A History of Research and a Review of Recent Developments

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Penetration and fragmentation
Figure 7.5 Penetration of US GP bombs in clay (from Stipe, ref. 7.11).
plastic materials like clay, granular materials like sand or gravel, and the softer
rocks such as chalk and sandstone. He assumed that for soil penetration the variables
were separable, so that the relationship between total track length, L, the diameter
of the projectile, d, and striking velocity, V, could be written in the form
(7.9)
If the velocities given to the material are largely independent of diameter, and
if , then
(7.10)
Using this as a governing relationship, the results of UK firing trials into
undisturbed natural clay at Dorking and Richmond Park using armoured
piercing shot, steel balls of in diameter, and flat-ended cylinders having
diameters of 0.50 and 0.78 in, are shown in Figure 7.6. Either maximum or
mean penetration times are given, but the results in general confirmed the
large scatter associated with soil experiments. Christopherson suggested that
missile instability caused the wide scatter, since it was known that almost all
the missiles turned over at least once—sometimes more often. He also observed
that penetration increased as the average grain size decreased.
The British Bomb Disposal Units recorded during the Second World War the
depths from which bombs were recovered, and these were plotted in the form