▎ 摘　　要

To compare enhancements of mechanical properties of polymer composites reinforced by carbon nanotubes and graphene sheet, molecular models of polymer matrix reinforced by the same weight percentage of carbon nanotubes and graphene sheet are developed. Pull-out process and strain constant method are applied to find mechanical properties of the nano-composites by examining the interfacial interactions between nano-reinforcements and polymer matrices. The results show that about 18% higher in Young's modulus, 8.7% higher in tensile strength, and 5% higher in surface crack energy are obtained for the composites by incorporation of graphene sheet than those by incorporation of carbon nanotubes. Graphene sheet is found to play a better role in delaying the propagations of cracks. To explore the mechanisms on the enhanced tensile and fracture properties, the interfacial interaction energy and shear forces between the nano-reinforcements and polymer matrices, and total van der Waals energy of the polymer composites are examined and interpreted accordingly. (C) 2017 Elsevier Ltd. All rights reserved.