Stress-Gage System for the Megabar (100 GPa) Range

The useful range of the manganin piezoresistive stress transducer was extended from the former limit of about 45 GPa 450 kbar to about 125 GPa 1250 kbar. The major problem encountered was shunting of the gage, caused by the increased electrical conductivity of insulators at high shock stresses. The effect of shunting was minimized through use of very-low-impedance 0.05 to 0. 15-ohm gages and through careful attention to gage geometry. Loading and release calibration data for manganin were obtained over the stress range between about 25 and about 125 GPa. The results of earlier work, calibrations to 45 GPa, are critically reviewed. All of the reliable data on the dynamic piezoresistance of manganin can be fitted by the piecewise calibration curve. A prototype high-stress mutual-inductance particle velocity gage was designed and tested. Six manganin gages, one background unpowered manganin gage, and one aluminum preheat temperature gage were fielded in the Debris Coupling Experiment of the Husky Pup nuclear event. Despite power supply failure, attributed to preshot flooding of the instrumentation alcove, excellent time-of-arrival data were obtained. These data disagree by about a factor of two with preshot predictions of shock-wave propagation in the Debris Coupling Experiment.