Particle size distribution and strain rate attenuation in hypervelocity impact and shock recovery experiments |
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Institution: | 1. Helmholtz-Zentrum Potsdam, Deutsches GeoForschungsZentrum (GFZ), Telegrafenberg, D-14473 Potsdam, Germany;2. Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstraße 43, D-10115 Berlin, Germany;3. Humboldt Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany;4. Institut für Geo- und Umweltnaturwissenschaften, Albert-Ludwigs-Universität Freiburg (ALU), Albertstr. 23-B, D-79104 Freiburg, Germany;1. School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA;2. Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, HI 96822, USA;3. The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA;4. Intergraph Corporation, Box 75330, Kapolei, HI 96707, USA |
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Abstract: | Particle size distribution (PSD) is an often used parameter to describe and quantify fragmentation of deformed rock. Our analyses of shock deformed sandstone show that dynamic fragmentation influences the PSD, expressed as fractal dimension (D-value). Image analysis was used to derive fractal dimensions from a hypervelocity impact cratering experiment (2.5 mm steel sphere, 4.8 km/s) and a planar shock recovery experiment (2.5 GPa). The D-values in the cratering experiment decrease from 1.74 at the crater floor to 0.84 at a distance of 7.2 mm to the crater floor. The D-values found in this experiment are closely related to the microstructural features found at distinct distances from the crater floor. The obtained values are in good agreement with the D-values reported for fault zones, impact sites and deformation experiments. The D-value measured in the shock recovery experiment is 2.42. Such high D-values were usually attributed to abrasive processes related to high strain. Since the strain in our experiment is only ~23% we suggest that at highly dynamic deformation very high d-values can be reached at small strain. To quantify this, numerical impact modelling has been used to estimate strain rates for the impact experiment. This is related to the activation of more inherent flaws and fracture bifurcation at very high strain rates ~>102 s?1. |
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Keywords: | Particle size distribution Dynamic fragmentation of sandstone Hypervelocity impact experiment Shock recovery experiment Hydrocode modeling Deformation microstructures |
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