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| Titel |
Damage and cracking of synthetic and natural glasses subjected to triaxial deformation |
| VerfasserIn |
Audrey Ougier-Simonin, Jerome Fortin, Yves Guéguen, Alexandre Schubnel, Frédéric Bouyer |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036002
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| Zusammenfassung |
| Glass is an ideal elastic-brittle material. Although cracking in glass has been much
investigated, going back to the pioneer work of Griffith, investigations under confining
pressure have not been done so far. Besides, as glass results of the solidification of
variable fused silicate mix, the impact of thermal cracking in this material cannot be
neglected.
Our study aims at investigating thermo-mechanical cracking effects on elastic wave velocities
and mechanical strength, both under pressure, to document damage evolution on glass. We
performed the experiments on a triaxial cell at room temperature, with and without pore fluid
pressure, on borosilicate glass. The crack evolution has been monitored with: (i) elastic wave
velocity measurements and (ii) acoustic emissions (MiniRichter system). We also
measured the global mechanical behavior of our synthetic glass samples with strain
gages.
The original glass, produced in ideal conditions of slow cooling that prevent from any
crack formation, exhibits a linear and reversible mechanical behavior and isotropic
elastic velocities, as expected. It also presents a high strength as it fails at about 700
MPa of deviatoric stress for a confining pressure of 15 MPa. The damage develops
progressively, with increasing acoustic emission rate, parallel to the deviatoric stress
orientation and probably starts on the rare air bubbles trapped in the amorphous
matrix.
We choose to apply to some original glass samples a reproducible method (thermal treatment
with a thermal shock of ÎT = 100, 200 and 300-C) which creates cracks with a
homogeneous distribution. The impact of the thermal treatment is clearly visible through the
elastic wave velocity measurements as we observe crack closure under hydrostatic conditions
(at about 30 MPa). Anisotropy is also observed for increasing deviatoric stress. For ÎT
higher than 200-C, the glass mechanical behavior becomes non linear and records
an irreversible damage. The total damage observed with the acoustic emissions
in these samples underlines the combination of the thermal and the mechanical
cracks which drive to the sample failure. The preliminary results obtained with
pore fluid pressure show a very small permeability even for a high damage level
(10-21 -¤ Ï -¤ 10-17).
However, the glass amorphous structure makes it very different from any rock structure. In
order to quantify these differences and to compare glass to rock, we managed to find a
micro-crystallized basalt (Seljadur basalt, Iceland) with very low porosity (k -¤ 2%) and close
chemical composition, and studied its behavior in the same experimental conditions.
We show that a micro-crystallized rock remains different from a glass in terms of
mechanical behavior but exhibits dynamical elastic parameters close from the glass ones. |
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