Replacing the equations of Fano and Fisher for cased charge blast equivalence

摘要

The initial velocity of casing fragments from bombs, shells etc. was first calculated by R. W. Gurney in 1943. This derivation was based on a reasonable simplification of the casing and gas dynamics. Subsequently, Gurney's wartime co-worker, if. Fano, issued a further report on the blast equivalence of cased explosive charges, i.e. the blast impulse they deliver as a fraction of the impulse from the same charge uncased. Fano claimed to have calculated the proportion of kinetic energy remaining with the explosive gases following energy partition with the casing. This paper will show that Fano's equation for cased charge blast equivalence is inconsistent with Gurney's reasonable physical model, as is a further equation by Fisher. Attention will be drawn to a new equation which gives similar predictions to that of Fisher, while being consistent with Gurney's original derivation. Also, based on CONWEP data, it can be established for the first time that the use of such equations for cased charge blast equivalence is valid. Furthermore, by combining Gurney's kinetic energy equation with G.I. Taylor's equation for case fracture strain, a casing-gas energy balance at fracture can be obtained. A comparison with historic AWE cased charge blast impulse data shows reasonable agreement, but further experimental data are required.