Compression tests were performed at room temperature on solid circular cylinders of medium‐grained granodiorite from the Hardhat Event conducted at the Nevada Test Site. Confining pressures ranged from 1 to 7000 bars. A piston‐cylinder apparatus equipped with an internal axial load cell and manganin coil was used. The confining fluid was a low‐viscosity oil. Pre‐detonation specimens were cut 0°, 45°, and 90° to the drill core axis and were taken from 195‐, 225‐, and 255‐meter depths. Post‐detonation rock was sampled at 23 and 27.5 meters from ground zero, which was located at a depth of 290 meters and experienced a calculated peak shock pressure of approximately 20 kb. Specimens mechanically shocked in the laboratory (35 to 40 kb) were from the 195‐meter depth pre‐detonation sample. No orientational effects were observed. The failure of granodiorite under compressional stresses was found to be adequately described by a modified Coulomb maximum shear stress theory. Under uniaxial compression, the mode of failure was brittle shear. Under triaxial compression, a quiet slip failure was observed at low confining pressures and brittle shear at high confining pressures. A possible explanation for the occurrence of slip failure may be the presence of a fluid pore pressure within the specimen. Strain measurements were made on several specimens. At atmospheric pressure, the stress histories of the rock were clearly apparent. Under confining pressure, shock effects rapidly disappeared, and, at 4.5 kb, the behavior was essentially that of normal granodiorite. Young's modulus at atmospheric confining pressure for unshocked rock was found to be 0.64 ± 0.26 × 106 bars, which in the upper limit agrees with the reported dynamic value. The average value for rock shocked by nuclear blast is 0.18 × 106 bars and that for mechanically shocked rock is of the order 0.01 × 106 bars.
ponent 1 do not appear to be satisfactorily described component 1 is less than M,, to obtain sufficiently by the molecular theory in its present form. It may direct and precise information for a complete analysis. be necessary to measure them by diff ereiit experi-Acknowledgment.-This work was supported in mental means, especially when the molecular weight of part by a grant from the National ScTence Foundation.The actinide elements neptunium,.plutonium, and americium are materials of considerable interest to the high pressure investigator. The possibility of pressure-induced electronic transitions such as those in cerium and cesium is suggested by the electronic configurations of the actinides. Such transitions are usually detectable by a discontinuous change in the electrical resistance of the sample. A matter of additional interest is the known one atmosphere polymorphism of plutonium with six allotropic forms between room temperature and its melting point, of neptunium with two allotropic forms, and a suspected allotropism in americium. The program therefore involved the development of apparatus capable of developing high pressures and temperatures which could allow electrical resistance measurements to be made on milligram quantities of metal. In addition, the apparatus was t o be resistant t o breakage or blowout which could contaminate the laboratory, permanent equipment, and, of course, laboratory personnel.
~n apparatus ~s described which has been developed to shear bulk samples under nearly hydrostatic pressure. This apparatus gives complete stress-strain curves in the plastic region at pressures from about 10 to approximately 70 kilobars.A simple current-to-frequency converter has been developed which works directly with photomultiplier currents. It has full scale input current ranges of 3 X 10-10 to 3 X 10-6 A. The feedback pulse is a square pulse that is clocked on and off by a continuously running oscillator. Drift in the oscillator frequency is compensated if the oscillator also serves as ~he t~me.base of the counter used to count the pulses. With oscillator frequencies up to and including 20 kHz the lmearlty IS 0.01 % or better and the drift less than 0.01 % of full scale per hour.
The shear strengths of beryllium, uranium, and tungsten were measured at strain rates of 3.5 × 10−5, 3.6 × 10−3, and 3.7 × 10−1 sec−1. The measurements were taken under nearly hydrostatic pressures of 21, 44, and 63 × 108 N/m2. The shear strength versus shear strain curves are presented along with the pressure and in strain rate derivatives of the experimental parameters.
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