A hierarchical scheme from nano to macro scale for the strength and ductility of graphene/metal nanocomposites

Abstract

Recent experiments have shown that grain size of metals in graphene/metal nanocomposites has a significant effect on their strength and ductility. As the grain size decreases, the strength tends to increase while the ductility tends to decrease. But quantitative assessment of these observations remains a challenge. In this paper, we establish a hierarchical scheme from nano to macro scale to evaluate the dependance of these properties on the grain size and graphene volume concentration. In the nano scale, the elastic properties of graphene nanofiller and metal matrix are evaluated via the density functional theory (DFT). In the micro scale, the plasticity of the ductile metal is described by a dislocation density-based constitutive equation, and its degradation process is accounted for by the generation of micro voids. In the macro scale we consider the system of randomly distributed graphene nanosheets in the degraded metal matrix. The grain-size dependent stress-strain relation of the overall graphene/metal nanocomposites are calculated by a two-scale homogenization method with the assistance of the field-fluctuation approach. In this process, the grain-size dependent thermodynamic driving force for the progressive generation of micro voids and the influence of an ultrathin imperfect interphase surrounding the graphene nanofiller are also considered. It is demonstrated that the predicted results from the developed hierarchical scheme agree well with the experimental data of graphene/aluminum nanocomposites. The developed multiscale theory can provide a useful guideline for the design and applications of graphene/metal nanocomposites through the grain-size controlled process.