Spatial scale effect of homogeneous cavitation in liquid aluminum

Abstract

Dynamic damage under extreme loading exhibits strong scale-dependent behavior, yet system spatial dimensions remain a critical but underexplored factor in bridging molecular dynamic (MD) simulations to macroscopic cavitation mechanisms. This study investigates the scale effects in the damage and fracture of liquid aluminum across different strain rates using MD simulations and a theoretical model. By systematically varying system sizes (4,000 to 32 million atoms) and strain rates (3.0 × 10⁸/s to 1.0 × 10¹¹/s), we elucidate the interplay between spatial scale, strain rate, and dynamic tensile strength. Key findings reveal that smaller systems exhibit pronounced size-dependent strength due to stochastic void nucleation dominated by thermal fluctuations, while larger systems transition to size-independent behavior governed by collective void interactions. A critical system size threshold emerges, beyond which strain rate becomes the primary determinant of strength. Additionally, we observe that the dispersion in tensile strength decreases with increasing system size due to statistical homogenization of void nucleation. A theoretical model integrating void nucleation kinetics and Rayleigh–Plesset growth dynamics successfully predicts stress evolution and damage mechanisms across scales, validated against MD results and experimental data. The model also reveals a non-monotonic relationship between critical void radius and strain rate, linking this behavior to the size-dependents damage mechanisms. These findings provide essential insights for modeling dynamic damage in liquids and enhance our understanding of scale effects in highly non-equilibrium processes.