Game Development Reference
In-Depth Information
The right-hand side of Equation (12.5) tells us which factors influence steel armor penetration.
The thickness of the armor and the resistance of the armor to penetration increase (obviously)
the kinetic energy of the projectile required to penetrate the armor. The diameter of the projectile
also has an effect in that a thicker projectile requires more kinetic energy to penetrate a given
thickness of armor than a thinner projectile. The greater the angle of impact, the more kinetic
energy is required.
The Thompson “F-Formula” all-purpose armor penetration formula was originally designed
to model the ballistic impacts and penetrations of naval armor, but it works fairly well for bullet
impacts as well. As an example, let's use Equation (12.5) to compute the necessary kinetic
energy to penetrate a 0.01
m
steel plate with a 9
mm
bullet. We'll assume the impact is head-on
and use Equation (12.4) to compute the
F
coefficient value.
⎛
0.01
⎟
⎜
(
)
F
=
1.8288
−
0.45
⎟
2000
+
12192
=
14610
(12.6)
⎜
⎝
⎟
⎠
0.009
The kinetic energy required to penetrate the steel plate is computed from Equation (12.5).
1
J
2
2
2
2
mv
=
8.025* 0.01* 0.009 *14610
=
1387.5
(12.7)
A high-velocity 9
mm
bullet has a mass of 0.0082
kg
and a muzzle velocity of about 440
m/s
. The
corresponding kinetic energy of the bullet is 794
J
, which is less than the kinetic energy required
to penetrate the plate, so the steel plate will stop the 9
mm
bullet.
A projectile that doesn't penetrate steel armor can still damage it. Armor is susceptible to
flaking or chipping (also called
spalling
) and fracturing. If any of these things happens, it
weakens the ability of the armor to resist future ballistic impacts.
Body Armor
Armor was used to protect soldiers for thousands of years, but it was largely abandoned from
military use in the eighteenth, nineteenth, and early twentieth centuries. During World War I,
there were English and American officers who considered it an act of cowardice to wear anything
that would protect oneself during combat. In more modern times, people have come to their
senses, and it is now standard practice for soldiers and police officers to wear body armor when
in a combat situation.
Rather than the metal armor that was worn in ancient times, modern body armor is gener-
ally constructed from Kevlar or a similar type of carbon composite material, which is strong yet
significantly lighter than metal. The National Institute of Justice (NIJ) conducts tests of various
types of police and personal body armor.
2
The armor is classified according to the types of
bullets that the armor will stop. The armor is tested against both soft-tipped (typically exposed
lead) bullets and hard-tipped (lead covered with a metal jacket) bullets.
The NIJ body armor classification standards are summarized in Table 12-1. The NIJ refer-
ence documents present the results in terms of types of bullets that a particular body armor
class can stop, but these have been converted into kinetic energy values in Table 12-1. The
kinetic energy values represent the maximum bullet kinetic energy that the body armor can
stop. For example, a bullet with a kinetic energy value of 750
J
would penetrate Type IIA body
armor but would be stopped by Type II body armor.
