 |
| Titel |
Crack networks in damaged glass |
| VerfasserIn |
Celine Mallet, Jerome Fortin, Yves Guéguen |
| Konferenz |
EGU General Assembly 2013
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250072926
|
|
|
|
|
|
| Zusammenfassung |
| We investigate how cracks develop and propagate in synthetic glass samples. Cracks are
introduced in glass by a thermal shock of 300oC. Crack network is documented from optical
and electronic microscopy on these samples that have been submitted to a thermal shock
only.
Samples are cylinder of 80 mm length and 40 mm diameter. Sections were cut along the
cylinder axis and perpendicular to it. Using SEM, crack lengths and apertures can be
measured. Optical microscopy allows to get the crack distribution over the entire sample. The
sample average crack length is 3 mm. The average aperture is 6 ± 3μm. There is however a
clear difference between the sample core, where the crack network has approximatively a
transverse isotrope symmetry and the outer ring, where cracks are smaller and more
numerous. By measuring before and after the thermal treatment the radial P and S wave
velocities in room conditions, we can determine the total crack density which is
0.24.
Thermally cracked samples, as described above, were submitted to creep tests.
Constant axial stress and lateral stress were applied. Several experiments were
performed at different stress values. Samples are saturated for 48 hours (to get an
homogeneous pore fluid distribution), the axial stress is increased up to 80% of the sample
strength. Stress step tests were performed in order to get creep data. The evolution
of strain (axial and radial strain) is measured using strain gages, gap sensors (for
the global axial strain) and pore volume change (for the volumetric strain). Creep
data are interpreted as evidence of sub-critical crack growth in the cracked glass
samples.
The above microstructural observations are used, together with a crack propagation
model, to account for the creep behavior. Assuming that (i) the observed volumetric
strain rate is due to crack propagation and (ii) crack aspect ratio is constant we
calculate the creep rate. We obtain some value on the crack propagation during a 24
hours of constant stress test. At each of these test, crack propagate of 0.3 to 0.4
mm. From the initial average crack length of 3 mm, the crack reach the size of 5.8
mm at the end of a complete creep test (with 8 constant stress step of 24 hours). |
|
|
|
|
|
|