• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.727-729
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• 1992

In this study, the piezoelectric composites with 1-3 connectivity have been studied. A piezoelectric ceramics PZT prepared by Flux method is used as a filler in a epoxy Eccogel polymer matrix. The piezoelectric coefficients were increased as PZT volume% increases, and resonance frequency was moved to lower frequency as the sample thickness increased. The acoustic matching impedance with water is lowered than single phase PZT ceramics.

• Macromolecular Research
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• v.10 no.4
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• pp.236-239
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• 2002

Centrifugation is a method to create functionally graded materials (FGM) with a thermosetting matrix. In this study the movement of short carbon fibers in an epoxy resin during the centrifugation process was modeled to determine the fiber distribution in the final product. For this purpose a form factor K was introduced to modify a set of equations that was previously shown to be valid for the motion of spheres. It was shown that the results of the simulation were in good agreement with the experimental data, when an empirical K factor of four was chosen.

• Interaction and multiscale mechanics
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• v.4 no.3
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• pp.173-185
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• 2011

A multiscale modeling scheme that addresses the influence of the nanoparticle size in nanocomposites consisting of nano-sized spherical particles embedded in a polymer matrix is presented. A micromechanics-based constitutive model for nanoparticle-reinforced polymer composites is derived by incorporating the Eshelby tensor considering the interface effects (Duan et al. 2005a) into the ensemble-volume average method (Ju and Chen 1994). A numerical investigation is carried out to validate the proposed micromechanics-based constitutive model, and a parametric study on the interface moduli is conducted to investigate the effect of interface moduli on the overall behavior of the composites. In addition, molecular dynamics (MD) simulations are performed to determine the mechanical properties of the nanoparticles and polymer. Finally, the overall elastic moduli of the nanoparticle-reinforced polymer composites are estimated using the proposed multiscale approach combining the ensemble-volume average method and the MD simulation. The predictive capability of the proposed multiscale approach has been demonstrated through the multiscale numerical simulations.

• Carbon letters
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• v.15 no.2
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• pp.117-124
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• 2014

Conductive polymer composites (CPCs) consist of a polymeric matrix and a conductive filler, for example, carbon black, carbon fibers, graphite or carbon nanotubes (CNTs). The critical amount of the electrically conductive filler necessary to build up a continuous conductive network, and accordingly, to make the material conductive; is referred to as the percolation threshold. From technical and economical viewpoints, it is desirable to decrease the conductive-filler percolation-threshold as much as possible. In this study, we investigated the effect of polymer/conductive-filler interactions, as well as the processing and morphological development of low-percolation-threshold (${\Phi}c$) conductive-polymer composites. The aim of the study was to produce conductive composites containing less multi-walled CNTs (MWCNTs) than required for pure polypropylene (PP) through two approaches: one using various mixing methods and the other using immiscible polymer blends. Variants of the conductive PP composite filled with MWCNT was prepared by dry mixing, melt mixing, mechanofusion, and compression molding. The percolation threshold (${\Phi}c$) of the MWCNT-PP composites was most successfully lowered using the mechanofusion process than with any other mixing method (2-5 wt%). The mechanofusion process was found to enhance formation of a percolation network structure, and to ensure a more uniform state of dispersion in the CPCs. The immiscible-polymer blends were prepared by melt mixing (internal mixer) poly(vinylidene fluoride) (PVDF, PP/PVDF, volume ratio 1:1) filled with MWCNT.

• Macromolecular Research
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• v.13 no.3
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• pp.206-211
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• 2005

Multi-walled carbon nanotubes (MWNTs) pre-treated by concentrated mixed acid or oxidized at high temperature were melt mixed with poly(methyl methacrylate) (PMMA) using a twin screw extruder. The morphologies and electrical properties of the MWNT/PMMA composites were investigated. The thermally treated MWNTs (t-MWNTs) were well dispersed, whereas the acid treated MWNTs (a-MWNTs) were highly entangled, forming large-sized clusters. The resulting electrical properties of the composites were analyzed in terms of the carbon nanotube (CNT) dispersion. The experimental percolation threshold was estimated to be $3 wt\%$ of t-MWNTs, but no percolation occurred at similar concentrations in the a-MWNT composites, due to the poor dispersion in the matrix.

• Elastomers and Composites
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• v.50 no.1
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• pp.62-67
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• 2015

The surface modification of microfibriled cellulose (MFC) was carried out through the hydrolysis-condensation reaction using (3-aminopropyl)triethoxysilane (APS) and 3-glycidyloxypropyltriethoxysilane (GPS) and then the modified cellulose was compounded with bio-degradable poly(lactic acid) (PLA). Also, pristine MFC was compounded with PLA as a control groups. The confirmation of surface modification for the pristine MFC was characterized by FT-IR and SEM/EDX. The thermal and mechanical properties of the PLA/MFC composites depended on the content of MFC and the type of silane coupling agents. From the thermal, morphological and mechanical behaviors of the PLA/MFC composites, it was found that GPS-MFC was more successful to improve the interface adhesion between PLA matrix and the surface of MFC than that of APS-MFC.

• Polymer(Korea)
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• v.24 no.4
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• pp.556-563
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• 2000

In general, the development of thermoplastic composites has been confronted with difficult problems such as the weak bonding strength between fibers and matrix. However, now, such problems are being surmounted by the development of resins, the improvement of processes, and introduction of interphase. Especially, the introduction of interphase between fiber and matrix can help a dissipation of the impact energy and provide a good adhesion between fibers and matrix. In this study, polymeric interphase was introduced by electrodeposition, modified polypropylene was added to improve the weak bonding strength between interphase and polypropylene matrix. By evaluation of interlaminar shear strength and impact strength of the composites, it was found that composites with introduced composites showed higher mechanical properties than those of composites without interphase. Reactive polymers which have either anhydride or free acid functional group were used as interphase materials, and these polymers also behave as charge carrier in aqueous solution during the electrodeposition process. Weight gain on the carbon fibers was evaluated by changing process parameters such as concentration of solution, current density, and electrodeposition time.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.10
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• pp.1609-1618
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• 1997

Thermo-mechanical behaviors of polymer matrix composite(PMC) with continuous TiNi fiber are studied using theoretical analysis with 1-D analytical model and numerical analysis with 2-D multi-fiber finite element(FE) model. It is found that both compressive stress in matrix and tensile stress in TiNi fiber are the source of strengthening mechanisms and thermo-mechanical coupling. Thermal expansion of continuous TiNi fiber reinforced PMC has been compared with various mechanical behaviors as a function of fiber volume fraction, degree of pre-strain and modulus ratio between TiNi fiber and polymer matrix. Based on the concept of so-called shape memory composite(SMC) with a permanent shape memory effect, the critical modulus ratio is determined to obtain a smart composite with no or minimum thermal deformation. The critical modulus ratio should be a major factor for design and manufacturing of SMC.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.91-94
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• 2005

Polypropylene as a matrix has been used for wood polymer composites(WPC). In preparing WPC, the coupling agent, Polypropylene grafted Maleic Anhydride(PP-G-MA) was used in order to obtain a good interfacial bonding force between matrix and fillers and dispersion of wood powders. In this study, the effects of wood powder contents and water absorption on the mechanical properties were experimentally investigated. The tensile strength and flexural strength of composites reached its peak value when the wood powder content was around 60 wt%. However, the peak value of the impact was observed about 30 wt% of wood powder content. The tensile strength and flexural strength increase with increasing the wood power contents. But the impact strength decrease with increasing the wood powder contents. The slight change was observed with the water absorption in the WPC. The optimal condition of the compositions such as Anti-oxidant and UV stabilizers for the outdoor application was suggested in this research.

• Structural Engineering and Mechanics
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• v.76 no.5
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• pp.613-618
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• 2020

Exhausting oil resources and increasing pollution around the world are forcing researchers to look for new, renewable, biodegradable materials to lead sustainable development. The use of fiber reinforced composites based on natural fibres has increasingly begun as prospective materials for various engineering applications in the automotive, rail, construction and aerospace industries. The natural fiber chosen to make the composite material is plant-based fibre, e.g. jute fibre, and hemp fibre. Thermosetting polymer based Epoxy (LY556) was utilized as matrix material and The composites were produced using hand lay-up technique. The fabricated composites were tested for acoustic testing, thermo-gravimetric analysis (TGA) and flammability testing to asses sound absorption, thermal decomposition and fire resistivity of the structures. Hemp fibre composites have shown improved thermal stability over Jute fibre composites. However, the fire resistance characteristics of jute fibre composites are better as compared to hemp fibre composites. The sound absorption coefficient of composites was found to enhance with the increase of frequency.