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Project I

Investigation of the transient early-stage physical processes of hypervelocity impacts into solid target rocks.

continuation of TP-1 

Project directors:

Klaus Thoma, Frank Schäfer
Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut (EMI)

Research staff:

Tobias Hoerth (PhD student, EMI)
Christoph Michalski (PhD student, EMI)

 

Summary

In the second application period of the multidisciplinary research project MEMIN, project 1 focusses on the investigation of the physical processes during the transient early stages of hypervelocity penetration at perpendicular and oblique impacts into sandstone (SiO2) and limestone (CaCO3). Early stages denote the initial few microseconds after projectile-target contact in the laboratory tests. More specifically, the following will be investigated:

• the physical state of the material jetted at shallow angles to the target surface (“jetting phenomenon”)
• the thermodynamic properties of the impact plasma and
• the particle size and velocity distribution in the early ejecta cloud

To enable this fundamental geological research, the existing world-class light gas gun acceleration technology available at EMI will further be improved e. g., by application of novel methods in sabot design, enhanced methods for velocity measuring during projectile acceleration and improved high-speed imaging methods. For the investigation of the physical processes during early stages of penetration, novel diagnostics will be developed and applied, such as

• time-resolved optical spectroscopy for recording the light emission from the impact plasma to gain insight into the physical processes occurring close to the interface between projectile and target, and
• particle imaging visualization (PIV) techniques using laser-sheet technology for the investigation of particle size and velocity distribution in the ejecta cloud.

The proposed work for the second application period of the MEMIN research unit complements the work performed in the first application period of MEMIN, where the main interest was the improvement of our understanding of the transient impact processes, such as the scale-dependent early crater formation and ejection processes, in dry and wet sandstone at perpendicular impact angles (e. g. Hoerth et al. 2012).
A core task of project 1 is the conduction of a series of precisely defined and highly instrumented hypervelocity impact experiments at EMI’s light gas guns. These experiments will be well-coordinated within the research unit to reflect the requirements with regards to measurement techniques of each sub-project. These tests are yielding the required experimental data base for the other subprojects. The impact experiments will be conducted at EMI’s Space Light Gas Gun (SLGG) facility and the X-Large Light Gas Gun (XLLGG) facility. Since thermodynamic processes are investigated, and vaporization and ionization play a key role in the understanding of the underlying physics, the majority of the hypervelocity impact tests will be performed at the SLGG facility where ultra-high vacuum pressures of down to 10-5 mbar have been reached recently (this is a unique performance for light gas gun facilities). At such low pressure, any influence of the residual gas on the plasma cloud and its optical emission spectra almost can be ruled out. It is specifically this combination of extremely high impact velocities, high-resolution ultra-fast spectroscopy, laser-sheet technique and the possibility to perform the tests under high vacuum conditions that is providing us with a unique opportunity for novel geoscience research in this project.