Author(s)

SOPHIE TRÉLAT, MICHEL-OLIVIER STURTZER

Abstract

Law enforcement agencies commonly use combinations of explosive charges and water containers. Commercial companies already propose off-the-shelf products based on water-tamped explosive devices using the principle of impulse profile modification. The objective of this concept is to characterize the efficiency of bare explosive charges while minimizing surrounding blast effects in order to mitigate collateral damage, as a significant part of the energy of the explosion is transferred to the water in the form of kinetic energy. Based on existing and already-in-use geometries and volumes, we designed reference explosive charges comprising C4 parallelepipedal charges and water containers. In this study, the loading of the system was evaluated using a ballistic pendulum able to record the total mechanical load transferred. By recording the trajectory of the pendulum, it is possible to determine the transferred impulse. Influence of the ratio between explosive and water was investigated to analyse the system breaching efficiency and potential collateral damages. Collateral damage includes not only water ram effect, but also air blast effects. A side-on pressure sensor was consequently installed near to the pendulum to evaluate the influence of the water on peak overpressure propagating in the breach environment. Initial propagation of the blast wave occurs in aqueous medium. Comparison with highspeed images recorded during previous underwater detonation tests conducted close to water surface or reflective surfaces was thus possible. This analysis provided guidelines for future work on the optimization of water-based contact charges.

Keywords

blast, explosion effects, combined effects, water-based experiments, protection of infrastructures, pressure sensors, high-speed videos