Fracture related mechanical properties of low and high graphene reinforcement of epoxy nanocomposites

Tensile ductility and fracture toughness of nano-reinforced epoxy resin with different types and concentrations of graphene nanoplatelets (GnPs) are investigated. GnPs types with small (2 nm) and large (15 nm) lateral size were used and for various weight percentages in order to fabricate a series of epoxy/GnPs nanocomposites. Tensile mechanical properties as well as fracture toughness (according to compact tension C(T) geometry) were experimentally assessed. The results indicate that the fracture mechanism vary according to the GnPs concentration and type used. For low filler concentrations (<0.25 wt% GnPs), an approximate 15% increase in ultimate tensile strength Rm and 12% in fracture toughness was noticed for the fine dispersion of small lateral size GnPs type. For the case of the large lateral size GnPs type, lower enhancement in Rm was observed, while fracture toughness was decreased. Reinforcement at higher concentrations (>1 wt% GnPs) revealed that the fracture mechanism altered and this was attributed to the “whitened zones” of the soft interphases of GnPs/matrix. An almost 30% increase in tensile ductility was attributed to the GnPs tilting for the fine dispersion of the small lateral size GnPs and therefore an essential loading transfer was involved. For reinforcement with extreme filler concentrations (>5 wt% GnPs) a decrease in all investigated mechanical properties was noticed and this was attributed to the particles agglomeration.