Behind-armor Fragments from Tungsten Rods Penetrating Steel

Damage done by penetrating projectiles is mainly determined by the debris projected behind the target. Debris formation is a stochastic process, and characterization of debris requires a statistical approach. We have developed an analysis tool capable of estimating behind- target debris statistics, including a new experimental technique using x-ray tomography. This technique allows one to obtain statistical data for direction, mass, and shape factor for the thousands of particles generated in a typical impact. Data are reported for 15 mm diameter tungsten alloy rods penetrating steel at nominally 1.7 and 2.0 km/s. Among the observations are that the mass distribution is uncorrelated with angular distribution, and the number of fragments increases while the size of fragments decreases with velocity. The hydrocode EPIC with its mesh-to-particle algorithm was used to calculate debris fields, with the parameters that control fragment size being calibrated from the statistical data on recovered fragments. Good agreement was obtained, provided the normal fragmentation algorithm was suppressed. This allows predictions of relative damage as velocity is changed.