Impact Failure of Planetary Materials:

Abstract

The dynamic fragmentation of a fine grained granitoid material has been examined. Target thicknesses ranged from 7 to 40 mm and impact energies from 12 to 2,500 J. Combined particle image velocimetry and image enhancement techniques are introduced and have been used to measure the size and velocity of material ejected laterally from the rear of the target during impact testing. Non-dimensional groups were formed and fitted with coefficients to predict median values of the distribution of mass and kinetic energy among radial distance, R, from the impact centre, ejecta velocities, v, and ejecta lengths, L. The statistics are well correlated with increasing non-dimensional impact energy (positive correlation for radial distance and velocity, and negative correlation for ejecta length). Median values were used to collapse cumulative distributions and non-centred Gaussian fits were used to describe these curves. Approximately 85 % of the total mass and kinetic energy is captured between R/R50 % = 0.3 to 2, v/v50 % = 0.3 to 2, and L/L50 % = 0.2 and 3. This data facilitates a better comparison among a wide range of test conditions, especially when attempting to extrapolate principal features of impacts into brittle materials at higher velocities. The ejecta tracking techniques and methodologies can be used to improve current impact testing experiments and computer modelling validation.