Impact of a Bullet
In order to arrive at a clear understanding of what takes place when the motion of a projectile is arrested by any resisting medium, it is necessary to recall some of the elementary principles upon which these phenomena depend. The manner in which a projectile acquires its velocity, is a good illustration of the manner in which its motion is destroyed. If the mean pressure of the gas be multiplied by the space passed over by the projectile while acquiring its velocity, the result will be the measure of the work done by the charge of powder; and it will also be equal to the work of stopping the same projectile, no matter how or by what means it may be brought to rest. The same result is generally arrived at by measuring the velocity imparted to the projectile under the circumstances mentioned, and multiplying the square of the velocity by one-half of the mass of the projectile. The following are the different effects produced by the impact of a projectile upon any solid body; some of these being so connected as to render their relative importance extremely doubtful.
Compression.—The first effort of impact is to compress or drive back those portions of both projectiles and target first coming in contact upon those immediately behind them; the amount of this compression depending upon the material and velocity of impact, as well as upon the form of the projectile.
Elongation.—The greater part of the work of the projectile in penetrating wrought-iron and similar materials is expended in overcoming the tenacity of the material, or in elongating the fiber. This is evident when we consider that punching or shearing consists not so much in cutting the fiber, as in bending it, and afterwards pulling it in two lengthwise.
Shearing.—This, as just stated, consists chiefly in the two strains already mentioned.
Bending.—This also implies tension and compression; the back of the target being elongated, and the front compressed.
Pulverizing—a portion of the material. This takes place only in case of hard materials, as a stone or cast-iron, and it then absorbs a very great amount of work. Like bending and shearing, it involves compression and elongation, the material being compressed until it yields laterally to a tensile strain.
Motion.—While the work is being expended, a certain amount of time is allowed for the force of the projectile to impart motion to the target, especially that portion immediately in front of the projectile.
Friction.—The friction is very great, especially in the case of the more pointed form of projectile, and varies inversely with the velocity of the projectile.
Heat.—This is due to friction, both external and internal, that is, of the projectile and the fragments against the target, and against each other during the distortion of the material, from compression, bending, etc. The suddenness with which this heat is generated is almost unequalled by any known source of heat.
Farrow, Edward S. American Small Arms; a Veritable Encyclopedia of Knowledge for Sportsmen and Military Men. New York: Bradford, 1904. Print.
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