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MIL-HDBK-1013/1A
6.4.2
Transparent Armor.  Transparent armor is composed of materials with
dual properties of being virtually transparent while having a resistance to
penetration of small-arms projectiles and fragments. In general, transparent
armors are laminate composites of glass and elastomers.  Spallation has an
important role in the impact process of transparent armors.  A potential
disadvantage of glass is breakup on projectile impact and the subsequent
shattering and formation of sharp, needle-like splinters which can prove to
be hazardous.  Safety glass, which consists of two or more sheets of tempered
glass bonded together by synthetic resin, produces cubical pieces on impact
that usually have rounded edges.  The energy absorbing mechanics of plastic
materials offer an advantage over glass with regard to spallation.  Plastics
often can be designed not to shatter, and when combined with glass as a spall
shield or a laminated glass/plastic configuration, can inhibit the shattering
of the glass by containing the glass particles.  The suppression of
spallation is a powerful method of enhancing impact resistance of transparent
armor. A laminated and bonded composite transparent armor consisting of
safety glass and polycarbonate layers provides visual clarity and
demonstrates resistance to small-arms projectiles.
6.4.3
Opaque Armor.  Opaque armor is armor that obstructs transmission of
light.  Various types of opaque armor are described in the following
paragraphs.
6.4.3.1
Common Structural Materials.  Various tests have been performed on
common structural building elements and concrete walls to determine their
ballistic resistance to small-arms fire.  Concrete masonry units, reinforced
concrete, and steel/plywood wall systems have been ballistically tested
against small-arms fire.  Examples of these tests are covered later in this
section.
Fibrous Materials.  Fibrous armor is armor which incorporates the
6.4.3.2
use of fibers or fabrics in a plastic matrix.  The fibers work as an
excellent reinforcing material for polymers.  Three types of laminated
fabrics include fiberglass, nylon, and Kevlar. Glass-fiber-reinforced-polymer
(GRP) laminate consists of a number of laminations of woven rovings of glass
fibers bonded with a polyester resin.  Its performance at close range is
limited mainly to protection against fragmentation.  Test data indicate that
a 2.5-inch (63.5-mm)-thick GRP can defeat a 0.30-caliber (7.62-mm) AP round
at a range of 110 feet (34 m). Kevlar has a high tensile strength compared to
nylon, but neither material is considered a satisfactory armor with regard to
a 0.30-caliber (7.62-mm) projectile fired at 25 yards (22.9 m). Its principal
attribute, as with laminated glass fibers, is to shield against scabbing and
fragmentation by absorbing the low kinetic energy of the ballistic threat.
6.4.3.3
Ceramic Composite Materials.  Ceramics encompass all inorganic
materials except metals and metal alloys.  Ceramic composite armor systems
usually consist of aluminum oxide or boron carbide tile bonded to a rear
panel, usually a GRP laminate, which acts as a shield against ceramic
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