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CNRS/CEA
Joint Press Release
What if glass, a material
that has been qualified as "fragile" up until now, behaved in
the same way as metals at the mechanical level? Researchers at the "Laboratoire
des Verres" (CNRS Glass Laboratory, Université Montpellier
2, France), in partnership with researchers at the "Service de Physique
et Chimie des Surfaces et Interfaces" (CEA - Saclay), have demonstrated
that the processes involved when glass breaks are actually very similar
to those of metals, but at length scales that are thousands of times smaller.
This research will certainly upset preconceived notions and find applications
in the glass industry as well as in geology.
Glass, despite its many extraordinary properties (optical transparency,
electrical insulation, etc.) has limited industrial applications because
of its fragility. The mechanisms that regulate its mechanical resistance
occur at nearly atomic length scales and are poorly known as a result.
It is common knowledge that vitreous materials break without prior deformation.
This behavior, qualified as "fragile," is assumed to be the
exact opposite of that of metals, capable of undergoing strain over great
lengths before the structure completely breaks (the extreme case is that
of the aluminum pellet that is transformed by cupping into a tube of toothpaste).
Physicists generally classify the mechanical behavior of materials into
two distinct classes, according to their fracture mode: "fragile"
on the one hand, and "ductile" on the other.
This recent discovery made within the framework of a partnership between
two research teams, one from the "Laboratoire des Verres" (CNRS
Glass Laboratory, Université Montpellier 2, France) and the other
from the "Service de Physique et Chimie des Surfaces et Interfaces"
(CEA - Saclay), demonstrates that the processes involved when glass breaks
are actually very similar to those of metals, but at length scales that
are thousands of times smaller: a crack tip occurs in the glass under
specific conditions, according to a three-step process (nucleation, growth
and the coalescence of damaged cavities) that is very similar to the what
occurs with metals, but at nanometer scales (that is, at interatomic or
intermolecular distances).
These results make it possible to understand some analogies that have
been discovered in the last few years between the morphologies of fracture
surfaces of glass, metal and rocks broken by the movement of geological
faults. All these materials have several physical values in common, which
are, however, observed at different length scales: tenths of nanometers
for glass1 , kilometers for rocks and micrometers2 for metals.
This research, in general, and these "scale" laws, in particular,
can be applied to geology as well as to the glass industry. They should
lead us to undertake new research into the propagation of geological faults
in the earth's crust made up of material that has been qualified as "fragile"
up until now.
Moreover, progress in developing glass that is much more resistant to
cracking has now become a reality.
Reference: Physical Review Letters
(P.R.L. 90, 2003, p. 075504): "Glass Breaks like Metal, but at the
Nanometer Scale," F. Célarié, S. Prades, D. Bonamy,
L. Ferrero, E. Bouchaud, C. Guillot, and C. Marlière.
1 - A nanometer is a billionth
of a meter.
2 - A micrometer is a thousandth of a meter.
Researcher contact:
Christian Marlière
Laboratoire des Verres - CNRS
Tel: +33 4 67 14 37 06
E-mail: christian.marliere@ldv.univ-montp2.fr
Elisabeth Bouchaud
Service de Physique et de Chimie des Surfaces et Interfaces – CEA
Tel: +33 1 69 08 26 55
E-mail: bouchaud@drecam.cea.fr
Press contact:
CNRS
Muriel Ilous
Tel: +33 1 44 96 43 09
E-mail: muriel.ilous@cnrs-dir.fr
CEA
Alexandra Bender
Tel: +33 1 55 43 85 50
E-mail: a.bender@cea.fr
Contact – Physical Sciences and Mathematics
Department:
Frédérique Laubenheimer
Tel: +33 1 44 96 42 63
E-mail: frederique.laubenheimer@cnrs-dir.fr
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