Effects of Reorientation of Graphene Platelets (GPLs) on Young's Modulus of Polymer Nanocomposites under Uni-Axial Stretching

The orientation of reinforcement fillers in composites plays a vital role in their mechanical properties. This paper employs the Mori⁻Tanaka micromechanics model, incorporating the effect of stretching-induced reorientation of graphene platelets (GPL), to predict Young's modulus of GPL/polymer nanocomposites. Subjected to uni-axial stretching, dispersion of GPLs is described by an orientation distribution function (ODF) in terms of a stretching strain and two Euler angles. The ODF shows that GPLs tend to realign along the stretching direction. Such realignment is enhanced at a higher Poisson's ratio and under a larger stretching strain. It is found that the out-of-plane Young's modulus of GPL nanofillers has a limited effect on the overall Young's modulus of the composites. With an increase in stretching strain and GPL concentration, Young's modulus increases in the stretching direction while it decreases in the transverse direction. A larger aspect-ratio of GPLs with fewer layers is preferred for enhancing Young's modulus in the stretching direction, but it is unfavorable in the transverse direction. Moreover, Young's moduli in both longitudinal and transverse directions are more sensitive to the reorientation of smaller-sized GPLs with a greater concentration in the composites.