A History of Research and a Review of Recent Developments

10
The nature of explosions
Figure 1.1 Overpressure/duration curve for detonation in air (idealization with
exponential decay) (from Friedlander, ref. 1.19).
of TNT generates a blast energy of approximately 4600 joules/gram, which is
equivalent to about 1100 calories/gram. In fact, the definition of a ‘standard’
gram of TNT is that which gives a blast energy of 4610 joules. The definition
of a standard ton of TNT is an energy release of one million kilo-calories.
For a given type of chemical high explosive, energy is proportional to total
weight, so it has become customary for design purposes to rewrite Eq. (1.1) as
p =K W/R (1.2)
0 1
K1 is no longer non-dimensional and great care must be used in applying the
formula. Experiments suggested that the equation did not give very accurate
values of p0 over the entire range, and an improved version was proposed in
the US Army Technical Manual Fundamentals of Protective Design (Non-nuclear),
No. TM5–855–1, published originally in 1965 [1.10]. In imperial units the
equation became
3 .
(1.3)
where
p0=peak pressure in psi
z=R/W 1/3
(R in feet, W in lb).
The relationship should only be applied when 160>p0>2 psi, and
20>R/W 1/3 >3 ft/lb 1/3 .