Investigating fracture toughness of graphene epoxy nanocomposites using single edge notched bending specimens

The purpose of this study was to examine the fracture toughness of epoxy-based graphene nanocomposites. The single edge notched bending (SENB) samples with precrack tips were created by either tapping or sliding methods. For the tapping method, a single tap was conducted on a razor blade such a crack with a length of 2 mm was instantly propagated. For the sliding method, a razor blade was slid forward and backward into the samples, and a crack was generated with the blade edge. The SENB samples with graphene loadings (0.15 and 0.3 wt%) were subjected to three-point bending tests to evaluate fracture toughness. Results indicated that the graphene loading did not considerably affect the fracture toughness of the samples with tapping-induced precrack tips. However, the fracture toughness of the samples with sliding-induced precrack tips decreased as the graphene loading increased. For the 0.3-wt% graphene nanocomposites, the fracture toughness levels of the samples with sliding- and tapping-induced precrack tips were equal. In order to explicate the experimental results, the plastic zone sizes around the crack tip were evaluated using finite element analysis. For the sharp precrack tips (tapping method), the plastic zone was comparatively small (brittle behavior); hence, the effect of graphene on the inception of crack extension was minimal. Nevertheless, for blunt crack tips (sliding method), the plastic zone was larger and the size decreased as graphene loading increased; thus, the fracture behavior measured from the sliding method was dramatically influenced by the graphene loading.