ABSTRACT
Terminal ballistics is the regime that the projectile enters at the conclusion of its flight. It has been delivered into its flight by the interior ballistician, pursued and guided through its flight by the exterior ballistician, and now at its target becomes the responsibility of the terminal ballistician. The basic objective of firing the projectile is to defeat some type of target and we will study the widely varying phenomena of terminal effects that are the tools of the terminal ballistician. These end effects are dependent on the design and mission of the projectile. The most common of the missions are as follows: fragmentation of the projectile body by its cargo of high explosives; penetration or perforation of the target by the application of kinetic or chemical energy; blast at the target area delivered by the chemical energy of the explosive cargo; and the dispersal of the cargo for lethal or other missions, e.g., smoke, illumination, propaganda dispersal, etc. Since most terminal ballistic phenomena involve the generation and effects of stress
waves in solids, we will spend some time examining the details of this field. We must gain some knowledge of terminal ballistic terminology to be able to study the theories of kinetic energy penetration of solid targets; detonation, deflagration, and burning of energetic materials; the fundamentals of shaped charges; fragmentation theories; blast effects; and lethality with the study of wound ballistics. We shall begin by introducing some concepts that we shall use throughout our study of
this field. In examination of penetration theories, we need to consider the following items: What
constitutes defeat of the target? What is the source of the data for which we have to create a theory? Does the theory track with respect to momentum balance or energy balance? How many empirically derived constants are there in the model (this tells us how universal the theory will be)? What simplifications and assumptions were made? Penetration is defined as an event during which a projectile creates a discontinuity in the
original surface of the target. Perforation requires that, after projectile or its remnants are removed, light may be seen through the target. Since penetration is a somewhat stochastic event, we need to define some statistical parameters. V10 is the velocity at which a given projectile will defeat a given target 10% of the time. V50 is the velocity at which a given projectile will defeat a given target 50% of the time, and V90 is the velocity at which a given projectile will defeat a given target 90% of the time. These quantities are depicted in Figure 14.1. The 50% penetration velocity is commonly used as both experimental measurement as
well as a production check. The following procedure illustrates its usage in an experiment. The reader should refer to Figure 14.2 to illustrate the meaning. First, we should estimate V50 through a calculation. Once this is accomplished, we fire a projectile with a Vs as close to V50 as we can achieve. Let us say, the velocity of this experimental firing is a bit over our estimate (at 1 in Figure 14.2). Assuming shot 1 only partially penetrated, we increase the velocity considerably, and let us say that we achieve complete penetration at 2 in the
figure. We now assume that V50 is midway between 1 and 2. We now would attempt to fire at the velocity halfway between 1 and 2 (at 3) and, say, we get complete penetration. We would next lower the velocity to get a partial penetration, say at 4, then we would increase it to get a complete penetration (but let us say, we get only a partial penetration at 5). We would then have to increase the next shot velocity to 6. We would continue the above procedure, commonly known as an up and down test,
until we obtained three complete penetrations and three partial penetrations with the difference between the highest and the lowest velocities in the set less than 200 ft=s. At that point, we would calculate the experimental V50 from
V50 ¼ P6 i¼1
Vi
6 (14:1)
The limit velocity, Vi (sometimes called the ballistic limit when referring to the armor), is the velocity below which a given projectile will not defeat a given target. The technique for determining it was invented by the U.S. Army Ballistics Research Laboratory (BRL), Aberdeen, Maryland. The object is to fire a few projectiles that achieve complete penetration, measuring the residual velocity through the use of flash x-rays, and then generate a curve as shown in Figure 14.3. Now we plot the residual velocity after penetration versus the striking velocity. Usually, there will be a lower limit that develops below which the armor is not penetrated or the projectile gets stuck in the armor.
