▎ 摘　　要

Elastic constants of silicon nitride composites with variable content (3-18 wt.%) of two kinds of graphene fillers (nanoplatelets and reduced graphene oxide sheets) are determined using resonant ultrasound spectroscopy. The corresponding Young's modulus (E), shear modulus (G) and Poisson's ratio (v) are calculated for each material. Composites show a noticeable anisotropy that grows stronger with the graphene filler content, owing to the preferential alignment of the graphene layers and to their own anisotropy as well. E and G monotonically decrease with the filler concentration for both types of fillers, showing a maximum decrease in E of 75% along the direction perpendicular to the graphene plane for the composite with the highest filler content (Si3N4-18 wt.% GNP) and a reduction in G of 63% for shear along the graphene plane for the same composite. Influence on the fracture pattern of the composites is also addressed. (C) 2015 Elsevier Ltd. All rights reserved.