Ballistic Limit Scaling Studies Using Laser-Driven and Conventional Guns

To determine the ballistic limit of a new armor configuration, approximately ten tests are needed where the impact velocity is measured and a fail/pass criterion is defined. When possible, it is very useful to measure the residual velocity as well to build the impact velocity vs. residual velocity curve. The number of tests needed per material makes screening new materials for ballistic applications a costly exercise. If a manufacturer wished to explore tens of materials, the number of ballistic tests could increase very fast to several hundred or thousands of tests. Additionally, material manufacturers, when creating new formulations, only produce small amounts of material and specimens so small that cannot be tested with conventional size bullets.

A new technology, based on launching projectiles with lasers, has been in use to launch both micro-flyers and micro-projectiles. The laser pulse is used to illuminate an ablative material that creates a gas cloud or plasma at high pressures and pushes the projectile at high velocities. With this technique we have been able to drive aluminum flyers (50 mm thick, 2-mm diameter) at velocities up to ~1,000 m/s and 300 mm-diameter steel spheres at velocities up ~400 m/s.

This paper presents a scaling study performed on two aluminums Al6061-T6 and Al7075-T6, , one ductile and one brittle, where experiments have been performed at 1x scale (300 mm projectile), 10x scale (3 mm projectile), and 100x (30 mm projectile). Ballistic tests were performed on all the scales to determine the ballistic limit. The paper and presentation will highlight the experiment set-up for the different scales, slightly touch the scaling theory, and show movies and pictures of failed targets discussing reasons to expect or not expect the scaling.