- (;) (2) R= R= f(W) . f(w, D,) . f(m) i among wnich are: £(¥, m) . fw, Di)* In attempting to correlate crater cata from TNT blasts with those from nuclear explosions, it has in the past appeared useful to include a factor less than unity (0.3 to 0.9) in tne value of W assigned to nuclear charges in terms of equivalent tons of TNT, based on radiochemical data. This nas deen justified by tue fact that the energy partition is totally different for the two types of explosives and that the nuclear weapons deliver radiant energy while conventional explosives do not. It is believed, however, tnat at best correlation will be uncertain, and with the advent of megaton weapons the disparity of sizes is s0 great that good correlation should not be expected.** The effect of cnarge depth (or heignt) (A) is fairly well estab- lished for TNT. If scaled crater diameter is plotted against scaled charge deptn, it is clear botn from experiment and physical reasoning tnat the curve wili ce concave downward, since no surface crater is produced if tne charge is sufficiently high above the surface or sufficiently deep below it. For TNT, the maximim of this curve is rather broad and occurs in the range of 1 < 4 <3, where 4 is in ft/(lbd ent )+/3, The effect of tne medium, f(m), has been shown to be as large as a factor of 2 in field experiments with TNT. Unfortunately, the specific properties of the medium which affect the crater are not yet established. It is postulated that strength, either shear or tension, and density are sensitive parameters. It is possible that the elastic moduli are also important. In regard to strengtn, it is of course the strength under shock load conditions that is important. It is very difficult to make laboratory tests under snock load conditions and the heterogeneous character of eartl makes the extrapolation ‘rom laboratory to field conditions very uncertain. Thus, while appropriate values for strength under shock load are not known, it appears clear that the strength under such conditions may differ widely from tne strength under static load. The density of the medium may in 4 theoretical sense affect crater size Significantly. In practice, however, the range of densities found is trivial compared to the range of strengths and hence the density is believed to be 8s parameter of only mino~ importance in affecting the crater, As has been mentioned, the application of similitude principles * The data at nand nave seemed to the author to fit better into an equation ot Form (2) tran into one 2° Form (1), namely as-elaborated in Chapter 4. It is to be noted that these two forms are drastically different in the implications of extrapolation from less than Kiloton charges up to megaton ciarges. “** Thus Fig. --i. nas been plotted witn no consideration of relative efficiency«while in Fig. 4.1. a relative efficiency of 60% for nuclear charges compared to TNT nas seen used.