A History of Research and a Review of Recent Developments
A History of Research and a Review of Recent Developments
A History of Research and a Review of Recent Developments
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
160<br />
Penetration <strong>and</strong> fragmentation<br />
Figure 7.17 The process <strong>of</strong> fragmentation <strong>and</strong> penetration into rock rubble by the<br />
finite block method (from Gebara et al., ref. 7.21).<br />
points. This produces fragments that are reasonably equal in length <strong>and</strong> breadth,<br />
rather than heavily elongated, <strong>and</strong> is thought to be well representative <strong>of</strong><br />
experiments. Figure 7.17, taken from ref. [7.21], shows a penetrator hitting a<br />
single block, causing it to fragment. The size <strong>of</strong> rocks in a rock rubble fabrication<br />
is about three times the diameter <strong>of</strong> the projectile, so the fragmentation <strong>of</strong><br />
individual rocks is highly likely. This results in less deflection from the direction<br />
<strong>of</strong> the projectile path than would be the case in a non-fragmenting block<br />
analysis.<br />
Earlier mention <strong>of</strong> the SAMPLL computer code is a reminder that<br />
considerable efforts have been made in recent years to establish computer<br />
s<strong>of</strong>tware for the prediction <strong>of</strong> penetration into soils <strong>and</strong> other materials. In<br />
1987 a paper by Schwer, Rosinsky <strong>and</strong> Day [7.25] presented a computational<br />
technique for earth penetration, which included direct coupling between a<br />
deformable target <strong>and</strong> a deformable penetrator. In their review <strong>of</strong> recent<br />
computational work they called attention to the code PENCO, which was<br />
established at the US Army Waterways Experiment Station in the early 1980s,<br />
<strong>and</strong> reported on at the time by Creighton [7.26]. This code treats multi-layered<br />
targets <strong>of</strong> hard or s<strong>of</strong>t rock materials, where the target resistance is specified<br />
by the unconfined compressive strength, or by the S factor in Young’s equations<br />
(see Eq 7.5). It does not treat the interaction between penetrator <strong>and</strong> target<br />
for deformable penetrators, <strong>and</strong> appears to be limited in its treatment <strong>of</strong> very<br />
thin targets having thicknesses <strong>of</strong> only one or two penetrator diameters.<br />
Reference was also made to the possible use for soil penetration, using rigid<br />
penetrators, <strong>of</strong> the codes HULL [7.27] <strong>and</strong> TRIFLE [7.28], which were Eulerianbased<br />
finite difference codes developed mainly for fluid dynamics problems.<br />
The Lagrangian penetration grid consists <strong>of</strong> a narrow tunnel that coincides<br />
with the line <strong>of</strong> the penetrator trajectory, <strong>and</strong> a typical target grid, taken from<br />
ref. [7.25] is shown in Figure 7.18. The use <strong>of</strong> the tunnel is to reduce computation