Quantcast Section 7: Standoff Weapons Hardening

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Introduction.  This section begins with a description of the threat
from a standoff Rocket Propelled Grenade (RPG) type of attack, followed by
the general mechanisms by which RPGs can be stopped, and ends with hardening
design options available for both new and retrofit construction.  An RPG
attack is a very high-severity level attack directed primarily toward killing
or injuring personnel inside a building, although some critical assets might
also be subject to destruction.  An RPG is not used to gain entrance or cause
significant damage to a building.  A high-velocity jet of material is created
by the RPG which penetrates significant distances and kills or injures by
direct impact and spallation.  The jet itself creates only a small hole.
The RPG Threat
RPG Characteristics.  An RPG, like the Soviet built RPG-7 antitank
grenade, is a rocket-assisted projectile fired from light hand-held launchers
(see Figure 68).  The grenade is first ejected from the launcher at a
velocity of about 390 feet (120 m) per second by a small strip powder charge.
Approximately 36 feet (11 m) from the launcher a sustainer rocket ignites and
boosts the rocket to a maximum velocity of about 980 to 1310 feet (300 to 400
m) per second.  The general characteristics of the weapon are summarized in
Table 51.  The RPG warhead consists of a conical-shaped charge within an
outer steel casing called the ogive.  On detonation, the material of the
inner lining of the cone of the shaped charge collapses and forms a metallic
jet having a very high velocity.  The following gives a brief summary of the
jet formation and target penetration mechanisms associated with a shaped
charge of this type as background.
RPG Jet Formation.  On detonation of the shaped charge, the metal
jet is initially in a continuous stretching condition similar to a
wire-drawing process.  Because there is more explosive near the tip of the
conical liner than around the base, there is an inherent variation in the
velocity of each element of the jet.  This results in stretching of the jet
along its length until it eventually breaks up and separates into a column of
small rod-like particles aligned one after another in tandem fashion.
RPG Jet Penetration.  When the jet is in its early continuous
state, it can penetrate virtually any material regardless of the hardness of
that material.  The density of the target material is its most significant
protective property.  However, once the jet is broken into discrete
particles, the penetration mechanism changes, and factors such as target
hardness become more important to the penetration process.  Maximum depth of
penetration is achieved when the jet is absolutely straight with each element
exactly following its predecessor.  As the jet impinges on a target material,
the pressure exerted by the jet tip pushes the material away in all
directions.  The tip is used up continuously and converted into a
high-temperature liquid with possibly some vapor formed and pressure
generated at the contact point.  New jet material continuously comes into
contact at the rapidly moving


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