How Glass Breaks: Four Theories

on the macroscopic scale
can be deceiving. Measured
in microns, the fracture surface
resembles the long-lost, infinitesimal
twin of a rent in metal —
that famously elastic break.
So too, then, with glass:
cavities as narrow as a few nanometers
open ahead of the crack,
flowing together
in the last fraction of a second before
the wineglass shatters under
the bridegroom’s shoe.

Atom separates from
individual atom
in rapid sequence
wherever the amorphous
solid — glass —
encounters stress.
The blind cane of an atomic
force microscope can tap
all along the edge of a crack
& find no sign of deformation,
no pits or pockmarks.
Glass must therefore be
as we’d always thought:
immaculately brittle.

Atoms under pressure slip
& slide across each other;
nothing is simple. Friction
leads to atom-sized cracks
& the cracks widen into
the necessary cavities, yes.
But all along the fracture zone,
the same pressure
responsible for the break
makes the gaps snap shut
immediately thereafter.
Let’s call them nanovoids,
these model wounds,
healing as perfectly as if
they had never been.

Approaching the fracture origin,
the surface of a crack appears
increasingly smooth. But under
an electron microscope, each region
shows the same kinds of features
at a finer & finer scale — a fractal
self-affinity. Beginning at ground
zero, we name these regions
mirror, mist, hackle,
macroscopic crack branching
energy magnified in chaotic order.
Given an opening, given vibration,
atoms in the amorphous silica will
change partners — a choreography
of rings that first contract, then
join together, encircling ever
larger volumes until the last
bonds fail & the atoms
dance irrevocably


Originally appeared in qarrtsiluni.