  A novel phase-flip model is proposed for thermodynamically consistent and
computationally efficient description of spallation and cavitation in pure
liquids within the framework of ideal hydrodynamics. Aiming at ultra-fast
dynamic loads, the spall failure of a liquid under tension is approximated as
an instantaneous decomposition of metastable states upon reaching the spinodal
stability limit of an appropriate two-phase liquid-gas equation of state. The
spall energy dissipation occurs as entropy jumps in two types of discontinuous
solutions, namely, in hypersonic spall fronts and in pull-back compression
shocks. Practical application of the proposed model is illustrated with
numerical simulations and a detailed analysis of a particular problem of
symmetric plate impact. The numerical results are found to be in good agreement
with the previously published molecular-dynamics simulations. Also, new
approximate nonlinear formulae are derived for evaluation of the strain rate,
fractured mass, and spall strength in terms of the observed variation of the
free-surface velocity. The new formula for the spall strength clarifies complex
interplay of the three first-order nonlinear correction terms and establishes a
universal value of the correction factor for attenuation of the spall pulse,
which in the limit of weak initial loads is independent of the equation of
state.
