Atomistic simulations and modeling analysis on the spall damage in lead induced by decaying shock

This study reveals some dynamic properties of the spall damage under decaying shock loadings based on atomistic simulations of lead, where a series of shock peak stresses and decaying profiles are introduced. Firstly, different failure modes from the typical spallation to cavitation fragmentation are analyzed with the wave system and relevant statistics. The velocity and mass distributions in the cavitation region approximately satisfy a linear function, where the velocity of the outermost spall layer can be estimated from the surface velocity peak. The spall strengths derived from surface and from bulk are compared. The former is distinctly higher than the latter and too sensitive to the high strain rate, while the latter reduces linearly with the shock breakout stress until the melting slows down this variation law. Furthermore, we propose approximate descriptions of the spall layer thickness and the damage depth under triangular waves, using the strength from bulk and propagation rules of simple waves. Besides, the characteristic size of the voids or fragments at the extreme strain rate is found to approximately satisfy the energy-based fragmentation theory.