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Project IX

Numerical modeling of impact cratering processes

continuation of TP-5

Project directors:

Kai Wünnemann, Berlin (MfN)
Martin Sauer, Freiburg (EMI)

Research staff:

Nathanael Durr (PhD student, EMI Freiburg)
Nicole Güldemeister (PhD student, EMI Freiburg)

Summary

For a comprehensive understanding of impact processes in nature numerical modelling is a powerful tool complimentary to small-scale laboratory experiments. Although so-called hydrocodes have grown in sophistication over the last 30 years, further developments are crucial to contribute to a better quantitative understanding of processes observed during hypervelocity impact experiments, to explain detailed observations at natural impact craters, and to simulate the formation of the complex variety of natural crater morphologies. Key to modelling of hypervelocity impact processes is an adequate description of the material’s response to high shock pressure, subsequent release, and mechanical deformation at high strain rate, known as the material model.
The development of material models accurate and sophisticated enough to represent the complexity of geologic materials remains the major challenge for numerical modelling of natural impacts.
During the first phase of the MEMIN project we focused on meso-scale modelling to study the material behaviour of porous wet and dry sandstone during shock wave compression. We developed a macroscopic description of the decrease and increase of pore space as a result of shock compressing and shear/tensile bulking, and we proposed an EoS to parameterize the bulk thermodynamic behaviour of porous dry and (partly) water-saturated rocks that is based on ANEOS. The new material models were compared against and calibrated by observations at the MEMIN cratering experiments. In addition, models have been used to provide quantitative data to support other projects of the network (interpretation of shock deformation features at low shock pressure and cratering experiments - P2, P7; ultrasound imaging of target damage – P3; scaling of crater dimensions – P6; thermodynamic conditions at projectile-target contact – P8; setup of cratering experiments – P1). In the follow-up project we remedy specific weaknesses we identified in the material models and include new processes in our models that have been recognized to be more important than initially expected (e.g. impact flash and ejecta plume, spallation of near surface material). The project will focus on (1) the extension and generalization of the newly developed material models; (2) we will include the generation and expansion of the ejecta plume in the simulations; (3) we will upscale the results from the laboratory scale to natural impact events including processes that cannot be simulated in the laboratory. Such a process is the formation of the complex morphology of natural crater structures that is related to some temporary strength degradation mechanism of the target rocks. In particular the last point addresses the important link between observations at the laboratory scale and natural crater dimensions. All objectives are complementary to laboratory experiments and natural craters and, therefore, modelling is key for the interlinking among the MEMIN projects.