Blast phenomena associated with high-speed impact

An experimental, analytical, and numerical investigation was conducted in order to measure air pressure at the target surface near the point of normal impact into semi-infinite rolled homogeneous armor (RHA) of a high-speed, 10 mm diameter tungsten carbide sphere. Impact speeds varied from 0.9 to 3.8 km/s. Numerical simulations of the impact were conducted in which the crater lip and ejecta motion were successfully coupled with the surrounding air. An analytical model of the air blast field resulting from the impact has been developed employing the blast generated by a small explosive charge initiated at the time and point of impact. This is a one-dimensional solution in which all characteristics of the blast field are a function only of the radius from the charge center and the energy released by the charge. Thus, a single empirically derived parameter—the equivalent explosive charge energy—completely defines the blast field. For each test, this parameter was obtained from a least squares fit to the peak pressures measured as a function of distance from the impact (explosion) center. The model predicts the data well at all test speeds. The tests, analytical modeling, and numerical simulations resulted in the following conclusions: The air blast field contains about 0.7% of the kinetic energy of the impacting projectile and results from three sources: (1) the air entrained by the projectile which impinges upon the target plate; (2) the air accelerated by the radially expanding crater lip; and (3) the air entrained by the impact induced ejecta.