• Composites Research
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• 제28권5호
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• pp.260-264
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• 2015

본 논문에서는 CNT강화 에폭시 복합재의 열기계적 거동을 예측하고 그 경향을 분석하기 위해 분자동역학 시뮬레이션을 이용하여 해석을 수행하였다. 에폭시 내부 CNT의 체적비율을 0~25%까지 총 6개의 모형을 구성하였다. 열적 거동을 보기 위해 300~600 K까지 일정하게 온도를 상승시켰으며, 온도와 비체적 관계를 이용하여 유리전이 온도와 열팽창 계수를 산출하였다. 또한 일정 변형도 하중을 통해 탄성 계수를 산출하여 기계적 거동을 예측하였다. 추가적으로 CNT의 표면처리에 따른 기계적 거동을 분석하였다. 질소 도핑 및 COOH, OH 그룹을 처리한 3개의 모형을 구성하였으며, 각 모형의 탄성 계수 및 경계면 거동에 대한 해석을 수행하였다. 이를 통해 에폭시 내부 CNT의 응집은 열기계적 거동에 교란을 가지고 올 수 있으며, 표면처리는 복합재의 기계적 물성뿐만 아니라 경계면 특성까지도 향상시킬 수 있음을 확인하였다.

• 한국재료학회지
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• 제20권9호
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• pp.478-482
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• 2010

A series of molecular dynamic (MD), finite element (FE) and ab initio simulations are carried out to establish suitable modeling schemes for the continuum-based analysis of aluminum matrix nanocomposites reinforced with carbon nanotubes (CNTs). From a comparison of the MD with FE models and inferences based on bond structures and electron distributions, we propose that the effective thickness of a CNT wall for its continuum representation should be related to the graphitic inter-planar spacing of 3.4${\AA}$. We also show that shell element representation of a CNT structure in the FE models properly simulated the carbon-carbon covalent bonding and long-range interactions in terms of the load-displacement behaviors. Estimation of the effective interfacial elastic properties by ab initio simulations showed that the in-plane interfacial bond strength is negligibly weaker than the normal counterpart due to the nature of the weak secondary bonding at the CNT-Al interface. Therefore, we suggest that a third-phase solid element representation of the CNT-Al interface in nanocomposites is not physically meaningful and that spring or bar element representation of the weak interfacial bonding would be more appropriate as in the cases of polymer matrix counterparts. The possibility of treating the interface as a simply contacted phase boundary is also discussed.

• Design & Manufacturing
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• 제10권3호
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• pp.14-19
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• 2016

Thermally or electrically conductive filler reinforced polymer composites are extensively being developed as the demand for light weight material increases rapidly in industiral applications need good conductivity such as heat sink of the electronics or light. Carbon or ceramic materials like graphite, carbon nanotube or boron nitride are typical conductive fillers with good thermal or electical conductivity. Using these conductive fillers, the polymer composites in the market show wide range of thermal conductivity from approximately 1 W/mK to 20 W/mK, which is quite enhanced considering the thermal conductivity lower than 0.5 W/mK for most polymeric materials. The practical use of these composites, however, is yet limited to specific applications because most composites are still not conductive enough or too difficult to process, too brittle, too expensive for higher conductivity. For practical use of conductive composite, the thermal conductivity required depending on the heat releasing mode are studied first for simplified unit cooling geometry to propose thermal conductivities of the composites for reasonable cooling performance comparing with the metal heat sink as a reference. Also, as a practical design for heat sink based on polymer composite, composite and metal sheet hybrid structures are investigated for LED lamp heat sink and audio amplication module housing to find that this hybrid structure can be a good solution considering all of the cooling performance, manufacturing, mechanical performance, cost and weight.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 봄 학술논문 발표대회
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• pp.95-96
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• 2023

In this study, the table flow of fiber reinforced cement composites mixed with CNTs dispersed differently according to the dispersion method was evaluated. The mixture was composed of plain mixture according to the presence or absence of ultrasonic dispersion and PCE-based dispersants A and B of 0.5% and 1.0%, respectively, CNT was mixed with 0.03% of cement weight and fiber was mixed with 1.5% of total volume. As a result of the experiment, NC-A0.5 showed a fluidity similar to that of P without CNT. The fluidity of NC-A0.5 and P-N showed a similar tendency, which is considered to be due to the distribution of evenly dispersed CNT particles without agglomeration between cement particles due to the dispersant. NC-B0.5 showed a similar level of firmness to P-U, but after hitting 250 mm, B Agent seems to have a significant effect on liquidity improvement.Both NC-A1.0 and NC-B1.0 seem to have increased flow due to excessive dispersion.

• Steel and Composite Structures
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• 제33권1호
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• pp.93-109
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• 2019

In the present study, vibration analysis of double bonded micro sandwich cylindrical shells with saturated porous core and carbon/boron nitride nanotubes (CNT/BNNT) reinforced composite face sheets under multi-physical loadings based on Cooper-Naghdi theory is investigated. The material properties of the micro structure are assumed to be temperature dependent, and each of the micro-tubes is placed on the Pasternak elastic foundations, and mechanical, moisture, thermal, electrical, and magnetic forces are effective on the structural behavior. The distributions of porous materials in three distributions such as non-linear non-symmetric, nonlinear-symmetric, and uniform are considered. The relationship including electro-magneto-hydro-thermo-mechanical loadings based on modified couple stress theory is obtained and moreover the governing equations of motion using the energy method and the Hamilton's principle are derived. Also, Navier's type solution is also used to solve the governing equations of motion. The effects of various parameters such as material length scale parameter, temperature change, various distributions of nanotube, volume fraction of nanotubes, porosity and Skempton coefficients, and geometric parameters on the natural frequency of double bonded micro sandwich cylindrical shells are investigated. Increasing the porosity and the Skempton coefficients of the core in micro sandwich cylindrical shell lead to increase the natural frequency of the structure. Cylindrical shells and porous materials in the industry of filters and separators, heat exchangers and coolers are widely used and are generally accepted today.

• 대한기계학회논문집A
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• 제37권5호
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• pp.657-664
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• 2013

에폭시 수지에 다중벽 탄소나노튜브를 첨가하여 초음파 처리와 전단혼합 방법으로 분산시켜 다중벽 탄소나노튜브로 강화된 에폭시 복합재료를 제조하였으며, 에폭시 수지 내 다중벽 탄소나노튜브의 분산 적정성을 판단하고 기계적 및 열적 물성을 고찰하였다. 충전재 분산에 대한 평가를 위해 정성적인 방법으로 주사전자현미경(scanning electron microscope, SEM) 이미지를 사용하였고, 정량적인 판단을 위해 인장실험을 실시하였다. 또한, 열적 특성을 평가하기 위해 열팽창계수(coefficient of thermal expansion, CTE)를 측정하였다. 주사전자현미경 사진 및 인장 강도와 영률(Young's modulus)의 작은 편차를 통해서 다중벽 탄소나노튜브가 에폭시 수지 내에 적절히 분산되었음을 확인하였다. 충전재 함량에 따라 인장 강도와 영률이 증가함을 보였고 열팽창계수 측정에서는 열안정성 개선을 고찰하였다.

• 접착 및 계면
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• 제22권4호
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• pp.136-143
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• 2021

폴리우레아 소재는 폴리우레탄 화학결합과 높은 유사성을 가지고 있으면서, 높은 기계적 강성 및 탄성을 가지고 있어 경량 복합재의 고분자 기지 상으로 연구되어 왔다. 본 연구에서는 이방성을 가진 CNT (carbon nanotube)와 GO (graphene oxide)를 폴리우레아 기지 상에 첨가하여 제작한 복합재를 제작하였고 그 특성을 분석하였다. 원자힘현미경 이용해 CNT와 GO의 각각 1차원의 선형 및 2차원의 층상의 이방성을 확인한 후, 5 wt%으로 각각 폴리우레아 Resin에 혼합 후 cross-link 형성 및 건조 과정을 거쳐 복합재를 제작하였다. FTIR과 Raman 분광법을 이용해 제조한 CNT/폴리우레아와 GO/폴리우레아 복합재의 화학적 구조를 분석하였다. 그 결과, 폴리우레아와 첨가물의 화학결합 변화없이 혼합된 것이 확인되었다. 전자현미경을 이용해 첨가제/폴리우레아/유리섬유 직물 복합재의 표면과 단면에서의 CNT와 GO의 분포를 관찰하였다. 인장 강도 시험 결과, 1 wt%의 CNT와 GO가 첨가된 폴리우레아의 경우 인장강도 향상이 관측되었다.

• 폴리머
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• 제38권2호
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• pp.240-249
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• 2014

다중벽 탄소나노튜브(MWNT)로 보강된 폴리에스터(PET) 복합재료에 관한 연구를 수행하였다. PET와 MWNT간의 계면결합력을 향상시키기 위하여, MWNT 표면에 bishydroxyethylene-terephthalate(BHET)를 도입하였다. 이렇게 기능화된 MWNT를 0.5~2.0 wt% 범위에서 이축압출기를 이용하여 PET와 용융 혼합하였다. MWNT/PET 복합재료를 필라멘트로 방사하고, 이를 연신 및 열처리하여 특성 분석을 하였다. 이로부터 복합섬유의 결정화 온도와 열분해 온도가 MWNT로 인하여 증가함을 알 수 있었으며, 항복응력과 인성은 MWNT의 1 wt%의 첨가만으로도 30%이상 증가함을 알 수 있었다. 따라서 MWNT를 BHET로 기능화하는 방법은 폴리에스터에 탄소나노튜브를 효과적으로 분산시키고 계면결합력을 증가시키는데 매우 효과적임을 알 수 있었다.

• Advances in aircraft and spacecraft science
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• 제5권1호
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• pp.21-49
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• 2018

In this paper, geometric nonlinear bending characteristics of single wall carbon nanotube reinforced composite (SWCNTRC) doubly curved shell panels subjected to uniform transversely loadings are investigated. The nonlinear mathematical model is developed for doubly curved SWCNTRC shell panel on the basis of higher-order shear deformation theory and Green- Lagrange nonlinearity. All nonlinear higher order terms are included in the mathematical model. The effective material properties of SWCNTRC are estimated by using Eshelby-Mori-Tanaka micromechanical approach. The governing equation of the shell panel is obtained using the total potential energy principle and a Newton-Raphson iterative method is employed to compute the nonlinear displacement and stresses. The present results are compared with published literature. The effect of SWCNT volume fraction, width-to-thickness ratio, radius-to-width ratio (R/a), boundary condition, linear and nonlinear deflection, stresses and different types of shell geometry on nonlinear bending response is investigated.

• Structural Engineering and Mechanics
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• 제68권3호
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• pp.313-323
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• 2018

A numerical study is performed to investigate the impacts of thermal loading on the vibration and buckling of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) conical shells. Thermo-mechanical properties of constituents are considered to be temperature-dependent. Considering the shear deformation theory, the energy functional is derived, and applying the variational differential quadrature (VDQ) method, the mass and stiffness matrices are obtained. The shear correction factors are accurately calculated by matching the shear strain energy obtained from an exact three-dimensional distribution of the transverse shear stresses and shear strain energy related to the first-order shear deformation theory. Numerical results reveal that considering temperature-dependent material properties plays an important role in predicting the thermally induced vibration of FG-CNTRC conical shells, and neglecting this effect leads to considerable overestimation of the stiffness of the structure.