Nanoscale fracture of tetrahedral amorphous carbon by molecular dynamics: Flaw size insensitivity

The fracture of tetrahedral amorphous carbon at the nanoscale was investigated with molecular dynamics simulations using the environment-dependent interatomic potential. It was found that the fracture strength of amorphous carbon nanospecimens is insensitive to initial cracks with diameters smaller than about 40 Å, i.e., the material exhibits flaw tolerance at the nanoscale. It was also found that amorphous carbon nanospecimens fracture very differently from diamond; (i) failure is gradual instead of catastrophic and (ii) it is accompanied with voidlike defect growth and coalescence. This fracture behavior appears to result from the structural disorder of amorphous carbon. In order to further explore the effect of crack size in materials with structural disorder, larger two-dimensional random network models were studied and found to also exhibit void growth during fracture and flaw tolerance.