The material response of PPE against Dual Impacts

Police and Armed Forces have reported Personal Protective Equipment failure against fast fired subsequent multiple shots within close proximity. This technique is well known as the double tap. Double tap is being used by the military because of its increased effectiveness in neutralizing an opponent. Currently, the ballistic performance of PPE is only tested under the condition of a threat of a singular impact. The interactions of multiple impacts have been considered negligible regardless of the application. In this article, the double tap technique is analysed thoroughly and its main characteristics are examined. 7 fragmentation vests from the Belgian Armed Forces were tested under dual impacts with the 9mm bullets. In total 26 double shots within a broad spectrum of time intervals were fired, with 8 of them being considered as infinite time between the shots. The distances between the impacts ranged from 44 to 78mm and the projectile velocities were measured with the use of a high speed camera.
The tests have shown that the first shots never result in perforation. The second shots, with decreasing time intervals, the probability of perforation is increasing up to 50%. Double shots within a few milliseconds exhibited intense penciling. In order to better understand the results a concept of proximity was created as a function of time and space intervals. The diagrams of terminal ballistics opposed to impacting velocities and proximity are submitted and discussed.