Molecular dynamics simulation on temperature and stain rate-dependent tensile response and failure behavior of Ni-coated CNT/Mg composites

This paper focuses on the molecular dynamics (MD) simulation of the tensile response of Ni-coated CNT-reinforced magnesium matrix composites (Ni-CNT/Mg) subjected to uniaxial tension at different temperatures and strain rates. The results show that Ni-CNTs can improve the mechanical properties of the composites effectively. The maximum stress of Ni-(6,6)CNT/Mg is, respectively, increased by 25.66 and 11.13%, while the elastic modulus is increased by 23.69 and 14.43% compared with those of the single-crystal Mg and uncoated (6,6)CNT/Mg at 300 K and 1 × 10 9 s −1 . In addition, the calculated elastic modulus of the Ni-(6,6)CNT/Mg composite is consistent with the prediction based on the rule-of-mixture. The Ni-CNT/Mg composites still have better mechanical properties at 500 K but exhibit a significant temperature softening effect in the temperature range 100–500 K and a strong positive strain-rate sensitivity at a strain rate greater than 1 × 10 9 s −1 . The various failure modes of the composite at the nano-scale are mainly determined by the combined effects of the different factors such as the atomic disordering, the void and dislocation nucleation, structural phase transformations in Mg nanocrystals near the interface, and the subsequent fracture of the Ni-coated CNT close to the voids.