SHOCK UNLOADING CHARACTERISTICS OF CRUSHABLE ROCKS.
Final rept. for 1 May 63-31 Mar 64,
IIT RESEARCH INST CHICAGO ILL
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The unloading characteristics of dry volcanic tuff were observed for two initial shock states. The unloading paths in the stress-particle velocity plane differed substantially from the reflected Hugoniot curve passing through the corresponding initial shock state. Thus the unloading proc ess does not follow the usually assumed Hugoniot unloading path. The net results of this behavior are that 1 the quantity of energy dissipated in the shock process is considerably greater than that normally assumed, and 2 the propagation speeds of the unloading waves are considerably greater than those normally assumed. For shock stress intensities of approximately 100 and 200 kilobars it was determined that the amount of energy dissipated at the shock front has been underestimated by 20 to 30 percent, and that the remaining useful energy has been overestimated by approximately 50 percent. Furthermore, the unloading wave speed for these cases has been underestimated by approximately 20 to 25 percent. A correlation was made between Hugoniot data obtained during this program and other Hugoniot data for dry volcanic tuff of various initial densities. It was found that, when presented in terms of absolute density, all of the Hugoniot states above a critical stress level were located on a single Hugoniot curve. This resulting aggregate mineral Hugoniot correlates well with Hugoniots for the basic nonporous constituents of the geologic materials. Author