Influence of secondary dust on the internal detonation effects of a cased charge

M. Romann, G. Seisson, A. Dufourmentel, Y. Barbarin, M. Lavayssiere, N. Stephanopoli, A. Rouquand

Since the works of Fano (1944) and Fisher (1953), the attenuating effect on pressure and impulse of the metallic casing of an explosive charge is a well-known phenomenon. It is mainly attributed to the kinetic energy transferred from the high explosive to the casing but attempts have been made to quantify the contribution of secondary mechanisms to this phenomenon such as the yield stress of the metal (e.g. Hutchinson, 2014). More recently, authors (Baum et al., 2018 and Ohrt, 2019) have suggested an additional attenuating effect in the case of the detonation of cased charges inside closed or vented rooms. The metallic debris produced by the fragmentation of the envelop strike the walls generating secondary debris and dust. The later consume energy (kinetic and thermal) from the detonation products that implies the decrease of the apparent pressure and impulse. For the first time, the present work experimentally verifies this phenomenon thanks to cylindrical bare and cased charges detonating at the center of a vented small-scale concrete building. Internal pressure and impulse are measured by pressure sensors and deduced by the mobile roof movement recorded by high-speed videos. It appears that the impulse decrease endorsed by the secondary dust is highly significant since it is of the same order of magnitude that the one attributed to the Fano’s effect. These results pave the way for a better insight into internal detonation effects, particularly for safety studies on munition storage.

Keywords: cased charge, internal detonation, dust, impulse, quasi-static pressure, small-scale experimentation.