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Multiscale hybrid composites consisting of carbon nanotubes (CNTs), woven carbon fiber (CF), and polycarbonate (PC) were fabricated via solution processing to overcome the difficulty of controlling the melt viscosity of thermoplastic resins. The hybrid composites were fabricated in two steps: impregnation of PC solution into CF textile followed by hot pressing. Experimental studies were performed to identify the optimal conditions to maximize the degree of CNT dispersion in chloroform and fiber-resin interfacial adhesion via plasma treatment of CF surface. Characterization of CNT dispersion state, surface chemical composition and surface roughness of CF revealed the optimal dispersion time of 8 hours, and various plasma treatment conditions were applied at speeds of 2, 4, 6, 8 and 10 m/min to investigate the effects of plasma irradiation time. From the XPS results, carboxylic group on the CF surface increased from 16 to 30% (in terms of relative peak area) with decreasing plasma treatment speed. Surface roughness was measured using three-dimensional topography measurement, which revealed the arithmetic roughness (Ra) of CF surface increased from 135 to 254 nm with decreasing plasma treatment speed. Dynamic mechanical analysis performed on CNT/CF/PC composites under temperature ramp-frequency sweep mode showed the storage modulus and tan delta peak were maximum at 16 GHz and 0.35 (at a frequency of 1 Hz) for 2 m/min samples. The proposed processing method provides a viable, effective technique for manufacturing thermoplastic-matrix composites containing nano and fiber reinforcements, which would otherwise be difficult to perform in melt state. [ABSTRACT FROM AUTHOR]

One of the features of carbon nanomaterials, namely, exfoliated graphite nanoplatelets (xGnPs) and multi-walled carbon nanotubes (MWCNTs), is their ability to form electrically conductive networks in insulating polymers. Here, we fabricated hybrid nanocomposites consisting of xGnPs, MWCNTs and PDMS with varying xGnP:MWCNT ratios and measured the electrical resistance change when subjected to cyclic loading at two different levels of compressive strain. All the samples showed a decrease in electrical resistance when compression was applied, known as piezoresistive behavior, and the electrical response matched well with the cyclic compressive strain. We found that sensitivity increases with increasing xGnP:MWCNT ratio, which implies that as the proportion of xGnP increases, it is easier to disrupt the conductive network formed by the nanomaterials under the same loading conditions. Depending on the xGnP:MWCNT ratio, we obtained a sensitivity range of 2.2~3.7, which is similar to the range covered by conventional metal-foil-based strain gages. This suggests the ratio between 1D and 2D conductive fillers can be used as one of design parameters to tailor the sensitivities of nanocomposite strain sensors. [ABSTRACT FROM AUTHOR]

Optimal design of a piping system connected in the multi-stage turbo blower has been performed using response surface method and three-dimensional Navier-Stokes analysis to reduce pressure loss in the piping system. To analyze three-dimensional flow field in the piping system including a multi-stage turbo blower, general analysis code, CFX, is employed in the present work. SST turbulence model is employed to estimate the eddy viscosity. Unstructured grids are used to represent a composite grid system including circular duct, blower impeller, casing and gate valve. Throughout the optimization of a piping system using two design variables defined the radius of an inlet and outlet ducts, the pressure loss in the piping system is successfully reduced by decreasing local losses in the piping system. Detailed flow analysis is performed using the reference and optimum shape of the connecting duct. [ABSTRACT FROM AUTHOR]