Investigation of size effects on spall damage behavior in nanocrystalline aluminum during high impact

Numerous studies have demonstrated that, under fixed impact loading conditions, the spallation strength and void evolution characteristics of polycrystalline aluminum display complex grain size effects. However, a significant gap remains in the literature concerning the influence of grain size on these properties across varying impact velocities. Consequently, this study utilizes nonequilibrium molecular dynamics simulations to investigate the spall damage behavior of polycrystalline aluminum at different impact velocities, with a particular focus on grain size effects. The results indicate that at 1.5 km/s and 2 km/s, spallation strength trends across grain sizes align with damage rates. However, this consistency disappears at 2.5 km/s. Notably, in comparison to the lower impact velocity (1.5 km/s), the higher impact velocity (2 km/s) demonstrates a shift in the critical grain size toward smaller dimensions. This shift is attributed to increased impact strength, causing a sharp rise in internal stress. Combined with the higher grain boundary density of smaller grains, this leads to premature nucleation within small grain boundaries. These findings identify grain sizes most prone to spallation fracture and provide insights into nanocrystalline material failure in extreme environments. •Revealed the consistency between grain size effects on spall strength and damage rate at impact speeds up to 2 km/s.•As impact velocity rises, intragranular nucleation increases, shifting critical grain size for spall strength and damage rate smaller.•At 1.5 km/s, voids evolve from node cavitation to boundary growth; above 2 km/s, only cavitation occurs.