S. M. Karakhanov

Electric Resistance of Polytetrafluoroethylene under Shock Compression

The postshock resistivity of polytetrafluoroethylene is determined in the pressure range of 35–63 GPa. The measurements were conducted using a cell 0.2 mm thick with uniform distribution of the resistivity over the thickness. At pressures above 35 GPa, as both the coordinate of the cell and time increase, the resistivity decreases monotonically, reaching an equilibrium value in a characteristic time of about 0.5 μsec at a distance of several millimeters from the plane of discontinuity decay. The results indicate destruction of the polymer in the pressure range of 35–63 GPa. Over the entire range, the average value of the empirical dissociation energy is (3.3 ± 0.7) eV, which coincides within the error with the energy of the C–C single bond, equal to 3.6 eV. Key words: electric resistance of polytetrafluoroethylene, shock waves, polymers, electric conductivity.

Measurement of the brightness temperature of shock-compressed epoxy resin

The brightness temperature of shock-compressed EC141 NF epoxy resin was measured by a pyrometric method in the pressure range of 19–42 GPa. The experimental points are in good agreement within the error with the calculation performed in the work. From the results of experiments, it follows that the presumed phase-transition region is not apparent in the pressure—temperature plane. Particle velocity records at the epoxy-water interface suggest the absence of a chemical reaction in EC141 NF epoxy compound at a pressure of 22.5 GPa during the observation time.

The dynamic behavior of polytetrafluoroethylene in reshock and unloading waves

The behavior of polytetrafluoroethylene under loading by a shock wave and a wave of a complicated structure that consists of a shock wave, subsequent loading, and a rarefaction wave is studied. The front structure that includes a stress jump up to 0.92-0.95 of the equilibrium amplitude and a stress-relaxation zone whose duration is up to 0.5 μsec was recorded. The velocity measurements for the selected points with constant levels of stress in the wavefront show that the reshock wave moves over the shock-compressed polymer in a stationary regime. The phase trajectories of change in the polytetrafluoroethylene state in the coordinates of gauges on the “stress-specific volume” diagrams, which were obtained using the Lagrangian analysis of the stress profiles, show the marked effect of the hysteresis upon variation of the direction of loading of the sample. Depending on the magnitude of the hysteresis, the shear stresses were estimated to be (0.6±0.3) and (0.3+0.15) GPa at dynamic stresses of 18.5 and 32.5 GPa, respectively.

Shock-wave structure in a unidirectional composite with differently oriented fibers

We have studied experimentally stress profiles upon propagation of a shock wave in a unidirectional composite in the case where the normal to the surface of the wave front is directed at angle θ to a reinforcing fiber. For θ=5 and 15°, the elastic precursor behind which the shock wave propagates was registered. For the case θ=45°, the elastic precursor becomes a plastic wave with a smeared front, and, for θ=90°, a single shock wave was recorded. Measurement results show that the stress at the yield point depends on the orientation of the fiber and on the direction of the shock-wave motion.

Temperature measurements for shocked polymethylmethacrylate, epoxy resin, and polytetrafluoroethylene and their equations of state

This paper presents the results of computational and experimental studies of the temperature along the shock adiabat for three polymers. Measurements of the brightness temperatures of shock-compressed epoxy resin and polymethylmethacrylate and the brightness and color temperatures of shock-compressed polytetrafluoroethylene were carried out. The temperatures of the shock-compressed polymethylmethacrylate were determined in the range 1390–1900 K for shock pressures of 22–39 GPa. Similar measurements performed for epoxy resin in the pressure range of 18–40 GPa showed values of 940–1900 K, and the temperatures of polytetrafluoroethylene in the pressure range of 30–50 GPa were equal to 2000–3200 K. The equation of state for the three polymers with a nonspherical strain tensor was constructed to describe shock-wave and high-temperature processes in a wide range of thermodynamic parameters. In the proposed model, two Gruneisen parameters were used: the thermodynamic parameter corresponding to intrachain vibrati...

Temperature measurements of a shock-compressed emulsion matrix

The temperature of a shock-compressed invert emulsion based on an aqueous solution of ammonium and sodium nitrates was measured using two experimental techniques: using planar thermocouples at pressures of 3.4–12.0 GPa and optical pyrometry at pressures of 9–22 GPa. The experimental data obtained using the thermocouple method are consistent with the calculated values. The optical measurement results are significantly higher than the calculated data and indicate the presence of a spatially inhomogeneous temperature field behind the shock front in the emulsion due to the structural inhomogeneity of the medium.

Attenuation of a shock wave in organoplastic

The attenuation of a plane shock wave in organoplastic was experimentally and numerically investigated during its interaction with an overtaking rarefaction wave. Measurements were carried out with manganin gauges, An earlier formulation model of the dynamic deformation of composites was used in calculations. A comparison of calcualted and experimental data has shown their good agreement.

Detonation temperature of an emulsion explosive with a polymer sensitizer

Dependences of the brightness temperatures of the detonation front and detonation products on detonation pressure were determined in the range of 0.7–9.4 GPa by a pyrometric method. The pressure was varied by changing the initial density of the emulsion explosive in the range of 0.43–1.2 g/cm3. Polymer microballoons were used as sensitizer. The dependence of the brightness temperature in the Chapman–Jouguet plane on detonation pressure was found to be nonmonotonic. In the investigated pressure range, the measured temperature values varied from 2250 to 1830 K. A comparative analysis of the application of polymer and glass microballoons as sensitizers was performed. The obtained experimental data were compared with the calculation results available in the literature.

Time of hot-spot formation in shock compression of microballoons in a condensed medium

The optical thermal radiation arising from the shock collapse of glass or polymer microballoons in a transparent condensed medium (water or polymerized epoxy resin) was detected. The temporal characteristics of the detected radiation in the pressure range 0.5–29 GPa at different viscosities of the material surrounding the pore were determined. The brightness temperature of hot spots was estimated to be 1600–3200 K at a pressure of 2–29 GPa. The length of the leading edge of the radiation pulse corresponding to the time of hot-spot formation increases from 2 · 10−8 to 30 · 10−8 s, depending on the shock-wave intensity and the viscosity of the material surrounding the pore. Analysis of the data shows that in the pressure range 5–29 GPa, hot-spot formation is dominated by the hydrodynamic mechanism of collapse and in the range 0.5–5 GPa, by the viscoplastic mechanism.

Optical radiation from shock-compressed epoxy with glass microspheres

Hot-spot temperature in shock compression of a mixture of epoxy resins with glass hollow microspheres is estimated. The obtained hot-spot temperature of 3200 K at a shock pressure of 20 GPa significantly exceeds the temperature of shock-loaded homogeneous epoxy resin, which at this pressure is in the range of 1100–1400 K. The time characteristics of the radiation generated during viscoplastic compression of a monolayer of hollow microspheres in an epoxy matrix at a pressure of 9, 20, and 29 GPa were determined by an optical pyrometer. Experimental data are shown to be in good agreement with estimates based on the viscoplastic deformation model.