분자동역학 시뮬레이션을 이용한 Al₂O₃/epoxy 나노복합재의 물성해석

유수영(Suyoung Yu),양승화(Seunghwa Yang),조맹효(Maenghyo Cho) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

Alumina(Al₂O₃) particles reinforcing effects of cross-linked epoxy resin composites was investigated using molecular dynamics simulation. For considering cross-linked effects in the simulations the epoxy monomer unit of the matrix was made of Diglycidyl Ether of Bisphenol F(EPON862<SUP>®</SUP>) cured by Triethylenetetramine(TETA<SUP>®</SUP>). To investigate the size effects of particles in composites, the unite cells with various sizes(l~20㎚ diameter) alumina particles were considered. For particle size larger than 20nm micromechanical method using the effective interface model was applied. When the size of alumina particle decreased, the reinforce effects was more significant.

비평형 분자동역학을 이용한 기계적 하중이 부여된 고분자재료의 열전도율 변화 해석

유수영(Suyoung Yu),양승화(Seunghwa Yang),조맹효(Maenghyo Cho) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11

The design of the polymetric composites which have a desirable thermal property is one of important issues in composites materials. To verify the mechanism of thermal conduction, the non-equilibrium molecular dynamics simulation is applied to nylon6 polymer under the mechanical loading conditions such as extension, unloading and compression. During the mechanical loading process, structural ordering and disordering of polymer molecules are observed. When the nylon6 chain is aligned and have lager orientation order due to the mechanical loading, nylon6 polymer shows enhanced thermal conductivity on the deformed direction. The structure-property relationship obtained from this study can be a useful reference for the design of polymer-based nanomaterials and nanocomposites

수분 흡수율에 따른 에폭시 나노복합재의 물성 변화 해석

유수영(Suyoung Yu),양승화(Seunghwa Yang),최준명(Joonmyung Choi),조맹효(Maenghyo Cho) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11

In this study, by analyzing structural change and degradation of material properties which are induced by the cross-linking and moisture absorption, hygrothermal effects on epoxy materials are investigated through molecular dynamics simulation. To verify the effect of cross-linking ratio and particle size on hygrothermal degradation, three different cross-linked states are considered in epoxy matrix and silica nanoparticles of various sizes are contained in nanocomposites. To verify the mechanism of hygrothermal degradation, structural changes such as change of volume, density, and free volume, and diffusion of water molecules are analyzed.

계면 결합력과 나노튜브의 응집에 따른 나노튜브/고분자 복합재의 탄소성 거동 예측에 대한 연구

양승화,유수영,류정현,조맹효,Yang, Seunghwa,Yu, Suyoung,Ryu, Junghyun,Cho, Maenghyo 한국전산구조공학회 2013 한국전산구조공학회논문집 Vol.26 No.6

본 연구에서는 탄소나노튜브와 폴리프로필렌 기지 간 계면결합력과 나노튜브의 국부적 응집에 따른 나노복합재의 탄소성 거동 변화에 대한 파라메트릭 연구를 수행한다. 나노복합재의 탄소성 거동 예측을 위해 분자동역학 전산모사를 수행하고, 분자동역학 결과와 Mori-Tanaka 모델을 적용한 비선형 미시역학 모델을 연계하여 나노복합재 내 흡착계면의 탄소성 거동을 역으로 도출하는 2단계 영역분할 기법을 적용하였다. 미시역학 모델에서는 시컨트 계수방법을 Mori-Tanaka 모델에 적용하여 나노복합재의 비선형 거동을 예측하는 방법을 적용하였으며, 나노튜브와 기지 간 재료계면의 불완전 결합을 고려하기 위해 변위 불연속 조건을 적용하였다. 흡착영역을 고려한 미시역학 모델을 통해 흡착계면의 유무 및 재료계면 결합력 변화 그리고 나노튜브의 국부적 응집현상에 따른 나노복합재의 응력-변형률 관계를 예측하였다. 그 결과 나노튜브의 국부적 응집이 나노복합재의 강화효과를 저하시키는 가장 중요한 변수임을 확인하였다. In this research, a paramteric study to account for the effect of interfacial strength and nanotube agglomeration on the elastoplastic behavior of carbon nanotube reinforced polypropylene composites is performed. At first, the elastoplastic behavior of nanocomposites is predicted from molecular dynamics(MD) simulations. By combining the MD simulation results with the nonlinear micromechanics model based on the Mori-Tanaka model, a two-step domain decomposition method is applied to inversely identify the elastoplastic behavior of adsorption interphase zone inside nanocomposites. In nonlinear micromechanics model, the secant moduli method combined with field fluctuation method is used to predict the elastoplastic behavior of nanocomposites. To account for the imperfect material interface between nanotube and matrix polymer, displacement discontinuity condition is applied to the micromechanics model. Using the elastoplastic behavior of the adsorption interphase zone obtained from the present study, stress-strain relation of nanocomposites at various interfacial bonding condition and local nanotube agglomeration is predicted from nonlinear micromechanics model with and without the adsorption interphase zone. As a result, it has been found that local nanotube agglomeration is the most important design factor to maximize reinforcing effect of nanotube in elastic and plastic behavior.

Kapitza 열저항이 존재하는 나노복합재의 열전도 특성 예측을 위한 순차적 멀티스케일 균질화 해석기법에 관한 연구

신현성,양승화,유수영,장성민,조맹효,Shin, Hyunseong,Yang, Seunghwa,Yu, Suyoung,Chang, Seongmin,Cho, Maenghyo 한국전산구조공학회 2012 한국전산구조공학회논문집 Vol.25 No.4

본 연구에서는 분자동역학 전산모사와 유한요소해석 기반의 균질화 기법을 통해 나노복합재의 열전도 특성을 정확하고 효율적으로 예측할 수 있는 순차적 멀티스케일 균질화 해석기법을 제안하였다. 나노입자의 크기효과가 나노복합재의 유효 열전도 특성에 미치는 영향을 조사하기 위해 크기가 다른 구형 나노입자가 첨가된 나노복합재의 열전도 계수를 분자동역학 전산모사를 통해 예측했고, 그 결과 나노입자의 크기가 작아질수록 계면에서의 Kapitza열저항에 의해 나노복합재의 열전도 계수가 점차 감소하는 것으로 나타났다. 이러한 나노입자의 크기효과를 균질화 해석모델을 통해 정확하게 묘사하기 위해 Kapitza 열저항에 의한 계면에서의 온도 불연속 구간과 고분자 기지가 높은 밀도를 가지며 흡착되는 유효계면을 추가적인 상으로 도입하여 나노복합재를 입자, Kapitza 계면, 유효계면, 기지로 구성된 4상의 연속체 구조로 모델링하였다. 이후 순차적 멀티스케일 균질화 해석기법을 통해 유효계면의 열전도 계수를 나노복합재의 열전도 계수로부터 역으로 예측했으며, 이를 입자의 반경에 대한 함수로 근사하였다. 근사 함수를 토대로 다양한 입자 체적분율과 반경에 대한 나노복합재의 유효 열전도 특성을 예측하였으며, 유효계면에 대한 매개변수 연구를 수행하였다. In this study, a sequential multiscale homogenization method to characterize the effective thermal conductivity of nano particulate polymer nanocomposites is proposed through a molecular dynamics(MD) simulations and a finite element-based homogenization method. The thermal conductivity of the nanocomposites embedding different-sized nanoparticles at a fixed volume fraction of 5.8% are obtained from MD simulations. Due to the Kapitza thermal resistance, the thermal conductivity of the nanocomposites decreases as the size of the embedded nanoparticle decreases. In order to describe the nanoparticle size effect using the homogenization method with accuracy, the Kapitza interface in which the temperature discontinuity condition appears and the effective interphase zone formed by highly densified matrix polymer are modeled as independent phases that constitutes the nanocomposites microstructure, thus, the overall nanocomposites domain is modeled as a four-phase structure consists of the nanoparticle, Kapitza interface, effective interphase, and polymer matrix. The thermal conductivity of the effective interphase is inversely predicted from the thermal conductivity of the nanocomposites through the multiscale homogenization method, then, exponentially fitted to a function of the particle radius. Using the multiscale homogenization method, the thermal conductivities of the nanocomposites at various particle radii and volume fractions are obtained, and parametric studies are conducted to examine the effect of the effective interphase on the overall thermal conductivity of the nanocomposites.

나노입자의 크기 효과를 고려한 나노복합재의 순차적 다중스케일 해석

양승화(Seunghwa Yang),유수영(Suyoung Yu),조맹효(Maenghyo Cho) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

Multi-scale analysis to characterize the size effect of nanoparticle on the mechanical properties of nanoparticle/polymer composites is developed and verified through molecular dynamics simulation and continuum micro mechanics model. This study focuses on the construction of the nanoscale information transfering scheme to validate continuum micro scale model for the analysis and design of nano-structured composites with efficiency and accuracy. In order to obtain the nano-scale effect of nanoparticle in detail, totally five different unit cells with different particle size and same volume fractions were prepared and simulated using molecular dynamics approach. The atomistic structures of nanocomposites were prepared with spherical silica nanoparticle and amorphous polyimide chains as periodic unit-cell and Parrinello-Rahman fluctuation method was used to calculate mechanical properties of each unit-cells. In micro mechanics model, particle-matrix interface was incorporated as the resultant phase of particle size effects and the size and elastic properties of interface were decided from radial distributions of matrix polymer and molecular dynamics results respectively. Postulating that the Young's modulus and shear modulus of the interface as functions of particle radius, monotonous decaying functions to represent Young's modulus and shear modulus were obtained from least square approximation. As a result, enhanced reinforcing effect was observed in smallier-sized nanoparticle cases and our developed micro mechanics solutions exactly reflect the size effect of nanoparticle.

나노튜브의 크기효과와 계면의 불완전 결합을 고려한 나노튜브-고분자 나노복합재의 멀티스케일 해석

양승화(Seunghwa Yang),유수영(Suyoung Yu),조맹효(Maenghyo Cho) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11

In this study, an efficient micromechanics-based multiscale bridging model is developed to account for the size effect of carbon nanotube(CNT) and the weakened bonding effect at the interface on the elastic modulus of CNT/Polypropylene nanocomposites. Under the fixed volume fraction conditions, different zigzag CNTs are embedded into a polymer matrix and elastic stiffness is calculated from the uniaxial and shear tests via molecular dynamics simulations. In order to describe the slippage and separation of CNT at the interface, a modified multi-inclusion model with effective particle and effective matrix concept is suggested. Due to the weak bonding at the interface, neat CNT reinforced nanocomposites showed insufficient reinforcing effect with CNT-size dependency and present modified bridging model accurately estimated the size and weakened interface effect in continuum regime.

다중입자 모델과 균질화 해석기법을 이용한 나노입자 복합재의 다중스케일 해석

양승화(Seunghwa Yang),유수영(Suyoung Yu),장성민(Seongmin Jang),조맹효(Maenghyo Cho) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

In this study, multi-scale analysis to characterize mechanical properties of nanoparticle/polymer nanaocomposites is implemented through a molecular dynamics simulation, multi-inclusion model, and homogenization method. In order to describe the particle size effect, effective interface is adopted as an extra phase to describe the particle size-dependent elastic modulus of the nanocomposites. The interaction between each constituent was described from the variation of the infinite medium. The elastic modulus of the effective interface was implicitly obtained from the multi-inclusion model. In homogenization method, the base-cell of the nanocomposites domain was modeled as three-phase structure and the elastic modulus of the effective interface was numerically obtained. As a result, elastic modulus of the effective interface obtained from multi-inclusion model and homogenization method successfully reproduced MD simulation results from continuum-based analysis.

높은 체적분율을 가진 나노복합재의 기계적 물성 예측을 위한 순차적 브리징 해석기법에 관한 연구

양승화(Seunghwa Yang),유수영(Suyoung Yu),장성민(Seongmin Jang),조맹효(Maenghyo Cho) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

An efficient scale bridging method to describe the particle size effect of the nano particle on the elastic modulus of the nanocomposites at high volume traction condition is developed. In order to obtain the physical information of the size effect, molecular dynamics simulation is performedand elastic modulus of the 12% nanocomposites at various particle sizes are obtained. In continuum modeling of the nanocomposites, an effective interface is considered as a characteristic phase and an additional phase is adopted to describe the non-dilute concentration effect. As a result, present bridging model efficiently estimated the interface elastic properties with accuracy and the elastic modulus of the nanocomposites at high volume fraction are exactly reproduced from current bridging approach.

가교율에 따른 에폭시의 비선형 탄성 거동 연구

김원배(Wonbae Kim),유수영(Suyoung Yu),신현성(Hyunseong Shin),조맹효(Maenghyo Cho) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

In this work, a study on hyperelastic characteristics of epoxy resin according to cross-link ratio is presented. The epoxy resin is widely used as matrix material of composite laminate or nano composite, so its elastic properties are very important in structural analysis of composite materials. The cross-link ratio of epoxy resin could change elastic properties such as elastic modulus, elastic range, and yield stress. To investigate hyperelastic behavior of epoxy resin according to cross-link ratio, molecular dynamics simulations are performed, and some discussions about hyperelastic modeling using the simulation results are presented.