MIL-STD-376A
3.8 Ballistic limit, protection criteria (V50BL(P)). The V50BL(P) may be
defined as the average of an equal number of highest partial penetration
velocities and the lowest complete penetration velocities which occur within a
specified velocity spread. The normal up-and-down firing procedure is used. A
0.020 in. (0.51 mm) thick 2024 T3 sheet of aluminum is placed 6 ± 1/2 in.
(152 ± 12.7 mm) behind and parallel to the target to witness complete
penetrations. Normally, at least two partial and two complete penetration
velocities are used to complete the BL(P). Four, six, and ten-round ballistic
limits are frequently used. The maximum allowable velocity span is dependent on
the armor material and test conditions. Maximum velocity spans of 60, 90, 100
and 125 feet per second (ft/s) (18, 27, 30 and 38 m/s) are frequently used.
3.9 Ballistic limit. The minimum velocity at which a particular projectile
is expected to consistently, completely penetrate armor of given thickness and
physical properties at a specified angle of obliquity. The ballistic limit may
also be defined as 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. Because of the expense of firing
tests and the impossibility of controlling striking velocity precisely, plus the
existence of a zone of mixed results in which a projectile may completely
penetrate or only partially penetrate under apparently identical conditions,
statistical approaches are necessary, based upon limited firings. Certain
approaches lead to approximation of the V50 Point, that is, the velocity at which
complete penetration and incomplete penetration are equally likely to occur.
Other methods attempt to approximate the VO Point, that is, the maximum velocity
at which no complete penetration will occur. Other methods attempt to
approximate the V100 Point, that is, the minimum velocity at which all
projectiles will completely penetrate.
3.10 Ballistic resistance. A measure of the capability of a material or
component to stop or reduce the impact velocity and mass of an impacting
projectile or fragment.
3.11 Break screens. A screen with a conductive pattern printed on the
surface which is broken (opened) by a projectile impacting the screen. Used
to activate or deactivate a chronograph upon passage of a projectile.
3.12
Cell size.
The lateral dimensions of an armor tile used in an armor
array.
3.13 Ceramic armor. Any ceramic material which is employed as a
component of an armor array for protection against projectiles. In this
sense, includes glasses as well as polycrystalline materials.
3.14 Ceramic percentage. The fraction of ceramic present in an armor
system as determined from dividing the areal density of its ceramic components
by the total areal density of the system.
3.15 Chronograph. An electronic instrument used to determine the time
interval of projectile flight between two fixed measuring stations.
3.16 Comminution. Fracture or fragmentation of ceramic material into
fine particulates as a result of projectile impact.
3.17 Composite armor. An armor system consisting of two or more
different armor materials bonded together to form a protective unit.
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