Failure Behavior and Scaling of Graphene Nanocomposites

Abstract

This work proposes an investigation on the structural scaling of polymer/graphene nanocomposites. To this end, fracture tests on geometrically scaled Single Edge Notch Bending (SENB) specimens with varying contents of graphene nanoparticles were conducted to study the effects of nanomodification on the scaling. It is shown that, while the strength of the pristine polymer scales according to Linear Elastic Fracture Mechanics (LEFM), this is not the case for nanocomposites, even for very low graphene contents. In fact, small specimens exhibited a more pronounced ductility with limited scaling and a significant deviation from LEFM whereas larger specimens behaved in a more brittle way, with scaling of nominal strength closer to the one predicted by LEFM. This behavior, due to the significant size of the Fracture Process Zone (FPZ) compared to the specimen size, needs to be taken into serious consideration. In fact, it is shown that, for the specimen sizes investigated in this work, neglecting the non-linear effects of the FPZ can lead to an underestimation of the fracture energy as high as 113%, this error decreasing for increasing specimen sizes. A study on a large bulk of literature data confirmed that this is not a salient feature of polymer/graphene nanocomposites only but also of several other nanocomposites. It is shown that most of the specimen sizes investigated in the literature belong to the transitional region between ductile and brittle behavior where LEFM cannot characterize the fracturing behavior of these nanocomposites. In such cases, neglecting the non-linear effects of the FPZ can lead to an underestimation of the fracture energy as high as 156.8%, the underestimation being more significant for smaller specimen sizes and higher weight contents of nanofiller.