A History of Research and a Review of Recent Developments

7
Penetration and fragmentation
7.1 INTRODUCTION
The analysis of dynamic impact is an important feature in the study of explosive
effects on structures, partly because military or terrorist activities frequently
involve the transportation of explosive charges by high-speed projectiles, and
partly because the explosion of the charge is often accompanied by the highspeed
distribution of fragments of disintegrating containers. Sometimes the
disintegration of one part of a bombed structure sends fragments of that
structure over a larger area.
An explosive warhead can be aimed at a structure by a variety of means:
aerial bombs, rockets, artillery, missiles. The degree to which these warheads
penetrate a surface structure, or the earth adjacent to a buried structure before
exploding, has a large effect on the eventual damage. We therefore need to
survey the state of research in the fields of bomb or missile penetration into a
range of materials, from soil to concrete, and from steel sheet to sophisticated
armour plating. We must take account of the possible deformation and
crumpling of the charge casing during the penetrative process, because this
will affect the penetration depth.
The fragmenting casing usually projects small pieces of virtually undeformable
metal at high velocities. When these strike solid structures such as protective
concrete bunkers considerable surface damage may occur. When these solid
fragments strike relatively light structures, like aircraft wings or the cellular
walls of naval craft, the fragments remain in good shape, but the sheet metal is
penetrated and deformed. Certain military weapons like high-velocity cannons
can spray large areas of plated structures with projectiles that produce a pepperbox
type of damage to large areas of unsupported sheeting. If the holes are
irregular in shape, and occur in brittle material, fast-growing cracks can be
formed. These can limit the residual life of the structure under cyclic loading.
The original scientific investigations of dynamic penetration were linked
to the development of military weapons in the eighteenth and nineteenth
centuries, and this section will therefore include a historical reference to the
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