Modeling of fracture toughness enhancement and reduction in fully dense ceramic/graphene composites

A model is suggested that describes the combined effects of crack bridging and ceramic/graphene interface strength on the fracture toughness of fully dense ceramic/graphene composites. Within the model, we consider the situation where ceramic/graphene interfaces are weaker than the matrix grain boundaries and are therefore more prone to cracking. Using the fracture mechanics combined with the percolation theory, we calculate the effects of graphene content and interface strength on the fracture toughness of composites. The dependences of the fracture toughness on the graphene content and the sizes of the graphene platelets are calculated in the exemplary case of alumina/graphene composites. The calculations reveal the transition from toughening, associated with crack bridging, to fracture toughness reduction due to crack percolation over ceramic/graphene interfaces. They demonstrate that ceramic/graphene composites with high toughness should have large graphene platelets and/or small grain size.