Direct observation of impact cratering

Abstract

In this study, using a laser sheet, we observed the formation and collapse processes of transient crater for different targets. Polycarbonate projectiles were impacted vertically into soda-lime glass sphere targets with different material properties. We found that the increase rate in diameter of crater cavity during excavation processes does not follow a simple power-law relation; the increase rate at late stages of excavation processes decreases with increasing time, and depends on target material properties. We also showed that the transient crater collapses owing to gravity, resulting in increase in diameter and decrease in depth. The degree of collapse was also shown to depend on target material properties. In addition, the crater shape (depth-diameter ratio) for final craters showed target material property dependence, while that for transient craters did not. Based on these results, we discuss the effects of target material properties on the scaling relation.