Hypervelocity crater penetration depth and diameter — a linear function of impact velocity?

Abstract

Historically, the crater penetration depth has been taken to be a power function of velocity with an exponent value of approximately 0.6. Since the shape of the hypervelocity crater was often assumed to be hemispherical, or at least ellipsoidal, it followed that the crater diameter would also be the same function of velocity. A recent re-examination of the crater data by Baker and Persechino [1] led them to suggest that the crater diameter is actually a linear function of the impact velocity. This paper compares both the linear and the power function models of crater diameter for macroparticle steel/aluminum impacts between 2.5 and 5 km/s and for microparticle iron/aluminum impacts between 6.5 and 27 km/s. While the comparison with the data does not, in itself, conclusively favor one model over the other, certain implications of the two models suggest that the linear model is more likely to be the correct one. This paper also shows that a crater shape factor, which varies with velocity, is needed in order to best fit the volume data. An empirical equation for the crater shape factor is presented.