A History of Research and a Review of Recent Developments

Above-ground explosions 33
Figure 2.8 Variation of p r /p 0 with angle of incidence (from Glasstone and Dolan,
ref. 2.9).
The properties of obliquely reflecting shock waves have been a subject of
much theoretical and experimental research over the years. Theories due to
von Neumann [2.7] and more recently to Dewey and McMillin [2.8] have
used different approaches (pseudo-stationary and non-stationary) to predict
more accurately the point at which transition to Mach reflection occurs. It is
near this transition that the total pressure exceeds the normal reflection pressure.
The theoretical results have been used to predict the peak hydrostatic
overpressure at ground level from an air burst explosion, and are often expressed
as isobars of overpressure plotted on the axes of height of burst and ground
radius. Curves of this type were presented by Glasstone and Dolan [2.9], and
an adaptation of their results by Satori [2.10].
In a paper in 1985 by Dewey, Heilig and Reichenbach [2.11] on oblique
reflections, experiments performed at the Ernst Mach Institut in Freiburg,
Germany were reported for the first time. Small spherical charges of hexogen
(0.016 to 1.024 kg) were detonated at heights ranging from 0.15 to 6.5 m
over flat concrete reflecting surfaces. Pressure gauges were flush mounted in
the surface between 0 and 8 m radius from a point immediately below the
charge. The test results were compared with experiments at the Defence
Research Establishment, Suffield, where 500 kg charges of TNT and 100 and
500 kg charges of pentolite were detonated at heights ranging between 1.2
and 44 m. The results were also compared with experiments at Suffield with
450 000 kg of TNT at a height of 4 m. By applying the scaling laws to the
hexogen and pentolite explosions it was possible to compare the relation
between p 0/p a and the primary shock front radius in metres, on a basis of a 1
kg charge mass of TNT. This comparison is shown in Figure 2.9, where a