• 전기화학회지
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• 제25권4호
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• pp.191-200
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• 2022

Na-β"-Al₂O₃ has been widely employed as a solid electrolyte for high-temperature sodium (Na) beta-alumina batteries (NBBs) thanks to its superb thermal stability and high ionic conductivity. Recently, a vapor phase conversion (VPC) method has been newly introduced to fabricate thin Na-β"-Al₂O₃ electrolytes by converting α-Al₂O₃ into β"-Al₂O₃ in α-Al₂O₃/yttria-stabilized zirconia (YSZ) composites under Na⁺ and O^2- dual percolation environments. One of the main challenges that need to be figured out is lowered conductivity due to the large volume fraction of the non-Na⁺-conducting YSZ. In this study, the effect of lithia addition in the β"-Al₂O₃ phase on the grain size and ionic conductivity of Na-β"-Al₂O₃/YSZ solid electrolytes have been investigated in order to enhance the conductivity of the electrolyte. The amount of pre-added lithia (Li₂O) precursor as a phase stabilizer was varied at 0, 1, 2, 3, and 4 mol% against that of Al₂O₃. It turns out that ionic conductivity increases even with 1 mol% lithia addition and reaches 67 mS cm^-1 at 350 ℃ of its maximum with 3 mol%, which is two times higher than that of the undoped composite.

• Steel and Composite Structures
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• 제45권3호
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• pp.409-423
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• 2022

Nowadays, there is a high demand for great structural implementation and multifunctionality with excellent mechanical properties. The porous structures reinforced by graphene platelets (GPLs) having valuable properties, such as heat resistance, lightweight, and excellent energy absorption, have been considerably used in different engineering implementations. However, stiffness of porous structures reduces significantly, due to the internal cavities, by adding GPLs into porous medium, effective mechanical properties of the porous structure considerably enhance. This paper is relating to vibration analysis of fluidconveying cantilever porous graphene platelet reinforced (GPLR) pipe with fractional viscoelastic model resting on foundations. A dynamical model of cantilever porous GPLR pipes conveying fluid and resting on a foundation is proposed, and the vibration, natural frequencies and primary resonant of such a system are explored. The pipe body is considered to be composed of GPLR viscoelastic polymeric pipe with porosity in which Halpin-Tsai scheme in conjunction with the fractional viscoelastic model is used to govern the construction relation of nanocomposite pipe. Three different porosity distributions through the pipe thickness are introduced. The harmonic concentrated force is also applied to the pipe and the excitation frequency is close to the first natural frequency. The governing equation for transverse motions of the pipe is derived by the Hamilton principle and then discretized by the Galerkin procedure. In order to obtain the frequency-response equation, the differential equation is solved with the assumption of small displacement, damping coefficient, and excitation amplitude by the multiple scale method. A parametric sensitivity analysis is carried out to reveal the influence of different parameters, such as nanocomposite pipe properties, fluid velocity and nonlinear viscoelastic foundation coefficients, on the primary resonance and linear natural frequency. Results indicate that the GPLs weight fraction porosity coefficient, fractional derivative order and the retardation time have substantial influences on the dynamic response of the system.

• Composites Research
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• 제19권6호
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• pp.16-22
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• 2006

다양한 조건 하에서 최상의 관통 특성을 발휘하기 위한 최적 조건에 대해 연구하였다. 섬유 종횡비(AR: 섬유 길이/섬유 직경), 계면 조건 그리고 섬유 함유량을 관통 저항력과 마찰력에 지대한 영향을 미치는 변수들로 고려하였다. 단섬유 강화고무의 관통 저항력은 기지에 비해 최대 3.4배 증가하였다. 동일한 섬유 종횡비와 섬유 함유량에서 계면 조건이 우수할수록 더 높은 관통 저항력을 보였다. 기지와 섬유 종횡비가 155이하인 일부 단섬유 강화고무의 마찰력은 존재치 않았다. 우수한 계면과 높은 섬유 종횡비를 갖는 단섬유 강화고무의 마찰력은 기지의 관통 저항력보다도 더 높았다. 전체적으로 계면 조건과 섬유 종횡비 그리고 섬유 함유량이 단섬유 강화고무의 관통 특성에 지대한 영향이 미침을 확인하였다.

• Steel and Composite Structures
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• 제46권1호
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• pp.1-13
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• 2023

Elastic bending of imperfect functionally graded sandwich plates (FGSPs) laying on the Winkler-Pasternak foundation and subjected to sinusoidal loads is analyzed. The analyses have been established using the quasi-3D sinusoidal shear deformation model. In this theory, the number of unknowns is condensed to only five unknowns using integral-undefined terms without requiring any correction shear factor. Moreover, the current constituent material properties of the middle layer is considered homogeneous and isotropic. But those of the top and bottom face sheets of the graded porous sandwich plate (FGSP) are supposed to vary regularly and continuously in the direction of thickness according to the trigonometric volume fraction's model. The corresponding equilibrium equations of FGSPs with simply supported edges are derived via the static version of the Hamilton's principle. The differential equations of the system are resolved via Navier's method for various schemes of FGSPs. The current study examine the impact of the material index, porosity, side-to-thickness ratio, aspect ratio, and the Winkler-Pasternak foundation on the displacements, axial and shear stresses of the sandwich structure.

• Journal of Electrochemical Science and Technology
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• 제13권2호
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• pp.269-278
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• 2022

Utilization of high-voltage electrolyte additive(s) at a small fraction is a cost-effective strategy for a good solid electrolyte interphase (SEI) formation and performance improvement of a lithium-rich layered oxide-based high-energy lithium-ion cell by avoiding the occurrence of metal-dissolution that is one of the failure modes. To mitigate metal-dissolution, we explored fluorinated dual-additives of fluoroethylene carbonate (FEC) and di(2,2,2-trifluoroethyl)carbonate (DFDEC) for building-up of a good SEI in a 4.7 V full-cell that consists of high-capacity silicon-graphite composite (15 wt% Si/C/CF/C-graphite) anode and Li_1.13Mn_0.463Ni_0.203Co_0.203O₂ (LMNC) cathode. The full-cell including optimum fractions of dual-additives shows increased capacity to 228 mAhg^-1 at 0.2C and improved performance from the one in the base electrolyte. Surface analysis results find that the SEI stabilization of LMNC cathode induced by dual-additives leads to a suppression of soluble Mn²⁺-O formation at cathode surface, mitigating metal-dissolution event and crack formation as well as structural degradation. The SEI and structure of Si/C/CF/C-graphite anode is also stabilized by the effects of dual-additives, contributing to performance improvement. The data give insight into a basic understanding of cathode-electrolyte and anode-electrolyte interfacial processes and cathode-anode interaction that are critical factors affecting full-cell performance.

• Steel and Composite Structures
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• 제44권5호
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• pp.721-740
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• 2022

In this paper, an accurate kinematic model has been developed to study the mechanical response of functionally graded (FG) sandwich beams, mainly covering the bending, buckling and free vibration problems. The studied structure with homogeneous hardcore and softcore is considered to be simply supported in the edges. The present model uses a new refined shear deformation beam theory (RSDBT) in which the displacement field is improved over the other existing high-order shear deformation beam theories (HSDBTs). The present model provides good accuracy and considers a nonlinear transverse shear deformation shape function, since it is constructed with only two unknown variables as the Euler-Bernoulli beam theory but complies with the shear stress-free boundary conditions on the upper and lower surfaces of the beam without employing shear correction factors. The sandwich beams are composed of two FG skins and a homogeneous core wherein the material properties of the skins are assumed to vary gradually and continuously in the thickness direction according to the power-law distribution of volume fraction of the constituents. The governing equations are drawn by implementing Hamilton's principle and solved by means of the Navier's technique. Numerical computations in the non-dimensional terms of transverse displacement, stresses, critical buckling load and natural frequencies obtained by using the proposed model are compared with those predicted by other beam theories to confirm the performance of the proposed theory and to verify the accuracy of the kinematic model.

• Steel and Composite Structures
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• 제51권1호
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• pp.73-91
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• 2024

This paper has focused on presenting vibration analysis of trapezoidal sandwich plates with a damaged core and FG wavy CNT-reinforced face sheets. A damage model is introduced to provide an analytical description of an irreversible rheological process that causes the decay of the mechanical properties, in terms of engineering constants. An isotropic damage is considered for the core of the sandwich structure. The classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. The First-order shear deformation theory of plate is utilized to establish governing partial differential equations and boundary conditions for the trapezoidal plate. The governing equations together with related boundary conditions are discretized using a mapping-generalized differential quadrature (GDQ) method in spatial domain. Then natural frequencies of the trapezoidal sandwich plates are obtained using GDQ method. Validity of the current study is evaluated by comparing its numerical results with those available in the literature. After demonstrating the convergence and accuracy of the method, different parametric studies for laminated trapezoidal structure including carbon nanotubes waviness (0≤w≤1), CNT aspect ratio (0≤AR≤4000), face sheet to core thickness ratio (0.1 ≤ ${\frac{h_f}{h_c}}$ ≤ 0.5), trapezoidal side angles (30° ≤ α, β ≤ 90°) and damaged parameter (0 ≤ D < 1) are carried out. It is explicated that the damaged core and weight fraction, carbon nanotubes (CNTs) waviness and CNT aspect ratio can significantly affect the vibrational behavior of the sandwich structure. Results show that by increasing the values of waviness index (w), normalized natural frequency of the structure decreases, and the straight CNT (w=0) gives the highest frequency. For an overall comprehension on vibration of laminated trapezoidal plates, some selected vibration mode shapes were graphically represented in this study.

• Steel and Composite Structures
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• 제50권2호
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• pp.201-216
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• 2024

This paper is motivated by the lack of studies relating to vibration and nonlinear resonance of fluid-conveying cantilever porous GPLR pipes with fractional viscoelastic model resting on nonlinear foundations. A dynamical model of cantilever porous Graphene Platelet Reinforced (GPLR) pipes conveying fluid and resting on nonlinear foundation is proposed, and the vibration, natural frequencies and primary resonant of such system are explored. The pipe body is considered to be composed of GPLR viscoelastic polymeric pipe with porosity in which Halpin-Tsai scheme in conjunction with fractional viscoelastic model is used to govern the construction relation of the nanocomposite pipe. Three different porosity distributions through the pipe thickness are introduced. The harmonic concentrated force is also applied on pipe and excitation frequency is close to the first natural frequency. The governing equation for transverse motion of the pipe is derived by the Hamilton principle and then discretized by the Galerkin procedure. In order to obtain the frequency-response equation, the differential equation is solved with the assumption of small displacement, damping coefficient, and excitation amplitude by the multiple scale method. A parametric sensitivity analysis is carried out to reveal the influence of different parameters, such as nanocomposite pipe properties, fluid velocity and nonlinear viscoelastic foundation coefficients, on the primary resonance and linear natural frequency. Results indicate that the GPLs weight fraction porosity coefficient, fractional derivative order and the retardation time have substantial influences on the dynamic response of the system.

• Steel and Composite Structures
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• 제51권2호
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• pp.185-202
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• 2024

In this research paper, and for the first time, wave propagations in sigmoidal imperfect functionally graded material plates are investigated using a simplified quasi-three-dimensionally higher shear deformation theory (Quasi-3D HSDTs). By employing an indeterminate integral for the transverse displacement in the shear components, the number of unknowns and governing equations in the current theory is reduced, thereby simplifying its application. Consequently, the present theories exhibit five fewer unknown variables compared to other Quasi-3D theories documented in the literature, eliminating the need for any correction coefficients as seen in the first shear deformation theory. The material properties of the functionally graded plates smoothly vary across the cross-section according to a sigmoid power law. The plates are considered imperfect, indicating a pore distribution throughout their thickness. The distribution of porosities is categorized into two types: even or uneven, with linear (L)-Type, exponential (E)-Type, logarithmic (Log)-Type, and Sinus (S)-Type distributions. The current quasi-3D shear deformation theories are applied to formulate governing equations for determining wave frequencies, and phase velocities are derived using Hamilton's principle. Dispersion relations are assumed as an analytical solution, and they are applied to obtain wave frequencies and phase velocities. A comprehensive parametric study is conducted to elucidate the influences of wavenumber, volume fraction, thickness ratio, and types of porosity distributions on wave propagation and phase velocities of the S-FGM plate. The findings of this investigation hold potential utility for studying and designing techniques for ultrasonic inspection and structural health monitoring.

• 한국식품영양과학회지
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• 제15권1호
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• pp.27-38
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• 1986

도마도 과실의 추숙 및 저장 과정에 있어서 품질(品質) 유지 및 저장(貯藏) 효과를 높이고자, 우리나라에서 많이 생산되고 있는 도마도 품종(品種) "강력미수"를 녹열기(緣熱期)에 수확하여 각각 추숙최적온도를 $25^{\circ}C$와 저장적온도 $15^{\circ}C$, 그 중간(中間) 온도(溫度)인 $20^{\circ}C$에서 저장(貯藏)하면서 저장중의 생리화학적(生理化學的) 변화(變化)에 따른 과실체내(果實體內)의 호흡량(呼吸量)의 변화(變化)와 경도(硬度)의 변화(變化) 그리고 지질성분(脂質成分)의 변화(變化)를 조사한 결과(結果)는 다음과 같다. 도마도 과실의 저장중(貯藏中) 호흡량(呼吸量)의 변화(變化)는 $25^{\circ}C$구(區)에 있어서 climacteric rise현상이 가장 빨리 나타났으며, climacteric maximum에 있어서의 호흡량(呼吸量)도 다른 저장구(貯藏區)보다 많았으며, $20^{\circ}C$구(區)와 $15^{\circ}C$구(區)의 순(順)으로 나타났다. 도마도 과실의 저장중 경도(硬度)의 변화(變化)는 $25^{\circ}C$區에 있어서, 저장 기간 전반(全般)에 걸쳐, 가장 빨리 감소(減少)하는 것으로 나타났고, $20^{\circ}C$구(區)와 $15^{\circ}C$구(區)의 순(順)으로 나타났다. 도마도 과실의 저장중 총(總) 지질(脂質) 함량(含量)의 변화(變化)는 $25^{\circ}C$구(區)에 있어서 저장중(貯藏中) 전반적(全般的)으로 큰 변화(變化)가 없었는데 비하여 $20^{\circ}C$구(區)와 $15^{\circ}C$구(區)는 저장(貯藏) 중기(中期) 및 후기(後期)에 감소(減少)하는 경향(傾向)을 나타냈으며, 증가(增加)하는 경향을 나타냈고, 그중에서도 특히 $15^{\circ}C$구(區)에서는 저장 후기인 저장(貯藏) 30일경 부터 저장 말기(末期)인 저장 40일경 까지 급격히 증가하는 경향(傾向)을 나타내었다. 도마도 과실의 저장중(貯藏中) 중성지질(中性脂質)의 변화(變化)는 저장기간(貯藏期間)을 통털어 전반적(全般的)으로 큰 변화(變化)가 없었다고 볼 수 있으며, 그에 비해 당지질의 변화(變化)는 일정치 않게 증가(增加)하는 경향(傾向)을 나타내었고, 인지질(燐脂質)의 변화(變化)도 비교적 안정되게 증가(增加)하는 경향을 나타내었다. 도마도 과실의 각각의 지질 성분(成分)의 구성 지방산의 조성을 저장(貯藏) 기간중(期間中) 조사한 결과(結果)는, 중성지질(中性脂質) 당지질(糖脂質), 인지질(燐脂質)에 있어서 포화지방산으로는 palmitic acid의 함량(含量)이 많았고, 불포화지방산으로는 linoleic acid, linolenic acid 그리고 oleic acid의 함량(含量)이 많았다. 도마도 과실(果實)의 저장중(貯藏中) 포화지방산(飽和脂肪酸)에 대한 불포화지방산(不飽和脂肪酸)에 있어서는, 전반적(全般的)으로 증가(增加)하는 경향이었으며 인지질(燐脂質)에 있어서는, 거의 변화(變化)가 없는 경향을 나타내었다. $C_{16}$지방산(脂肪酸)에 대한 $C_{18}$지방산(脂肪酸)의 함량비(含量比)는 중성지질(中性脂質)에 있어서는 저장 기간 전반(全般)에 걸쳐 대체적(大體的)으로 증가(增加)하였으며, 당지질(糖脂質)에 있어서는 약간(若干) 감소(減少)하였고, 인지질(燐脂質)에 있어서는 약간(若干) 증가(增加)하는 경향을 나타내었다.