Model for ballistic fragmentation and behind-armor debris

Abstract

The fracture of the target and projectile during normal penetration is described using a model of chaotic disintegration modifying the theory of chaotic disintegration of liquids. The radius of the locally smallest fragment is calculated equating its kinetic energy of deformation with its surface energy of fracture. The probability of lacunae opening in the target and projectile materials increases near the target/projectile interface. The percolation threshold for this probability determines the boundary of the fractured zone. When this fractured zone reaches the rear surface of the target the fragments can leave it. Mass distribution of the fragments was calculated with the help of percolation theory. Then, the shape of the debris cloud and the direction, velocity and range of its propagation are calculated to estimate vulnerability behind the perforated target. The calculations were compared with results of normal impact experiments performed with tungsten sinter alloy rods ( D=20 mm, L/ D=6) against 40 and 70 mm rolled homogeneous armor (RHA) at an impact velocity of 1700 m/s [1,2]. For observation of the bulging, breakup and fragmentation of the bulge as well as debris cloud formation and expansion, flash X-ray and laser stroboscope techniques have been applied. From the X-ray photographs and soft recovery tests the shape of the debris cloud and velocity field of the fragments as well as the fragment number and mass distributions have been determined, respectively. The calculations predict well the experimental data.