DC and AC Properties of Aligned Carbon Nanotube Forests and Polymeric Nanocomposites

International Journal of Solids and Structures

et al. 2015

a b s t r a c tIn this paper, the piezoresistive response (i.e. the change of resistance under the application of strain) of polymer composites reinforced by a novel material known as fuzzy fibers is characterized by using single tow piezoresistive fragmentation tests and modeled by using a 3D computational multiscale model based on the finite element analysis. In the characterization work, the fuzzy fiber tow is embedded in a dogbone specimen infused by epoxy, with resistance and displacement measured simultaneously to obtain its piezoresistive response. An approximately linear and stable piezoresistive response is observed within the fuzzy fiber tow region yielding gauge factors on average of 0.14. Using a 3D multiscale mechanicalelectrostatic coupled code and explicitly accounting for the local piezoresistive response of the anisotropic interphase region, the piezoresistive responses of the overall fuzzy fiber reinforced polymer composites are studied parametrically in an effort to provide qualitative guidance for the manufacture of fuzzy fiber reinforced polymer composites. It is observed from the model that the fuzzy fiber reinforced polymer composites with cylindrically orthotropic carbon nanotube interphase regions are dominated by the electrical tunneling effect between the nanotubes and can yield very large gauge factors while fuzzy fibers with randomly oriented carbon nanotubes in the interphase region yield smaller gauge factors as the material is electrically saturated by the carbon nanotubes. Finally, the modeling efforts provide plausible reasons for the observed small gauge factors in experiments in the form of a combination of high concentration randomly oriented carbon nanotube interphase regions separated by sparse nanotube regions along the fuzzy fiber length.

Section: Introductionmentioning

confidence: 97%

Computational multiscale modeling and characterization of piezoresistivity in fuzzy fiber reinforced polymer composites

Ren

Burton

International Journal of Solids and Structures

et al. 2015

“…the changes in CNT resistance on application of axial or bending distortions (Rochefort et al, 1999;Tombler et al, 2000;Cao et al, 2003;Megalini et al, 2009;Saravanos, 2009b, 2010) In the current study, the focus is on modeling the effect of electron hopping on the piezoresistive response of SWCNT-epoxy nanocomposites. The electrical conductivity of nanocomposites is believed to be strongly influenced by the nanoscale effect of electron hopping or quantum tunneling (Du et al, 2004;Smith et al, 2005;Curran et al, 2006;Du et al, 2006).…”

Section: Introductionmentioning

confidence: 98%

Computational micromechanics analysis of electron-hopping-induced conductive paths and associated macroscale piezoresistive response in carbon nanotube–polymer nanocomposites

Chaurasia

Journal of Intelligent Material Systems and Structures

2014

In this study, a computational model is developed using finite-element techniques within a continuum micromechanics framework to capture the effect of electron-hopping-induced conductive paths at the nanoscale which contribute to the macroscale piezoresistive response of the nanocomposite. This is achieved by tracking the position of the nanotubes under applied deformations and modifying the conductivity of the intertube region depending on the relative proximity of individual pairs of nanotubes. The formation and disruption of the electron-hopping pathways are highly dependent on intertube distances and under deformations can result in microstructural rearrangements in terms of electrostatic properties leading to transitions in material symmetries and component magnitudes of the effective electrostatic properties. Thus, in order to capture the complexities of changing inhomogeneous nanoscale electrostatic behavior, where analytical Eshelby's approaches cannot be used, a computational micromechanics model is needed. The effective conductivity and piezoresistive strain tensor coefficients are evaluated using volume-averaged energy equivalencies for aligned CNT-polymer nanocomposites in the transverse direction exploring different volume fractions of CNTs in the polymer and the maximum electron-hopping range. The impact of the electron-hopping mechanism on the effective piezoresistive response is studied through the macroscale effective gauge factors under different loading conditions. The effective piezoresistive strain coefficients and macroscale effective gauge factors are observed to be nonlinear with applied macroscale strain and are highly dependent on the type of boundary conditions. The effective macroscale gauge factors observed in the current study have magnitudes comparable to experimental observations reported in the literature with higher gauge factors observed closer to the percolation threshold.

“…CNT resistance changes on application of axial or bending distortions. 19,[26][27][28][29][30] The effective piezoresistive response of nanocomposites is believed to be strongly influenced by the nanoscale effect of electron hopping or quantum tunneling. 20,[31][32][33] In the current study, the focus is on modeling the effect of electron hopping induced conductive pathways at the nanoscale leading to observed macroscale effective piezoresistive response of Single Walled Carbon Nanotube (SWCNT)-epoxy nanocomposites.…”

Section: Introductionmentioning

confidence: 99%

Computational micromechanics analysis of electron hopping induced piezoresistive response in carbon nanotube-polymer nanocomposites

Chaurasia

54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference

2013

In this study, a multiscale micromechanics based computational model is developed to capture the effect of electron hopping induced formation/disruption of conductive paths at the nanoscale which govern the effective macroscale conductive and piezoresistive response of the CNT-polymer nanocomposite. The local nanoscale conductivity at the nanoscale is allowed to evolve by tracking the position of the nanotubes under applied deformations and modifying the conductivity of the intertube region depending on the relative proximity of individual pairs of nanotubes. The formation and disruption of the high conductivity bands are highly dependent on the applied strain and yield odd microstructural symmetries for the effective electrical properties, emphasizing on the need of a computational micromechanics model. The effect of local CNT volume fractions and maximum electron hopping range on the effective macroscale gauge factors is studied for different cases of microstructure morphology i.e. CNT-polymer nanocomposites uniformly dispersed aligned CNTs and aligned/randomly oriented microscale bundles composed of aligned CNTs. Random orientation of macroscale bundles is taken into account using micromechanics based techniques by averaging over a discrete number of orientations of microscale bundles in a consistent manner. The results presented herein indicate that the effective gauge factors follow a strain dependent nonlinear response with asymmetry on application of tensile/compressive strains. In addition, the effective gauge factors were observed to be smaller for a microstructure with aligned microscale bundles as compared to randomly oriented microscale bundle. The gauge factors obtained from the current work are of comparable magnitude with those reported in the literature based on experimental investigation indicating that electron hopping could be the dominant mechanism governing the macroscale piezoresistive response of CNT-polymer nanocomposites.