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
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
172<br />
Penetration <strong>and</strong> fragmentation<br />
where A, a <strong>and</strong> ß are constants to be determined from experiments, s a is an<br />
appropriate flow stress <strong>and</strong> K a constraint factor. Taking K=2 <strong>and</strong> s a=s y (the<br />
yield stress) <strong>and</strong> comparing Eq. (7.27) with experimental results, leads to<br />
E (7.28)<br />
p /(sud Much <strong>of</strong> the foregoing work has been connected with missiles versus military<br />
armour, missiles versus the protective shields <strong>of</strong> nuclear reactors, or fragments<br />
from exploding jet engines impinging on metal protective shields. A further<br />
area <strong>of</strong> great interest is the effect <strong>of</strong> missiles <strong>and</strong> fragments on the thin aluminium<br />
sheeting <strong>of</strong> aircraft structures. A good deal <strong>of</strong> work in this area has been reported<br />
in the publications <strong>of</strong> the Advisory Group for Aerospace <strong>Research</strong> <strong>and</strong><br />
Development (AGARD) <strong>of</strong> the North Atlantic Treaty Organization (NATO).<br />
In an overview <strong>of</strong> the problem Avery, Porter <strong>and</strong> Lauzze [7.59] considered three<br />
realistic threats: (a) from explosive penetrators, (b) high explosive (HE) projectiles<br />
<strong>and</strong> (c) warheads. They indicated that projectile damage can range from dents,<br />
cracks <strong>and</strong> holes to large petalled areas accompanied by extensive out-<strong>of</strong>-plane<br />
deformation. The measurement that has proved most useful is lateral damage,<br />
which is defined as the diameter <strong>of</strong> a circle that just encloses the limits <strong>of</strong> fracture,<br />
material removal or material deformation (Figure 7.22). Since damage is limited<br />
to sheet thickness, projectile speed <strong>and</strong> impact angle, it is possible to establish a<br />
damage regime diagram, as shown in Figure 7.23, which refers to a 0.30 calibre<br />
armoured piercing round impacting aluminium sheet <strong>of</strong> alloy 7075–T6. The<br />
variation in damage size with projectile velocity for sheet 0.125 inches thick<br />
damaged by 0.30 calibre ball ammunition is shown in Figure 7.24, taken from<br />
the work <strong>of</strong> Avery, Porter <strong>and</strong> Lauzze. It can be seen that the maximum lateral<br />
damage occurs just above the penetration limit, <strong>and</strong> that further increases in<br />
3 )=(2sy /su )[(p/4)(H/d) 2 +(s/d) 0.21 ·(H/d) 1.47 ].<br />
Figure 7.22 Lateral damage circle (from Avery et al., ref. 7.59).