A History of Research and a Review of Recent Developments

8
The nature of explosions
mass, and this must be produced in a very short space of time, either by firing
one sub-critical mass at another using explosive propellant, or by compressing
a sub-critical mass by the implosion forces of surrounding high explosive.
Information on the design of nuclear weapons was a matter of high security
for many years, but recently more information has become available on the
size, shape and action of the devices.
1.3 THE ANALYSIS OF DETONATION AND SHOCK IN FREE AIR
Before discussing the effects of explosions in the various constituents of the
physical world, such as air, water and earth, we must survey the build-up of
theoretical knowledge by scientists since the nineteenth century. Once high
explosives had been developed it was natural that attempts would be made
to predict the detonation behaviour and to deduce mathematical expressions
for the energy of explosions and for the propagation and decay of blast
waves in air.
It was noticed that detonation propagates as a wave through gas in a very
similar way to the propagation of a shock wave through air, so the work of
scientists on the physics of shock waves became important. It was inspired to a
great extent by earlier work on the theory of sound and sound waves, by Earnshaw
[1.1] in 1858 and Lamb [1.2], the English mathematician (1849–1934), who
became the acknowledged authority on hydrodynamics, wave propagation,
the elastic deformation of plates, and later on the theory of sound. The publication
of his works on the motion of fluids coincided with the growing interest in
explosions, and his contribution was discussed in the Introduction.
The conditions relating to pressure, velocity and density in a gas before
and after the passage of a shock wave were first investigated by Rankine [1.3]
in 1870, then by Hugoniot [1.4] in 1887. Their work was used a few years
later by D.L.Chapman, who suggested that a shock wave travelling through a
high explosive brings in its wake chemical reactions that supply enough energy
to support the propagation of the wave forward. At the same time the French
scientist J.C.E.Jouget suggested that the minimum velocity of a detonation
wave was equal to the velocity of a sound wave in the detonation products of
the explosive, which were at high temperature and pressure. All this work,
described recently by Davis [1.5], applied strictly to explosive gases, but was
assumed to apply to liquid and solid explosives. There was further research
on the subject in Russia, the USA and Germany in the 1940s, but the most
useful analysis of the detonation process was set down by G.I.Taylor [1.6] in
a paper written for the UK Civil Defence Research Committee, Ministry of
Home Security, in 1941, during the Second World War. He took a cylindrical
bomb, in which the charge was detonated from one end, and in which the
reaction might advance along the length of the bomb at a speed of over 600
m/sec if the charge were TNT. The internal pressure forces the casing to expand,
the expansion being greatest at the initiating end. When the case ruptures the