The stress–strain behavior of polymer–nanotube composites from molecular dynamics simulation S.J.V. Frankland a, *,V.M.Harik b ,G.M.Odegard a ,D.W.Brenner c ,T.S.Gates d a National Institute of Aerospace, 144 Research Drive, Hampton, VA 23666, USA b Swales Aerospace, M/S 186A, NASA Langley Research Center, Hampton, VA 23681, USA c Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695, USA d Mechanics and Durability Branch, M/S 188E, NASA Langley Research Center, Hampton, VA 23681, USA Received 23 August 2002; received in revised form 1 November 2002; accepted 15 December 2002 Abstract Stress–strain curves of polymer–carbon nanotube composites generated from molecular dynamics simulations of a single-walled carbonnanotubeembeddedinpolyethylenearepresented.Acomparisonismadebetweentheresponsetomechanicalloadingofa compositewithalong,continuousnanotube(replicatedviaperiodicboundaryconditions)andtheresponseofacompositewitha short, discontinuous nanotube. Both composites are mechanically loaded in the direction of, and transverse to, the nanotube axis. The long-nanotube composite shows an increase in the stiffness relative to the polymer and behaves anisotropically under the dif- ferentloadingconditionsconsidered.Theshort-nanotubecompositeshowsnoenhancementrelativetothepolymer,mostprobably because of its low aspect ratio. The stress–strain curves from molecular dynamics simulations are compared with corresponding rule-of-mixtures predictions. PublishedbyElsevierLtd. Keywords: A. Polymer-matrix composites (PMCs); B. Mechanical properties; B. Stress/strain curves; C. Computational simulation; Carbon nano- tubes 1. Introduction In the last few years, single-walled carbon nanotube- polymer composites have generated considerable inter- estinthematerialsresearchcommunitybecauseoftheir potential for large increases in strength and stiffness, when compared to conventional carbon-fiber-reinforced polymer composites. Even though some nanotube com- posite materials have been characterized experimentally [1–12],thedevelopmentofthesematerialscanbegreatly facilitatedbyusingcomputationalmethodsthatallowfor parametric studies of the influence of material and geo- metry. In particular, molecular dynamics (MD) simula- tions can predict the effect of mechanical loading on specificregionsofpolymer–nanotube(NT)composites. Various aspects of the mechanical reinforcement of polymersbycarbonnanotubes(NT)havebeenaddressed computationally. One example of recent work is an equivalent-continuum modeling method that was used to predict the elastic properties of two single-walled polyimide–NT composites for various NT volume frac- tions, lengths, and orientations [13]. At the continuum level,finiteelementanalysishasbeenusedtopredictthe macroscale effects of the waviness of NTs [14,15]. Molecular statics simulations of the transverse mechan- icalpropertiesofNTbundleshaveshownthatcohesion between NTs is strong, compared to a graphite–epoxy matrix [16]. Mechanical properties of NT yarns com- posed of twisted NT bundles have been predicted from the elastic constants of the NT bundles [17]. Molecular modelinghaspredictedtheadhesionbetweenaNTand various polymer matrices [18]. Molecular dynamics simulations have predicted that the polymer–NT inter- facecanbereinforcedbycovalentlybondingtheNTto thepolymermatrix [19]. The objective of this work is to explore the nanos- tructural effects of carbon NTs on the overall mechan- ical properties of polymer–NT composites. The overall 0266-3538/03/$ - see front matter Published by Elsevier Ltd. doi:10.1016/S0266-3538(03)00059-9 Composites Science and Technology 63 (2003) 1655–1661 www.elsevier.com/locate/compscitech * Corresponding author. +Tel.: 1-757-864-4049; fax: +1-757-766- 1855. E-mail addresses: sjvf@nianet.org (S.J.V. Frankland).