Towards a Dynamical Collision Model of Highly Porous Dust Aggregates

In the recent years we have performed various experiments on the collision dynamics of highly porous dust aggregates and although we now have a comprehensive picture of the micromechanics of those aggregates, the macroscopic understanding is still lacking. We are therefore developing a mechanical model to describe dust aggregate collisions with macroscopic parameters like tensile strength, compressive strength and shear strength. For one well defined dust sample material, the tensile and compressive strength were measured in a static experiment and implemented in a Smoothed Particle Hydrodynamics (SPH) code. A laboratory experiment was designed to compare the laboratory results with the results of the SPH simulation. In this experiment, a mm-sized glass bead is dropped into a cm-sized dust aggregate with the previously measured strength parameters. We determine the deceleration of the glass bead by high-speed imaging and the compression of the dust aggregate by x-ray micro-tomography. The measured penetration depth, stopping time and compaction under the glass bead are utilized to calibrate and test the SPH code. We find that the statically measured compressive strength curve is only applicable if we adjust it to the dynamic situation with a "softness" parameter. After determining this parameter, the SPH code is capable of reproducing experimental results, which have not been used for the calibration before.