• 천문학논총
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• 제30권2호
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• pp.65-67
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• 2015

The surfaces of most atmosphereless solar system objects are referred to as regolith, layers of loosely connected fragmentary debris, produced by meteorite impacts. Measurements of light scattered from such surfaces provides information about the composition and structure of the surface. A suitable way to characterize the scattering properties is to consider how the intensity and polarization of scattered light depends on the particle size, composition, porosity, roughness, wavelength of incident light and the geometry of observation. In the present work, the effect of porosity on bidirectional reflectance as a function of phase angle is studied for alumina powder with grain size of $0.3{\mu}m$ and olivine powder with grain size of $49{\mu}m$ at 543.5 nm. The optical constants of the alumina sample for each porosity were calculated with Maxwell Garnett effective medium theory. On using each of the optical constants of alumina sample in Mie theory with the Hapke model the variation of bidirectional reflectance is obtained as a function of phase angle with porosity as a parameter. Experimental reflectance data are in good agreement the model. For the olivine sample the effect of porosity is studied using Hapke (2008).

• Steel and Composite Structures
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• 제31권5호
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• pp.469-488
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• 2019

We in this paper study nonlinear bending of a functionally graded porous nanobeam subjected to multiple physical load based on the nonlocal strain gradient theory. For more reasonable analysis of nanobeams made of porous functionally graded magneto-thermo-electro-elastic materials (PFGMTEEMs), both constituent materials and the porosity appear gradient distribution in the present expression of effective material properties, which is much more suitable to the actual compared with the conventional expression of effective material properties. Besides the displacement function regarding physical neutral surface is introduced to analyze mechanical behaviors of beams made of FGMs. Then we derive nonlinear governing equations of PFGMTEEMs beams using the principle of Hamilton. To obtain analytical solutions, a two-step perturbation method is developed in nonuniform electric field and magnetic field, and then we use it to solve nonlinear equations. Finally, the analytical solutions are utilized to perform a parametric analysis, where the effect of various physical parameters on static bending deformation of nanobeams are studied in detail, such as the nonlocal parameter, strain gradient parameter, the ratio of nonlocal parameter to strain gradient parameter, porosity volume fraction, material volume fraction index, temperature, initial magnetic potentials and external electric potentials.

• Steel and Composite Structures
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• 제43권1호
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• pp.79-90
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• 2022

In this study, the dynamic behavior of functionally graded layered deep beams with viscoelastic core is investigated including the porosity effect. The material properties of functionally graded layers are assumed to vary continuously through thickness direction according to the power-law function. To investigate porosity effect in functionally graded layers, three different distribution models are considered. The viscoelastically cored deep beam is exposed to harmonic sinusoidal load. The composite beam is modeled based on plane stress assumption. The dynamic equations of motion of the composite beam are derived based on the Hamilton principle. Within the framework of the finite element method (FEM), 2D twelve -node plane element is exploited to discretize the space domain. The discretized finite element model is solved using the Newmark average acceleration technique. The validity of the developed procedure is demonstrated by comparing the obtained results and good agreement is detected. Parametric studies are conducted to demonstrate the applicability of the developed methodology to study and analyze the dynamic response of viscoelastically cored porous functionally graded deep beams. Effects of viscoelastic parameter, porosity parameter, graduation index on the dynamic behavior of porous functionally graded deep beams with viscoelastic core are investigated and discussed. Material damping and porosity have a significant effect on the forced vibration response under harmonic excitation force. Increasing the material viscosity parameters results in decreasing the vibrational amplitudes and increasing the vibration time period due to increasing damping effect. Obtained results are supportive for the design and manufacturing of such type of composite beam structures.

• Tribology and Lubricants
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• 제1권1호
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• pp.88-101
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• 1985

함유베어링의 성능특징과 다공율사이에는 어떤 관계가 있다. 그 관계를 뚜렷하게 하기 위하여 이 논문에서는 수치해석과 실험을 통하여 그 관계를 규명하였다. 수치해석과 실험결과는 잘 일치되며 다공율의 증가에 따라 姿勢角과 마찰인자가 증가하는데 다공율의 증가에 따라 負荷容量은 감소한다는 것을 보여 주고 있다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.707-717
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• 2021

To the date, shipbuilding companies have applied shop primer coating which protects the steel surface from global oxidization in environment. Proper shop primer requires either anti-corrosion ability during construction or anti-porosity ability during welding, and those properties contradict to each other. This report tried to derive an optimizing parameter on these conflicting properties to select a proper shop primer. First, sufficient amounts of the natural salt spray tests were carried out to achieve a series of data for the anti-corrosion ability. Second, lots of T-joint fillet welding test were performed to evaluate the trapped porosity formed in the weld pool. According to the experimental data, we could achieve either the rust-formation rate or the porosity-formation rate, then, each rate was generalized as formulae. Then, we tried to combine these conflicting properties to decide an optimum shop primer.

• Coupled systems mechanics
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• 제11권5호
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• pp.389-409
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• 2022

During the manufacture of FGM plates, defects such as porosities can appear. Those can change the entire behavior of these plates. This paper aims to investigate the free vibration characteristics of porous functionally graded (FG) plates resting on elastic foundations. The Young's modulus of the plate is assumed to vary continuously through the thickness according to a power-law formulation, and the Poisson ratio is held constant. Different types of porosity distribution rates are considered. To examine the accuracy of the present formulation, several comparison studies are investigated. Effects of variation of porosity distribution rate, foundation parameter, power-law index and thickness ratio on the fundamental frequency of plates have been investigated.

• Steel and Composite Structures
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• 제36권3호
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• pp.293-305
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• 2020

This article presented a nanoscale modified continuum model to investigate the free vibration of functionally graded (FG) porous nanobeam by using finite element method. The main novelty of this manuscript is presenting effects of four different porosity models on vibration behaviors of nonlocal nanobeam structure including size effect, that not be discussed before The proposed porosity models are, uniform porosity distribution, symmetric with mid-plane, bottom surface distribution and top surface distribution. The nano-scale effect is included in modified model by using the differential nonlocal continuum theory of Eringen that adding the length scale into the constitutive equations as a material parameter constant. The graded material is distributed through the beam thickness by a generalized power law function. The beam is simply supported, and it is assumed to be thin. Therefore, the kinematic assumptions of Euler-Bernoulli beam theory are held. The mathematical model is solved numerically using the finite element method. Results demonstrate effects of porosity type, material gradation, and nanoscale parameters on the free vibration of nanobeam. The proposed model is effective in vibration analysis of NEMS structure manufactured by porous functionally graded materials.

• Journal of Welding and Joining
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• 제15권3호
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• pp.88-98
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• 1997

Welding defects, such as porosity and spike, have sometimes occurred in deep penetration electron beam welds. These defects are known to be one of the serious problem in electron beam welds. So, effects of active parameters ($a_b$) on bead shape and occurrence of defects in electron beam welds of heavy section 9%Ni steel plates were investigated. Partial penetration welding in flat position, and deep penetration welding of 10 ~ 28mm depth were investigated in this study. It is desirable to select low accelerating voltage and above the surface focus position $a_b$$\geq$1.2 at which a wine-cup shaped bead is obtained to avoid the welding defects such as spike and root porosity. When the accelerating voltage of electron beam was low (90kV), active parameter ($a_b$) did not influence on the bead width, penetration depth and weld defects significantly. However, in case of high voltage ($\geq$120kV), active parameter ($a_b$) was sensitively associated with penetraton depth and weld defects, i.e. when the active parameter (($a_b$) was in the range of 0.6 to 1.0, the depth of penetration was always over the target (23mm), while the depth of penetration was dramatically decreased with further increase of active parameter ($a_b$). The weld defects were decreased with the increase of active parameter $a_b$ resulting in the decrease of energy density of the focused beam in the root part of fusion zone.

• Structural Engineering and Mechanics
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• 제73권3호
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• pp.225-238
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• 2020

This work treats the axisymmetric buckling of functionally graded (FG) porous annular/circular nanoplates based on modified couple stress theory (MCST). The nanoplate is located at the elastic medium which is simulated by Kerr foundation with two spring and one shear layer. The material properties of the porous FG nanostructure are assumed to vary through the nanoplate thickness based on power-law rule. Based on two variables refined plate theory, the governing equations are derived by utilizing Hamilton's principle. Applying generalized differential quadrature method (GDQM), the buckling load of the annular/circular nanoplates is obtained for different boundary conditions. The influences of different involved parameters such as boundary conditions, Kerr medium, material length scale parameter, geometrical parameters of the nanoplate, FG power index and porosity are demonstrated on the nonlinear buckling load of the annular/circular nanoplates. The results indicate that with increasing the porosity of the nanoplate, the nonlinear buckling load is decreased. In addition, with increasing the material length scale parameter to thickness ratio, the effect of spring constant of Kerr foundation on the buckling load becomes more prominent. The present results are compared with those available in the literature to validate the accuracy and reliability. A good agreement is observed between the two sets of the results.

• Smart Structures and Systems
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• 제18권5호
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• pp.911-930
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• 2016

The main purpose of this paper is to study the effects of initial stress, gravity, anisotropy and porosity on the propagation of shear wave (SH-waves) in a fiber-reinforced layer placed over a porous media. The frequency equations in a closed form have been derived for SH-waves by applying suitable boundary conditions. The frequency equations have been expanded and approximated up to $2^{nd}$ order of Whittaker's function. It has been observed that the SH-wave velocity decreases as width of fiber-reinforced layer increases. However, with the increase of initial stress, gravity parameter and porosity, the phase velocity increases. The results obtained are in perfect agreement with the standard results investigated by other relevant researchers.