Impact velocity dependence of transient cratering growth

The present paper describes observations of crater growth for various impact velocities up to approximate to 6kms(-1). Spherical polycarbonate projectiles (4.76mm) were impacted vertically into dry sand targets at impact velocities v(i) ranging from 0.7 to approximate to 6kms(-1), and the temporal change (diameter growth) in diameter of crater cavities was measured by a high-speed profilometer with 2000frames per second. Our data show that the diameter growth follows a power law relation at the early stages, but the data at the later stages deviate from the power law relation. It is also shown that the power law exponent at the early stages decreases with increasing v(i), indicating a possibility that the growth rate of the transient crater cavity decreases with increasing v(i). On the other hand, the power law relation for final crater sizes in our data is consistent with the classical scaling relation for final crater sizes, which is thought to be independent of v(i). Thus, our data may suggest that there is a difference in the power law behavior between the crater growth and the final crater sizes.