With the high rates at which plastic deformations occur in ballistic impacts, failure by adiabatic shear localizations often plays prominent role effecting the performance of both the attacking projectile and the defending armor materials.
Adiabatic shear failure has traditionally been viewed as a negative material behavior. In armor plates, the adiabatic shear bands provide a lower energy failure path to the rear surface and lead to an early “plugging” failure of the plate. However, absent a rear free surface on the armor plate, shear bands appear to have a negligible effect. The adiabatic shear bands do not lower penetration resistance of a thick armor plate by making it easier for the projectile to push aside the armor in its path.
By contrast, adiabatic shear failures have proven to be helpful to the high-density penetrator materials of high-velocity projectiles. Large, back-extruded heads form on most penetrator core materials as the projectile burrows through armor. With the large, hydrostatic pressures surrounding the back-extruding material, this deformation is difficult to interrupt via normal fracture failures. However, adiabatic shear localizations do operate in this environment. Penetrator materials susceptible to adiabatic shear (such as many depleted uranium alloys) interrupt the formation of large, mushroomed heads on the eroding projectiles, reducing the diameter of the penetration cavity burrowed into the armor. Since less of the projectile’s kinetic energy is expended to laterally displace the armor material, it efficiently produces a narrower but deeper penetration cavity.