R. Meyer J. Köhler A. Homburg Explosives

81 Detonation
perature and pressure conditions. The propagation of the shock wave
is maintained by the energy of the reaction.
The equations developed above are still valid, but the meaning of the
equation parameters are:
p1 – detonation pressure;
r1 – density of gaseous products in the front of the shock wave;
this density is thus higher than the density of the explosive r0;
D – detonation rate;
W – velocity of gaseous products (fumes).
Equation (1) remains unchanged.
Since p0 is negligibly small as compared to the detonation pressure
p1, we can write equation (2) as
p1 = r0DW (2d)*)
The detonation pressure in the wave front is proportional to the
product of the density, the detonation rate, and the fume velocity, or –
since the fume velocity is proportional to the detonation rate – to the
square of the detonation rate. For a given explosive, the detonation
velocity rises with increasing density. It is clearly seen from equation
(2d) that the detonation pressure increases very considerably if the
initial density of the explosive can be raised to its maximum value –
e.g., by casting or pressing – or if the density of the explosive is
intrinsically high (TNT 1.64; RDX 1.82; Octogen 1.96). High density of
the explosive is important if high W Brisance is needed, whereas the
blasting performance (W Strength) is less affected by it. The importance
of the maximum possible compaction of explosives is demonstrated
by the W Hollow Charge technique.
Conversely, the detonation pressure and detonation rate may be reduced
by reducing r0, i.e., by employing a more loosely textured
explosive. This is done if the blasting has to act on softer rocks and if a
milder thrust effect is required (see below: explanation of the concept
of impedance).
The determination of the maximum detonation pressure p1, in equation
(2d) has been studied by X ray measurements. While the detonation
velocity can be measured directly by electronic recorders or by the
W Dautriche Method, there is no direct measurement possibility for the
fume velocity W, but it can be estimated by the flow off angle of the
fumes behind the wave front; this angle can be taken from X ray flash
photographs. The relation between D and W is
* Equations of the detonation wave theory are denoted by numbers corresponding
to the respective equations of the shock wave theory, with a suffix “d” (for
“detonation”).
The pressure maximum p1 in the wave front is also called “Neumann spike”
pN.