EXPERIMENTAL AND NUMERICAL INVESTIGATIONS ON FLIGHT TRAJECTORY OF BLAST-DRIVEN BALL BEARING EMBEDDED IN REAR DETONATED SPHERICAL EXPLOSIVE USING THE BACKGROUND ORIENTED SCHLIEREN TECHNIQUE

In today’s society, the threat of terrorism is ever present. The number of terrorist attacks have increased during these last years, targeting civilians in many places but especially in high density public areas like airports, concert arenas, security check-points and public transport stations. These attacks are causing damage to both persons and infrastructures. Nail bombs, containing nails, screws, bolts and steel ball bearings SBB are very destructive. The main purpose in the present work is the establishment of reliable experimental set-ups and numerical Finite Element models with the aim to investigate the flight trajectory of SBB attached to a spherical explosive and detonated either in Free Air Blast or at the entrance of an Explosive driven shock tube using the Background Oriented Schlieren visualization technique and a projectile tracking software. The experimental work demonstrated that SBBs maintain a horizontal-like inflight trajectory in free air and were barely influenced by the multiple reflections of blast waves inside the tube. It also revealed that the dispersion of impacts into the target is governed by many parameters such as charge masses, projectile diameters, projectile velocities and loading conditions. On one hand, the BOS visualization technique was able to successfully capture the main characteristics of the flying projectiles flow fields. On the other hand, Finite Elements (FE) simulations using the commercial software LS-DYNA were able to reproduce the experimental data reasonably well.