Blast waves from cylindrical charges

Comparisons of explosives are often carried out using TNT equivalency which is based on data for spherical charges, despite the fact that many explosive charges are not spherical in shape, but cylindrical. Previous work has shown that it is possible to predict the over pressure and impulse from the curved surface of cylindrical charges using simple empirical formulae for the case when the length-to-diameter (L/D) ratio is greater or equal to 2/1. In this paper, by examining data for all length-to-diameter ratios, it is shown that it is possible to predict the peak over pressure, P, for any length-to-diameter ratio from the curved side of a bare cylindrical charge of explosive using the equation $P=K_PM(L/D)^{1/3}/R^3$ , where M is the mass of explosive, R the distance from the charge and $ K_P$ is an explosive-dependent constant. Further out where the cylindrical blast wave ‘heals’ into a spherical one, the more complex equation $P=C_1(Z^{\prime \prime })^{-3}+C_2(Z^{\prime \prime })^{-2}+C_3(Z^{\prime \prime })^{-1}$ gives a better fit to experimental data, where $ Z^{\prime \prime } = M^{1/3}(L/D)^{1/9}/D$ and $C_1,\, C_2 $ and $ C_3$ are explosive-dependent constants. The impulse is found to be independent of the L/D ratio.