A History of Research and a Review of Recent Developments

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Table 7.1
Penetration and fragmentation
the penetration path length and penetration normal to the face of the composite
specimen. The tests were carried out with either Polyester Polyurethane or a
blend of Polyether Polyurethane as the base material, and with aggregates of
crushed limestone, crushed basalt or river gravel. The percentage of polymer
by weight was about 9% for gravel and 7% for limestone and basalt. The
percentage of rock aggregate by weight was about 60%, and the rock size
was in the range 26.5 to 37.5 mm.
An indication of the results is given in Table 7.1, which gives the mean
normal penetration, and the maximum percentage of voids in the cast specimens
for the Polyether Polyurethane (the preferred material).
7.3 PENETRATION INTO CONCRETE
Since most new military protective structures since the beginning of the present
century have been constructed from reinforced concrete, and since military
targets such as buildings, bridges and airfield runways are frequently constructed
from this material, it is not surprising that the expenditure on research to
study the response of concrete to penetration has been very high. Let us take
as our starting point the scientific research of the Second World War, starting
as always with the work of Christopherson [7.12].
Much of the wartime research was concerned with the penetration of aerial
bombs into reinforced concrete slab-type structures, so it became necessary to
classify bombs in terms of their penetrative power. Four types of bombs were
recognized in Britain, and the first of these was armour-piercing (AP) bombs,
similar to naval shells, with low charge/weight ratio (10–15%) and relatively
high-length diameter ratio. Weights of 1000 lb and above were registered.
Although ‘armour piercing’ suggests metallic targets like battleships or tankers,
they were also used against protective concrete. The second type was ‘semiarmour-piercing’
(SAP) bombs, with a higher charge/weight ratio (20–30%),
and lower weights, in the range 250 to 1000 lb. The third type was demolition
bombs, also known as medium capacity or general purpose bombs. Charge/
weight ratios were in the range 45–50%, and weights covered a long range
from 250 lb upwards. Their damage effect was about double that of SAP
bombs, which was not surprising since they carried about double the charge
weight. The last category was the high capacity bombs, with a charge/weight