Role of Ripplocations and Ripplocation Boundaries on the Uniaxial Compression and Bending in Graphite

Graphite is considered to be the best refractory due to its high melting point, chemical inertness, thermal and electrical conductivity, resistance to thermal shock, and lubricity. The mechanical behavior of graphite remains intriguing due to its anisotropic bonding. This talk focuses on the mechanical response of graphite via deformation simulations using molecular dynamics. First, the interatomic potentials to simulate the graphite structure will be gleaned, this is carefully evaluated using the DRIP-REBO potentials. Using these potentials, 60 graphene layers were loaded uniaxially (UA) along the zig-zag configuration, or by double indentation (DI), normal to the basal planes. Following this, the talk discusses how uniaxial compression simulations reveal the nucleation and motion of ripplocations and ripplocation boundaries (RBs). Notably, the simulations demonstrate a novel phenomenon where tensile and compressive strains nest on the RBs during deformation under DI. Next, our results will be discussed where it is seen that in the linear elastic regime, the total energy, primarily reflects straining of the carbon-carbon bonds, with a modulus of 800 GPa. Following linear elasticity, both deformation mechanisms form RBs spontaneously. Consistent with buckling, the energy per atom required to nucleate RBs in the uniaxial compression configuration is nearly twice that of the double indentation case. The total remote strain for buckling is found to be 0.3% in the DI configuration, and 0.5% for the UA case. In the DI case, a local minimum correlated with face-centered stacking of the graphite layers is observed. Following this, loading-unloading will be discussed, where it is found that cycling significantly reduces the energy per atom to nucleate RBs, endowing a memory effect. The deformation indicates that nucleation of RBs is more challenging than their movement. Finally, our findings are corroborated by TEM evidence in the literature showing remarkable resemblance to experiments at extreme strains of 30 %. The resulting atomistic response is novel, in that, tensile and compressive strains nest at the RBs. This talk offers valuable insights into the mechanical properties of graphite, crucial for various applications.