An atomic-level understanding of the strengthening mechanism of aluminum matrix composites reinforced by aligned carbon nanotubes

In this paper, the strengthening and the deformation mechanisms associated with the aligned dispersion of single-walled carbon nanotubes (CNTs) in an aluminum matrix composite (AMC) are investigated at the atomic level. Our molecular dynamics (MD) simulations make use of a representative volume element (RVE) that accounts for geometrical constraints that manifest themselves in periodic boundary conditions (PBCs) of AMCs possessing nearly perfect crystalline structure. The tensile properties characterization of AMCs reinforced by aligned CNTs of different length and diameter was studied using the RVE concept. Our work reveals that there exists a critical CNT length beyond which the addition of a small amount of CNTs led to a significant enhancement in stiffness and strength of AMCs. It further reveals that the elasticity and strength enhancement is proportional to CNT diameter. The atomistic results are compared with those predicted by the well-known rule of mixture (ROM) technique and reveal that the ROM can provide a reasonable estimate of properties provided that the CNT length was comparable to a certain critical length. In addition, the AMCs reinforced by armchair CNTs show better enhancement in the mechanical behavior of reinforced matrix than those strengthened by zigzag CNTs. It further reveals that the fracture behavior of Al/CNT composite is mainly governed by size characteristics of CNTs.