Metal Foams: A Design Guide

peak pressure
MPa
Impulse/(mass of TNT) 1/3
Nsm-2kg-1/3 10 6
10 5
10 4
1000
100
10
1
0.1
Pressure,
water
Pressure,
air
Energy management: packaging and blast protection 167
Impulse, water
Impulse, air
0.01 0.1 1 10
radius/(mass of TNT) 1/3
0.01
Figure 11.15 Peak pressure and impulse as a function of distance R from
an explosion of a mass M of TNT
example, a charge of 1 kg of TNT in water produces a peak pressure of about
100 MPa and an impulse of 104Ns/m 2 at a distance of 1 m. The curves for
water blast are approximated by the formulae
and
p0 D 108
� �
1/3
1.13
M
R
Ji D 1.185 ð 10 4 M 1/3
MPa ⊲11.29⊳
� �
1/3
0.86
M
R
Ns m 2
⊲11.30⊳
where the mass, M, of TNT is given in kilograms and the distance from
the explosion, R, is given in metres. The energy content of other common
chemical explosives is similar to that of TNT, as shown in Table 11.4. In
order to estimate the blast from other explosives the simplest method is to
scale the mass of the explosive by its energy content relative to that of TNT:
this scale factor is included in the table.
Blast protection (and protection from projectile impact, which is treated in
a similar way) is achieved by attaching a heavy buffer plate, mounted on an
energy absorber, to the face of the object to be protected. The impulse accelerates
the buffer plate; its kinetic energy is dissipated in a benign way by the
energy absorber. Let the buffer plate have a thickness b and density b. Then