A History of Research and a Review of Recent Developments

His very early investigations of the effects of dynamic loads were of great
fundamental value. He appreciated the importance of ductility in the absorption
of kinetic energy and he was the first to demonstrate that a suddenly applied
load produces double the stress of the same load applied gradually. He also
demonstrated the danger of vibrational resonance and of fatigue. There is
little doubt that he was a genius, and his capacity for uncovering the roots of
structural and mechanical behaviour have been of great value in many fields.
7.2 PENETRATION INTO SOIL, STONE AND ROCK
Penetration into soil of falling bombs and artillery shells was a particularly
important research area supporting the development of military weapons during
the nineteenth and twentieth centuries, and many thousands of experiments at
large scales were carried out. For vertical penetration into well-compacted soil
the results confirmed (but only to an accuracy of ±20%) that Poncelet’s V 2 term
was suitable when impact velocity exceeds about 60 m/sec. At the beginning of
the nineteenth century many empirical expressions for the constants a and b
were developed, but later Petry [7.3] in 1910 proposed a modified formula,
where
Penetration into soil, stone and rock 143
p = depth of vertical penetration in feet
W p = total projectile weight in lb
A = cross-sectional area of the projectile in in 2
K = constant depending on target material
V = striking velocity in feet/sec.
(7.4)
The constant, K, was found to depend on V, as well as on the soil properties.
In the units of Eq. (7.4), the following approximate relationships were
recommended for a broad range of typical soils:
Sand: K = 154 – 0.07V
Sandy loam: K = 190 – 0.09V
Loam: K = 227 – 0.11V
Clay: K = 341 – 0.19V.
Further research, which has been summarized by Young [7.4], showed that
the form of Poncelet’s relationship, as presented by Petry, would be improved
if a factor were introduced to take account of the shape of the nose of the
projectile, if penetration was taken proportional to the square root of the
projectile pressure (W p/A) 1/2 , and if the relationship between penetration and
V 2 was replaced at higher striking velocities with a relationship between