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| Titel |
Particle Size Distrbution in an Experimental Hypervelocity Impact on Dry Sandstone. |
| VerfasserIn |
Elmar Buhl, Michael H. Poelchau, Alex Deutsch, Thomas Kenkmann, Georg Dresen |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250082032
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| Zusammenfassung |
| The particle size distribution (PSD) is a frequently used parameter to describe the
deformation-induced fragmentation of fault rocks. It has been shown that resulting particle
sizes may be described by a power law (fractal) size distribution:
N(d) ~ dD
where N(d) is the number of particles larger than diameter d, and Dis the D-value. PSDs
reported for impact deformation are still very few. D-values for natural and experimental
impacts have been reported to range between 1.2-1.8 and 1.4-1.7, respectively. Here we
show the systematic distribution of the PSD in the subsurface of an experimental
impact crater. The investigated experiment was performed in the framework of the
MEMIN project [1]. A 20 cm cube of quartz-rich sandstone (Seeberger Sandstein) was
impacted by a 2.5 mm steel sphere at 4.8 km/s, producing a crater of 5.76 cm diameter
and 11.0 mm depth [2]. For sample preparation the crater was impregnated with
epoxy and the block was bisected. Thin sections were prepared from the crater
sub-surface. Backscattered electron (BSE) micro-analysis was conducted by means of a
Zeiss Leo 1525 Scanning Electron Microscope. A succession of 20 images (400x
magnification) with increasing distance from the crater floor was analyzed. The image
analysis software JMicrovision was used for automated object extraction. Area and
perimeter of all detected particles were exported and used for PSD analysis. The
obtained PSD were fit with a linear function in a log-log plot over at least one order of
magnitude in diameter indicating that the PSD follows a power law relationship N(d) ~
dD.
The distinct modes of deformation in the crater sub-surface [3] are closely linked to the
fracture pattern and thus with the D-value. As expected, comminution was most
effective closest to the crater floor. The highest D-value of 1.74 was found at a
depth of 0.26-1.07 mm beneath the crater floor. Thus the largest fraction of fine
material is situated in there. With growing distance the D-values drop steadily to
~0.84.
We suggest that the D-value is a good parameter to describe impact induced
fragmentation. Our results for the first time show a spatial resolution of D-values for an
impact event. Comparison with the reported data from natural and experimental impacts
shows that our results cover almost all of the reported values but show systematic changes
with distance from the crater floor. A detailed and spatially resolved analysis of
the D-values of the ejected material from this experiment is planned. This will
improve our understanding of ejecta emplacement and size distribution of space
debris.
[1] Kenkmann T. et al. (2011) M&PS, 46, 890-902 [2] Poelchau M. H. et al. (2013)
M&PS, (48), in press [3] Buhl E. et al. (2013) M&PS, (48), in press. |
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