Failure mechanisms in pre-cracked Ni-graphene nanocomposites

SE Muller and RR Santhapuram and AK Nair, COMPUTATIONAL MATERIALS SCIENCE, 152, 341-350 (2018).

DOI: 10.1016/j.commatsci.2018.06.013

Graphene is a 2-D material with superior mechanical properties and is highly desirable as a filler in nano-composite materials. However, the mechanical properties of the resulting nanocomposite are anisotropic, with strengthening or weakening depending on the loading direction. The presence of graphene also introduces new failure mechanisms to the matrix it is embedded within. In addition, the structure of graphene, pristine or polycrystalline, can affect its interfacial properties in the nanocomposite. We use molecular dynamics to predict the failure mechanisms of Ni-graphene nanocomposites for different loading directions with a crack present in the Ni matrix. We observe a variety of failure mechanisms including dislocation nucleation, graphene bond breaking, and delamination. We also compare the yield stress and strain of nanocomposites with either pristine or polycrystalline graphene. We find that graphene of either kind can improve the yield stress of Ni by 27-76% when loaded parallel to the graphene sheet. We also find that, compared to pristine graphene, polycrystalline graphene can improve the yield stress of a Ni-graphene nanocomposite by up to 27%. This is explained by the higher interfacial shear stress of polycrystalline graphene on Ni's(1 1 1) surface compared to pristine graphene. This is in part related to the wrinkling of graphene sheets, which differs between polycrystalline and pristine sheets. Our research indicates that metal-graphene nanocomposites benefit from graphene's polycrystalline structure when superior mechanical properties are desired.

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