• 한국소음진동공학회논문집
• /
• 제20권9호
• /
• pp.805-815
• /
• 2010

This paper studies the influence of internal moving fluid and flow-induced structural instability of multi-wall carbon nanotubes conveying fluid. Detailed results are demonstrated for the variation of natural frequencies with flow velocity, and the flow-induced divergence and flutter instability characteristics of multi-wall carbon nanotubes conveying fluid and modelled as a thin-walled beam are investigated. Effects of various boundary conditions, Van der Waals forces, and non-classical transverse shear and rotary inertia are incorporated in this study. The governing equations and three different boundary conditions are derived through Hamilton's principle. Numerical analysis is performed by using extended Galerkin's method which enables us to obtain more exact solutions compared with conventional Galerkin's method. This paper also presents the comparison between the characteristics of single-wall and multi-wall carbon nanotubes considering the effect of van der Waals forces. Variations of critical flow velocity for different boundary conditions of two-wall carbon nanotubes are investigated and pertinent conclusion is outlined.

• 한국생산제조학회지
• /
• 제18권4호
• /
• pp.369-374
• /
• 2009

In micro/nano-scale contacts in MEMS and NEMS, capillary and van der Waals forces generated around contacting micro-asperities significantly influence the performance of concerning device as they are closely related to adhesion and stiction of interacting surfaces. In this regard, it is of prime importance to accurately estimate the magnitude of surface forces so that an optimal solution for reducing friction and adhesion of micro/nano-surfaces may be obtained We introduced an effective method to calculate these surface forces based on topography information obtained from an atomic force microscope. This method was used to calculate surface forces generated in the contact interface formed between diamond-like carbon coating and $Si_3N_4$ ball. This method is shown to effectively demonstrate the influence of capillary force in the contact area, especially in humid atmosphere.

• Composites Research
• /
• 제33권1호
• /
• pp.19-24
• /
• 2020

본 연구에서는 Poly(vinylidene fluoride) (PVDF) 필름 제작 과정 중 마이크로웨이브 처리 과정을 도입하여 β 결정성 향상에 어떠한 영향을 미치는지 분석하였다. 또한, 나노 입자 보강제로써 금속산화물인 TiO₂를 혼합하여 PVDF 복합재료 필름을 만들어, 전기적 음성도 차이로 인한 반데르발스 힘을 통해 β 결정 형성을 추가적으로 향상시키려고하였다. FTIR과 XRD 분석을통하여해당필름시편들에대해결정화도(Crystallinity) 및결정성(Crystalline)을 분석하였다. 이러한 분석 결과를 바탕으로, 용매 증발 과정 중 마이크로웨이브 처리 과정이 PVDF 필름의 결정화도를 높여주는 것을 확인하였고, 추가적인 연신(Stretching) 공정을 통해 α 결정에서 β 결정 변화(Crystalline phase change)가 발생함으로써 결과적으로 더 많은 β 결정성을 나타내었다. 그리고 금속산화물을 넣은 PVDF 복합재료 필름이 Neat PVDF 필름보다 상대적으로 더 높은 β 결정성을 나타내는 것을 확인하였다.

• 대한기계학회논문집A
• /
• 제26권10호
• /
• pp.2180-2186
• /
• 2002

In a micro-scale contact, capillary force and van der Waals interaction significantly influence the contact between asperities of rough surfaces. Little is, however, known about the variation of these surface forces as a function of chemical property of the surface (wet angle), relative humidity and deformation of asperities in the real area of contact. A better understanding of these surface forces is of great necessity in order to find a solution for reducing friction and adhesion of micro surfaces. The objective of this study is to investigate the surface forces in micro-scale rough surface contact. We proposed an effective method to analyze capillary and van der Waals forces in micro-scale contact. In this method, Winkler spring model was employed to analyze the contact of rough surfaces that were obtained from atomic force microscopy (AFM) height images. Self-mated contact of DLC(diamond like carbon) coatings was analyzed, as an example, by the proposed model. It was shown that the capillary force was significantly influenced by relative humidity and wet angle of the DLC surface. The deformation of asperities to a critical magnitude by external loading led to a considerable increase of both capillary and van der Waals forces.

• 한국건축시공학회지
• /
• 제20권1호
• /
• pp.11-18
• /
• 2020

탄소나노튜브는 우수한 역학성, 전기전도성 등으로 다양한 산업에 이용되고 있다. 건설산업에서는 구조체에 자기센싱 기능을 부여하는 연구가 진행되고 있지만, 연구자들마다 실험결과가 상이하게 나타나고 이에 대한 분석은 미비한 실정이다. 따라서 본 연구에서는 MWCNT가 첨가된 시멘트페이스트의 수화열, 공극률, 리트벨트 정량분석법, 압축강도, 거리에 따른 전기저항값을 측정하여 수화와 강도특성 및 전기특성을 분석하였다. 실험결과 수화열은 MWCNT가 증가할수록 감소되는 것으로 나타났다. 또한 XRD 리트벨트 정량분석법 결과 MWCNT 첨가율 증가에 따른 수화생성물의 양은 큰 차이가 없는 것으로 나타났고, 압축강도 저하의 원은은 공극률 분석결과 MWCNT가 시멘트페이스트내에서 공극의 양을 증가시겼기 때문으로 판단되며 SEM분석결과 MWCNT가 반데르발스힘에 의해 뭉쳐져 있어서 이 부위가 공극 및 취약부로 발생것으로 판단된다. 전기저항값은 첨가율이 증가될수록 감소하여 추후 자기센싱에 대한 역할을 할 수 있을 것으로 판단된다.