Distinct element method for multiscale modeling of cross-linked carbon nanotube bundles: From soft to strong nanomateria
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Roberto Ballarini Department of Civil and Environmental Engineering, University of Houston, Houston, Texas 77204, USA
Traian Dumitricăa) Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota 55455, USA; and Department of Civil Engineering, University of Minnesota, Minneapolis, Minnesota 55455, USA (Received 28 May 2014; accepted 18 August 2014)
Predicting the impact of cross-links on the mechanics of carbon nanotube-based materials is a challenging endeavor, as the micro- and nanostructure is composed of continuous nanofibers, discontinuous interfaces, and covalent bridges. Here we demonstrate a new modeling solution in the context of the distinct element method (DEM). By representing nanotubes as bonded cylinder segments undergoing van der Waals adhesion, viscous friction, and contact bonding, we are able to simulate how cross-linking transforms a soft bundle into a strong one. We predict that the sp3-sp cross-links formed by interstitial carbon atoms can improve the tensile strength by an order of magnitude, in agreement with experiment and molecular dynamics simulations. The DEM methodology allows performing the multiscale simulation needed for developing strategies to further enhance the mechanical performance. I. INTRODUCTION 1
Since their discovery, carbon nanotubes (CNTs) have attracted significant interest in applications, especially because of their extraordinary mechanical properties.2–7 These properties include Young’s modulus close to 1 TPa,8 and over 150 GPa and 16% yield stress5 and strains,4 respectively. Assemblies of CNTs, such as freestanding and supported films,9 yarns,10 and fibers,11,12 have been accomplished to extend the characteristic properties of a single CNT in the macroscopic scale. However, mechanical properties of such structures are inferior compared to those of individual CNTs. The reason these CNT assemblies belong to the category of soft nanomaterials is the poor load transfer by the van der Waals (vdW) interaction between CNTs.7 Various strategies are currently being pursued to overcome this problem, including the covalent bridging of CNTs introduced by irradiation methods13–16 and the mechanical interlocking.17 In this respect, an order of magnitude in the moduli and tensile strengths of irradiated CNT bundles have been already reported.18 While much of the current work is directed at modeling the outcomes of irradiation on the CNT structure a)
Address all correspondence to this author. e-mail: [email protected] This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs.org/jmr-editor-manuscripts/. DOI: 10.1557/jmr.2014.279 J. Mater. Res., Vol. 30, No. 1, Jan 14, 2015
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and mechanical properties, and at understanding the microscopic details of the cross-links, 19,20 it remains unclear how one can leverage this knowledge to predict the global mechanical behavior
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