A History of Research and a Review of Recent Developments

14
The nature of explosions
As Figure 1.4 shows, the differences were very small, and all the results lay
within a narrow scatterband. Note that the results summarized in Figure 1.4
lie at the far right end of Philip’s curve, because the charges were small and
the peak pressures very low. Philip’s work still remains as one of the most
authoritative pieces of work on high-explosive bombs, although based on a
dangerously small number of tests. Her results were also given by
Christopherson in reference [1.9]. What they suggest is that the decay of peak
instantaneous pressure with range is exponential, which seems logical. In fact
the lower scatterband on Figure 1.4 is close to the ‘inverse square law’ given
by p 0=500/z 2 , which is a simple rule still in use in preliminary calculations
(after conversion to metric units).
The 4000 lb high-capacity bomb tested by Philip must have been one of
the ‘blockbuster’ bombs containing a high proportion of charge and a relatively
low containment mass, designed by Barnes Wallis to attack heavily reinforced
concrete protective structures by earth transmitted shock rather than by
penetrative impact. It is interesting to note that during the Gulf War in
1991, when the standard 2000 lb laser-guided bombs dropped on bunkers
by the US Air Force were clearly not entirely demolishing the targets, it was
reported in the press and elsewhere that an accelerated manufacturing
programme was undertaken to produce 4000 lb bombs. Readers who wish
to see what a UK 4000 lb bomb looked like may find examples mounted on
Figure 1.4 Relationship between peak overpressure and scaled range for UK Second
World War bombs (from Philip, ref. 1.15).