Molecular dynamics studies of brittle failure in silica: effect of thermal vibrations

• Published in: Journal of non-crystalline solids 1991-03, Vol.128 (1), p.57-68
• Main Authors: Ochoa, Romulo, Swiler, Thomas P., Simmons, Joseph H.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Fatigue, brittleness, fracture, and cracks; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Physics
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/0022-3093(91)90776-3

The brittle failure of amorphous and crystalline structures of SiO 2 is examined by molecular dynamics (MD) calculations. A number of structure-dependent effects are observed which appear to be associated with the non-crystalline state and relatively insensitive to the exact form of the modeled interatomic potentials. Brittle failure (fracture) is observed as a peak in the resultant stress from strains applied at a variety of strain rates. The maximum stress of the amorphous structures is strongly strain-rate dependent and nearly independent of total strain. An observed 60% decrease in strength at lower strain rates indicates that the dynamic lattice, due to structural rearrangements from thermal vibrations of the atoms, is much weaker than the static lattice (lattice strained within an acoustic vibration period). At very high strain rates, the glass undergoes failure by an extension of interatomic bonds. At lower strain rates, the rearrangements correspond to a rotation of (SiO 4) 4− tetrahedra in order to increase the SiOSi bond angle in the direction of the applied strain. The crystalline lattice stays near equilibrium at all strain rates beyond the initial straining period; therefore, the stress maximum is nearly independent of strain rate and total strain. In the initial straining period, at low strain rates, the cubic phase of the high cristobalite lattice undergoes a change to tetragonal symmetry through a displacive transformation.