[PPS07-P16] Impact cratering on a silica dust layer with high porosity and the effect of porosity on the crater size scaling law
Keywords:Impact crater, scaling law, porous bodies
In this study, commercial amorphous silica dusts with the average particle size of 0.5mm and the density of 2.2gcm-3 (ρ) were used to prepare the target with the bulk porosity from 50% to 78%, and the target was simply consolidated by the cohesion force of Van Der Waals force with the tensile strength from 100 Pa to 104 Pa. We made impact cratering experiments using this porous target to study the effect of the porosity on the crater morphology including the crater size. Impact experiments were conducted by using a horizontal type two-stage light gas gun set at Kobe University and a glass bead projectile with the diameter of 2mm and the mass of 10 mg (mp) was launched at the impact velocity at 3.60 kms-1. The projectile was impacted on the target surface normally set in a large vacuum chamber less than 20 Pa.
The crater morphology was found to change with the increase of the porosity, that is, the shallow dish type crater was observed on the target with the porosity of 50% having the tensile strength of 104 Pa, and as the porosity increased the impact spherical cavity was formed to grow and expanded below the shallow dish crater. The recovered target was hardened by epoxy resin and cut at the center of the crater to observe the cross section to measure the cavity diameter (D), the depth of the crater (d) and the diameter of the shallow dish crater. The relationship between the distension (a=ρ/ρbulk) and the normalized cavity diameter, πD=(ρbulk D/mp)1/3, was found to follow the empirical equation of πD=3.8a0.7, where rbulk is bulk density of the target, and the relationship between the distension and the normalized depth, πD=( ρbulk d/mp)1/3, was found to follow the empirical equation of πD=3.0a1.0. While the crater diameter of the shallow dish crater found at the entrance of the cavity was recognized to be constant irrespective of the porosity. These empirical equations could be used to incorporate the effect of porosity on the crater size scaling law.