A History of Research and a Review of Recent Developments

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Penetration and fragmentation
Figure 7.9 Penetration of projectiles into chalk (from Christopherson, ref. 7.12).
range of striking velocities between 500 and 1200 km/s, the axial resultant
nose force (F) was given by
F=109V 1.29 ,
(7.11)
where F and V have units of KN, km/s.
In the late 1970s, the study of fragment ballistics led to experiments on the
penetration mechanics of steel fragments into sand, because sand was frequently
used as a protective medium around buildings and hardened structures against
flying steel projectiles. The tests were reported after a gap of some years by
Stilp, Schneider and Hülsewig of the Ernst Mach Institute [7.18], and concerned
penetration depths associated with idealized fragments in the form of spheres
and cylinders. Steel spheres with a diameter of 1 cm and a mass of 4.07 g were
shot into dry loose sand by Schneider and Stilp in 1977, at velocities between
118 m/s and 3553 m/s. The sand had a density of 1.8 g/cm 3 and maximum
grain sizes of 1.05 and 2 mm.
It was noted that for low impact velocities (400 m/s the sand grains also
became fragmented and the projectile material was eroded. The amount of
erosion was linked to the hardness of the projectile steel. At velocities >2000
m/s the projectiles broke into two or three parts. It was also concluded that
during the penetration process the projectile remained at a constant orientation,
with a cavity-like transient penetration channel formed behind it.