Tp. Swiler et al., MOLECULAR-DYNAMICS STUDY OF BRITTLE-FRACTURE IN SILICA GLASS AND CRISTOBALITE, Journal of non-crystalline solids, 182(1-2), 1995, pp. 68-77
A non-equilibrium molecular dynamics simulation approach is used to mo
del the structure of silica glass and cristobalite using a two-body an
d a two-body/three-body potential. A comparison of the total correlati
on function is made between the two simulations and neutron scattering
data. Differences in structure obtained by each simulation method sho
w the influence of a lack of directional bond components in the two-bo
dy potential simulation and the result of strong directional component
s in the three-body potential simulation. The effect of an applied uni
axial strain on the structure of the simulated glass and crystalline p
hases is studied by following the resulting longitudinal stress. Data
analysis shows that the glass exhibits a large strain-rate dependence
in the maximum stress sustained, while the crystal does to a lesser ex
tent or none at all depending on the potential function. The large str
ain rate dependence in the glass is interpreted as arising from a rear
rangement of the free volume structure, whereby, at low strain rates,
strain added uniformly to the structure is allowed to flow from higher
density regions of the glass to lower density regions. This effect le
ads to coalescence of voids eventually causing fracture propagation th
rough the simulated structure. The crystal, having no ability to assim
ilate the applied strain, can only stretch its bonds until fracture.