Role of ultrafine microstructures in dynamic fracture in nanophase silicon nitride

Using 106-atom molecular-dynamics simulations, we investigate dynamic fracture in nanophase Si3N4. The simulations reveal that intercluster regions are amorphous, and they deflect cracks and give rise to local crack branching. As a result, the nanophase system is able to sustain an order-of-magnitude larger external strain than crystalline Si3N4. We also determine the morphology of fracture surfaces: For in-plane fracture surface profiles the roughness exponent ζ = 0.57 and for out-of-plane profiles the exponents ζ⊥ = 0.84 and ζ|| = 0.75 are in excellent agreement with experiments. © 1997 The American Physical Society.