Thermal imaging during ballistic testing of armour materials

During the interaction between a projectile and a target material the kinetic energy of the projectile is transferred into elastic and plastic deformation of both the projectile and target materials. Using a rigid penetrator the loss in kinetic energy is fully converted into energy absorbed by the target, both as kinetic and strain energy.
Using optical high speed imaging the kinetic energy (e.g. velocity of fragments, plug and residual projectile) can generally be obtained. However, the strain energy remains invisible using high speed imaging.
By thermal imaging using an IR video camera, the temperature distribution of the target material (on both the strike and rear face) can be obtained. In order to convert the camera recordings into a temperature distribution, the emissivity of the target material in the infra-red range of wave length needs to be known.
For most armour materials the density, thickness and heat capacity are known, while the emissivity can be determined using the IR-camera and the target material at a known temperature. This enables one to calculate the amount of energy in the target that was dissipated by plastic and/or visco-elastic strain. Examples of thermal images will be shown for metallic, polymer and weaves/fabrics. From the temperature distributions the total thermal energy is obtained and compared to the total loss in kinetic energy of the projectiles.
Thermal imaging provides a non-contact, remote measuring technique that can be used to directly see where and how much energy was dissipated by target materials. As the dissipated energy can be quantified, this technique is also of use for direct comparison with energy-based projectile-target interaction models.