Spalling and melting in nanocrystalline Pb under shock loading: Molecular dynamics studies

The mechanisms of spalling and melting in nanocrystalline Pb under shock loading are studied by molecular dynamics simulations. A wide range of shock intensity is conducted with the lowest one just above the threshold of solid spallation, and the highest one higher than the threshold of compression melting. The spallation mechanism is dominated by cavitation, i.e., nucleation, growth, and coalescence of voids. Our results show that grain boundaries have significant influences on spalling behaviors in cases of classical spallation and releasing melting. In these cases, cavitation and melting both start on grain boundaries, and they display mutual promotion: melting makes the voids nucleate at smaller tensile stress, and void growth speeds melting. Influences of microstructure, strain rate, and temperature on spall strength are qualitatively discussed. Due to grain boundary effects, the spall strength of nanocrystalline Pb varies slowly with the shock intensity in cases of classical spallation. In cases of releasing melting and compression melting, spall strength of both single-crystalline and nanocrystalline Pb drops dramatically as shock intensity increases. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4799388]Physics, AppliedSCI(E)EI6ARTICLE14null11