Two ballistic test methods combined; residual energy method and digital image correlation (REM/DIC)

In order to determine the ballistic efficiency of armour materials and armour systems several ballistic tests are available. In most tests only a binary test result is obtained; perforated or partially penetrated armour. TNO has used an alternative test method in which the material or armour system to be tested is always overmatched (sample perforated). The kinetic energy of the residual projectile is calculated from its mass and velocity. This kinetic energy is subtracted from the kinetic energy of the projectile before impact to obtain the projectile energy loss created during target perforation. This, so called, Residual Energy Method (REM) can be used on bare armour materials, as well as on complete armour systems and allows to determine changes in ballistic efficiency due to misuse, previous shots, aging, temperature changes, etc.When the target is not (yet) overmatched the response of the target can be determined using a digital image correlation (DIC) technique. For this method a speckle pattern is applied on the rear of the target or on a backing material. Two high-speed video cameras (each with a different angle towards the target) record the speckle pattern during and after projectile impact. These two video recordings are used in a post-processing software package that calculates the axial deflection and strain in the layer that holds the speckle pattern. From the time resolved data the distribution and history of the deflection, strains, velocities and strain-rates can be obtained. DIC data can be used to better understand the projectile-target interaction as well as for the validation of projectile target interaction simulations. By combining these test methods, a useful test result is always obtained as for a perforating shot mainly the REM results are of importance, while for a stopped projectile the DIC results provide the relevant information.