• Coupled systems mechanics
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• v.13 no.1
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• pp.43-60
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• 2024

This work presents an analytical approach to investigate wave propagation in bi-directional functionally graded cantilever porous beam. The formulations are based on Touratier's higher-order shear deformation beam theory. The physical properties of the porous functionally graded material beam are graded through the width and thickness using a power law distribution. Two porosities models approximating the even and uneven porosity distributions are considered. The governing equations of the wave propagation in the porous functionally graded beam are derived by employing the Hamilton's principle. Closed-form solutions for various parameters and porosity types are obtained, and the numerical results are compared with those available in the literature.The numerical results show the power law index, number of wave, geometrical parameters and porosity distribution models affect the dynamic of the FG beam significantly.

• Geomechanics and Engineering
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• v.36 no.2
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• pp.121-130
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• 2024

Many foundation projects are built on red-bed soft rocks, and the damage evolution of this kind of rocks affects the safety of these projects. At present, there is insufficient research on the damage evolution of red-bed soft rocks, especially the progressive process from mesoscopic texture change to macroscopic elastoplastic deformation. Therefore, based on the dual-porosity characteristics of pores and fissures in soft rock, we adopted a cellular automata model to simulate the propagation of these voids in soft rocks under an external load. Further, we established a macro-mesoscopic damage model of red-bed soft rocks, and its reliability was verified by tests. The results indicate that the relationship between the number and voids size conformed to a quartic polynomial, whereas the relationship between the damage variable and damage porosity conformed to a logistic curve. The damage porosity was affected by dual-porosity parameters such as the fractal dimension of pores and fissures. We verified the reliability of the model by comparing the test results with an established damage model. Our research results described the progressive process from mesoscopic texture change to macroscopic elastoplastic deformation and provided a theoretical basis for the damage evolution of these rocks.

• Korean Journal of Materials Research
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• v.18 no.12
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• pp.645-649
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• 2008

Graphite for the nuclear reactor is used to the moderator, reflector and supporter in which fuel rod inside of nuclear reactor. Recently, there are many researches has been performed on the various characteristics of nuclear graphite, however most of them are restricted to the structural and the mechanical properties. Therefore we focused on the thermal property of nuclear graphite. This study investigated the thermal emissivity following the oxidation degree of nuclear graphite with IG-11 used as a sample. IG-11 was oxidized to 6% and 11% in air at 5 l/min at $600^{\circ}C$. The porosity and thermal emissivity of the sample were measured using a mercury porosimeter and by an IR method, respectively. The thermal emissivity of an oxidized sample was measured at $100^{\circ}C$, $200^{\circ}C$, $300^{\circ}C$, $400^{\circ}C$ and $500^{\circ}C$. The porosity of the oxidized samples was found to increase as the oxidation degree increased. The thermal emissivity increased as the oxidation degree increased, and the thermal emissivity decreased as the measured temperature increased. It was confirmed that the thermal emissivity of oxidized IG-11 is correlated with the porosity of the sample.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.4
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• pp.265-273
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• 2002

In this paper, wave absorbing characteristics of a horizontal submerged punching plate are investigated throughout the calculation and the experiment. The punching plate with the array of circular holes can force the flow to separate and to form eddies of high vorticity and cause significant energy loss. As an analytic tool, the linear water wave theory and the eigenfunction expansion method is applied. Darcy's law that the normal velocity of the fluid passing through the punching plate is linearly proportional to the pressure difference between two sides of the punching plate is assumed. The proportional constant called the porous coefficient is deeply dependent to the porosity. To obtain the relationship between the porosity and the porous coefficient the systematic model test for the punching plates with 6 different porosities is conducted at 2-dimensional wave tank. It is found that the porous coefficient is linearly proportional to the porosity(b=57.63P-0.9717). It is also noted that the optimal porosity value is near P=0.1 and the optimal range of submergence depth is $d/h\\leq0.2$ within entire frequency range.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.8
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• pp.767-773
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• 2013

This study suggested the variations of porosity and gas permeability of gas diffusion layers (GDLs), which are easily deformed among the components of a highly compressed PEMFC stack. The volume change owing to compression was measured experimentally, and the variations in the porosity and gas permeability were estimated using correlations published in previous literature. The effect of polytetrafluoroethylene (PTFE) which is added to the GDLs to enhance water discharge was investigated on the variations of porosity and gas permeability. The gas permeability which strongly affects the mass transport through GDL, decreases sharply with increasing compression when the GDL has high PTFE loading. As a result, the mass transport through the pore network of GDL can be changed considerably according to the PTFE loading even with the same clamping force. The accuracy of modeling of transport phenomena through GDL can be improved due to the enhanced correlations developed based on the results of this study.

• Journal of the Korea Concrete Institute
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• v.16 no.5 s.83
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• pp.597-604
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• 2004

This work involves quantitatively investigating the correlation between reductions in strength and variations in pore structure under high temperature that can be utilized as estimation for predicting the inner temperature of member damaged by fire. The experimental results were remarkedly affected by micro-filling effect of silica fume and the different water-binder ratios. The increase of the exposure temperature caused the increase of porosity, which resulted from the reason that evaporable water in gel pore or capillary pores as well as chemically bound water was eliminated from hardened cement paste due to the dehydration of C-S-H and $Ca(OH)_2$. Thermal shrinkage of hardened cement paste gives rise to micro-crack, which cause the increase of porosity. Based on the experimental result that the increase of porosity is in charge of exposure temperature, how porosity is distributed can predict temperature-time history and assess the performance of concrete damaged by fire.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.875-881
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• 2004

The quality of recycled aggregate is affected by original concrete strength and the manufacturing process of recycled aggregates. In this study, the porosity of old and new mortar, and the compressive strength of concrete were investigated to examine the influence of recycled aggregate on the concrete. Six kinds of recycled coarse aggregates were produced from concrete blocks of differing strength levels (A:60. 1MPa, B:41.7MPa, C:25.5MPa). Original concrete strength and the bond mortar of recycled aggregate influences the pore structures of both old and new mortar. The pore size distribution of old mortar was found to be greatly affected by age, and the reduction of the porosity of bond mortar on low strength recycled aggregate increased at a greater rate than that of bond mortar on high strength recycled aggregate. The pore size distribution of new mortar in recycled aggregate concrete changed in comparison with that of new mortar in virgin aggregate concrete. The total porosity of new mortar using B level recycled aggregates was smaller than that of new mortar with A, and C level recycled aggregates. Moreover, the compressive strength of recycled aggregate concrete was found to have been affected by original concrete strength. The compressive strength of concrete only changed slightly in the porosity of new mortar over $15\%$, but increased rapidly in the porosity of new mortar fewer than $15\%$.

• Elastomers and Composites
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• v.42 no.2
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• pp.86-92
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• 2007

A few of polytetrafluoroethylene(PTFE) membranes and PTFE fine powders were analyzed to chooce an optimum resin. The bi-axial stretching process was developed to set up the foundation of the preparation process and control the pore size and porosity of PTFE membrane. The pretreatment of PTFE fine powder used in the preparation process for PTFE was needed. The mixing of additives, the ripening of mixture, paste extrusion process of ripening powder, calendering process and the bi-axial process were conducted for controlling pore size, porosity and thckness of membrane. The aftertreatment which strengthened the mechanical properties was necessary. The control of pore size and porosity of the membrane were determined. The ratio of PTFE fine powder and additives at the paste extrusion process, the ripening time, the ripening temperature and the parameters of temperature and pressure at the paste extrusion process were optimized.

• Geophysics and Geophysical Exploration
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• v.17 no.3
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• pp.121-128
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• 2014

As the permeability is an important parameter to characterize the ease with which a porous medium transmits fluids, it is usually obtained by fluid flow experiment using core samples. In order to measure the permeability, however, an experimental apparatus is required and it might take long measurement time, especially for tight samples. In this study, the relationship between permeability and porosity as well as drying rate has been investigated to predict the permeability without a series of measuring experiments. Porosity is measured by drying monitoring method, which measures weight variation continuously while drying surface-dried saturated sample, and drying rate is obtained from weight variation ratio with respect to the water saturation. The total of 6 Berea sandstone samples, which have a permeability range of 70 to 670 mD, were used in this work, and a new and empirical equation which could predict permeability of porous sandstone by using porosity and drying rate were obtained through regression analysis.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.137-147
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• 2002

Maturity models involving curing temperature and curing ages have been widely used to predict concrete strength, which can accurately estimate concrete strength. However, they may not consider physical quantities such as the characteristics of hydrates and the capillary porosity of microstructures associated with strength development. In order to find out the effects of both factors on a strength increment, the hydration model and the estimation method of the amount of capillary porosity were established, and the compressive strength test of concrete nth various water/cement ratios was carried out considering two test parameters, curing temperature and curing age. In this study, by analyzing the experimental results, a strength estimation model for early-age concrete that can consider the microstructural characteristics such as hydrates and capillary porosity was proposed. Measured compressive strengths were compared with estimated strengths and good agreements were obtained. Consequently, the proposed strength model can estimate compressive strength of concrete with curing age and curing temperature within an acceptable error.