Shock-recovery fixture

Figure 6.10. Schematic drawing of the shock-recovery fixture design.

Fig. 6.5. The shock-compression conditions imposed on powder compacts preserved for post-shock analysis are controlled by details of the shock-recovery fixtures. In all the work of Chap. 6, the Sandia Bear and Bertha fixtures are used. The fixtures represent a standardized system that is highly reproducible and has been subject to extensive numerical simulation.

In an experiment in which a sample is subjected to controlled shock loading and preserved for post-shock analysis, the shock-recovery experiment, the quantification, and the credibility of the experiment rest directly upon the apparatus in which the experiments are carried out. Quantification must be established with two-dimensional numerical simulation and this can only be accomplished if the recovery fixtures are standardized. The standardized fixtures must be capable of precise assembly so that the conditions actually achieved in the experiment are those of the simulation. 

The author s work has included the development of the Sandia Bear and Bertha explosive recovery fixtures, that provide a standardized set of fixtures in which recovery experiments can be routinely carried out at peak shock pressures from 4 to 500 GPa. Shock-induced, mean-bulk temperatures from 50 to 1200°C are achieved with variation in the density of the powder compacts under study. 

Shock-synthesis experiments were carried out over a range of peak shock pressures and a range of mean-bulk temperatures. The shock conditions are summarized in Fig. 8.1, in which a marker is indicated at each pressure-temperature pair at which an experiment has been conducted with the Sandia shock-recovery system. In each case the driving explosive is indicated, as the initial incident pressure depends upon explosive. It should be observed that pressures were varied from 7.5 to 27 GPa with the use of different fixtures and different driving explosives. Mean-bulk temperatures were varied from 50 to 700 °C with the use of powder compact densities of from 35% to 65% of solid density. In furnace-synthesis experiments, reaction is incipient at about 550 °C. The melt temperatures of zinc oxide and hematite are >1800 and 1.565 °C, respectively. Under high pressure conditions, it is expected that the melt temperatures will substantially Increase. Thus, the shock conditions are not expected to result in reactant melting phenomena, but overlap the furnace synthesis conditions. 

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