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The influence of carbon nanotube dispersion techniques (surfactant-assisted dispersion, ultrasonication and magnetic stirring) and surface functionalization of carbon nanotubes on mechanical properties of nanocomposites fabricated via powder metallurgy techniques is characterized. Functionalized multiwalled carbon nanotubes dispersed using a combination of techniques results in Al/functionalized multiwalled carbon nanotube composites with excellent microstructure and enhanced mechanical properties. Nonfunctionalized carbon nanotubes dispersed using zwitterionic surfactants show good dispersion patterns on Al powder surfaces and results in composites with good strength and relative densities are also obtained. Carbon nanotubes dispersed solely via shear mixing techniques resulted in highly embrittled composites with poor microstructure. Also discussed in this study is the usefulness of scanning electron microscopy in conjunction with image analysis techniques in characterizing porosity in Al/carbon nanotube composites. [ABSTRACT FROM AUTHOR]

We report a study of the electrical and mechanical effects of the inclusion of a thin layer of multiwalled carbon nanotubes (MWCNTs) into the surface of polydimethylsiloxane (PDMS) as a method of creating an electrically actuated, flexible microfluidic valve. Samples of PDMS with various surface loadings of MWCNTs were prepared and tested using a uniaxial tension tester, combined with a four-point probe electrical test. In contrast to other works reporting the inclusion of MWCNTs in the bulk of the material, we have found that inclusion of the MWCNTs on the surface only has no discernible effect on the mechanical properties of the PDMS samples, but causes a significant and repeatable change in the electrical performance. We have found that a loading of 4.16 g m−2 results in an electrical resistivity of 7.31 × 10−4 Ω cm, which is 200% lower than that previously reported for bulk inclusion samples. The microstructure of the MWCNTs was found to consist of both individual fibers and spherical clumps of fibers. We suggest that, due to the microstructure of the MWCNTs used in this study, the mechanical properties can be modeled as a thin layer of particulates, while the electrical properties can be modeled as a thin bed of bulk MWCNTs. © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: In micromechanics, accurate quantification of the elastic field (stress, strain, and displacement) caused by the presence of an inclusion in an infinite body is desired for both the particle and matrix materials. Ideally, the solution should be applicable to any particle geometry or shape and for any distribution of misfit along the interface (i.e. misfit profile). This work presents a dislocation-based numerical method, that is an extension to earlier work in this journal [Lerma, J.D., Khraishi, T., Shen, Y.L., Wirth, B.D., 2003. The elastic fields of misfit cylindrical particles: a dislocation-based numerical approach. Mech. Res. Commun. 30, 325–334], for determining the elastic fields of volume misfit particles with arbitrary misfit distribution or particle shape. [Copyright &y& Elsevier]

Abstract: In the current investigation the microstructural and mechanical properties of zinc compacted pallets were investigated. The pallets were compacted to different normalized densities (81–93%) under different pressures of 150, 200 and 450MPa, respectively. The effect of sintering the samples under inert environment at 378°C was also studied. Instrumented nanoindentation tests were utilized to deduce the mechanical properties of the compacted pallets. Nanoscratch tests were employed to qualitatively measure the sample resistance to plastic deformation. It was observed that there are two mechanisms driving the improvement of the mechanical properties. One mechanism is due to recrystallization driven by the increasing dislocation density and the other mechanism is due to consolidation of the particles into a continuous network due to diffusion and grain growth under high temperature sintering. The results also reveal that the mechanical properties and densities of the tablets are not linearly proportional to the compaction pressure. Higher compaction pressures resulted in denser tablets with higher elastic modulus and hardness. Upon sintering the compacts soften but also form a solid network due to the neighboring particles diffusion. Therefore, the hardness value drops but the reduced modulus increases. Furthermore, the nanoscratch tests revealed that higher compaction pressure produce not only a more compacted tablet, but also a more homogeneous one. [Copyright &y& Elsevier]