Gurney constants

Initial velocities of explosively driven metal fragments can be accurately estimated by the so-called Gurney formula (see Vol 6, G195-R). The writer (Ref 81a) used the Ref 45 data referred to above to compute a Gurney constant /2E1 (for tangential detonation) of 3.04mm/ psec for 1.765g/cc PETN... 

Another Dupont sheet explosive is EL506D. It contains about 70% PETN and has a density of 1.4g/cc. Gurney constants for it are 2.50mm/ psec (Roth, Ref 81a) and 2.28mm/psec (Kennedy, Ref 88, p 117)... 

The measured Gurney constants for the same material seem to vary from experimenter to experimenter. Those presented in Reference 8 differ from those presented in References 11 and 12. These differences are on the order of 5-10 percent. Table II is taken from data presented in Reference 8. If data from either Reference 11 or 12 had been used instead, it would have resulted in a difference in the initial velocity of about 5 percent. 

The initial velocity of fragments is quite accurately predicted by the Gumey formulas described by us under "Gurney Constant and Gumey Formulas" in Vol 6 of Encycl More detailed discussion on "Fragmentation Characteristic " is given in ... 

VQ initial fragment velocity, fc/sec yjlE = Gurney constant, ft/sec Wc = charge weight, lb Wm wt of fragmenting metal, lb... 

This is an important result because it enables us to estimate the Gurney constant for expls for which-y/2E has not been determined exptly. 

Flyer velocity data for 1-D configurations were used to compute the Gurney constants for the six expls shown in Table 2. Most of the data for PBX 9404, Comp B, and Baratol are from SRI flyer plate experiments, and the other data are largely from LRL. The PWG s are either P-80 s or P-120 s (for the six-inch-thick drivers), and we have assumed the same L for both. 

There are many exptl measurements of plate velocities or metal cylinder expansions from which we can obtain 21, the Gurney constant for 2-D configurations. We have chosen to rely primarily on LRL data (Ref 7) of cylinder expansion, but we will demonstrate that the LRL data lead to y/2E values in agreement with values obtained from the plate velocity experiments of Hoskin et al (REf 5), Defoumeaux Jacques (Ref 12), and Akst (Ref 28) for cylinder expansion... 

The second grouping is based almost entirely on LRL data (Ref 7). The expls in this grouping are HMX or HMX in combination with TNT or inert materials. An interesting aspect of these data is that the Gurney constant for HMX/inert mixts is well represented by ... 

The writer (unpublished work) thru a semi-empirical approach developed the concept that the Gurney constant ( / 2E) of an expl is approx D/3. The Gurney constant for RDX is given in Ref 58a as 2930m/sec B. CJ Pressures. 

In the Ballistic Mortar and Trauzl Block tests, Tetryl is 130% and 125% of TNT, respectively (Ref 46a). In air shock overpressure, in the 3—20psi range, the TNT equivalent weight of Tetryl is 1.07 (Ref 62). In underwater performance, the pentolite equivalent weight of Tetryl is 1.00 for shock energy and 0.98 for bubble energy (Ref 20), The Gurney Constant for 1.62g/cc Tetryl (quoted in Ref 71) is 2.5km/sec. This value seems low... 

To obtain comparable data, the experimental conditions have to be defined precisely. Especially the Gurney constant... 

The here cited Gurney constant is an average value from several experiments. 

The conditions of the charge detonation in metal cylinders, i.e., warheads, are well described by Eq. (5.39). From this equation, it can be seen that the wall velocity during expansion depends on the ratio between the masses of the cylinder and the explosive. The quantity yj2Ef, is called the Gurney constant. 

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