To reveal the impact velocity (U<sub>p</sub>) effect on the spalling and fracture behavior of single crystal nickel, a non-equilibrium molecular dynamics approach is performed to investigate the free surface velocity curve, radial distribution function, atomic crystal structures, dislocations, and void evolution process. The results show that the critical U<sub>p</sub> for spalling behavior in single crystal nickel is 1.5 km/s, the spallation mechanism is classical spallation damage (U<sub>p</sub>≤1.5 km/s) and micro-spallation damage (U<sub>p</sub>＞1.5 km/s). The number and distribution area, and stress distribution area under micro-spallation damage much higher than those under classical spallation damage. Analyzed the influence of impact velocity on the classical spalling damage behavior (U<sub>p</sub> ≤ 1.5 km/s) and obtained the corresponding spalling strength, an accident of spalling strength occurs at the U<sub>p</sub> of 1.3 km/s. The spalling strength of single crystal nickel is influenced by the combined effects of stacking faults, phase transformation, and dislocation mechanisms. The nucleation and emission of dislocations increase lead to a decrease in the spalling strength. When U<sub>p</sub> <1.3 km/s, spalling damage is primarily influenced by stacking faults. When U<sub>p</sub> =1.3 km/s, spalling strength is mainly affected by the competition between stacking faults and phase transformation. When U<sub>p</sub> >1.3 km/s, spalling strength is predominantly influenced by the body-centered cubic (BCC) phase transformation mechanism (transformation path: FCC → BCT → BCC). This study reveals the impact velocitydependent patterns, mechanisms, and effects on spalling damage and fracture, providing a theoretical basis for the protective application of nickel-based materials under extreme impact conditions.
