projectile and protect the wearer of body armor is contained in Appendix E. This deformation, however, has the potential for creating injuries in the thorax behind the armor that may generally be characterized as blunt trauma. These injuries are often termed “behind-armor blunt trauma.”
This study focuses on hard body armor (referred to as “body armor”) and helmets.
The Phase II report (NRC, 2010, p. 4) described the use of ceramic materials in body armor as follows:
Ceramic materials have been used successfully in personal armor systems to defeat small-arms threats. They are preferred for personal armor systems because they are lighter than more traditional armor made of metallic alloys. Properties that contribute to the performance of ceramic armor include superior hardness, low density, favorable elastic constants, and high compressive strength. However, as stand-alone items, ceramics would not be particularly good because of their low tensile strength, brittle response, and sensitivity to small mechanical defects such as pores and cracks. Hence, ceramics are used in combination with other materials, such as polymers and metals, to form laminar composites that provide excellent properties for body protection. A typical insert (also referred to as a “plate”) of body armor consists of a layer of dense boron carbide or silicon carbide backed by a layer of metal or polymer composite; the entire plate is wrapped in tightly woven ballistic fabric. The ceramic layer breaks up an incoming projectile and dissipates its kinetic energy. The layer of polymer composite and/or metallic alloy provides ductility and structural integrity and spreads the forces resulting from the impact of a projectile over a larger area.
The use of ceramic materials has been successful. The military collects data on casualties resulting from possible penetrations of body armor by enemy rounds, and there have been no known soldier deaths due to small arms that were attributable to a failure of issued ceramic body armor (NRC, 2010).
Like body armor, current ballistic protective helmets employ a passive momentum defeat mechanism in which a bullet with a small mass and high velocity progressively engages a larger mass of high-performance fiber/resin composite, decreasing the bullet velocity and locally transferring momentum to the helmet. This process continues until all the momentum of the incoming round is deposited into the helmet or the helmet is defeated and penetrated by the incoming round. Even if the incoming round does not penetrate the helmet, there is still potential for substantial local head contact from sufficient helmet