AIR BLAST CAUSED BY HYPERVELOCITY IMPACT

摘要

An experimental, analytical, and numerical investigation was conducted to measure air pressure at ambient conditions on the target surface near the point of normal impact into semi-infinite rolled homogeneous armor (RHA) of a high-speed, 3/8-inch diameter tungsten carbide sphere launched from a two-stage light gas gun. Numerical simulations of the impact using CTH were also conducted in which the crater lip and ejecta motion were successfully coupled with the surrounding air. Impact speeds varied from 0.9 to 3.8 km/s. In addition to modeling the blast using the CTH code, 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, accompanying modeling, and CTH calculations 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 fee projectile and impinging the target plate; (2) the air accelerated by the radially expanding crater lip; and (3) the air entrained by the ejecta.