• 한국산림과학회지
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• 제99권1호
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• pp.102-110
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• 2010

옻나무 추출액을 섭취하며 운동훈련을 부하하였을 때 항산화기능 및 염증성사이토카인의 차이에 대하여 연구하고자 하였다. 이를 위하여 Sprague-Dawley(SD)계 수컷 쥐를 대상으로 SED(안정군), TRA(운동훈련군), RVE(옻나무 추출액 섭취군), 그리고 RVE-TRA(옻나무 추출액 섭취와 운동 병행군)으로 구분하였다. TRA와 RVE-TRA는 점증적부하법을 이용한 트레드밀 훈련을 실시하였으며, RVE와 RVE-TRA에게는 10 mL/kg의 옻나무 추출액을 경구투여 하였다. 항산화기능을 분석하기 위하여 혈중 superoxide dismutase(SOD), glutathione peroxidase(GSH-Px), malondialdehyde(MDA)를 분석하였으며, 염증성사이토카인의 변화분석을 위하여 interleukin-6(IL-6), tumor necrosis factor-alpha(TNF-${\alpha}$), C-reactive protein(CRP), nitric oxide(NO)를 분석하였다. SOD는 RVE-TRA가 다른 집단에 비하여 가장 높았으며, TRA가 SED와 RVE에 비하여 유의하게 높았다. GSH-Px는 SED가 다른 집단에 비하여 유의하게 낮았다. MDA는 SED에 비하여 다른 집단에서 모두 유의하게 낮았다. IL-6와 TNF-${\alpha}$는 RVE와 RVE-TRA가 다른 두 집단에 비하여 낮았다. 또한 CRP는 SED가 다른 집단에 비하여 가장 낮았다. NO는 SED와 TRA가 다른 두 집단에 비하여 높았다. 이러한 결과를 볼 때, 운동시옻나무 추출액의 섭취는 지질과산화를 억제시키고 항염증성 반응을 유발하여 운동시 발생가능한 부작용을 억제할 수 있는 결과를 보였다. 이점을 고려하여 옻추출물이 가지고 있는 특성을 최대한 활용하여 다양한 방법으로 접근한다면 우리나라 전역에 걸쳐 자생하고 있는 옻나무의 활용도를 증대시킬 수 있으리라 생각된다.

• Journal of Mechanical Science and Technology
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• 제20권10호
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• pp.1722-1729
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• 2006

Predicting the mechanical properties of the 3-D scaffold using finite element method (FEM) simulation is important to the practical application of tissue engineering. However, the porous structure of the scaffold complicates computer simulations, and calculating scaffold models at the pore level is time-consuming. In some cases, the demands of the procedure are too high for a computer to run the standard code. To address this problem, the representative volume element (RVE) theory was introduced, but studies on RVE modeling applied to the 3-D scaffold model have not been focused. In this paper, we propose an improved FEM-based RVE modeling strategy to better predict the mechanical properties of the scaffold prior to fabrication. To improve the precision of RVE modeling, we evaluated various RVE models of newly designed 3-D scaffolds using FEM simulation. The scaffolds were then constructed using microstereolithography technology, and their mechanical properties were measured for comparison.

• 대한한방내과학회지
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• 제36권1호
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• pp.13-21
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• 2015

Objectives : In Korea, Rhus verniciflua Stokes (RVS) has been used in traditional medicine for various diseases such as back pain, syndromes of the blood system in women, gastrointestinal disease, and cancer. However, the molecular mechanisms of its anti-cancer activity have not been clearly elucidated yet. Methods : This study investigated the possible mechanisms by which RVS extract (RVE) exerts its anti-proliferative action in cultured human breast carcinoma MCF-7 cells. Results : Treatment with RVE in MCF-7 cells resulted in inhibition of cell viability through G1 arrest of the cell cycle and induction of apoptosis in a time- and concentration-dependent manner, as determined by MTT assay and flow cytometry analysis. The induction of G1 arrest by RVE treatment was associated with the inhibition of cyclin D1, cyclin-dependent kinase (Cdk) 2, retinoblastoma protein (pRB), and mouse double minute 2 (MDM2) expression. Moreover, RVE treatment concentration dependently increased the levels of tumor suppressor p53, which was associated with the marked induction of Cdk inhibitors such as p21 (Waf1/Cip1) and p27 (Kip1). However, the inhibition of p53 function by the wild-type p53-specific inhibitor, pifithrin-α, abolished the above-mentioned effects of RVE, showing that p53 was responsible for the cytotoxicity of RVE Conclusions : These data indicate that a molecular pathway involving p53-dependent G1 cell cycle arrest plays a pivotal role in the cellular response to RVE, and demonstrate the potential applications of RVE as an anti-cancer drug for breast cancer treatment.

• Computers and Concrete
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• 제9권1호
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• pp.35-50
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• 2012

The 2D representative volume element (RVE) for softening quasi-brittle materials like concrete is determined. Two alternative methods are presented to determine a size of RVE in concrete subjected to uniaxial tension by taking into account strain localization. Concrete is described as a heterogeneous three-phase material composed of aggregate, cement matrix and bond. The plane strain FE calculations of strain localization at meso-scale are carried out with an isotropic damage model with non-local softening.

• Steel and Composite Structures
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• 제44권5호
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• pp.685-690
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• 2022

In this paper, the equivalent material properties of cellular metamaterials with different types of perforations have been presented using finite element (FE) simulation of tensile test in Abaqus commercial software. To this end, a Representative Volume Element (RVE) has been considered for each type of cellular metamaterial with regular array of circular, square, oval and rectangular perforations. Furthermore, both straight and perpendicular patterns of oval and rectangular perforations have been studied. By applying Periodic Boundary conditions (PBC) on the RVE, the actual behavior of cellular material under uniaxial tension has been simulated. Finally, the effective Young's modulus, Poisson's ratio and mass density of various metamaterials have been presented as functions of relative density of the RVE

• Composites Research
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• 제34권1호
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• pp.70-75
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• 2021

본 논문은 단섬유 칩으로 구성된 Sheet Molding Compound(SMC) 복합재료를 실험적으로 관찰된 특징들을 바탕으로 메소스케일(meso-scale) 대표체적요소(RVE: Representative Volume Element)를 재구성하는 새로운 알고리즘을 제시한다. 전산해석을 이용하여 SMC 복합재료의 비등방성 거동의 정확한 예측은 어려운 문제이다. 이를 극복하기 위해, SMC 복합재료를 위한 일련의 이미지 프로세싱 기술과 재구성 알고리즘 및 유한요소(FE: Finite Element) 생성기로 구성된 SMC RVE 모델을 개발하였다. 첫째, micro-CT 이미지 프로세싱은 SMC 물성에 직접적인 상관관계를 가지는 섬유칩의 배향 및 분산의 확률적 분포를 평가한다. 둘째, 해당 통계적 분포를 바탕으로 섬유칩 간의 겹침효과를 고려한 섬유칩 팩킹 재구성 알고리즘을 개발한다. 마지막으로, SMC 복합재료 멀티스케일 해석을 이용하여 매크로스케일(macro-scale)에서의 거동을 파악하고 실험데이터를 통해 검증을 수행한다.

• Composites Research
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• 제35권3호
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• pp.188-195
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• 2022

본 논문은 멀티스케일 공정-구조 해석의 방법론을 제안하고 단섬유층과 직물층으로 이루어진 배터리 하우징 파트에 적용한다. 특별히 마이크로스케일 대표체적요소(RVE: Representative Volume Element)안 기지의 불확정성을 고려하였다. 마이크로스케일의 RVE내 기지 물성의 랜덤한 공간내 분포는 KLE(Karhunen-Loeve Expansion)을 통해 구현하였다. 공간상 랜덤분포된 기지 물성을 갖는 RVE의 유효 물성을 전산균질화를 통해 얻어 매크로스케일 유한요소 모델에 매핑하였다. 또한 하이브리드 공정해석을 통해 압축 성형 해석으로부터 얻은 잔류응력과 섬유배향을 매핑한 유한요소 모델과 드레이핑 공정 해석결과로부터 얻어진 섬유배향을 매핑한 모델을 결합하였다. 본 연구에 제안된 방법은 배터리 하우징 뿐만 아니라 다양한 재료 구성을 갖는 복합재료의 공정-구조해석을 통해 설계요구도를 엄밀하게 평가할 수 있을 것이라 기대된다.

• Steel and Composite Structures
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• 제21권5호
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• pp.1085-1103
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• 2016

The present paper is aimed to evaluate and compare the effective elastic properties of CNT- and graphene-based nanocomposites using 3-D nanoscale representative volume element (RVE) based on continuum mechanics using finite element method (FEM). Different periodic displacement boundary conditions are applied to the FEM model of the RVE to evaluate various elastic constants. The effects of the matrix material, the volume fraction and the length of reinforcements on the elastic properties are also studied. Results predicted are validated with the analytical and/or semiempirical results and the available results in the literature. Although all elastic stiffness properties of CNT- and graphene-based nanocomposites are found to be improved compared to the matrix material, but out-of-plane and in-plane stiffness properties are better improved in CNT- and graphene-based nanocomposites, respectively. It is also concluded that long nanofillers (graphene as well as CNT) are more effective in increasing the normal elastic moduli of the resulting nanocomposites as compared to the short length, but the values of shear moduli, except $G_{23}$ of CNT nanocomposite, of nanocomposites are slightly improved in the case of short length nanofillers (i.e., CNT and graphene).

• 소성∙가공
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• 제32권1호
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• pp.28-34
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• 2023

In this research, a representative volume element (RVE)-based FE Model is presented to estimate the mechanical properties of additively manufactured continuous fiber-reinforced composites with different fiber orientations. To construct the model, an ABAQUS Python script has been implemented to produce matrix and fiber in the desired orientations at the RVE. A script has also been developed to apply the periodic boundary conditions to the RVE. Experimental tests were conducted to validate the numerical models. Tensile specimens with the fiber directions aligned in the 0, 45, and 90 degrees to the loading direction were manufactured using a continuous fiber 3D printer and tensile tests were performed in the three directions. Tensile tests were also simulated using the RVE models. The predicted Young's moduli compared well with the measurements: the Young's modulus prediction accuracy values were 83.73, 97.70, and 92.92 percent for the specimens in the 0, 45, and 90 degrees, respectively. The proposed method with periodic boundary conditions precisely evaluated the elastic properties of additively manufactured continuous fiber-reinforced composites with complex microstructures.

• Structural Engineering and Mechanics
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• 제38권4호
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• pp.503-516
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• 2011

Uncertainty in concrete properties, including concrete modulus of elasticity and modulus of rupture, are predicted by developing a microstructural homogenization model. The homogenization model is developed by analyzing a concrete representative volume element (RVE) using the finite element (FE) method. The concrete RVE considers concrete as a three phase composite material including: cement paste, aggregate and interfacial transition zone (ITZ). The homogenization model allows for considering two sources of variability in concrete, randomly dispersed aggregates in the concrete matrix and uncertain mechanical properties of composite phases of concrete. Using the proposed homogenization technique, the uncertainty in concrete modulus of elasticity and modulus of rupture (described by numerical cumulative probability density function) are determined. Deflection uncertainty of reinforced concrete (RC) beams, propagated from uncertainties in concrete properties, is quantified using Monte Carlo (MC) simulation. Cracked plane frame analysis is used to account for tension stiffening in concrete. Concrete homogenization enables a unique opportunity to bridge the gap between concrete materials and structural modeling, which is necessary for realistic serviceability prediction.