More precise, efficient ballistic testing methodology developed

Southwest Research Institute (SwRI) has expanded the scope of a ballistic-resistance testing technique, the Laser-Induced Particle Impact Test (LIPIT), previously only applicable for impact testing of very small projectiles. By improving this technique, SwRI has dramatically increased the precision and efficiency of material ballistic resistance testing at scales not possible before.

“Essentially, we’ve bridged the gap between LIPIT and conventional ballistics testing,” said Dr. Daniel Portillo of SwRI’s Engineering Dynamics Department, who co-authored a study detailing these results with SwRI’s Dr. F. Michael Heim and Dr. Sidney Chocron. “The efficient new technique allows researchers to launch larger projectiles than previous LIPIT processes at a higher rate. Normally, we’d do 30 to 40 ballistics tests a day. We now have an automated process that can do 200 tests in an hour.”

Ballistic resistance testing determines a material’s response to high-speed impacts. It is often used to evaluate protective materials, such as armor for soldiers and military vehicles or spacecraft shielding. These tests determine a material’s ballistic protection performance based on the impact speed that gives a projectile a 50% chance of penetrating the test material.

The traditional LIPIT process uses a high-powered laser to launch microscopic stainless-steel spheres at target materials to evaluate their ballistic limits. It uses the same basic principles as a gun, which ignites gunpowder to create hot gas to propel a bullet through its barrel.

LIPIT uses a laser to heat gas to propel projectiles. The precision of the laser allows the researchers to automate several aspects of the process, but it requires small projectiles and test articles for accurate results. In some cases, target materials can be scaled down, but many cannot be made thin enough to match the size of the projectiles, which are about 0.1 millimeters or the width of a strand of hair, for standard LIPIT evaluations.

To remedy this and make LIPIT results more applicable to full-scale ballistics testing, SwRI engineered a LIPIT system to launch larger projectiles of 0.3 millimeters, or the size of a grain of salt. The process has also been automated and, as a result, hundreds of tests can be performed in an hour.

To accomplish this, the researchers improved the laser pulse energy, material and chamber design to optimize how the heated gas accelerates the projectiles.

“Using larger projectiles allows us to create scaled-down targets with meaningful thickness and material properties,” Portillo said. “We can use scaled targets that behave in realistic ways under impact, without pushing the limits of material fabrication to an impractical degree.”

SwRI now offers a wider range of LIPIT ballistic evaluations to clients and plans to continue expanding the method and to explore new applications.

The paper “High-Throughput Ballistic Limit Testing Using Laser-Induced Particle Impact Tests” is available in the Proceedings of the 34th International Symposium on Ballistics.