Graphene/epoxy nanocomposites for improved fracture toughness: A focused review on toughening mechanism

•Progression of graphene/epoxy nanocomposites is overviewed.•Highlighting the correlation between graphene weight percentage and fracture toughness.•The toughening mechanisms behind the improved fracture toughness of graphene/epoxy nanocomposites are described.•Summarized challenges, future directions and opportunities in graphene/epoxy nanocomposite.