[PPS03-P06] Experimental study of low velocity impact onto granular media under reduced gravities:Effects of the regolith layer strength
Keywords:Crater formation expertiments, Microgravity, Regolith layer strength
We developed a mechanism which can simulate gravities smaller than 1 G: a target container was suspended by springs of constant force. We conducted impact experiments under a gravity range of 0.01 -1 G. We used silica sand grain of average diameter 140 μm as the target material, and used stainless steel spheres and glass spheres as the projectiles. Stainless steel sphere is 7.9 g cm-3 in density and glass sphere is 2.5 g cm-3 in density and diameter of the projectiles was 8 mm. The impact velocity was between 1 and 5 ms-1. As a result, the crater diameter formed under the gravity range between 0.01-1 G was proportional to about -0.2 power of the gravitational acceleration (Kiuchi and Nakamura, 2015 JPGU meeting). This gravitational dependence is roughly in agreement with the previous studies at hypervelocity (Schmidt and Housen,1987; Gault and Wedekind,1977).
Next, we used alumina particles of average diameter 60 μm as the target material with larger cohesion force than the silica sand grain. Alumina particles were filled in the target container and compressed to a porosity of 0.42 which was approximately equivalent to the porosity of the silica sand target. We measured the penetration resistance of target materials using a stainless steel cylinder of 10 mm in diameter and found that the strength of the alumina target is about five times larger than the silica sand target. We conducted impact experiments under similar conditions to the previous experiments of the silica sand target. As a result, the crater diameter formed under 0.1 G was not different from the one formed under 1 G. Since the gravitational dependence was not observed, the effect of the strength seems to exceed the effect of gravity. Furthermore, we will conduct additional impact experiments onto the target materials with intermediate strength between the silica sand target and the alumina target. Based on the results, we will discuss the boundary conditions between the gravity regime and the strength regime quantitatively.