.

• Geomechanics and Engineering
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• 제30권2호
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• pp.153-167
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• 2022

This study proposes a method to analyze the distribution of coal porosity disturbances after the excavation of ultra-large-diameter water jet boreholes using a coal wetting and softening model. The high-pressure jet is regarded as a short-term high-pressure water injection process. The water injection range is the coal softening range. The time when the reference point of the borehole wall is shocked by the high-pressure water column is equivalent to the time of high-pressure water injection of the coal wall. The influence of roadway excavation with support and borehole diameter on the ultra-large-diameter jet drilling excavation is also studied. The coal core around the borehole is used to measure the gas permeability for determining the porosity disturbance distribution of the coal in the sampling plane to verify the correctness of the simulation results. Results show that the excavation borehole is beneficial to the expansion of the roadway excavation disturbance, and the expansion distance of the roadway excavation disturbance has a quadratic relationship with the borehole diameter. Wetting and softening of the coal around the borehole wall will promote the uniform distribution of the overall porosity disturbance and reduce the amplitude of disturbance fluctuations.

• 한국분말재료학회지
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• 제18권2호
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• pp.129-134
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• 2011

Herein, macroporous carbon materials were readily prepared by carbonization of cured body of resorcinol and formaldehyde using poly(methyl methacrylate) colloid microspheres which were employed as the template in the gelation of resorcinol with formaldehyde. The gel in the water was solvent exchanged with methanol and the wet gel was dried. After carbonization of the template-gel composite at $800^{\circ}C$, it was found that pores were left corresponding to the size of the template, yielding carbon materials with a fine porous structure with enlarged surface area and significant porosity. Properties of the carbon foams including the structure, morphology, thermal stability, and porosity were investigated. Finally, it was concluded that the method using polymer colloids as the template provided a facile route to prepare carbon foams.

• Structural Monitoring and Maintenance
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• 제6권2호
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• pp.147-159
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• 2019

In present article, a size-dependent refined thick beam element has been established based upon nonlocal elasticity theory. Next, it is used to explore vibration response of porous metal foam nanobeams on elastic medium. The established beam element introduces ten degrees of freedom. Different porosity distributions called uniform, symmetric and asymmetric will be employed. Herein, introduced thick beam element contains shear deformations without using correction factors. Convergence and verification studies of obtained results from finite element method are also provided. The impacts of nonlocality factor, foundation factors, shear deformation, slenderness ratio, porosity kinds and porosity factor on vibration frequencies of metal foam nano-sized beams have been explored.

• Advances in nano research
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• 제12권3호
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• pp.281-290
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• 2022

In the current research, the thermal buckling characteristics of the bi-directional functionally graded nano-scale tapered beam on the basis of a couple of nonlocal Eringen and classical beam theories are scrutinized. The nonlocal governing equation and associated nonlocal boundary conditions are constructed using the conservation energy principle, and the resulting equations are solved using the generalized differential quadrature method (GDQM). The mechanical characteristics of the produced material are altered along both the beam length and thickness direction, indicating that it is a two-dimensional functionally graded material (2D-FGM). It is thought that the nanostructures are defective because to the presence of porosity voids. Finally, the obtained results are used to design small-scale sensors and make an excellent panorama of developing the production of nanostructures.

• Structural Engineering and Mechanics
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• 제87권1호
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• pp.29-46
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• 2023

Critical thermal buckling of functionally graded porous (FGP) sandwich plates under various types of thermal loading is considered. It is assumed that the mechanical and thermal nonhomogeneous properties of FGP sandwich plate vary smoothly by distribution of power law across the thickness of sandwich plate. In this paper, porosity defects are modeled as stiffness reduction criteria and included in the rule of mixture. The thermal environments are considered as uniform, linear and nonlinear temperature rises. The critical buckling temperature response of FGM sandwich plates has been analyzed under various boundary conditions. By comparing several numerical examples with the reference solutions, the results indicate that the present analysis has good accuracy and rapid convergence. Further, the effects of various parameters like distribution shape of porosity, sandwich combinations, aspect ratio, thickness ratio, boundary conditions on critical buckling temperature of FGP sandwich plate have been studied in this paper.

• 전기화학회지
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• 제16권3호
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• pp.157-161
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• 2013

다공성 $LiMn_{0.6}Fe_{0.4}PO_4$ (LMFP)를 졸-겔법을 이용하여 합성하였고, 원료물질을 양론비로 혼합한 후 혼합물을 $600^{\circ}C$에서 10시간 동안 가열하여 입자 표면 전체에 전도성 탄소물질이 균일하게 형성된 LMFP을 제조하였다. LMFP의 결정구조는 리트펠트법에 의해 조사하였고, 표면구조와 기공특성은 주사전자현미경, 투과전자현미경, BET로 분석하였다. 제조된 LMFP는 표면적이 크고, 입자 표면에는 웹(web) 형태의 다공성 탄소층이 균일하게 형성되어 있는 것을 확인하였다. 상온에서 LMFP를 양극으로 사용하여 0.1 C의 전류밀도에서 초기방전용량은 152 mAh/g, 에너지밀도는 570 Wh/kg로 높았고 사이클 성능도 장기적으로 안정적이었다. 졸-겔법에 의해 제조된 LMFP는 높은 기공도와 균일한 탄소코팅에 의한 시너지효과로 이온확산이 용이하여 우수한 전기화학적 특성을 나타내었다.

• Structural Engineering and Mechanics
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• 제59권2호
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• pp.343-371
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• 2016

In this paper thermo-mechanical vibration analysis of a porous functionally graded (FG) Timoshenko beam in thermal environment with various boundary conditions are performed by employing a semi analytical differential transform method (DTM) and presenting a Navier type solution method for the first time. The temperature-dependent material properties of FG beam are supposed to vary through thickness direction of the constituents according to the power-law distribution which is modified to approximate the material properties with the porosity phases. Also the porous material properties vary through the thickness of the beam with even and uneven distribution. Two types of thermal loadings, namely, uniform and linear temperature rises through thickness direction are considered. Derivation of equations is based on the Timoshenko beam theory in order to consider the effect of both shear deformation and rotary inertia. Hamilton's principle is applied to obtain the governing differential equation of motion and boundary conditions. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of several parameters such as porosity distributions, porosity volume fraction, thermal effect, boundary conditions and power-low exponent on the natural frequencies of the FG beams in detail. It is explicitly shown that the vibration behavior of porous FG beams is significantly influenced by these effects. Numerical results are presented to serve benchmarks for future analyses of FG beams with porosity phases.