Mechanical responses of nanoporous aluminum samples under shock in different crystallographic orientations (, , , and ) are investigated by molecular dynamics simulations. The shape evolution of void during collapse is found to have no relationship with the shock orientation. Void collapse rate and dislocation activities at the void surface are found to strongly dependent on the shock orientation. For a relatively weaker shock, void collapses fastest when shocked along the orientation; while for a relatively stronger shock, void collapses fastest in the orientation. The dislocation nucleation position is strongly depended on the impacting crystallographic orientation. A theory based on resolved shear stress is used to explain which slip planes the earliest-appearing dislocations prefer to nucleate on under different shock orientations.

We investigate spalling behaviors of Ni/Al nanolaminates by molecular dynamics simulations. First, we discuss spalling damage distributions in shocked Ni/Al nanolaminates. Voids nucleate in Al layers, while no voids are located in Ni layers or along the Ni/Al interfaces. This is because the spall strength of single-crystalline Ni is higher than that of single-crystalline Al. We reveal influences of a shock-induced chemical reaction on dynamic spalling damage and fracture processes. An abnormal “decrease $\to$ increase $\to$ decrease” zigzag variation tendency of the spall strength of Ni/Al nanolaminates as the impact velocity increase is observed in our simulations, which resulted from combining effects of micro-structures, chemical reactions, and temperature softening. When the impacting intensity is relatively low, the spall strength of Ni/Al nanolaminates decreases as the impact velocity increases due to micro-structure effects. However, when the loading velocity increases to a certain magnitude (2.5 km/s), the intimate contact of liquid Al with amorphous Ni near the interface makes the chemical reaction rate increase rapidly to form a large amount of Ni/Al alloys and enhances the spall strength.

Mechanical responses of nanoporous Cu samples under various loading conditions are investigated by molecular dynamics simulations. Effects of loading mode, initial void size, temperature, and void distribution are analyzed. The simulations show that the collapse time under uniaxial compression is about three times that under triaxial compression, and the collapse rate increases as the temperature rises. Dislocation nucleation is found to stimulate the collapse of void. For samples with a single void, the final dislocation density under triaxial compression is lower than that under uniaxial compression, which is due to that the dislocation accumulation rate greatly slows down after the void is fully collapsed. For samples with multiple voids, the dislocation accumulation rate under triaxial compression is much faster than that under uniaxial compression, resulting in higher dislocation density under triaxial compression. Irrespective of the initial void size, the evolutions of compression stress and void volume fraction remain invariant when the initial void volume fraction is fixed; however, the dislocation density decreases as the initial void radius increases.