Dislocation-kinetic analysis of FCC and BCC crystal spallation under shock-wave loading

Abstract

Within the dislocation-kinetic model of the formation and propagation of shock waves in crystals under their intense shock-wave loading, the crystal spallation mechanism at micro- and macrolevels has been discussed taking into account published empirical data. It has been shown that the spallation time t _f for Cu, Ni, α-Fe, and Ta crystals in the time interval of 10⁻⁶–10⁻⁹ s at the macroscopic level changes with variations in the wave pressure σ as $t_f = \varepsilon _f /\dot \varepsilon = K_f (E/\sigma )^4$, where = $\dot \varepsilon = K_\sigma (\sigma /E)^4$ is the plastic strain rate according to the Swegle-Grady relation; K _f , K _σ, and ε _f = K _f K _σ ≈ 3–5% are the pressure-independent spallation coefficients and strain, respectively; and E is the Young’s modulus. At the microlevel, the dislocation-kinetic calculation of plastic zones around pore nuclei as stress concentrators and plastic strain localization regions at the shock wave front has been performed. It has been shown that the pore coalescence and spall fracture formation result from the superposition of shear stresses and plastic deformations in interpore spacings when the latter decrease to a size of the order of two pore sizes.