Scaling of sub-surface deformation in hypervelocity impact experiments on porous sandstone

Abstract

Two hypervelocity impact experiments into dry sandstone (Seeberger Sandstein, ~23% porosity), performed under similar impact conditions but with different projectile sizes, have been analyzed to investigate the size scaling of impact damage. For one experiment a 2.5mm steel projectile was impacted at 4.8kms−1 onto a sandstone cube of 20cm side length. For the other experiment a 10mm iron meteorite projectile was impacted at 4.6kms−1 onto a sandstone cube of 50cm side length. The resulting kinetic impact energies of 773 and 42,627J led to crater cavities of 7600 and 612,000mm3. Investigation of thin sections along cross-sections through both craters revealed that the same deformation microstructures are present in both experiments. The occurrence of different microstructural patterns was mapped and zones of characteristic deformation were defined. This mapping was used to calculate the volumes of material deformed by specific mechanisms. Comparing the results, normalized to the size of the projectile, showed that the sub-surface damage is very similar in size, volume and geometry for both experiments. Analysis of deformation bands found in both experiments regarding their long axes orientation showed that these features are developed under shear deformation. Particle size distributions (PSD), expressed as power-law fits, were measured to quantify the impact damage. Comparison showed that the decay of the power-law exponents with increasing distance from the impact point source is similar for both experiments. Reconstruction of the loading path allowed to infer the stresses under which distinct deformation microstructures are developed.