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PART I. BASIC PRINCIPLES 
1. Introduction 
a. The detonation velocity. When a stick of explosive is detcnated from 
one end, the chemical reaction which occurs takes a very short, but never- 
theless. finite, time to travel to the other end. This velocity of propaga- 
tion of the chemical reaction is called the detonation velocity (D) and is a 
constant for a given material and density, provided that some conditions are 
Satisfied, e.g.: the stick is not too narrow, the particle size not too 
large, initiation was strong enough, etc.. The progress of the explosion down 
the stick is accompanied by an immediate and very large increase in pressure 
and temperature. In fact the pressure in the burnt gases immediately behind 
the detonation front may be as great as one hundred thousand atmospheres and 
the temperature may run from 3,000 to 5,000 degrees Centigrade. In addition, 
the burnt gases acquire a very high forward velocity, Whereas the detonation 
velocity, which is the velocity of progress of a condition and not of any 
mtter, may run from 3,000 to 8,000 meters per second (ca. 7,000 to 18,000 
mph!), the actual material velocity falls in the range 1, 000° to 2,000 meters 
per second. 
b. The reaction zone. The time required for the explosive to react 
essentially completely to the burnt gases is, under favorable conditions, so 
Short that the zone in which reaction is takins place at any instant is ap- 
parently very narrow, Consequently a mathematical plane dividing the un- 
touched explosive from the burning material travels along the stick with 
velocity D, followed very closely by the plane which divides the burning 
mterial from the essentially completely reacted gases. The rise in pressure, 
temperature and mterial velocity takes place in this narrow reaction zone, 
Little quantitative information is available about the thickness of this 
zone except that it must be quite narrow. It may well be that this thickness, 
which measures the peepeucee of the rise in pressure, is an important measure 
of the ability of the explosion to cause destruction. However, for the pur- 
pose of calculating ee velocity of detonation its exact value is not 
important and for mathematical Simplicity, the zone is assumed to be 
infinitely narrow. 
c. Rarefaction behind the detonation. Even when the explosive is 
strongly confined in a pipe with the end containing the initiator closed, the 
region of high pressure, temperature and material velocity must be followed 
by @ region in which the pressure and temperature are falling to somewhat 
lower valves while the material velocity falls to zero. Such a travelling 
region of falling pressure is called a rarefaction wave. Its front moves 
with approximately the velocity D but its back surface moves somewhat more 
slowly, actually with the velocity of sound in the burnt gases in the condi- 
tion in which they are left after the passage of the rarefaction wave, It 
will be shown that the detonation velocity D is equal to the velocity of 
sound in the heated, compressed gases in front of the rarefaction wave plu 
the material velocity of these gases. The rarefaction wave thus i ore 
Spreads out. 
