Impact of spherical projectiles into a viscoplastic fluid

Abstract

We study the behavior of a yield-stress fluid following the impact of a vertically falling sphere. Since the impact produces shear stresses larger than the yield stress, the material in the vicinity of the impact becomes fluidized. The sphere entrains air when it enters the fluid, and the resulting cavity pinches off below the surface. The upper part of this cavity then rebounds upward. For sufficiently fast impacts, a vertical jet is produced by the cavity collapse. While many aspects of this process are similar to that in Newtonian fluids or granular materials, the rheological properties of our target material change the scaling of the cavity pinch-off depth and have a dramatic effect on the height of the jets. The material returns to a solid-like behavior once the stresses due to the impact have relaxed to below the yield stress, leaving a crater in the surface of the material. We find that the diameter of this crater depends nonmonotonically on the impact speed. The crater shape also changes with speed, reflecting the dynamics of the impact process.

Fingering induced by a solid sphere impact to viscous fluid

“…Particularly, a liquid droplet impact either onto a liquid pool or a hard floor has been studied well so far [2]. A solid sphere impact to a non-Newtonian target fluid has been also investigated experimentally [5,6]. Furthermore, some recent studies have concerned granular target impacts as well as fluid target impacts.…”

Viscoelastic characterization of low-velocity impact of a solid ball on an agar gel

“…We suppose that the current experiment is still in the low-R e regime. In the viscoplastic impact experiment, 17 crater diameter and cavity pinch-off depth showed almost constant values in the low-R e regime, i.e., R e < 10. This implies that the low-R e regime lasts until R e ' 10.…”

“…Cheny and Walters have found that jet formation is very sensitive to the viscoelasticity of the target fluid. 15 Crater morphology, penetration, and rebound properties have been discussed for viscoelastic 16 and viscoplastic 17 fluids.…”

“…In spite of the recent progress of soft impact studies, [2][3][4][5]16,17 impact between a solid impactor and a viscoelastic soft target has not been studied well so far. Moreover, direct drag force measurement has not been performed for the impact of soft matter.…”

Physics of Soft Impact and Cratering

“…(3.7)) was also used as a target of the solid sphere's impact experiment [122]. (3.7)) was also used as a target of the solid sphere's impact experiment [122].…”