Understanding cone crack formation in cosmic dust aerogel collectors by low-velocity similitude impact test

Abstract

Low-density silica aerogel is an ideal medium for capturing cosmic dust in space, as the perforated tracks provide valuable insights into the characteristics of interplanetary particles. However, the mechanism underlying track formation remains unclear. This study examines the skirt-shaped or cone-in-cone cracks commonly observed in both ground experiments and returned aerogel samples. Similitude impact tests using various techniques are conducted to compare the cone cracks formed at different velocities. Results show that cone cracks typically form at lower impact velocities. Additionally, impact tests with hard spherical projectiles at speeds below 50 m s^-1, conducted using an electromagnetic coilgun, produce multiple tracks with single cone cracks. The impact process is captured in real-time using a high-speed camera, and the formation mechanism is investigated. A theoretical model, based on contact mechanics and energy methods, is developed to quantify the relationship between cone crack morphology and projectile impact parameters. The model accuracy is validated through experimental results. This study reveals the formation of cone cracks in penetration tracks within silica aerogel. The proposed model identifies the energy absorption mechanism during single cone crack formation, potentially improving the understanding of key parameters (initial size, composition, velocity distribution, and astrophysical source) from the perforated tunnels in cosmic dust aerogel collectors.