RESISTANCE TO SHOCK-FRONT PROPAGATION IN SOLIDS

The structure of a strong shock front is modeled using a wall of dislocations. Motion of these dislocations changes the density of the solid medium and simultaneously relaxes the shear strains that would otherwise exist behind the front. The dislocation motion is highly dissipative because it requires atoms in intimate contact to slide over one another. This transports momentum down the velocity gradient. It is shown that the energy dissipation rate associated with dislocation motion is larger than for any other general mechanism in the system, including electron-electron, electron-phonon, and phonon-phonon interactions. The reason for this is that electrons are not effective in transporting momentum, and atomic thermal velocities are substantially smaller than the velocities of the dislocations which move with the shock front. The viscosity coefficient associated with the dislocations is propertional to the shock velocity, so the viscous drag stress is proportional to the square of the shock velocity. This can lead to large drag pressures.