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Atomic Force Microscopy experiments and MD (Molecular Dynamics)
simulations have revealed a process zone (PZ) near the crack tip in amorphous
silica (a-SiO2). Within this PZ pores nucleate and coalesce with one another up
to 20 nm ahead of the crack tip. After which the cavities merge with the
advancing crack to cause mechanical failure. Similarly, when a-SiO2 sample is
nanoindented one finds permanent damage under the indenter in the form of
densified silica.
To shed light on the origin of irreversible deformation in amorphous media,
where the notion of dislocations is irrelevant, MD simulations have been
performed in a-SiO2 systems which are subjected to (1) a cyclic loading and
unloading of the hydrostatic pressure and (2) a shearing force at room
temperature. In particular, the so-called fabric tensor commonly used in granular
physics is computed and allows to evidence anisotropy setting in the structure
silica.