Observations of projectile penetration into a transparent soil

• We used transparent soils to observe projectile penetration into granular material.
• An opaque zone attributed to dilation was observed traveling ahead of the projectile.
• Healing and contraction of the dilation zone is observed at the end of penetration.
• The technique permits observing transient response which is not visible in natural sands.

In this study, a transparent sand surrogate was employed along with high-speed imagery to un-intrusively visualize the penetration of a spherical projectile into the center of a saturated granular target, representing angular sand, at speeds ranging between 60 and 150 m/s. The transparent sand was made by saturating an angular granular fused quartz waste product with a matched refractive index pore fluid made of sucrose. A distinct zone of opacity was observed traveling ahead of the projectile. The opacity zone appears circular during initial penetration and transitions into the shape of an elongated cone in shots with higher initial velocities. Some healing was also observed with time and some increase in transparency was observed. Some of the opacity is attributed to dilatancy of the granular fused quartz during penetration, and healing is attributed to flow of pore fluid into the dilated zone.