Deformation and damage characteristics of copper/honeycomb-graphene under shock loading

Three-dimensional graphene networks have been promising structures for improving the mechanical properties of metallic composites. This work investigated the deformation and damage characteristics of a single-crystalline and polycrystalline copper matrix with a honeycomb graphene network based on atomistic simulations. The graphene interface exerts a minor influence on the shock Hugoniot relation compared with that of the crystalline orientation of the copper matrix. Shock-induced dislocation nucleation occurs at the junction of the graphene interface and then propagates along the (111) plane of the copper matrix, and the graphene interface can be penetrated by copper atoms under strong shock. The graphene interface will dramatically reduce wave transmission and convert some shock energy into heat at the grain boundary, forming local hot spots and disordered regions. With shock wave releasing to the tensile stage, the graphene interface undergoes wrinkling, folding, and even fracture. Differing from the classical spall, the composites easily spall at the graphene interface under the release wave due to the weak Cu-C interfacial interaction, which significantly reduces the damage degree inside grains and leads to a special failure mode of grain flying. In addition, this fracture dominated by interface separation will produce a complex fracture interface and lead to a nonuniform distribution of spall strength on the fracture surface, with obvious local spallation waves, which makes the estimation of spall strength based on the acoustic approximation method difficult. The average strength of the graphene/single-crystalline copper composite is close to that of polycrystalline copper but higher than that of the graphene/polycrystalline copper composite.