This section describes the testing and analysis of complete armor systems. The experimental approaches used to understand the behavior and measure the properties of individual materials are discussed in Chapters 3 through 5.
Measurement of both partial and complete penetration by threats of the separate material composing the system and of the full armor system is key to understanding how materials are selected for use in armor systems to protect against ballistics. In the case of body armor, in addition to the ability of the armor to stop the projectile, there is another requirement—namely, that the deflection of the backside of the armor toward the wearer be small.
The specifics of the tests used to qualify armor systems for field use are well documented and will not be described at length here. As an example, the very elaborate requirements for the testing of body armor are described in great detail in the National Institute of Justice (NIJ) standard.2 In addition, a recent National Research Council (NRC) report examined specific aspects of the techniques used to evaluate body armor.3Yet another recent report by the Department of Defense (DoD) Office of the Inspector General4 described the Army’s testing to certify armor. Although the purchase specification for body armor might seem insensitive, it allows for an “acceptable number of complete and partial penetrations,” as shown in Figure 2-1. An additional parameter for body armor certification is the maximum depth of the back-face deformation for partial penetrations. (Back-face deformation is the depth of the crater left by each partial penetration in the clay placed behind the armor during testing with threats. It represents the blunt force trauma inflicted on the wearer, which can contribute to injury or even death.) The accepted deformation of the back face of an armor system is currently 44 mm (1.73 in.) or less5 (see Figure 2-1).
To assess the different threats against a particular armor system, two key measurements, V0 and V50, are made. V0, the ballistic limit, is “the maximum velocity at which a particular projectile is expected to consistently fail to penetrate armor of given thickness and physical properties at a specified angle of obliquity.”6 If the measured V0 exceeds the maximum velocity for a particular threat (see Table 2-1) the armor system is said to defeat that threat. Essentially, the
3NRC. 2009. Phase I Report on Review of the Testing of Body Armor Materials for Use by the U.S. Army: Letter Report. Washington, D.C.: The National Academies Press. Available online at http://www.nap.edu/catalog.php?record_id=12873. Accessed April 7, 2011.
4Inspector General, Department of Defense. 2009. DoD Testing Requirements for Body Armor, Report No. D-2009-047. Available online at http://www.dodig.mil/audit/reports/fy09/09-047.pdf. Last accessed April 15, 2011.
6Department of Defense. 1997. Department of Defense Test Method Standard: V50 Ballistic Test for Armor, MIL-STD-662F, December 18. Aberdeen Proving Ground, Md.: U.S. Army Research Laboratory.