Effect of impact velocity on spall behaviors of nanocrystalline iron: Molecular dynamics study

LQ Chen and K Zhao and K Zhang and ZZ Wen and HJ Mei and ZB Xiong, CHINESE PHYSICS B, 34, 096201 (2025).

DOI: 10.1088/1674-1056/add4ff

This study investigates the effect of shock velocity (up) on damage evolution mechanisms in nanocrystalline iron via molecular dynamics simulations. As up increases, shock wave propagation accelerates, and stress distribution transitions from grain boundary concentration to homogeneity. This causes a transition in fracture mode from cleavage to ductile behavior. When up exceeds 1.5 km & sdot;s-1, micro-spallation emerges as the dominant failure mode. During micro-spallation, localized melting within the material impedes the propagation of the shock wave. As up increases, the growth rate of the void volume fraction initially rises but then decreases. Higher up leads to earlier void nucleation. At lower up, the cavitation of the model is mainly characterized by the growth and penetration of a few voids. With increasing up, the number of voids grows, and their interactions expand the delamination damage region. The spall strength demonstrates stage-specific dependence on up. In the classical spallation stage (C_I), temperature softening reduces spall strength. In the plastic strengthening regime (C_II), strain hardening enhances spall strength. In the micro-spallation stage (M_III), further increases in up cause melting during tensile and compressive phases, reducing spall strength. Finally, in the compression-melting regime (M_IV), local temperatures exceed the melting point, diminishing plastic damage and accelerating spall strength reduction. This study provides new insights into the dynamic response of nanocrystalline iron.

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