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| Titel |
Propagation of Crack in Glasses under Creep Conditions |
| VerfasserIn |
C. Mallet, J. Fortin, Y. Gueguen, A. Schubnel |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063376
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| Zusammenfassung |
| The context of our study is the observation of the mechanical behaviour of glass used for the
storage of radioactive wastes. This implies to measure the crack propagation characteristics in
glass. Results on the investigation of the micromechanics of creep under triaxial loading
conditions are presented in the framework of this study.
We performed the experiments in a triaxial cell, with pore fluid pressure, on boro-silicate
glass. The chemical composition of the investigated glass is very close to the composition of
waste vitrified packages. The matrix of the original glass (OG) is perfectly amorphous,
without porosity. A few isolated air bubbles are trapped during the glass flow. Cracks are
introduced in the OG through thermal shocks. The evolution of deformation (axial and radial
strain) is measured using strain gages. The elastic P and S wave velocities and the acoustic
emissions (AE) are also recorded.
An experiment in dry conditions was performed (the pore fluid was argon gas) with a
confining pressure fixed at 15 MPa. Stress step tests were performed in order to get creep
data. A similar experiment was performed in water saturated conditions.
Crack-closure is first observed at very low strains. Then elastic deformation is observed
up to a stress level where elastic anisotropy develops. This can be clearly detected from É
Thomsen parameter increase. At last, at a deviatoric stress of 175 MPa (in dry conditions), we
observe dilatancy. This behaviour has never been observed in original glass. Indeed,
the OG behaviour is perfectly elastic and brittle. In addition, the constant stress
tests show that dilatancy develops during a time constant that depends on the stress
level.
It can be inferred that crack propagation takes place during the constant stress steps. This
behaviour is under investigation. We are also quantifying the velocity of the crack
propagation by modelling this phenomenon. Indeed, the crack density can be expressed as a
volumic strain, Év = ÏξÏc. Then, using a model of penny shaped cracks of a radius, "a", we
can express the crack density as: Ïc = N-V a3 (for N cracks in a volume V). Knowing that ξ
is the crack aspect ratio we can estimate Év using in a first approximation that ξ is a constant.
Thus the variation of Év with time can be directly related to crack propagation ȧ. |
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