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| Titel |
Damage and Rupture Dynamics at the Brittle/Ductile Transition: the Case of Gypsum |
| VerfasserIn |
Nicolas Brantut, Alexandre Schubnel, Yves Guéguen |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250055204
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| Zusammenfassung |
| Triaxial tests on gypsum polycrystals samples are performed at confining pressures Pc
ranging from 2 to 95 MPa and temperatures up to 70 degrees C. During the tests, stress,
strain, elastic wave velocities and acoustic emissions are recorded. At Pc -¤ 10 MPa the
macroscopic behaviour is brittle, and above 20 MPa the macroscopic behaviour becomes
ductile. Ductile deformation is cataclastic, as shown by the continuous decrease of elastic
wave velocities interpreted in terms of microcracks accumulation. Surprisingly, ductile
deformation and strain hardening is also accompanied by small stress drops from 0.5 to 6
MPa in amplitude. Microstructural observations of the deformed samples suggest
that each stress drop corresponds to the generation of a single shear band, formed
by microcracks and kinked grains. At room temperature, the stress drops are not
correlated to acoustic emssions (AEs). At 70 degrees C, the stress drops are larger and
systematically associated with a low frequency AE (LFAE). Rupture velocities
can be inferred from the LFAE high frequency content and range from 50 to 200
m/s. The LFAEs amplitude also increases with increasing rupture speed, and is
not correlated with the amplitude of the macroscopic stress drops. LFAEs are thus
attributed to dynamic propagation of shear bands. In Volterra gypsum, the result of the
competition between microcracking and plasticity is counterintuitive: dynamic
instabilities at 70 degrees C may arise from the thermal activation of mineral kinking. |
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