Cratering efficiency

The maximum potential power of an explosive can be calculated, or it can be measured by techniques such as those developed by Cook. A typical method consists of firing the explosive under water and measuring the energy liberated in the various forms, such as shock wave in the water, the work of expansion of the gas bubble, etc. These figures have limited practical value as the methods of application of explosives are of low and variable efficiency. A more practical measurement of strength can be obtained by the measurement of cratering efficiency. This, again, demands considerable expense and also requires the availability of uniform rock. 

Let US examine the effect of dirt type first. A large number of explosive tests as well as a series of very near surface nuclear shots have been condueted on very different types of geology. From these experiments, statistical values for cratering efficiency, Eqk, as a function of geological type were determined. The efficiency, cr, is related to crater volume. This same number can be used in relation to radius as well as depth in the form cr > since the volume of a crater is roughly proportional to the cube of its linear dimensions. Table 29.1 gives cr values for various geological materials. 

Table 29.1 HE Cratering Efficiencies for Various Earth Materials at a Zero Height of Burst...

Material Test Area (Project) Cratering Efficiency Ecr (ftVton)"... 

Figure 29.5. Descriptive geologic effect on HE cratering efficiency.

The cratering efficiency found from Table 29.1 is 0.75, and now the crater radius can be estimated as... 

The crater volume increases with the projectile kinetic energy. This relationship for the snow sintered for 15 minutes at different temperatures is shown in Figure 5. The empirical equation shows that the crater volume is almost proportional to the root square of the projectile kinetic energy, which means that it is simply proportional to the impact velocity (Vj). Thus, we can describe the cratering efficiency as follows This... 

The efficiency of an explosive in any given rock can be determined by cratering experiments. In these, boreholes are drilled vertically downwards into the rock and loaded with increasing charges of explosive. The effects which are produced are shown in Fig. 14.2. The optimum charge produces... 

There are few pubhshed Lu-Hf isotope studies of mantle xenohths because of difficulties in efficient ionization of hafnium by thermal ionization mass spectrometers. Multicollector plasma mass spectrometers are a solution to this problem and data are emerging that promise to be a more revealing tool in mantle environments than neodymium isotopes. The variety of Lu/Hf fractionation displayed by mantle minerals (Figure 42) indicates that, as with other isotope systems, isotopic variation should be considerable and initial results are confirming this. Salters and Zindler (1995) found very radiogenic Hf/ Hf at relatively unradiogenic neodymium isotope compositions in spinel peridotites from Salt Lake Crater, Hawaii. Radiogenic Hf/ Hf also characterizes low-T circum-cratonic... 

The rapid increase in crater depth above the threshold irradiance for phase explosion correlates with a significant increase in signal intensity. The ratio of crater volume to signal intensity, which represents the entrainment efficiency, remains the lowest at laser irradiances slightly above the phase explosion threshold. Such a ratio, however, increases at irradiances well above the threshold (> 10" W/cm ). 

The number of craters or holes forming the honeycomb-like structure increased rapidly with the quantity of evolved hydrogen, as can be seen from Fig. 42 which shows the dependence of the number of holes or craters formed due to the attachment of hydrogen bubbles on the average current efficiency of hydrogen evolution. 

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