Anisotropic elastic moduli and internal friction of graphene nanoplatelets/silicon nitride composites

Elasticity and internal friction of graphene nanoplatelets (3 wt.%)/Si3N4 composite is analyzed by ultrasonic methods. It is shown that the composite exhibits a degenerate (elliptic) form of transversal isotropy with the graphene nanoplatelets acting effectively as spheroidal voids and inducing significant softening in all directions. The shear internal friction is strongly anisotropic with the maximal value corresponding to the volume-preserving, ‘breathing’ vibrations of the nanoplatelets. Possible relations between the observed behaviors and the micromorphology of the composite are discussed.