Experimental Study Of The Cracked Shell Phenomenon

DRDC Valcartier is actively working on the assessment of the extent of energetic materials contamination on Canadian DND training ranges. This work is carried out with the objective of creating sustainable training conditions for the Canadian Forces. As part of this effort, research is being undertaken to study, in laboratory conditions, the leaching of explosives from cracked or opened munitions that are found on training ranges. To carry out this research, cracked munitions similar to those found in the field were required. The 81-mm mortar shell was selected as the candidate for the study. It was decided to try to obtain cracked 81-mm mortars using two different practical methods. The first one was the use of demolition explosive (C-4), in sub-critical quantities, in the form of blocks or linear shaped charges applied to the outside of the shell, to simulate the blow-in-place of unexploded ordnances (UXOs) by ammunition technicians. The second one was the detonation of a mortar shell next to another similar round, in order to simulate the attack of a UXO by another incoming round that functions. The experimental set-up for both methods are presented, as well as the results obtained for various conditions. It was shown that it is easy to obtain cracked shells using both methods. This study will demonstrate that the fragments generated by mortar rounds are very efficient at creating cracked shells, more so than the simple sympathetic reaction from the pressure created by an incoming projectile, as first hypothesized. It provides a possible explanation for the explosive contamination of the soil and underlying groundwater table at some training ranges.