Explosively Formed Projectile Soft-recovery Force Analysis

Abstract

The design of a soft-recovery system is critical to a researcher's ability to analyze hypervelocity projectiles. The researcher may decide to use one method over another based on several criteria, including whether or not non-deformed projectile measurements are required. This report analyzes the forces two different soft-recovery methods impart on the projectiles collected. Method 1 utilized three polyethylene water barrels placed “end-to-end” horizontally, providing 2.6 meters (9 feet) of water to stop the projectile. Method 2 is a modification of the soft-recovery method utilized in “Soft-Recovery of Explosively Formed Penetrators” by Lambert and Pope [1]. This method utilizes a series of several materials with an increasing density gradient, placed end-to-end over 14.3 meters (47 feet) to stop the projectile. Despite the fact that explosively formed projectiles (EFPs) of the same design were fired into each recovery method, the projectiles collected using the two methods differed in shape, size, weight, and the number of pieces collected. Since the EFP designs were identical to begin with, the physical differences are most likely due to the different magnitudes of the forces exerted on the projectile during deceleration. Drag force calculations will be performed for both recovery methods in an attempt to determine the differences in the drag forces exerted on the projectile during its deceleration. The results of the calculations will assist in determining to what extent the physical deformation of the projectile is due to the material selection of each recovery method. The consistency of the shapes and weights of the recovered projectiles will also be briefly addressed to assist the researcher in choosing the most useful recovery method for a given objective.