FOR 887: Experimental Impact Cratering - The MEMIN-Program (Multidisciplinary Experimental and Modeling Impact Research Network)
Zusammenfassung der Projektergebnisse
The DFG research unit FOR 887 is a Multidisciplinary Experimental and Modeling Impact Crater Research Network (MEMIN) that was founded from 2009 till 2018. It has been aimed at investigating impact cratering processes by experimental and modeling approaches. The general objective of MEMIN was to comprehensively quantify impact processes in various solid rock types including sandstone, quartzite, marble, stratified rocks, and high porosity rocks by conducting a strictly controlled experimental campaign on the laboratory scale. A guideline for the experiments was to match natural systems as closely as possible. Main objectives of the MEMIN project included the understanding of the dynamics of impact cratering, impact-induced damaging of rocks and the formation of geophysical anomalies. To improve the dimensional scaling from the laboratory to natural impact craters, the validation of numerical hydrocodes and material models in use for the simulation of impact processes was among the primary goals. More specific aims were related to the understanding of the influence of porosity, pore fluids, and rheological stratification on shock effects, strain localization, cratering efficiency, and the ejection flow field. We wanted to gain insights into the early impact phase and the distribution of projectile matter in the crater floor, its dissemination in the early ejecta, fractionation, and mixing with the target. Ultimately, we wanted to establish an in-depth understanding of processes that occur during rapid loading and unloading, dynamic fragmentation, spallation, and shock metamorphism from the nano- to the decimeter-scale. The concerted approach of the research unit allowed to acquire a unique data set from 51 impact cratering experiments, 26 shock recovery experiments, along with numerous flyer plate tests, split-Hopkinson pressure bar experiments, membrane-driven diamond anvil tests, and laser radiation experiments that elucidated the arisen questions. The dynamics of crater formation could be quantified for various target lithologies and impact conditions. We found that target porosity exponentially reduces crater volumes and cratering efficiency while it increases crater depth relative to non-porous rocks, and also flattens ejecta angles. A higher degree of water saturation of porous targets yields an increase in total ejecta mass, up to 400% higher ejecta velocity, and steeper ejecta cone angles, with respect to dry targets. The experiments provided insights in the energy budget of an impact. Non-destructive geophysical analysis of targets showed that the damage zones beneath craters is wider than indicated by microstructure. The latter showed power law distributions of fragment size with the exponent depending on radial distance and strain rate. It was found that significant inter-element fractionation occurs between projectile and target material in the early cratering stage and that the degree of fractionation is controlled by the lithophile or siderophile character of the respective elements. A new pressure calibration of shock metamorphic features could be established for porous rocks in the low shock regime. The conditions for shatter cone formation could be narrowed down. For the first time stishovite was experimentally produced in low-pressure shock experiments which indicates ultrafast crystallization from silica melt at high-pressure. New Mesoscale numerical models and homogenized macro-scale models could be validated with the experiments. The combined approach of numerical modeling and cratering experiments led to improved scaling-laws and a better understanding of the effects of porosity and strength on crater size scaling.
Projektbezogene Publikationen (Auswahl)
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Experimental impact cratering: A summary of the major results of the MEMIN research unit. Meteoritics and Planetary Science, 53: 1543-1568
Thomas Kenkmann, Alex Deutsch, Klaus Thoma, Matthias Ebert, Michael H. Poelchau, Elmar Buhl, Eva- Regine Carl, Andreas N. Danilewsky, Georg Dresen, Anja Dufresne, Nathanaël Durr, Lars Ehm, Christian Grosse, Max Gulde, Nicole Güldemeister, Lutz Hecht, Stefan Hiermaier, Tobias Hoerth, Christopher Hamann, Astrid Kowitz, Falko Langenhorst, Bernd Lexow, Hanns-Peter Liermann, Robert Luther, Ulrich Mansfeld, Dorothee Moser, Manuel Raith, Wolf Uwe Reimold, Martin Sauer, Frank Schäfer, Ralf Thomas Schmitt, Frank Sommer, Jakob Wilk, Rebecca Winkler, Kai Wünnemann
