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 $\mu$sec 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 $\pm$ 0.3) and (0.3 $\pm$ 0.15) GPa at dynamic stresses of 18.5 and 32.5 GPa, respectively.