Surface roughness of alumina fragments caused by hypervelocity impact

Hypervelocity impact experiments are carried out with alumina ceramic targets at impact velocities of 2–4 km/s. The fractal dimension (or roughness exponent) of fragment surfaces is estimated by two different methods (different length scales). One is a divider method (large scale) and the other is a gas-absorption one (small scale). The obtained fractal dimensions are different: ∼2.2–2.4 for larger scale and ∼2.5–2.7 for smaller scale. These values are regardless of the degree of fragmentation.