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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.
에폭시/PES 복합소재의 인성 향상을 위한 멀티스케일 해석
신현성(Hyunseong Shin),한진규(Jin-Gyu Han),김병조(Byungjo Kim),이만영(Man Young Lee),박종규(Jong Kyoo Park),조맹효(Maenghyo Cho) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Epoxy resins are widely used as phase materials of matrix in fiber-reinforced composites. To overcome brittleness of cross-linked epoxy, thermoplastic modified epoxy has been extensively studied. However, specific toughening mechanism of thermoplastic modified epoxy has not been established in molecular viewpoint. Allegedly, toughening mechanisms of particle debonding, plastic yielding of nanovoids, and localized shear banding are primary origin of fracture toughness enhancement. The purpose of this study is to investigate the contribution of each toughening mechanism. In this study, PES is used as a toughening agent for the cross-linked epoxy composed of TGAP and DDS. Cohesive interface is also considered as it can affect toughening mechanisms. As a result, methodology of construction of finite element PES/epoxy model with cohesive interface is proposed.
유효 계면 상의 침투 현상을 반영한 고분자 나노복합재료의 멀티스케일 균질화 모델
신현성(Hyunseong Shin),최준명(Joonmyung Choi),장성민(Seongmin Chang),유수영(Suyoung Yu),조맹효(Maenghyo Cho) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
In this study, a multiscale homogenization modeling of polymer nanocomposites is conducted. The fundamental physics about mechanical behavior has not been established in view of nanoparticle/nanoparticle interaction and nanoparticle/polymer interaction when the fillers are agglomerated. In this study, molecular statics/dynamics approach is employed in order to characterize these kinds of fundamental physics. The interphase characteristics are investigated in continuum-based homogenization modeling. The elastic constants of polymer nanocomposites are decreased when the distance of nanoparticles are less than 1 nm. This is because the characteristics of interaction between polymer and nanoparticles are reduced as the polymer chains are difficult to be entangled in the vicinity of nanoparticles due to repulsive potential energy of nanoparticles. The degree of nanoparticle/polymer interaction is reflected in the elastic constants of effective interphase.
이동격자와 몬테카를로 전산모사를 통해 미시적 불확실성을 고려한 균질화 기법에 관한 연구
신현성(Hyunseong Shin),장성민(Seongmin Chang),정준호(Joonho Jeong),조맹효(Maenghyo Cho) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
Nano-structures have been widely used due to their high-performances and multi-functionality which comes from size-effect. Surface effect from nano-thickness film, is considered in size-dependent continuum elasticity model. In the real nano-scale structures, however, randomness exists in the size and position of pores or particles because of their tendency to agglomeration and the limits of manufacturing process. Owing to these uncertainties, dispersion of the homogenized material properties occurs. Moreover, the size effect such as surface effect and interphase effect aggravates this dispersion. Therefore, stochastic approach on the nano-structures is necessary to consider the size effect and uncertainties in real nano-structures. In this study, the influence of nano-scale uncertainties on homogenized material properties is considered. Porous materials model including geometric uncertainties are considered in this study. Monte-Carlo simulation is performed to show the distribution of homogenized modulus against uncertainties.
다이 부착용 솔더 재료 내의 미시결함들을 고려한 다중 스케일 열-기계적 해석
신현성(Hyunseong Shin),오철민(Chulmin Oh) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
In this study, a multiscale thermo-mechanical analysis framework of die-attach solder material considering microscopic voids is proposed. Microscopic voids cause the degradation of solderability, thermal conductivity, electrical conductivity, and fatigue life. In spite of the significance of the issue, there has been no study on the efficient numerical analysis framework of thermo-mechanical behaviors of die-attach solder material including the small-sized microscopic void (< thickness of solder) as well as relatively large-sized microscopic void. Here, we focus on the effective thermal conductivity and thermal expansion efficient of the solder materials. Micromechanical approach is employed to develop the multiscale framework. In the presentation, the homogenized Anand viscoplastic model, which is widely employed in the thermal fatigue analysis, will be provided. It is expected that this work will be the foundation of the thermo-mechanical design of die-attach solder material.