poetree

How Glass Breaks: Four Theories

1.
Brittleness
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,
not-glass
flowing together
in the last fraction of a second before
the wineglass shatters under
the bridegroom’s shoe.

2.
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.

3.
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.

4.
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
apart.

__________

Inspired by an article in Research: Penn State, “What Makes Glass Break,” by Walt Mills (online, 2005). Also consulted:
F. Célarié, S. Prades, D. Bonamy, L. Ferrero, E. Bouchaud, C. Guillot, and C. Marlière, “Glass Breaks like Metal, but at the Nanometer Scale.” Physical Review Letters 90, 075504 (2003).
J.-P. Guin and S. M. Wiederhorn, “Fracture of Silicate Glasses: Ductile or Brittle?” Physical Review Letters 92:21, 215502 (2004).
R. K. Kalia, A. Nakano, P. Vashishta, C. L. Rountree, L. Van Brutzel and S. Ogata, “Multiresolution atomistic simulations of dynamic fracture in nanostructured ceramics and glasses.” International Journal of Fracture 121:1-2, 71 (2003).
J. J. Mecholsky, J. K. West, and D. E. Passoja, “Fractal dimension as a characterization of free volume created during fracture in brittle materials.” Philosophical Magazine A, 82:17/18, 3163 (2002).

*

I wrote this poem as a submission for qarrtsiluni back in 2005 (before I became managing editor). Maria Benet and Alison Kent were soliciting submissions for the theme "Science as Poetry." Research Penn State was a nicely written glossy quarterly, designed I guess to remind alumni like me about all the cool research going on at the university, just in case we happened to be in a giving mood or something. I've heard from scientist friends that the mostly non-scientist types who interviewed the scientists and wrote the articles didn't always get the facts straight, so for this piece, though I was under a fairly tight deadline, I did feel I ought to try and work my way through at least one paper each on the competing theories. Did I get the facts exactly right? Well, I don't know. But if I did flub one or two details, hopefully that would be covered by poetic license.

I was pleased that the poem made the issue, citations and all. I harbor ambitions to write more poems like this some day, appreciating scientific theories as the often-beautiful products of the imagination that they are. But even generating a chapbook-length collection of such poems would be a daunting challenge for a guy like me, who slept through math class and sleep-walked through chemistry and physics. So, so far I've tended to stick with the life sciences for longer poem cycles, as you'll see with my next couple of examples.