Browsing by Author "Nam, Tran Huu"

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    Effects of high-temperature thermal annealing on properties of aligned multi-walled carbon nanotube sheets and their composites
    (TAYLOR & FRANCIS LTD, 2-4 PARK SQUARE, MILTON PARK, ABINGDON OR14 4RN, OXON, ENGLAND, 2019-01-01) Nam, Tran Huu; Goto, Ken; Shimamura, Yoshinobu; Inoue, Yoku; Yamamoto, Go; Shirasu, Keiichi; Hashida, Toshiyuki
    Aligned multi-walled carbon nanotube (MWCNT) sheets were thermally annealed at high temperatures of 1800 degrees C, 2200 degrees C, and 2600 degrees C. Pristine and thermally annealed MWCNT/epoxy composites were fabricated using hot-melt prepreg processing. Effects of thermal annealing on properties of aligned MWCNT sheets and their composites were examined. Transmission electron microscope images and Raman spectra measurements of the aligned MWCNT sheets showed an improvement of the MWCNT nanostructure after high-temperature thermal annealing. High-temperature thermal annealing did not cause the change in microstructural morphologies of the MWCNT sheets. Although the strength of the MWCNT sheets after high-temperature thermal annealing did not improve, their stiffness enhanced significantly. Particularly, high-temperature thermal annealing increased markedly both the tensile strength and elastic modulus of the aligned MWCNT/epoxy composites. The enhancement in the tensile strength and elastic modulus of the composites is mainly attributed to significant improvement of the MWCNT nanostructure by high-temperature thermal annealing. Generally, high-temperature thermal annealing improved the stiffness of the aligned MWCNT sheets and their composites considerably.
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    Experimental characterization and viscoelastic modeling of isotropic and anisotropic magnetorheological elastomers
    (ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND, 2020-01-01) Nam, Tran Huu; Petříková, Iva; Marvalová, Bohdana
    The paper presents experimental research and numerical modeling of dynamic properties of magnetorheological elastomers (MREs). Isotropic and anisotropic MREs have been prepared based on silicone matrix filled by microsized carbonyl iron particles. Dynamic properties of the isotropic and anisotropic MREs were determined using double-lap shear test under harmonic loading in the displacement control mode. Effects of excitation frequency, strain amplitude, and magnetic field intensity on the dynamic properties of the MREs were examined. Dynamic moduli of the MREs decreased with increasing the strain amplitude of applied harmonic load. The dynamic moduli and damping properties of the MREs increased with increasing the frequency and magnetic flux density. The anisotropic MREs showed higher dynamic moduli and magnetorheological (MR) effect than those of the isotropic ones. The MR effect of the MREs increased with the rise of the magnetic flux density. The dependence of dynamic moduli and loss factor on the frequency and magnetic flux density was numerically studied using four-parameter fractional derivative viscoelastic model. The model was fitted well to experimental data for both isotropic and anisotropic MREs. The fitting of dynamic moduli and loss factor for the isotropic and anisotropic MREs is in good agreement with experimental results.
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    Mechanical properties of the composite material with elastomeric matrix reinforced by textile cords
    (Technická Univerzita v Liberci, 2004-01-01) Nam, Tran Huu
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    Property improvement of CNT spun yarns and their composites through pressing, stretching and tensioning
    (2019-05-03) Nam, Tran Huu; Goto, Ken; Shimamura, Yoshinobu; Inoue, Yoku; Ogihara, Shinji
    Untwisted multi-walled carbon nanotube (CNT) yarn was spun from vertically aligned CNT arrays by solid-state drawing CNT webs through a ceramic die. CNT yarn-reinforced epoxy composites were developed using a resin drop method. Waviness and poor packing of CNTs in the untwisted spun yarns have limited the mechanical properties of the yarns and their composites. Therefore, pressing along with sliding was applied to create thin-twisted yarns with dense packing of the CNTs. Besides, stretching and tensioning techniques were applied to the twisted yarns to reduce twist angle as well as waviness of the CNTs and their bundles. Stretching and tensioning of the press-slid yarns under constant loads of 0.15, 0.25, 0.35 N enhanced the mechanical properties of the yarns significantly. Moreover, stretching and tensioning of the press-slid CNT yarns increased the mechanical properties of the yarn composites considerably. However, tensioning of the press-slid yarns is more effective than their stretching.