Browsing by Author "Wang, Tai-Yuan"

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Characterization of Young's modulus and thermal conductivity of graphene/epoxy nanocomposites
(2019-03-01)
Wang, Tai-Yuan
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Tseng, Po-Ying
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Tsai, Jia-Lin
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交大名義發表
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機械工程學系
Atomistic simulation together with micromechanical analysis was employed to characterize the Young's modulus and thermal conductivity of graphene/epoxy nanocomposites. Nanocomposites containing pristine graphene, carboxyl (COOH)-functionalized graphene, and COOH- and amine (NH2)-functionalized graphene were considered in the simulations. The effect of atomistic interaction between the graphene and the surrounding epoxy was accounted for in the molecular dynamics simulations and then used to derive the effective properties of graphene. Subsequently, the Young's modulus and thermal conductivity of nanocomposites containing randomly oriented graphene were modeled using the Mori-Tanaka micromechanical model. The results indicated that the COOH- and NH2-functionalized graphene nanocomposite had superior mechanical and thermal properties to the other two material systems. Moreover, the model predictions were in favorable agreement with the experimental data.
Characterizing the interfacial shear strength of graphite/epoxy composites containing functionalized graphene
(2016-08-01)
Lee, Ming-Wei
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Wang, Tai-Yuan
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Tsai, Jia-Lin
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機械工程學系
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Department of Mechanical Engineering
This study investigated the interfacial shear strength (IFSS) of graphite/epoxy composites containing functionalized graphene. Epoxy resin together with pristine graphene and functionalized graphene were employed as a matrix in the fiber composites, with graphene loadings in the epoxy matrix of 0.1, 0.3, and 0.5 wt%. The functional groups grafted on the functionalized graphene were characterized through Fourier transform infrared spectra and X-ray photoelectron spectroscopy. The IFSS of the fiber composites were evaluated through microdroplet testing, and the corresponding failure mechanism was examined using scanning electrical microscopy. The experimental results indicated that the IFSS increased with the graphene loadings in the matrix. Furthermore, both functionalized graphene and pristine graphene provided a similar IFSS in the fiber composites. Observation of the failure interface showed that the failure mechanism of the IFSS was dominated by interfacial failure between the fiber and matrix in conjunction with adhesive failure in the matrix. Introducing graphene in the matrix can enhance IFSS by improving the adhesive strength in the interface as well as complicating the crack extension in the matrix. (C) 2016 Elsevier Ltd. All rights reserved.
Investigating thermal conductivities of functionalized graphene and graphene/epoxy nanocomposites
(2016-09)
Wang, Tai-Yuan
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Tsai, Jia-Lin
;
機械工程學系
;
Department of Mechanical Engineering
This research investigated the thermal conductivities of functionalized graphene (FG) and FG/epoxy nanocomposites by using molecular dynamics simulation. The functional groups considered in FG are carboxyl and amine groups. The results indicated that the thermal conductivity of FG is markedly reduced compared with that of pristine graphene. However, the FG/epoxy nanocomposites demonstrated higher thermal conductivity than did the pristine graphene nanocomposites. To understand the enhancement mechanism, the interfacial thermal conductance (ITC) between the FG and the surrounding epoxy matrix was examined. The effects of the FG on ITC were explicated using vibrational density of state and normalized interaction energy. The improvement of the thermal conductivity of FG/epoxy nanocomposites was attributable to the enhancement of the ITC resulting from the functional groups grafted on the graphene surface. In addition, establishing the functional groups facilitates atomistic interaction between the graphene and epoxy, which can reduce the phonon mismatch and enhance the thermal transport efficiency in the nanocomposite. The enhanced thermal conductivity in the FG/epoxy nanocomposites was validated by experimental observation. (C) 2016 Elsevier B.V. All rights reserved.
Mechanical properties of nanocomposites with functionalized graphene
(2016-11)
Lee, Ming-Wei
;
Wang, Tai-Yuan
;
Tsai, Jia-Lin
;
機械工程學系
;
Department of Mechanical Engineering
The research investigated the thermal and mechanical properties of graphene/epoxy nanocomposites. Pristine graphene and functionalized graphene were used as nano-reinforcement in the nanocomposites. The graphene loadings employed in the nanocomposites were 0.1, 0.3, 0.5, and 1.0wt%. The functional groups grafted on the functionalized graphene were characterized through Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Results indicated that two kinds of functional groups are grafted on the functionalized graphene surfaces: one contains only COOH group and the other contains both COOH and NH2 groups. Moreover, from mechanical and thermal testing, it was found that the nanocomposites with functionalized graphene demonstrate better mechanical and thermal properties than those with pristine graphene. The graphene containing NH2 and COOH functional groups exhibits superior mechanical and thermal properties than the graphene with only COOH functional group. In addition, Young\'s modulus and thermal conductivity of the nanocomposites increase as the graphene loading increases. However, the fracture toughness and tensile strength of the nanocomposites attain peak values when the functionalized graphene loading is 0.1wt%. The effects of the functional groups on the mechanical and thermal properties of nanocomposites were elaborated using molecular dynamics (MD) simulation. It was revealed that the interfacial thermal conductance and normalized interaction energy increase between the functionalized graphene and epoxy matrix, which may be responsible for the enhanced mechanical properties in the functionalized graphene/epoxy nanocomposites.
Micromechanical stick-slip model for characterizing damping responses of single-walled carbon nanotube nanocomposites
(2016-01-01)
Wang, Tai-Yuan
;
Liu, Shou-Chi
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Tsai, Jia-Lin
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機械工程學系
;
Department of Mechanical Engineering
A micromechanical stick-slip model was developed to characterize the damping response of single-walled carbon nanotube nanocomposites. Depending on the strength of the interfacial bonding and the extent of applied loading, the single-walled carbon nanotube embedded in the matrix may either completely stick to the matrix or partially slide relative to the matrix. The slippage in the interface, together with the contact friction, may lead to the energy dissipation of single-walled carbon nanotube nanocomposites. The effects of the aspect ratio of single-walled carbon nanotube, interfacial bonding strength, volume fraction of single-walled carbon nanotube, and interfacial friction on the damping behavior of single-walled carbon nanotube nanocomposites were accounted for in the micromechanical stick-slip model. In order to validate the analytical model, the energy dissipation was also evaluated using the finite element method. A cylindrical finite element method, with an embedded single-walled carbon nanotube, was developed where the stick-slip behavior of the interface between the single-walled carbon nanotube and surrounding matrix was characterized using a contact element. It was found that the energy dissipation obtained from the finite element analysis agrees with that derived from the micromechanical stick-slip model. Moreover, the energy dissipation may significantly increase, when the single-walled carbon nanotube slippage takes place. The increment of the energy dissipation could be attributed to the interfacial contact friction between the single-walled carbon nanotube and the surround matrix as well as the viscoelastic properties of the matrix materials.
The Index of Dry-Jet Wet Spinning for Polyacrylonitrile Precursor Fibers
(2015-01-10)
Wang, Tai-Yuan
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Chang, Hsiao-Chuan
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Chiu, Yu-Tsung
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Tsai, Jia-Lin
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機械工程學系
A new spinning index for a PAN precursor fiber is proposed that includes the viscosity of a spinning dope, the thermodynamic affinity, and the draw ratio during the spinning process. Through dry-jet wet spinning, six types of PAN precursor fibers with different spinning parameters, including solid content, solvent content in a bath, and draw ratio, were fabricated and analyzed with tensile tests, SEM, and XRD. The results show that the spinning index can reflect the mechanical properties of the fibers but is less indicative of crystallinity. Hence, the current spinning index is recommended for use as an indicator for the mechanical properties of PAN precursor fibers. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41265.