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for the P-po relationship suggested in the present series of papers. Some additional least-squares analyses of the experimental results in Table I and of RUBY detonation pressure predictions discussed in Parts I and II are given in the Appendix.
In the light of our earlier discussions regarding “buffered’1 equilibria in the detonation of C-H-N-0 explosives,2 it is of interest that no consistent trend toward “too high” or “too low” experimental detonation pressures with changing po is shown in Table I and Fig. 1 either by highly tmderbalanced or by near-COj-balanced materials. As was mentioned in Sec. V.D of Paper II,2 calorimetric “heat of detonation” measure- 1 ments provide strong evidence that detonation product compositions change markedly with loading density in the the case of compounds of the former type (e.g., TNT, DATB, TATB, tetryl, TNB), while with explosives of the latter type (e.g., TNETB, TNM, NG, PETN, RDX, HMX) product compositions are much less dependent on density. That the experimental P vs po behavior appears to be the same for both classes of explosives emphasizes the relative insensitivity of P to the positions of detonation equilibria.
That the exponents 1.0, 0.5, and 0.5 for N, M, and Q in Eq. (1) do not grossly misrepresent the influences of these properties of the explosive on the detonation pressure also seems to follow from the fact that we were able to discern no trends with ôøú, N*rb, Ììú, Qt*b, or Ñ»* 28 (see also the Appendix). Nor, insofar as we were able to discern this factor in the available references, was there a consistent difference between cast and pressed charges. If such trends do or should
appear in the data, they were effectively masked by other factors. **
Some important trends did appear, however, when distinction was made among the experimental detonation pressures in Table I according to the laboratories where the determinations were carried out. Represented in Fig. 2 are the safcie results as in the previous figure, but with the data divided into the following seven groupings24: (A) NOL results (Footnotes g, i, and q of Table I) show a tendency to run low relative to most other experimental determinations; (B) earlier results from the LASL (Los Alamos Scientific Laboratory) (Footnotes d, e, f, and r) do not show any consistent tendency in either direction; (C) more recent LASL results (Footnotes 1, m, o), in marked contrast, are invariably on the high side; (D) when reinterpreted by Petrone (Footnote n), however, the more recent LASL experiments conform more closely with predictions from Eq. (I)25; (E) earlier Russian measurements (Footnotes c, b, j) tend to run high, particularly, at the higher densities; (F) only a few more recent Russian measurements have come to our attention (Footnotes b, s), but the same authors have revised at least some detonation pressures downward; (G) insufficient results are available from BRL (Footnotes k) to discern a trend.
A more quantitative basis for these observations arises when we compare “experimental” values of Ê (Kexpti=^«cp11/Ôàãüðî2) for the various sets of results as follows:
Equation (1) K = 15.58
all experimental results = 15.83:fc0.84 (80 measurements)
(A) NOL results =15.41±0,68 (22 measurements)
(A') NOL results excluding EDNA28 = 15.22±0.55 (20 measurements)
(B) earlier LASL results = 15.63±0.64 (15 measurements)
(C) later LASL results =16.89±0.82 (15 measurements)
(D) later LASL measurements, Petr one’s reint^rpretation =15.11 ±0.32 (4 measurements)
(E) earlier Russian results = 15.92zfc0.90 (16 measurements)
(F) later Russian results =15.15±0,68 (5 measurements)
(G) BRL results = 16.07=fc0.48 (3 measurements).
These trends may be rationalized, at least in part, from what is known or may be inferred about methods used to arrive at these results in the various laboratories. Factors influencing the reported detonation pressures might include (1) charge diameters in the determination wherein, if too small, detonation properties of some of the less powerful explosives might not yet have reached “infinite diameter” values and (2) differ-
** It should be noted that, although Eq. (1) seemingly takes no account of the amount of solid carbon formed in the detonation, NM = G, and (1.00— G) equals the weight proportion of solid carbon. Thus the lack of a diecemable trend with if aba significant.
“ Because sources of experimental information were sometimes not explicitly stated in the secondary references available to us, a few of the results may inadvertently have been fticluded in the wrong grouping. These should not materially affect the general conclusions.